Environmental Chemistry of Lakes and Reservoirs - ACS Publications

17

Downloaded by UNIV OF CALIFORNIA SAN DIEGO on December 29, 2015 | http://pubs.acs.org Publication Date: May 5, 1994 | doi: 10.1021/ba-1994-0237.ch017

Environmental Behavior and Fate of Anionic Surfactants Nicholas J. Fendinger, Donald J. Versteeg, E l s Weeg, Scott D y e r , and Robert A . Rapaport Procter and Gamble Company, Ivorydale Technical Center, Cincinnati, OH 45217

Linear alkylbenzenesulfonates, alcohol sulfates, and alcohol eth oxysulfates are used in a variety of household cleaning and personal care products that are generally disposed of "down the drain". Even though these surfactants are characterized as highly biodegradable and are not expected to persist in aquatic environments, the current use of anionic surfactants in consumer products requires increased understanding of anionic surfactant degradation, toxicity, and en vironmental behavior. This chapter reviews anionic surfactant biodegradation, removal during sewage treatment, environmental con centrations, and aquatic-effects data that illustrate the environmental safety of these materials.

ALNIONIC

SURFACTANTS USED IN SHAMPOOS,

cosmetics,

toothpaste,

and

l a u n d r y products i n c l u d e l i n e a r alkylbenzenesulfonates ( L A S ) , a l c o h o l s u l fates (AS), a l c o h o l ethoxysulfates ( A E S ) , alcohol g l y c e r o l e t h e r sulfonates, a n d alpha-olefln sulfates. H o u s e h o l d e n d use o f anionic surfactants i n the U n i t e d States was 7.3 Χ 10 m e t r i c tons i n 1987; L A S , A S , a n d A E S ac c o u n t e d for 9 8 % o f the total (I). L A S , t h e major anionic surfactant u s e d i n the w o r l d today, accounts for a p p r o x i m a t e l y 2 8 % o f a l l synthetic surfactant use. I n t h e U n i t e d States i t is w i d e l y i n c l u d e d i n detergent formulations (about 270,000 m e t r i c tons p e r year) (I). It is u s e d i n almost e v e r y h o u s e h o l d c l e a n i n g a p p l i c a t i o n except automatic d i s h w a s h e r detergents (2). L A S represents a m i x t u r e o f homologs w i t h a l k y l c h a i n lengths r a n g i n g f r o m 10 to 15 c a r b o n units a n d w i t h isomers o f v a r y i n g p h e n y l p o s i t i o n (structure 1). D o d e c y l b e n z e n e s u l f o n a t e ( C L A S ) 5

1 2

0065-2393/94/0237-0527$08.75/0 © 1994 American Chemical Society

In Environmental Chemistry of Lakes and Reservoirs; Baker, Lawrence A.; Advances in Chemistry; American Chemical Society: Washington, DC, 1994.

528

ENVIRONMENTAL CHEMISTRY O F L A K E S A N D RESERVOIRS

CH3CH(CH2) CH3 n

η

= 7

to

12


1 is the h o m o l o g most w i d e l y u s e d i n detergent applications. T h e r e f o r e t h e f o l l o w i n g discussion o f aquatic h a z a r d w i l l focus o n this h o m o l o g . A l c o h o l sulfates (AS) are c u r r e n t l y u s e d i n shampoos, b a t h preparations, cosmetics, m e d i c i n e s , toothpaste, r u g shampoos, hard-surface cleaners, a n d light- a n d h e a v y - d u t y l a u n d r y applications (2). Total A S use i n t h e U n i t e d States is about 136,000 m e t r i c tons p e r year. T h e 91,000 m e t r i c tons p e r year u s e d i n h o u s e h o l d products (3) ranges f r o m C to C i n a l k y l c h a i n lengths (structure 2) a n d m a y contain some e t h y l or m e t h y l b r a n c h i n g . T h e C A S h o m o l o g is w i d e l y u s e d i n detergent formulations a n d approximates the average c o m m e r c i a l A S c h a i n l e n g t h . T h e r e f o r e , o u r aquatic h a z a r d discussion w i l l focus o n the C h o m o l o g . 1 2

1 8

1 4

1 4

9-

R-O-S-0 M

•

II

ο

R-alkyl chain length from 10 to 18 carbons 2 A l c o h o l ethoxysulfates ( A E S ) are w i d e l y u s e d i n h o u s e h o l d a n d p e r s o n a l care applications (dishwasher detergents, l a u n d r y detergents, a n d shampoos; 204,000 m e t r i c tons p e r year i n t h e U n i t e d States) (3) (structure 3). A E S are d e s c r i b e d b y t h e d o m i n a n t a l k y l c h a i n l e n g t h ( C ) a n d n u m b e r of ethoxylate units (E ) i n the technical-grade material. Because the v o l u m e o f A E S u s e d i n h o u s e h o l d c l e a n i n g applications is d i v i d e d almost e q u a l l y b e t w e e n C 1 2 _i 3 E S a n d C 1 4 _i 5 E S , the h a z a r d assessment w i l l focus o n t h e a p p r o x i m a t e average c h a i n l e n g t h o f C E S . t

y

3

3

1 3

3

RO-(CH CH O) -SO " 2

2

η

3

R-alkyl chain length from 10 to 18 carbons η = 1 to 5 3



17.

FENDINGER ET AL.

Behavior and Fate of Anionic

Surfactants

529

Figure 1. Factors considered in determination of environmental hazard assessment for anionic surfactants. G i v e n the c u r r e n t use of L A S , A S , a n d A E S i n c o n s u m e r p r o d u c t s , u n d e r s t a n d i n g o f anionic surfactant degradation, toxicity, a n d e n v i r o n m e n t a l b e h a v i o r is n e e d e d . E v e n t h o u g h these surfactants are a l l r e a d i l y b i o d e gradable (easily c o n v e r t e d to c a r b o n d i o x i d e a n d c e l l u l a r material) a n d are not e x p e c t e d to persist i n t h e e n v i r o n m e n t , i n t e g r a t i o n o f m a t e r i a l usage, e n v i r o n m e n t a l fate, exposure, a n d aquatic toxicity data is necessary to o b t a i n a c o m p r e h e n s i v e e n v i r o n m e n t a l h a z a r d assessment (4) ( F i g u r e 1). T h i s c h a p ter presents i n f o r m a t i o n o n the use, biodégradation o r r e m o v a l d u r i n g sewage treatment, e n v i r o n m e n t a l concentration, a n d aquatic effects o f L A S , A S , and A E S . T h e s e data are t h e n u s e d to calculate p r o t e c t i o n factors.

Fate Studies Biodégradation, h y d r o l y s i s , a n d sorption i n f l u e n c e t h e e n v i r o n m e n t a l fate of L A S , A S , a n d A E S . P r i m a r y degradation o f surfactants is i m p o r t a n t b e cause this process usually results i n loss o f surfactancy a n d r e d u c e d toxicity (5, 6). C o m p l e t e m i n e r a l i z a t i o n ensures that persistent i n t e r m e d i a t e s w i l l not b e f o r m e d a n d that biodégradation w i l l b e an effective m a s s - r e m o v a l m e c h a n i s m i n t h e e n v i r o n m e n t . S o r p t i o n a n d association o f surfactants w i t h particles o r d i s s o l v e d organic substances are processes that decrease b i o availability a n d c a n b e correlated w i t h decreased surfactant toxicity (7). Photolysis also m a y degrade surfactants i n surface waters. It is n o t l i k e l y to b e a d i r e c t degradation m e c h a n i s m for A S a n d A E S because these m o l ecules lack a c h r o m o p h o r i c g r o u p , b u t it c o u l d affect t h e fate o f L A S . B e c a u s e surfactants are i n t r o d u c e d i n t o the e n v i r o n m e n t m a i n l y t h r o u g h waste-



530


treatment systems, biodégradation is expected to b e the major e n v i r o n m e n t a l r e m o v a l m e c h a n i s m . T h u s , it w i l l b e discussed i n the most d e t a i l . L A S Biodégradation. T h e i n i t i a l e n z y m a t i c attack o f L A S occurs b y o m e g a oxidation o f the t e r m i n a l c a r b o n o f the a l k y l side c h a i n . T h e e n z y m e s i n v o l v e d i n this reaction, although not y e t isolated, are p r o b a b l y associated w i t h c e l l m e m b r a n e s . T h i s e n z y m a t i c attack results i n a carboxylated a l k y l c h a i n o r sulfophenylcarboxylate. T h e a l k y l c h a i n biodegrades f u r t h e r t h r o u g h b e t a oxidation, w i t h t w o carbon units c o n v e r t e d into acetic a c i d at a t i m e (8). O n c e carboxylated, the m o l e c u l e loses its surfactant p r o p e r t i e s because it n o l o n g e r has a h y d r o p h o b i c side c h a i n . F o l l o w i n g c o m p l e t e m i n e r a l i z a t i o n of the a l k y l c h a i n , the b e n z e n e ring is desulfonated a n d c l e a v e d (9, 10). M i n e r a l i z a t i o n of the L A S a l k y l c h a i n c a n b e a c c o m p l i s h e d b y p u r e bacterial cultures (11). H o w e v e r , c o m p l e t e L A S m i n e r a l i z a t i o n i n n a t u r a l systems is most l i k e l y to b e a c c o m p l i s h e d b y a c o n s o r t i u m o f m i c r o o r g a n i s m s (12). J i m e n e z et al. (13) i d e n t i f i e d a c o n s o r t i u m o f four bacterial species that are capable of c o m p l e t e I A S m i n e r a l i z a t i o n f r o m activated sludge. O t h e r types o f consortia that are capable o f L A S m i n e r a l i z a t i o n p r o b a b l y also exist. Biodégradation Rate. T h e biodégradation rate i n surface w a t e r d e p e n d s o n m a n y variables such as biomass a n d substrate concentration, p r e s e n c e o f s u s p e n d e d material, a n d availability o f nutrients. L a r s o n a n d P a y n e (14) a n d L a r s o n (15) investigated factors that c o n t r o l l e d L A S m i n e r a l i z a t i o n i n r i v e r water b y f o l l o w i n g C 0 e v o l u t i o n a n d C i n c o r p o r a t i o n i n t o biomass f r o m samples a m e n d e d w i t h C r i n g - l a b e l e d L A S homologs a n d p h e n y l isomers (2-phenyl C _ a n d 5 - p h e n y l C _ L A S ) . T h e r i v e r - w a t e r L A S half-life was a p p r o x i m a t e l y 24 h , d i d not vary significantly as a f u n c t i o n o f L A S h o m o l o g or i s o m e r , a n d was not affected b y h i g h concentrations o f c o m p e t i n g h o m o logs. Intermediates f r o m L A S biodégradation d i d not appear to a c c u m u l a t e . I n a d d i t i o n , the rate a n d extent o f L A S m i n e r a l i z a t i o n w e r e n o t significantly different b e t w e e n river w a t e r w i t h a l o w suspended-solids content a n d river water w i t h u p to 1000 m g / L o f s u s p e n d e d s e d i m e n t , despite the fact that significant amounts o f L A S homologs w i t h the l o n g e r a l k y l c h a i n l e n g t h w e r e s o r b e d o n s u s p e n d e d s e d i m e n t . L a r s o n (15) t h e o r i z e d that s o r p t i o n d i d not affect the extent or rate o f biodégradation as l o n g as L A S s o r p t i o n to solids was r e v e r s i b l e a n d the d e s o r p t i o n kinetics w e r e m o r e r a p i d than the k i n e t i c s of biodégradation. 1 4

1 4

2

1 4

1 0

1 4

1 0

1 2

A d d i t i o n o f s e d i m e n t solids to o v e r l y i n g surface water increases biomass a n d may increase t h e rate of L A S degradation i f the system biomass is l i m i t e d . F o r example, L a r s o n a n d P a y n e (14) correlated increases i n the L A S b i o degradation rate constants i n r i v e r water w i t h increased bacterial p o p u l a t i o n s r e s u l t i n g f r o m a d d i t i o n o f s e d i m e n t solids. S i m i l a r l y , Y e d i l e r et a l . (16) f o u n d that p r i m a r y L A S degradation i n lake water was affected b y t h e size o f t h e m i c r o b i a l p o p u l a t i o n present.


17.

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Surfactants

531

Laundromat Pond. F e d e r l e a n d Pastwa (17) c o m p a r e d L A S biodégradation i n sediments from a p o n d that r e c e i v e d discharge from a local l a u n d r o m a t to biodégradation that o c c u r r e d i n a p r i s t i n e c o n t r o l p o n d . S e d i m e n t cores c o l l e c t e d f r o m each of the ponds w e r e u s e d to d e t e r m i n e sedi m e n t d e p t h profiles for surfactant concentrations, bacterial n u m b e r a n d activity, a n d a b i l i t y to m i n e r a l i z e C r i n g - l a b e l e d C L A S . Biomass a n d


1 4

1 3

m i c r o b i a l activity w e r e f o u n d to decrease w i t h d e p t h i n the sediments for b o t h ponds, w i t h h i g h e r biomass a n d activity m e a s u r e d i n the l a u n d r o m a t p o n d . L A S was m i n e r a l i z e d w i t h o u t a lag p e r i o d b y the l a u n d r o m a t p o n d sediments at a l l depths w i t h half-lives that r a n g e d b e t w e e n 3.2 a n d 16.5 days. I n the p r i s t i n e c o n t r o l p o n d , L A S was m i n e r a l i z e d o n l y after a lag p e r i o d of 3 . 2 - 4 0 days. T h e m i n e r a l i z a t i o n progressed m o r e s l o w l y t h a n that o b s e r v e d i n the l a u n d r o m a t p o n d (calculated half-lives w e r e f r o m 5.2 to 1540 days). C l e a r l y , L A S undergoes r a p i d ( w i t h i n days) a n d c o m p l e t e biodégradation i n natural water systems. A l t h o u g h m a n y factors i n f l u e n c e L A S degradation i n natural waters, the g o v e r n i n g factor is p r o b a b l y a c c l i m a t i o n that results f r o m previous L A S exposure. H o w e v e r , because L A S has b e e n i n use for a p p r o x i m a t e l y 25 years, b o t h sewage-treatment operations a n d the rivers that receive treated sewage are already a c c l i m a t e d a n d c o n t a i n L A S m i n e r a l i z i n g consortia that are capable of r a p i d L A S degradation. F o r exa m p l e , M o r e n o et a l . (18) f o u n d that L A S r e m o v a l b y biodégradation i n aerated sewers can be as h i g h as 50%.

Anaerobic Environments. Because the i n i t i a l attack of the L A S m o l ecule is oxidative, L A S does not b i o d e g r a d e u n d e r anaerobic c o n d i t i o n s (19). T h e r e f o r e concerns are sometimes expressed that L A S m a y accumulate i n d e e p anaerobic s e d i m e n t layers, w h e r e it w i l l not b i o d e g r a d e f u r t h e r . H o w ever, g i v e n the h i g h rate of L A S r e m o v a l d u r i n g sewage treatment c o m b i n e d w i t h in-stream degradation, it is u n l i k e l y that L A S s e d i m e n t a c c u m u l a t i o n w i l l occur unless there is r a p i d d e p o s i t i o n i n t o an anaerobic e n v i r o n m e n t .

AS Biodégradation. T h e p r i m a r y step i n the aerobic degradation o f A S is the sulfatase-catalyzed h y d r o l y s i s of the sulfate ester from the h y d r o p h o b i c group to f o r m inorganic sulfate a n d an alcohol (20). D e g r a d a t i o n proceeds t h r o u g h oxidation o f the alcohol catalyzed b y dehydrogenases (12), to give first the c o r r e s p o n d i n g a l d e h y d e a n d t h e n the c o r r e s p o n d i n g fatty a c i d . T h e final degradation o f the fatty a c i d is b y b e t a o x i d a t i o n . T h o m a s a n d W h i t e (21) i n d i c a t e d that elongation a n d desaturation of the fatty a c i d c h a i n m a y also occur w i t h fatty acid residues that are r a p i d l y i n c o r p o r a t e d into l i p i d fractions. T h e y also d e m o n s t r a t e d (21) that h y d r o p h o b i c metabolites of the A S a l k y l c h a i n can b e i n c o r p o r a t e d i n t o c e l l u l a r c o m p o n e n t s ( l i p i d membranes) w i t h o u t p r i o r degradation b y b e t a oxidation.


532


Measurement of Biodégradation. N u m e r o u s studies have d o c u m e n t e d the aerobic b i o d e g r a d a b i l i t y o f various A S c o m p o u n d s (see ref. 12). M o s t o f these studies u s e d m e t h y l e n e b l u e active substance ( M B A S ) a n d o t h e r eolo r i m e t r i c d e t e r m i n a t i o n s , change i n surface tension, f o a m i n g capacity, a n d sulfate f o r m a t i o n as an i n d i c a t i o n o f p r i m a r y A S degradation. U l t i m a t e biodégradation o f A S has b e e n m e a s u r e d b y b i o l o g i c a l oxygen d e m a n d ( B O D ) , c h e m i c a l oxygen d e m a n d ( C O D ) , c a r b o n loss, C 0 p r o d u c t i o n , a n d C - l a b e l e d A S . T h e s e tests also indicate total degradation o f p r i m a r y straight- a n d b r a n c h e d - c h a i n A S i n laboratory experiments w i t h M e d i t e r r a n e a n Sea water (22), B l a c k Sea w a t e r (23), activated sludge (24-26), forest soil (27), a n d river w a t e r (12). H o w e v e r , h i g h l y b r a n c h e d A S (secondary a n d tertiary branched) are r e p o r t e d (28-30) to b e m o r e resistant to biodégradation than l i n e a r p r i m a r y A S . A S m a n u f a c t u r e d f r o m n a t u r a l oils (animal a n d vegetable) d o not contain a n y b r a n c h e d c o m p o n e n t s , a n d A S m a n u f a c t u r e d from p e t r o l e u m - d e r i v e d oils w i l l generally contain less than 2 0 % b r a n c h e d m a t e r i a l . V i r t u a l l y a l l o f the b r a n c h e d m a t e r i a l that is present i n p e t r o l e u m - d e r i v e d A S consists o f p r i m a r y m e t h y l o r e t h y l b r a n c h e d m a terial (Shell D e v e l o p m e n t C o r p o r a t i o n , u n p u b l i s h e d data). C _ A S w i t h this t y p e of b r a n c h i n g u n d e r w e n t r a p i d a n d c o m p l e t e degradation ( > 8 0 - l l l % b y C 0 p r o d u c t i o n ; P r o c t e r a n d G a m b l e , u n p u b l i s h e d data). 2


1 4

n

1 5

2

Studies o f A S degradation d u r i n g s i m u l a t e d sewage treatment also s h o w r a p i d a n d c o m p l e t e biodégradation. F o r example, M c G a u h e y a n d K l e i n (31) a n d K l e i n a n d M c G a u h e y (32) f o u n d c o m p l e t e p r i m a r y degradation o f A S based o n f o r m a t i o n o f S 0 " i n m o d e l septic tank systems. S t e b e r et a l . (26) u s e d u n i f o r m l y l a b e l e d C A S to demonstrate u l t i m a t e degradation i n a m o d e l activated-sludge treatment system. A n average o f 6 0 % o f t h e A S f e d into t h e system was m e a s u r e d as c a r b o n d i o x i d e . T h e effluent c o n t a i n e d 0 . 3 % o f t h e o r i g i n a l feed as intact A S a n d less than 1 0 % o f t h e total C spike. T h i s analysis indicates > 9 0 % carbon e l i m i n a t i o n d u r i n g wastewater treatment. 3 5

4

2

1 6

1 4

Bacterial e n z y m e s capable o f i n i t i a t i n g A S h y d r o l y s i s are w i d e s p r e a d i n the e n v i r o n m e n t . Sulfatase has b e e n isolated f r o m soil, activated sludge, r i v e r water, a n d r a w sewage bacteria (33-38). A l t h o u g h W h i t e et a l . (37) f o u n d m o r e AS-resistant strains a n d a greater p r o p o r t i o n o f alkylsulfatasep r o d u c i n g bacteria at p o l l u t e d sites than at clean sites i n t h e R i v e r E l y , 2 9 % of all bacterial isolates tested w e r e alkylsulfatase p r o d u c e r s . A n d e r s o n et a l . (39) isolated e p i l i t h i c bacteria f r o m r i v e r b e d stones c o l l e c t e d f r o m p o l l u t e d a n d clean sites f r o m t h e S o u t h W a l e s R i v e r a n d assessed t h e i r a b i l i t y to p r o d u c e alkylsulfatase. T h e n u m b e r o f alkylsulfatase-producing bacteria was greater i n p o l l u t e d sites, b u t they w e r e present at b o t h locations a n d v a r i e d as a f u n c t i o n o f season a n d water q u a l i t y . G r e a t e r n u m b e r s o f alkylsulfatase bacteria w e r e present at s a m p l i n g sites d u r i n g late s u m m e r than d u r i n g w i n t e r ; t h e count was l o w e r at sewage discharge sites than at d o w n s t r e a m locations. I n a d d i t i o n , because o f e n z y m e c o m p o s i t i o n (far m o r e constitutive


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533

than i n d u c i b l e enzymes), the e p i l i t h o n w o u l d not lose its a b i l i t y to degrade A S e v e n i f levels fluctuated. Microbial Degradation. Identification of bacteria responsible for A S degradation was a t t e m p t e d i n part to u n d e r s t a n d what conditions favor m i c r o b i a l degradation, either i n nature or u n d e r c o n t r o l l e d conditions. P u r e cultures of Escherichia coli, Serratia marcescens, Proteus vulgaris, a n d Pseudomonas fluorescens d e g r a d e d C A S (8). O t h e r researchers (36, 37) s h o w e d that Pseudomonas strains are also capable of d e g r a d i n g C A S . E x t e n s i v e degradation of t a l l o w C _ A S o c c u r r e d w i t h 35 out of 47 strains of bacteria f r o m the f o l l o w i n g genera: Acetobacter, Chromobacterium, Bacillus, Corynebacterium, Escherichia, Micrococcus, Mycobacterium, Pseudomonas, Staphylococcus, a n d Vibrio.


1 2

1 2

1 6

1 8

A n a e r o b i c degradation was also d e m o n s t r a t e d for A S (12, 26). O b a et al. (40) suggested that the anaerobic degradation of A S m a y consist of sulfate ester h y d r o l y s i s , w i t h formation of a fairly i n e r t alcohol. W a g n e r a n d S c h i n k (41) m e a s u r e d a c c u m u l a t i o n of sulfide a n d fatty acids d u r i n g the anaerobic degradation of C A S . D e g r a d a t i o n of the A S was i n i t i a t e d b y the h y d r o l y t i c cleavage of the sulfate. Because there was no other source of sulfur i n the system, W a g n e r a n d S c h i n k speculated that the sulfide r e s u l t e d f r o m red u c t i o n of the l i b e r a t e d sulfate. H i g h concentrations of acetate a n d valerate i n d i c a t e d that the A S residues w e r e at least p a r t i a l l y d e g r a d e d . H o w e v e r , S t e b e r et al. (26) f o u n d 9 0 % of the C l a b e l f r o m stearyl sulfate a n d d o d e c y l sulfate i n the final degradation products ( C 0 a n d C H ) w h e n they tested for t h e m i n a s i m u l a t e d anaerobic treatment system. 1 2

1 4

2

4

A E S Biodégradation. P r i m a r y degradation of A E S was a c c o m p l i s h e d e n z y m a t i c a l l y b y sulfatase o r etherase, or b y o m e g a a n d b e t a o x i d a t i o n . Sulfatase h y d r o l y z e d the A E S i n t o its c o r r e s p o n d i n g alcohol ethoxylate ( A E ) a n d inorganic sulfate. L i b e r a t i o n of the sulfate f r o m p r i m a r y A S was s h o w n to be a c c o m p l i s h e d b y p r i m a r y a l k y l sufatases (12). A l t h o u g h l i n e a r alcohol ethoxysulfates are structurally s i m i l a r to p r i m a r y A S , the sulfate may not b e h y d r o l y z e d b y the same e n z y m e . T h e rate of A E S degradation b y sulfatase varies as a f u n c t i o n of h y d r o p h o b e structure f r o m r a p i d a n d c o m p l e t e to no o b s e r v e d degradation, based o n the " f i t " of the e n z y m e (12). F o u r strains of bacteria (three Pseudomonas a n d one u n i d e n t i f i e d strain) w e r e s h o w n to u t i l i z e this pathway. T h e i r extent of degradation varies f r o m 6 % for T E S 5 to as h i g h as 3 9 % for C 1 2 B (42, 43). 1 2

3

T h e rate of p r i m a r y A E S degradation b y etherase is also strain-specific. F o r example, H a l e s et a l . (42, 43) r e p o r t e d that etherases of t h r e e strains of Pseudomonas a n d an u n i d e n t i f i e d strain isolated f r o m sewage effluent c o u l d cleave at each of the three available e t h e r linkages. E x t e n t of d e g r a dation (1-72%) v a r i e d as a f u n c t i o n of the bacterial strain a n d e t h e r linkage affected. G l y c o l sulfates that result f r o m etherase activity are d e g r a d e d f u r -


534


ther v i a oxidation o f the t e r m i n a l alcohol to a carboxylic a c i d . T e r m i n a l C - C units are sequentially r e m o v e d v i a h y d r o l y s i s to y i e l d the next shorter p o l y g l y c o l sulfate (12). D e g r a d a t i o n b y omega, b e t a oxidation was i d e n t i f i e d as a m e c h a n i s m that shortens the h y d r o p h o b e c h a i n b y two c a r b o n i n c r e m e n t s . T h i s route is responsible for 1 1 % of the parent A E S degradation (43).


Exposure Assessments E x p o s u r e of an organism to a surfactant i n surface water w i l l d e p e n d o n the a m o u n t of m a t e r i a l u s e d , disposal practice, r e m o v a l rate d u r i n g sewage treatment, d i l u t i o n i n the r e c e i v i n g stream, a n d s o r p t i o n o n particles or aquatic d i s s o l v e d organic c a r b o n . T h e exposure c o m p o n e n t of an e n v i r o n m e n t a l h a z a r d assessment utilizes i n f o r m a t i o n f r o m the fate studies d e s c r i b e d i n the p r e v i o u s section, mathematical m o d e l i n g to p r e d i c t e n v i r o n m e n t a l concentrations, a n d e n v i r o n m e n t a l m o n i t o r i n g to v e r i f y m o d e l p r e d i c t i o n s . Predicted Wastewater Concentrations of L A S , A S , and A E S . Wastewater concentrations o f L A S , A S , a n d A E S i n the U n i t e d States w e r e calculated b y u s i n g the f o l l o w i n g equation.

540 L/person-day · 365 days · 240 Χ 1 0

6

persons

w h e r e X is the a m o u n t of m a t e r i a l u s e d i n d o w n - t h e - d r a i n applications ( m i l ligrams) a n d C is the wastewater concentration i n m i l l i g r a m s p e r l i t e r . T h e p e r capita water use of 540 L / p e r s o n - d a y , o b t a i n e d f r o m the E n v i r o n m e n t a l P r o t e c t i o n A g e n c y ( E P A ) needs survey, was calculated b y d i v i d i n g treatmentplant flow rates (obtained f r o m survey information) b y p o p u l a t i o n s e r v i c e d b y the same plants (44). T h i s calculation y i e l d s a h i g h e r flow rate than the i n d i v i d u a l h o m e p e r capita flow rate of 200 L / p e r s o n - d a y because of c o n t r i b u t i o n s f r o m n o n d o m e s t i c wastewater sources. T h u s it is a m o r e realistic flow d e t e r m i n a t i o n for t r e a t m e n t - p l a n t - m o d e l i n g purposes t h a n the i n d i v i d u a l p e r capita h o m e flow (45). A n n u a l U n i t e d States L A S , A S , a n d A E S use i n d o w n - t h e - d r a i n applications w e r e stated p r e v i o u s l y . O n the basis o f these values, p r e d i c t e d wastewater concentrations o f L A S , A S , a n d A E S are 4.5, 1.8, a n d 4.3 p p m , respectively (45). L A S Treatability and Environmental Concentrations. T h e re m o v a l of L A S d u r i n g sewage treatment was c o n f i r m e d b y m o n i t o r i n g studies i n b o t h the U n i t e d States a n d E u r o p e . N u m e r o u s studies r e p o r t e d a n i o n i c surfactant concentrations i n surface waters m e a s u r e d b y nonspecific analyt ical techniques such as m e t h y l e n e b l u e active substance ( M B A S ) . H o w e v e r , the correlation b e t w e e n M B A S a n d L A S concentrations d e t e r m i n e d b y spe-


17.

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535


cific analytical t e c h n i q u e s are variable a n d , i n general, not u s e f u l . T h e r e f o r e , o n l y those studies that u s e d specific analytical t e c h n i q u e s for L A S are r e viewed here. I n the U n i t e d States the most extensive L A S m o n i t o r i n g studies w e r e r e p o r t e d b y R a p a p o r t a n d E c k h o f f (46) a n d M c A v o y et a l . (47). R a p a p o r t a n d E c k h o f f (46) d e s c r i b e d the results of 13 years (1973-1986) of L A S m o n i t o r i n g at 36 se wage-treatment plants, 35 r i v e r w a t e r - s e d i m e n t sites, a n d 5 s l u d g e - a m e n d e d soil sites. A m i c r o d e s u l f o n a t i o n - G C analysis t e c h n i q u e w i t h a d e t e c t i o n l i m i t of 0.01 m g / L was u s e d to measure L A S i n the c o l l e c t e d samples. Influent sewage L A S (average c h a i n l e n g t h C ) c o n c e n t r a t i o n averaged 3.5 ± 1.2 m g / L . E f f l u e n t L A S levels v a r i e d as a f u n c t i o n o f t r e a t m e n t t y p e . F o r example, L A S concentrations i n activated-sludge effluents averaged 0.06 m g / L a n d r a n g e d f r o m 0.01 to 0.13 m g / L , whereas p r i m a r y t r e a t m e n t effluents averaged 2.1 m g / L a n d r a n g e d f r o m 1.7 to 2.5 m g / L . Rapaport a n d E c k h o f f (46) also r e p o r t e d results f r o m a n extensive L A S study i n R a p i d C r e e k , S o u t h D a k o t a . L A S r i v e r - w a t e r concentrations w e r e r a p i d l y attenuated as a f u n c t i o n of distance d o w n s t r e a m f r o m a t r i c k l i n g filter treatment plant. L A S c o n c e n t r a t i o n i n sediments d o w n s t r e a m was p r o b a b l y d i m i n i s h e d b y m o v e m e n t of the surflcial s e d i m e n t s , biodégradat i o n , a n d d i l u t i o n b y bank solids. T h e L A S c o n c e n t r a t i o n of 190 ± 95 m g / k g i n sediments i m m e d i a t e l y b e l o w the p l a n t outfall was at the l o w range of the calculated steady-state concentrations, w h i c h r a n g e d f r o m 190 to 740 mg/kg. M c A v o y et a l . (47) m o n i t o r e d L A S levels f r o m several drainage basins at a v a r i e t y of treatment plants i n 11 states. T h e p l a n t types i n c l u d e d activated sludge (15 sites), t r i c k l i n g filter (12 sites), o x i d a t i o n d i t c h (6 sites), lagoon (8 sites), a n d rotating b i o l o g i c a l contactor (9 sites). I n f l u e n t wastewater, effluent, u p s t r e a m a n d d o w n s t r e a m r i v e r water, a n d s e d i m e n t samples w e r e c o l l e c t e d at each site. S a m p l i n g was c o n d u c t e d d u r i n g p e r i o d s o f l o w r i v e r flow, w h e n effluent d i l u t i o n w o u l d b e lowest. I n f l u e n t a n d effluent samples w e r e c o l l e c t e d as 24-h composites a n d t h e n c o m b i n e d i n t o 3-day flowaveraged composites. R i v e r - w a t e r samples w e r e c o l l e c t e d as grab samples across a h o r i z o n t a l transect of the r i v e r to assess m i x i n g o f the effluent plume. Solid-phase extraction a n d c l e a n u p w e r e u s e d , f o l l o w e d b y h i g h - p r e s s u r e l i q u i d c h r o m a t o g r a p h y ( H P L C ) - f l u o r e s c e n c e d e t e c t i o n for q u a n t i t a t i o n of L A S levels (48). D e t e c t i o n l i m i t s i n water samples a n d sediments w e r e 0.010 m g / L a n d 1 m g / k g , r e s p e c t i v e l y . T h e average i n f l u e n t c o n c e n t r a t i o n was 5 m g / L . E f f l u e n t L A S concentrations v a r i e d as a f u n c t i o n of treatment t y p e (Table I). A v e r a g e effluent concentrations r a n g e d f r o m 0.04 m g / L for activated-sludge plants to 1 m g / L for t r i c k l i n g - f i l t e r plants. I n t e r m s of r e m o v a l , this concentration corresponds to > 9 9 % for activated-sludge plants a n d an average of 7 7 % for t r i c k l i n g - f i l t e r plants. T h e average r e m o v a l for other types of treatment plants ranged f r o m 96 to 98%. 1 2


536


Table I. Sewage Treatment Plant Influent and Effluent Concentrations of L A S for Different Types of Sewage Treatment Average Cone. (mg/L)


Treatment Type Influent L A S concentrations Effluent L A S concentrations: Primary treatment Activated sludge Trickling filter Lagoons Oxidation ditch Rotating biological contactor

4.8

± 2.0

0.04 1.04 0.06 0.12 0.19

± 0.3

0.98

± 0.1 ± 0.27 ± 0.38

Removal Rate (%)

27 99.3 77.4 98.5 98.0 96.2

± ±

19 0.61 15.46 1.81 4.24 6.10

S O U R C E : Data are taken from refs. 4 6 and 4 7 .

F i g u r e 2 shows a histogram r e c o r d i n g the f r e q u e n c y o f o b s e r v e d i n stream concentration o f L A S m e a s u r e d b e l o w sewage-treatment outfalls. C o n c e n t r a t i o n s o f L A S m e a s u r e d i n samples f r o m the left, m i d d l e , a n d r i g h t stream channels f r o m s a m p l i n g locations w e r e consistent, w h i c h i n d i c a t e d c o m p l e t e m i x i n g . S t r e a m concentrations o f L A S w e r e g e n e r a l l y less t h a n

CO ζ ο

Lu h-

ÙJ Q L_ O cr Lu ω

0.05

0.10

0.15

0.20

0.25

0.30

0.35

LAS CONCENTRATION (mg/L) Figure 2. Frequency of observed in-stream LAS concentrations below sewage outfalls. (Data are from ref 47.)


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537


0.05 m g / L . H o w e v e r , a concentration o f 0.320 m g / L was m e a s u r e d at o n e location i n an i r r i g a t i o n d i t c h that s e r v e d as a r e c e i v i n g stream f o r a t r i c k l i n g filter p l a n t discharge. T h e stream-water concentrations r e p r e s e n t worse-case conditions because t h e samples w e r e c o l l e c t e d u n d e r l o w - f l o w c o n d i t i o n s at locations w i t h m i n i m a l effluent d i l u t i o n . D e H e n a u a n d M a t t h i j s (49) r e p o r t e d L A S s e d i m e n t m o n i t o r i n g results f r o m G e r m a n y (14 sites). S e d i m e n t concentrations o f L A S w e r e m e a s u r e d b y H P L C - U V spectroscopy a n d w e r e f o u n d to b e d e p e n d e n t o n the distance b e t w e e n s a m p l i n g location a n d sewage-treatment-plant (STP) outfall. M e a s u r e d concentrations r a n g e d f r o m a f e w m i l l i g r a m s p e r k i l o g r a m o f d r i e d s e d i m e n t at 48 k m d o w n s t r e a m to a m a x i m u m o f 275 m g / k g at o n l y 1 k m d o w n s t r e a m from t h e S T P effluent. AS Treatability and Environmental Concentrations. Studies o f A S degradation i n t h e e n v i r o n m e n t o r d u r i n g actual sewage t r e a t m e n t have b e e n l i m i t e d because specific analytical m e t h o d s to measure A S w e r e n o t available u n t i l r e c e n t l y . W e d e v e l o p e d a m e t h o d that isolated A S f r o m w a t e r samples o n a strong anion-exchange c o l u m n . T h e A S w e r e t h e n h y d r o l y z e d to a fatty a c i d a n d a n a l y z e d b y gas c h r o m a t o g r a p h y w i t h flame-ionization d e t e c t i o n ( G C - F I D ) . T h e m e t h o d has a d e t e c t i o n l i m i t o f 5 μ g / L p e r c o m p o n e n t (50). L e v e l s o f A S i n wastewater flowing i n t o sewage-treatment plants that discharge to surface water w e r e p r e d i c t e d to b e near 1.7 p p m (see e q 1). H o w e v e r , A S levels i n wastewater samples c o l l e c t e d as 1-h c o m p o s i t e sam ples f r o m t w o S T P s near C i n c i n n a t i , O h i o , averaged 0 . 2 7 ± 0.18 m g / L a n d r a n g e d f r o m 0.04 to 0.53 m g / L . R a p i d loss o f A S from wastewater b y e i t h e r m i c r o b i a l o r e n z y m a t i c h y d r o l y s i s m a y account for t h e m e a s u r e d A S c o n centrations b e i n g l o w e r than expected. Analyses o f A S i n A S - a m e n d e d r i v e r w a t e r a n d f i l t e r e d a n d u n f i l t e r e d wastewater as a f u n c t i o n o f t i m e c o n f i r m this h y p o t h e s i s . F o r e x a m p l e , A S levels i n u n f i l t e r e d wastewater decreased to less t h a n 4 0 % o f t h e o r i g i n a l spike after o n l y 6 h ( F i g u r e 3). A f t e r 24 h t h e A S levels r e m a i n e d at less than 4 0 % o f the o r i g i n a l s p i k e . A S concentrations i n r i v e r w a t e r ( F i g u r e 4) a m e n d e d w i t h A S also decreased to levels less t h a n 4 0 % o f the o r i g i n a l spike after 24 h . R e d u c e d A S degradation after a d d i t i o n o f f o r m a l d e h y d e to t h e samples i n d i c a t e d that t h e A S loss was b i o l o g i c a l l y m e d i a t e d . A S levels i n effluent from a n activated-sludge p l a n t near C i n c i n n a t i , O h i o , averaged 0.0178 ± 0.0091 m g / L (n = 5) w i t h a r e m o v a l rate o f 9 3 % (50). M a n n a n d R e i d (51) r e p o r t e d near c o m p l e t e p r i m a r y degradation o f A S d u r i n g t r i c k l i n g - f i l t e r treatment. G i v e n t h e h i g h rate o f A S degradation i n n a t u r a l waters a n d t h e h i g h r e m o v a l d u r i n g sewage treatment, surface-water concentrations are e x p e c t e d to b e v e r y l o w . E v e n d i r e c t discharge of A S - c o n t a i n i n g wastewater to a r i v e r or stream that feeds a lake o r r e s e r v o i r is not l i k e l y to transport measurable



Time (hours) Figure 4. Plot of AS concentrations in river water as a function of time.


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539

Surfactants

amounts o f A S because o f the abundance o f sulfatase-producing organisms in the environment. A E S Treatability and Environmental Concentrations. Removal of C _ E S d u r i n g laboratory-scale s e m i c o n t i n u o u s activated-sludge t e s t i n g was greater t h a n 9 5 % , w i t h greater than 9 8 % r e m o v a l b y activated-sludge treatment (52). R a p i d loss was also o b s e r v e d i n r i v e r w a t e r a n d estuarine water. F o r example, K i k u c h i (53) f o u n d 8 0 - 1 0 0 % of A E S d e g r a d e d i n r i v e r w a t e r w i t h i n 3 to 5 days, as m e a s u r e d b y M B A S . I n a d d i t i o n , V a s h o n a n d S c h w a b (54) m e a s u r e d 8 0 - 1 0 0 % A E S m i n e r a l i z a t i o n b y C 0 e v o l u t i o n w i t h i n 15 days i n estuarine water. A E S are t y p i c a l l y m e a s u r e d i n e n v i r o n m e n t a l matrices b y n o n s p e c i f i c c o l o r i m e t r i c analyses ( M B A S ) that c o l l e c t i v e l y measure L A S , A S , a n d natu r a l l y o c c u r r i n g a n i o n i c surfactants. A l t e r n a t i v e l y , a specific gas c h r o m a t o graphic m e t h o d f o r A E S , d e v e l o p e d b y N e u b e c k e r (55), was e m p l o y e d to measure A E S concentrations i n i n f l u e n t a n d effluent from S T P s a n d r i v e r water. Total A E S m e a s u r e d i n i n f l u e n t wastewater to a S T P was 1.88 m g / L . A E S r e m o v a l o f 9 4 - 1 0 0 % was m e a s u r e d d u r i n g actual sewage treatm e n t b y activated sludge; t h e r e s u l t i n g effluent c o n c e n t r a t i o n was 0.06 m g / L . T o t a l A E S levels i n r i v e r w a t e r w e r e less t h a n 0.01 m g / L . A E S a c c o u n t e d for 6 - 1 3 % o f M B A S m e a s u r e d i n n a t u r a l water.


1 2

1 5

3

1 4

2

Predicted Anionic Surfactant Concentrations in Surface Water. M o d e l i n g o f surfactant concentrations i n surface w a t e r p r o v i d e s exposure estimates w h e n large-scale m o n i t o r i n g data are n o t available. T h e m o d e l s w e u s e d to estimate surfactant concentrations i n surface waters are U S T E S T (56) a n d P G - R O U T (57). F o r b o t h m o d e l s o n l y wastewater levels f r o m actual m o n i t o r i n g are u s e d , along w i t h r e m o v a l rates f r o m actual sewage t r e a t m e n t (Table I). A S a n d A E S r e m o v a l rates for treatment types o t h e r t h a n activated sludge are not available. F o r these surfactants, L A S r e m o v a l rates w e r e u s e d to estimate r e m o v a l d u r i n g p r i m a r y a n d various forms o f secondary sewage treatment. T h i s a s s u m p t i o n p r o v i d e s a conservative estimate o f A S a n d A E S r e m o v a l because these surfactants are e x p e c t e d to b e r e m o v e d f r o m wastewater at least as efficiently as L A S . U S T E S T , d e v e l o p e d b y Rapaport (56) is a r i v e r c o n c e n t r a t i o n m o d e l applicable t h r o u g h o u t the U n i t e d States. T h e m o d e l p r e d i c t s concentrations b e l o w the m i x i n g zones of sewage-treatment plants. It is b u i l t o n t h r e e large databases that l i n k r i v e r flow, treatment t y p e , a n d sewage-discharge v o l u m e . T h u s d i l u t i o n factors are p r e d i c t e d for each o f t h e 11,500 p u b l i c l y o w n e d treatment w o r k s ( P O T W ) i n the U n i t e d States. T h e m o d e l l i n k s the t r e a t m e n t type to t h e d i l u t i o n factor so that different r e m o v a l rates f o r t h e c h e m i c a l b e i n g m o d e l e d can b e assigned for each treatment. T h e result is a n a t i o n a l f r e q u e n c y d i s t r i b u t i o n of r i v e r concentrations just b e l o w t h e m i x i n g zones of treatment-plant outfalls. T h e s e p r e d i c t i o n s c a n b e d o n e u n d e r m e a n o r



540


c r i t i c a l - l o w river flow rates. T h e latter closely approximates 7-consecutiveday, 10-year l o w - f l o w (7Q10) conditions (56). C o n c e n t r a t i o n s p r e d i c t e d b y U S T E S T are t y p i c a l l y the highest that are expected to o c c u r i n the e n v i r o n m e n t because the m o d e l does not take into account in-stream r e m o v a l processes s u c h as biodégradation a n d sorption onto particles w i t h settling out o f the w a t e r c o l u m n . M o d e l i n p u t i n c l u d e s wastewater concentration a n d r e m o v a l b y p r i m a r y , t r i c k l i n g - f i l t e r , a n d activated-sludge treatment. T r i c k l i n g - f i l t e r r e m o v a l , u s e d i n U S T E S T p r e d i c t i o n s , was calculated as the flow-weighted ( U n i t e d States) average removals for t r i c k l i n g - f i l t e r , r o t a t i n g b i o l o g i c a l contactor, lagoon, a n d o x i d a t i o n - d i t c h treatment systems. F i g u r e 5 shows the f r e q u e n c y d i s t r i b u t i o n for L A S b e l o w the 11,500 P O T W s i n the U n i t e d States u n d e r m e a n - f l o w a n d l o w - f l o w c o n d i t i o n s , p l u s r a n k e d d i s t r i b u t i o n o f the actual r i v e r - m o n i t o r i n g data from R a p a p o r t a n d E c k h o f f (46) a n d M c A v o y et a l . (47). T h e U S T E S T m o d e l p r e d i c t s that concentrations w i l l b e less than 0.148 a n d 0.038 m g / L for c r i t i c a l l o w - f l o w a n d m e a n - f l o w c o n d i t i o n s , r e s p e c t i v e l y , at 9 0 % o f the locations. C o n c e n t r a tions at m e a n - f l o w conditions are l o w e r because o f greater i n - s t r e a m d i l u t i o n . T h e m o n i t o r i n g results c o r r e s p o n d closely to the p r e d i c t e d l o w - f l o w c o n -

100

7Q10 FLOW MEAN FLOW MONITORING

h

90 80 70 60 50 -

\

w

V

20 10 h

100 LAS

200

300

400

CONCENTRATION (PPB)

Figure 5. Frequency distribution of LAS concentrations below the 11,500 publicly owned treatment works in the United States under mean-flow and low-flow conditions plus ranked distribution of actual river-monitoring data. (Data are from ref. 47.)



17.

FENDINGER E T AL.


Surfactants

541

centrations. T h e s e results indicate that the m o d e l is a good p r e d i c t o r o f actual L A S e n v i r o n m e n t a l concentrations. F i g u r e s 6 a n d 7 show the f r e q u e n c y d i s t r i b u t i o n s for A S a n d A E S , respectively, b e l o w the 11,500 P O T W s i n the U n i t e d States u n d e r m e a n flow a n d l o w - f l o w c o n d i t i o n s . A S concentrations are expected to b e less t h a n 0.010 m g / L u n d e r l o w - f l o w conditions a n d less than 0.002 m g / L u n d e r m e a n - f l o w conditions for 9 0 % of the locations. A E S concentrations are exp e c t e d to b e less than 0.063 a n d 0.015 m g / L u n d e r l o w - f l o w a n d m e a n - f l o w c o n d i t i o n s , r e s p e c t i v e l y , for 9 0 % of the locations. A s was the case w i t h L A S , the concentrations p r e d i c t e d at the 90th p e r c e n t i l e (only 10% of the treatm e n t plants are expected to have h i g h e r concentrations) are the highest concentrations that are expected to be e n c o u n t e r e d i n the e n v i r o n m e n t . P G - R O U T is a d e t e r m i n i s t i c river m o d e l applicable t h r o u g h o u t the U n i t e d States (57). P r e d i c t i o n s are based o n m o r e than 500,000 U n i t e d States river m i l e s . T h i s m o d e l also p r e d i c t s concentrations u n d e r 7 Q 1 0 a n d m e a n flow c o n d i t i o n s . T h e m o d e l is d r i v e n b y several large E P A databases. P r e dictions are m a d e b e l o w each o f the 11,500 P O T W s , at d r i n k i n g water intakes a n d at any d e s i r e d m i l e points i n the r i v e r systems. T h e m o d e l o u t p u t i n c l u d e s a f r e q u e n c y d i s t r i b u t i o n b y river m i l e a n d a d e t a i l e d P C database.

7Q10 FLOW MEAN FLOW

AS CONCENTRATION (PPB) Figure 6. Frequency distribution of AS concentrations below the 11,500 publicly owned treatment works in the United States under mean-flow and lowflow conditions.


542


-

7Q10

FLOW

MEAN FLOW

! 1

70 -

s

\ \ \ \ \ x\


60 50 40

-

\ \

30 20

*

\

*

\\

1*

\\

0

I

\

**•· _ ι

20

ι

1

Τ—ι—ι—ι—

40

60

AES

80

ι

100

1 1—*ϊ " Γ -l 120 140 160

CONCENTRATION

-i — 1 180

1 200

(PPB)

Figure 7. Frequency distribution of AES concentrations below the 11,500 publicly owned treatment works in the United States under mean-flow and low-flow conditions. F o r c o m p a r i s o n , b i o l o g i c a l oxygen d e m a n d ( B O D ) , a m m o n i a , a n d d i s s o l v e d oxygen concentrations are also p r e d i c t e d . A s an example of h o w the m o d e l w o r k s , an i n d i v i d u a l river reach can b e c o n s i d e r e d . T h e m o d e l first locates P O T W s , d r i n k i n g w a t e r intakes, a n d i n d u s t r i e s . T h e n the l o a d for each particular P O T W that discharges i n t o the stream is d e t e r m i n e d . T h e r e s u l t i n g concentration is a f u n c t i o n of the p e r capita usage rate for the c h e m i c a l , the type of treatment that the wastewatert r e a t m e n t plant e m p l o y s , the effluent f l o w rate, a n d the r i v e r f l o w rate at the discharge p o i n t . T h e treatment type a n d f l o w rates are accessed f r o m the E P A databases. T h e i n i t i a l concentration is a l l o w e d to decay b y firsto r d e r kinetics d e t e r m i n e d f r o m biodégradation studies to the next p o i n t of interest. T h i s process continues for selected m i l e points, i n d u s t r i e s , a n d P O T W s . A t each P O T W a n e w l o a d is a d d e d to the stream. F o r b o t h i n dustries a n d P O T W s , a m m o n i a a n d B O D l o a d i n g are s i m u l a t e d . T h i s process continues for a l l 500,000 r i v e r m i l e s i n exact h y d r o l o g i e s e q u e n c e . F i g u r e 8 shows a c o m p a r i s o n b e t w e e n L A S levels p r e d i c t e d b y P G R O U T a n d actual levels o b t a i n e d b y m o n i t o r i n g for the west b r a n c h of the T r i n i t y R i v e r (Texas). T h i s r i v e r reach is especially difficult to m o d e l because there are a n u m b e r of i m p o u n d m e n t s . H o w e v e r , p r e d i c t e d L A S concentrations r a n g i n g f r o m 0 to near 3.0 X 10 m g / L w e r e s i m i l a r to concentrations 2


17.

FENDINGER ET AL.


543

Surfactants

40 ο

ο PG Rout LAS (Κ-.45) • Observed LAS

30 +


D

c Φ υ c ο ο

10 +

350

400

450

500 550 RIVER MILE

600

650

700

Figure 8. Comparison between LAS levels predicted by PG-ROUT and actual levels from monitoring the west branch of the Trinity River (Texas). d e t e r m i n e d b y actual m o n i t o r i n g . M u c h of the variation b e t w e e n the m o d e l a n d m o n i t o r i n g data can be e x p l a i n e d b y discrepancies i n the discharge m i l e p o i n t location data. P G - R O U T was also u s e d to p r e d i c t L A S r i v e r - w a t e r concentrations as a f u n c t i o n of U n i t e d States r i v e r miles. F i g u r e 9 shows the L A S concentra tions p r e d i c t e d b y P G - R O U T o n a l o g scale versus the percentage of U n i t e d States river kilometers w i t h carbonaceous B O D ( C B O D ) a n d L A S as C B O D for c o m p a r i s o n . L A S concentrations are p r e d i c t e d to be less than 0.004 m g / L for 9 0 % a n d less than 0.020 m g / L for 9 5 % of U n i t e d States r i v e r k i l o m e t e r s . B y c o m p a r i s o n , C B O D is 9.8 m g / L for 9 5 % of U n i t e d States r i v e r k i l o m e t e r s . L A S expressed i n terms of C B O D is 0 . 5 % of the total C B O D at the 95th p e r c e n t i l e . P G - R O U T p r e d i c t i o n s have not b e e n c o n d u c t e d for A S or A E S .

Aquatic Toxicity LAS. T h e toxicity of C L A S to aquatic organisms has b e e n w i d e l y s t u d i e d a n d is r e p o r t e d to span a w i d e concentration range (Table II; see ref. 65 for a m o r e extensive r e v i e w ; the references w e r e p o r t i n this chapter w e r e selected for a p p l i c a b i l i t y to the U n i t e d States a n d E u r o p e a n d for data quality). T h e toxicity m e c h a n i s m of L A S a n d other surfactants (AS a n d A E S ) is u n k n o w n b u t is suspected to be polar narcosis. A c u t e toxicity to i n v e r tebrate species (48-h LCgo) range f r o m 1.7 m g / L for the oligochaete, Dero, 1 2



544


PERCENTAGE OF RIVER KILOMETERS Figure 9. LAS concentrations predicted by PG-ROUT versus United States river kilometers with carbonaceous BOD (CBOD) and LAS as CBOD for comparison. to 270 m g / L for the i s o p o d , Asellus (58). F o r the invertebrates u s e d most c o m m o n l y i n aquatic toxicity testing (the d a p h n i d s , Daphnia a n d Cenodaphnia, a n d the a m p h i p o d , Gammarus) acute toxicity values are r e p o r t e d to range from 3.3 to 8.6 m g / L . Because d a p h n i d sensitivity to C L A S is s i m i l a r to o r l o w e r t h a n t h e sensitivity o f other invertebrate species, acute toxicity values for the d a p h n i d s are u s e d to assess risk to a l l invertebrate organisms. 1 2

T h e available C L A S acute toxicity data for fish indicate little i n t r a species v a r i a b i l i t y (Table II). F o r the four species tested, the 96-h L C ^ concentrations of C L A S range from 1.2 m g / L for the fathead m i n n o w Pimephales promelas (64) to 6.2 m g / L for the m i n n o w Phoxinus phoxinus (68). A l t h o u g h the variety of species tested is not as b r o a d as for the i n v e r tebrates, the available data suggest that sensitivity of fish to C L A S is s i m i l a r to that of the most sensitive invertebrates. 1 2

1 2

1 2

N o studies o n the acute toxicity of C L A S to algae a n d aquatic plants w e r e f o u n d i n the literature. T y p i c a l toxicity-testing protocols use a test d u r a t i o n of 4 - 7 days. T h i s d u r a t i o n of testing represents a significant p o r t i o n of the organisms' life span for the taxa tested. T h u s these toxicity tests are a p p r o p r i a t e l y c o n s i d e r e d chronic-toxicity tests. 1 2

T h e c h r o n i c toxicity of C L A S to invertebrates, fish, a n d algae span a r e l a t i v e l y n a r r o w toxicity range (Table III). T o x i c i t y to fish a n d one algal species is comparable a n d slightly greater than toxicity to invertebrates. No-observed-effect concentrations ( N O E C ) for fish range from 0.3 to 1.1 m g / L for the fathead m i n n o w (64, 66). T h e most a p p r o p r i a t e c h r o n i c toxicity value from the F a i r c h i l d et a l . (64) study is the 0.7 m g / L v a l u e , as 1 2


17.

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545

Behavior and Fate of Anionic Surfactants

Table II. Acute Toxicity of C L A S to Invertebrates and F i s h 1 2

Organism


Invertebrates Dero (oligocheate) Daphnia magna (water flea) Dugesia (flatworm) Gammarus (amphipod) Daphnia pulex (water flea) Ceriodaphnia dubia (water flea) Rhadbitis (nematode) Paratanytarsus (midge) Goniobasis (snail) Asellus (isopod) Fish Pimephales promelas (fathead minnow)

Lepomis macrochirus (bluegill sunfish) Oncorhynchus mykiss (rainbow trout) Phoxinus phoxinus (minnow)

Test Duration (h) 48 48

(mg/L)

Ref

1.7

58

1.8

48

1.8

59 60 61 58

48

3.3

58

8.6

61

5.3

62

3.5 5.9

48 48

16

58

48

23

58

24 48 48

19 92 270

63 62 58

96 96 96 96 96

1.2 3.8 4.1 4.7 1.7

64 65 66 60 67

96

2.5

62

48 48

6.0 6.2

68

this was the 28-day early-life-eyele test. T h e other values r e p o r t e d b y F a i r c h i l d et al. are 7-day c h r o n i c estimator tests. T h e s e tests are o f shorter d u r a t i o n , m o r e h i g h l y variable, a n d thus not c o n s i d e r e d as good a measure of toxicity as the l o n g e r - t e r m test from the same study. S i m i l a r l y , the most appropriate c h r o n i c - t o x i c i t y value f r o m the H o l m a n a n d M a c e k (66) s t u d y is 1.1 m g / L , as this value was based o n results f r o m a life-cycle study. T h e other c h r o n i c - t o x i c i t y values for the fathead m i n n o w r e p o r t e d b y H o l m a n a n d M a c e k (66) are f r o m 30-day early-life-stage tests. A l g a l m e d i a n effective concentrations (EC50) range from a l o w of 0.9 m g / L for the b l u e - g r e e n alga Microcystis to 29 m g / L for Selenastrum (71).


546


Table III. Chronic Toxicity of C L A S to Invertebrates, F i s h , and Algae 1 2

NOEC -LOEC (mg/L) a

Organism

Toxicity Text


Invertebrates Hyalella azteca (amphipod)

7-day survival

21-day survival; reproduction

Daphnia magna (water flea)

0.9-2.1 1.4-2.9 0.9-2.0 0.6-1.5 1.2 4.9

life cycle (growth, survival, reproduction) early lifestage (40-day survival, growth) early lifestage early lifestage 7-day growth 7-day growth 7-day growth 7-day growth

Plants Microcystis aeruginosa (blue-green algae)

(NOEC)

1.4

1.1

C

(NOEC)

Ref. 64

65 69 70 62

66

0.48-0.49

0.65-0.98 0.7-1.8 0.9-2.1 0.3-0.6 0.3-0.9 0.6-1.5

64

7-day growth

0.9 10-20 0.09 2.7

71 72 73 59

2-day pop. growth

20-50

72

4-day pop. growth 2-day pop. growth

29 50-100

71 72

4-day pop. growth 2-day pop. growth

Lemna minor (duckweed) Nitzschia fonticula (diatom) Selenastrum capricornutum (green algae)

(NOEC)

1.5-2.25

7-day survival; reproduction

Ceriodaphnia dubia (water flea) Fish Pimephales promelas (fathead minnow)

b

" N O E C indicates no-observed-effect concentration. LOEC indicates lowest-observed-effect concentration. Mean of eight toxicity tests. fo

c

T h e EC50 value error. E v i d e n c e to b e 0.9 m g / L , corroborated b y

of 0.09 m g / L r e p o r t e d b y L e w i s (73) is b e l i e v e d to b e i n available i n p r o p r i e t a r y reports indicates the correct value as r e p o r t e d b y L e w i s a n d H a m m (71). T h i s value is f u r t h e r the study o f Yamane et a l . (72).

F o r invertebrates, F a i r c h i l d et a l . (64) r e p o r t e d results of 4- a n d 7-day s u r v i v a l studies w i t h Hyallela. N O E C values ranged f r o m 0.6 to 1.4 m g / L i n these studies. T h e C L A S 21-day N O E C for Daphnia range f r o m 1.2 (65) to 4 . 9 (70), a n d for Ceriodaphnia the 7-day N O E C was 1.4 m g / L (62). 1 2


17.

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Surfactants

547


A c u t e - to c h r o n i c - t o x i c i t y ratios based o n one o r several organisms can be u s e d to extrapolate f r o m acute data to c h r o n i c data for other groups o f organisms. A l t h o u g h a n u m b e r of assumptions are i n h e r e n t i n this a p p r o a c h , the m e t h o d generates c h r o n i c values that can b e u s e d i n i n i t i a l risk assessments. B y u s i n g the data f r o m Tables I I a n d I I I , a n d c a l c u l a t i n g g e o m e t r i c m e a n values w h e r e m o r e t h a n o n e toxicity value exists, acute-to-chronic ratios f o r Daphnia magna, Ceriodaphnia duhia, a n d Pimephales promelas w e r e d e t e r m i n e d to b e 2 . 2 , 3 . 8 , a n d 3.5, r e s p e c t i v e l y . AS. T h e acute toxicity o f C A S has r e c e i v e d a significant a m o u n t o f research (Table I V ) , i n part because o f the r e c o m m e n d a t i o n that s o d i u m d o d e c y l sulfate (SDS) be u s e d as a reference toxicant ( U . S . E P A , u n p u b l i s h e d reference literature). Results of toxicity tests w i t h three invertebrate species are r e p o r t e d , w i t h acute 24- a n d 48-h ECgo values r a n g i n g f r o m 1.4 m g / L for the rotifer Brachionus rubens to 10.3 m g / L for Daphnia magna. I n fish, 96-h acute LCgo values r e p o r t e d range from 4 . 5 m g / L for the b l u e g i l l sunfish (Lepomis tnacrochirus) to 18.3 m g / L for t h e adult g u p p y (Lebistes reticulatus). N e w s o m e (79) s t u d i e d C A S toxicity to three life stages o f fish—fry (3 weeks o f age), j u v e n i l e (12 weeks o f age), a n d adult (20 weeks o f a g e ) — a n d o b s e r v e d that fry w e r e generally the most sensitive a n d adults the least sensitive to t h e acute toxicity of A S . A n y g i v e n o r g a n i s m appears to have a fair a m o u n t o f v a r i a b i l i t y i n t h e acute toxicity of C A S . V a r i a b i l i t y occurs w i t h i n studies (tests c o n d u c t e d b y a single author), as w e l l as b e t w e e n studies. F o r e x a m p l e , i n t h e s t u d y o f L e B l a n c (75) the eight 48-h ECgo values for Daphnia magna w e r e r e p o r t e d to range f r o m 3 . 3 to 9.8 m g / L . B e t w e e n studies, t h e 4 8 - h E C 5 0 v a l u e f o r Daphnia magna ranges from 1.8 m g / L (59) to a h i g h o f 15.2 m g / L (77). 1 2

1 2

1 2

A p o r t i o n of the b e t w e e n - s t u d y v a r i a b i l i t y m a y indicate the d i r e c t effect of water hardness o n toxicity (83, 84). T h i s effect appears to result f r o m a n increased availability of A S i n h a r d water (84, 85), not a l l o f w h i c h is attributable to changes i n A S e n v i r o n m e n t a l c h e m i s t r y . T h e toxicity of A S appears to increase w i t h t h e hardness o f the a c c l i m a t i o n w a t e r w h e n organisms are tested at the same water hardness (84). T h i s study suggests that a c c l i m a t i o n conditions affect the susceptibilities of organisms to A S toxicity. S o m e of the v a r i a b i l i t y i n the toxicity estimates, b o t h w i t h i n a n d b e t w e e n studies, is expected to stem f r o m t h e r a p i d biodégradation o r o t h e r loss processes o f A S . A c u t e toxicity testing is usually c o n d u c t e d b y u s i n g a static exposure system w i t h o u t test substance r e n e w a l . U n d e r these conditions w e expect A S to degrade a n d t h e r e b y i n t r o d u c e a n u n q u a n t i f i e d l e v e l o f u n c e r t a i n t y into t h e acute toxicity test results. P u b l i s h e d reports o f the c h r o n i c toxicity o f C A S are s u m m a r i z e d i n Table V . L e B l a n c (75) exposed Daphnia magna to C A S i n a f o u r - g e n e r a t i o n toxicity test. Daphnia ( < 2 4 h old) w e r e exposed to C A S for 10 days; t h e n some o f the y o u n g w e r e isolated f r o m each concentration a n d exposures 1 2

1 2

1 2

A m e r i c a n Chemical Society

Library

1155 16th St. N.W, In Environmental Chemistry of Lakes and Reservoirs; Baker, Lawrence A.; Advances in Chemistry; Washington, American Chemical D.C. Society: 20036 Washington, DC, 1994.

548


Table IV. Acute Toxicity of C A S to Invertebrates and Fish I 2

Test Duration (h)

Organism


Invertebrates Brachionus rubens (rotifer) Daphnia magna (water flea)

Daphnia pulex (water flea) Lepomis macrochirus (bluegill sunfish) Oncorhynchus mykiss (rainbow trout) Brachydanio rerio (zebrafish)

Jordanella floridea (flagfish) Pimephales promelas (fathead minnow)

1.4

48 48 48 48 48

1.8 7.0 6.3 10.3

96 96 96 24 48 24 96 96 96 24

4.5 4.8 20.3 4.6 6.2 7.8 9 . 9 (fry)

96 45

Salmo trutta (brown trout) Phoxinus phoxinus (minnow) Carassius auratus (goldfish) Oryzias latipes (Japanese killifish)

(mg/L)

m

24

96 96 96 96 96

Lebistes reticulatus (guppy)

LC

24

6 96 24

E

6

b

8.9'

Ref. 74 59 75 76 77 77

59 65 78 79 78 79

1 2 . 8 (juv.) 2 0 . 1 (adult) 8.1

78

1 0 . 2 (fry)

79

17.0 22.5 13.5 16.2

(juv.) (adult) (adult) (juv.) 1 8 . 3 (fry)

79

18

80

30.5

81

60 28.4 70

82 79 83

"Indicates mean of six toxicity tests. Indicates mean of eight toxicity tests. Indicates mean of 10 toxicity tests. h

c

c o n t i n u e d w i t h t h e y o u n g as test o r g a n i s m for another 10 days. T h i s p r o c e d u r e was r e p e a t e d for four generations w i t h s u r v i v a l a n d r e p r o d u c t i o n u s e d as e n d points. O n t h e basis o f s u r v i v a l a n d r e p r o d u c t i o n , 2 . 0 m g / L was t h e no-observed-effect c o n c e n t r a t i o n . C o w g i l l a n d W i l l i a m s (86) i n v e s tigated t h e toxicity o f C A S to Ceriodaphnia dubia i n 7-day c h r o n i c toxicity tests. T h e m e a n E C v a l u e f o r r e p r o d u c t i o n , t h e most sensitive m e a s u r e of toxicity, was 36 m g / L . A no-observed-effect c o n c e n t r a t i o n was n o t r e ported. 1 2

5 0


17.

FENDINGER ET AL.

549

Behavior and Fate of Anionic Surfactants

Table V. Chronic Toxicity of C i A S to Invertebrates and Algae 2

Toxicity Test

NOEC\ ECso (mg/L)

10-day survival, reproduction, 4 generations tested 7-day chronic reproduction & survival

2.0 ( N O E C )

75

36 (ECso)

86

18 (EC )

59

60 (EQo, C A S )

72

Organism


Invertebrates Daphnia magna (water flea)

Cenodaphnia (water flea)

dubia

Plants Lemna minor (duckweed) Selenastrum capricornutum (green algae)

7-day growth

Ref

50

2-day population growth

13

° N O E C indicates no-observed-effeet concentration. N O T E : There are no data for fish.

B i s h o p a n d P e r r y (59) investigated the toxicity of six c o m p o u n d s , i n c l u d i n g C A S , w i t h d u c k w e e d (Lemna minor) i n a 7-day m u l t i g e n e r a t i o n flow-through toxicity test. Test concentrations w e r e analytically v e r i f i e d , a n d toxicities to f r o n d count, d r y w e i g h t , root w e i g h t , a n d g r o w t h rate w e r e assessed. A s w i t h most of the other c o m p o u n d s tested i n this study, the most sensitive i n d i c a t o r of C A S toxicity was root l e n g t h , w i t h a n E C 50 concentration of 18 m g / L . Yamane et a l . (72) r e p o r t e d a 2-day E C 5 0 v a l u e of 60 m g / L based o n the specific p o p u l a t i o n g r o w t h rate for the g r e e n alga, Selenastrum capricornutum. T h e r e are no p u b l i s h e d reports of the c h r o n i c toxicity of C A S to fish. C o n s i d e r i n g the comparable acute toxicity to fish a n d invertebrates o f C A S and the other anionic surfactants r e p o r t e d h e r e , f i s h c h r o n i c toxicity values for C A S are p r e d i c t e d to b e s i m i l a r to those r e p o r t e d for invertebrates. T h e c h r o n i c toxicity data r e p o r t e d h e r e for C A S is i n general a g r e e m e n t w i t h the p u b l i c a t i o n of S t e b e r et a l . (26). T h e s e authors r e p o r t e d c h r o n i c toxicity values to algae (Scenedesmus a n d Chlorella) a n d d a p h n i d s for the tallow A S (a m i x t u r e of C A S a n d C A S ) . T h e 21-day no-observed-effect concentration for Daphnia was 16.5 m g / L , a n d the E C levels w e r e 14.4 and 25.5 m g / L for Scenedesmus a n d Chlorella, respectively. The E C 5 0 concentrations w e r e 57.6 a n d 28.6 m g / L for the same species. 1 2

1 2

1 2

1 2

1 2

1 2

1 6

1 8

1 0

AES. T h e acute a n d c h r o n i c toxicity of A E S has not b e e n i n v e s t i g a t e d as t h o r o u g h l y as the toxicities o f other a n i o n i c surfactants. H o w e v e r , sufficient data are available to p r o v i d e a p r e l i m i n a r y assessment of the p o t e n t i a l h a z a r d to aquatic life (Table V I ) . M a k i (70) r e p o r t e d a 96-h L C value of 1.17 m g / L for Daphnia magna exposed to a C E S i n a f l o w - t h r o u g h toxicity test. T h e L C v a l u e was 5 0

1 4 7

2 2 5

5 0


550


Table V I . Acute Toxicity of C _ E S to Invertebrates and F i s h 1 2

3

Test Duration (h)

Organism Invertebrates Daphnia magna (water flea)


1 5

L£ {mgih)

48

70

1.17

(C14.7E2.258)

76

48

5 (C AE S) 13 (C AE S) 17 (C _i AE S) 20.2

96 96 96 96

1.6 (fry) 2.5 (juv.) 2.2 (adult) 1.5

79

96 96 96 96 96 96 96

2.2 (fry) 1.9 (juv.) 2.4 (adult) 2.4 (fry) 2.4 (juv.) 2.1 (adult) 1.0 (juv.)

79

96

3.0 (juv.)

79

12

Daphnia pulex (water flea) Fish Pimephales promelas (fathead minnow) Salmo trutta (brown trout) Brachydanio rerio (zebrafish) Lebistes (guppy)

Ref.

m

reticulatus

Oncorhynchus mykiss (rainbow trout) Carassius auratus (goldfish)

l2

3

12

5

4

22

87

e

88

79

79

"Indicates mean of two values.

based o n m e a s u r e d concentrations o f the A E S . T h i s v a l u e is less than t h e toxicity to a Daphnia species i n a static test system r e p o r t e d b y L u n d a h l et al. (76). T h e s e authors s t u d i e d t h e toxicity o f three samples o f A E S , t w o C A E S samples, a n d a ^ C _ A E S , a n d t h e y o b s e r v e d 4 8 - h E C values to range from 5 . 0 to 17 m g / L for these c o m p o u n d s (76). I n tests w i t h Daphnia pulex, M o o r e et a l . (87) r e p o r t e d a m e a n 4 8 - h E C 5 0 v a l u e o f 2 0 . 2 m g / L for an A E S . T h i s v a r i a b i l i t y i n t h e toxicity o f A E S to m e m b e r s o f t h e genus Daphnia m a y b e attributable, i n part, to differences i n species s u s c e p t i b i l i t y a n d t h e specific A E S tested. H o w e v e r , t h e role o f biodégradation s h o u l d not b e u n d e r e s t i m a t e d . L u n d a h l a n d C a b r i d e n c (68) d e m o n s t r a t e d that A E S toxicity to d a p h n i d s c a n b e c o m p l e t e l y r e m o v e d b y biodégradation w i t h i n 30 h . 1 2

3

1 2

1 4

2 2

5 0

T h e acute toxicity o f A E S to fish is s i m i l a r across fish species a n d s i m i l a r to the toxicity to Daphnia magna r e p o r t e d b y M a k i (70). L C values range from 1.5 for t h e b r o w n trout (Salmo trutto) (88) to 3.0 m g / L for t h e goldfish 5 0


17.

FENDINGER ETAL.

551

Surfactants

(Carassius auratus) (79). A l l of the fish toxicity values are based o n static exposures, b u t i n b o t h the N e w s o m e (79) a n d R e i i f et a l . (88) studies, test solutions w e r e r e n e w e d at least daily to m i n i m i z e biodégradation. C h r o n i c toxicity data for A E S exist for invertebrates, fish, a n d algae (Table V I I ) . M a k i (70) r e p o r t e d a N O E C based o n the most sensitive e n d p o i n t (total n u m b e r of y o u n g produced) of 0.27 m g / L for Daphnia magna exposed to C i . E S i n a flow-through, 21-day toxicity test. I n a flow-through life-cycle toxicity test w i t h fathead m i n n o w s (Pimephales promelas), g r o w t h was the most sensitive e n d p o i n t to C E S toxicity (70). T h e N O E C was 0.1 m g / L a n d the lowest-observed-effect concentration ( L O E C ) was 0.22 m g / L . T h e 2-day E C value for Selenastrum capricornutum population g r o w t h was r e p o r t e d as 65 m g / L for A E S (72). 4



7

3

1 4 7

3

5 0

Structure-Activity Relationships. T h e acute toxicity of a v a r i e t y of surfactants increased w i t h increased c h a i n l e n g t h of the h y d r o p h o b i c p o r t i o n of the surfactant (7, 61). T h i s effect was extensively s t u d i e d for L A S homologs for b o t h fish a n d invertebrates (5, 61, 65, 66). T h e s e data are s h o w n i n F i g u r e 10 a n d are quantitatively d e s c r i b e d b y eqs 2 a n d 3. F o r toxicity to f i s h , l o g (96-h LCso) = ( - 0 . 4 6 * C L ) + 5.99

(2)

F o r toxicity to invertebrates,

log (48-h LC50) = ( - 0 . 3 9 * C L ) + 5.41

(3)

w h e r e C L is the c h a i n l e n g t h of the c a r b o n atoms o n the a l k y l c h a i n . T h e data for fish are a c o m b i n a t i o n of i n f o r m a t i o n o n the b l u e g i l l sunfish (Lepomis macrochirus) (65) a n d the fathead m i n n o w (Pimephales promelas) (66). T h e data for the invertebrates are f r o m studies w i t h Daphnia magna (5, 61) a n d Daphnia pulex (61).

Table V I I . Chronic Toxicity of C . E S to Invertebrates, F i s h , and Algae 12

Organism

8

3

Toxicity Text

Invertebrates Daphnia magna (water flea) Fish Pimephales promelas (fathead minnow) Plants Selenastrum capricornutum (green algae)

21-day survival

NOEC-LOEC (mg/L) 0.27 (NOEC; C . E S)

70

0.10-0.22

70

14

life cycle

Ref

67

3

(C14.67E3S) 2-day population growth

65 (EC ) 50


72

552


10.00 h


Ε

Ο

ο to LOO

h

0.10h

12

14

ALKYL CHAIN LENGTH Figure 10. LAS LCso plotted as a function of alkyl chain length. A d d i t i o n o f carbons to the a l k y l c h a i n l e n g t h increases the h y d r o p h o b i c i t y of the surfactant. T h e increased h y d r o p h o b i c i t y results i n greater uptake rate constants, a n d toxicity increases b y a factor o f a p p r o x i m a t e l y 2.7 w i t h each a d d i t i o n a l a l k y l c a r b o n . A l i m i t e d a m o u n t of c h a i n - l e n g t h versus c h r o n i c - t o x i c i t y i n f o r m a t i o n exists for L A S , as w e l l as some c h a i n - l e n g t h versus acute-toxicity i n f o r m a t i o n for A S a n d A E S . T h e s e l i m i t e d data also s u p p o r t the relationship b e t w e e n a l k y l c h a i n l e n g t h a n d toxicity.

Risk Assessment R i s k assessments for anionic surfactants are o b t a i n e d b y c o m p a r i n g e n v i r o n m e n t a l exposure concentrations to effect levels (the q u o t i e n t method). A p r o t e c t i o n factor that reflects the e n v i r o n m e n t a l safety of the m a t e r i a l is calculated b y d i v i d i n g the exposure l e v e l b y the effect c o n c e n t r a t i o n . If the p r o t e c t i o n factor is greater than 1, the m a t e r i a l is d e e m e d safe. A l t h o u g h this approach to assessing risk yields a n u m e r i c a l value that c o u l d b e i n t e r p r e t e d as the relative safety of a c o m p o u n d , comparisons o f p r o t e c t i o n factors for different c o m p o u n d s s h o u l d be a v o i d e d . T h e risk assessment for each m a t e r i a l must be c o n s i d e r e d separately because of differences i n c h e m i c a l properties a n d differences i n the database u s e d to obtain the p r o t e c t i o n factor. I n a d d i t i o n , the degree o f u n c e r t a i n t y i n the exposure a n d effect


17.

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553

Surfactants


concentration d e t e r m i n a t i o n s s h o u l d b e t h o r o u g h l y u n d e r s t o o d so that the degree o f confidence i n the p r o t e c t i o n factor can be c o m m u n i c a t e d .

LAS. L A S e n v i r o n m e n t a l levels i n U n i t e d States surface w a t e r are expected to range f r o m < 0 . 0 4 to 0.14 m g / L , as p r e d i c t e d f r o m m o d e l i n g results a n d f r o m actual m o n i t o r i n g data (see E x p o s u r e A s s e s s m e n t section). Because of the agreement b e t w e e n results f r o m the n a t i o n a l L A S m o n i t o r i n g efforts a n d m o d e l p r e d i c t i o n s , there is a h i g h l e v e l of confidence i n this exposure assessment. F o r the effect l e v e l , a p p l i c a t i o n of the i n v e r t e b r a t e acute-to-chronic ratio to the most acutely sensitive invertebrate species, Dero, generates a c h r o n i c toxicity value o f 0.6 m g / L . T h i s value compares favorably w i t h the m e a s u r e d N O E C s of 1.2 a n d 1.4 m g / L , respectively, for the invertebrates Daphnia magna a n d Ceriodaphnia dubia. T h e fish species most sensitive to C L A S c h r o n i c toxicity is the fathead m i n n o w , Pimephales promelas. M o s t r e c e n t l y , F a i r c h i l d et a l . (64) r e p o r t e d a c h r o n i c C L A S N O E C o f 0.7 m g / L for the fathead m i n n o w . T h i s N O E C compares favorably w i t h the N O E C o f 1.1 m g / L r e p o r t e d b y H o l m a n a n d M a c e k (66) for the same species. 1 2

1 2

A n exposure l e v e l of 0.02 m g / L reflects m e a n r i v e r flow; w i t h a lowest n o effect c o n c e n t r a t i o n of 0.6 m g / L it y i e l d s a 9 0 t h p e r c e n t i l e p r o t e c t i o n factor of 30. T h i s agrees w i t h the risk assessment of K i m e r l e (89), w h o r e p o r t e d a L A S p r o t e c t i o n factor that e x c e e d e d 10. I n a d d i t i o n , c o n s i d e r i n g the literature a n d the k n o w n i n f l u e n c e of e n v i r o n m e n t a l factors o n the uptake a n d toxicity of C L A S i n aquatic organisms, a risk assessment for C L A S based o n laboratory toxicity studies is b e l i e v e d to b e conservative. F o r exa m p l e , L e w i s (73) c o m p a r e d the toxicity of C L A S to the b l u e - g r e e n algae Microcystis a n d the g r e e n algae Selenastrum, w h i c h w e r e exposed i n laboratory 4-day toxicity tests, w i t h a 10-day exposure of a n a t u r a l p h y t o p l a n k t o n assemblage (82 species o b t a i n e d from a lake). T h e s e assemblages w e r e assessed for effects of C L A S o n species d i v e r s i t y , s i m i l a r i t y , a n d n u m b e r , a n d for changes i n d i s s o l v e d oxygen. T h e N O E C for algae exposed i n this study was 27 m g / L . T h i s N O E C is far greater than the l a b o r a t o r y - d e r i v e d 96-h E C so for Microcystis a n d Selenastrum; a p p a r e n t l y laboratory algae tests p r o v i d e conservative estimates of safe concentrations i n the e n v i r o n m e n t . 1 2

1 2

1 2

1 2

I n a d d i t i o n , F a i r c h i l d et a l . (64) exposed an o u t d o o r stream c o m m u n i t y consisting of a d i v e r s e invertebrate b e n t h i c p o p u l a t i o n , Hyallela azteca, a n d Pimephales promelas. These organisms w e r e exposed to a m e a n concentrat i o n of 0.35 m g / L , a concentration not expected to cause adverse effects i f the laboratory-generated N O E C data w e r e p r o t e c t i v e of the s y s t e m . E n d points assessed d u r i n g the 45-day exposure i n c l u d e d a v a r i e t y o f p e r i p h y t i c a n d b e n t h i c invertebrate c o m m u n i t y m e a s u r e m e n t s . T h e s e authors f o u n d no effects o n the b i o t a c o n t a i n e d i n this study at 35 m g / L o f C L A S . 1 2


554


F i n a l l y , P i t t i n g e r a n d K i m e r l e (62) calculated h y p o t h e t i c a l w a t e r - q u a l i t y c r i t e r i a for C L A S . T h e values calculated are 0.23 m g / L for c o n t i n u o u s concentration a n d 0.625 m g / L for m a x i m u m concentration. T h e r e f o r e , l a b oratory a n d field data c o n f i r m that c u r r e n t concentrations of C L A S i n the aquatic e n v i r o n m e n t are safe. 1 2


1 2

AS. A S concentrations i n U n i t e d States surface waters are e x p e c t e d to b e less than 0.01 m g / L , based o n U S T E S T p r e d i c t i o n s a n d actual m e a s u r e d concentrations at S T P effluents. T h i s value w i l l serve as the A S exposure l e v e l for the aquatic risk assessment. T h e majority of the A S toxicity studies have b e e n c o n d u c t e d o n C A S . Because the average A S c h a i n l e n g t h u s e d i n c l e a n i n g p r o d u c t s is a p p r o x i mately C A S , a c h r o n i c N O E C for this m a t e r i a l is n e e d e d for the risk assessment. T h e quantitative s t r u c t u r e - a c t i v i t y relationship d e r i v e d for L A S a p p l i e d to the lowest C A S c h r o n i c N O E C of 2.0 m g / L for Daphnia magna y i e l d s an estimated C A S c h r o n i c N O E C of 0.27 m g / L . 1 2

1 4

1 2

1 4

T h e exposure to effect-level concentration ratio for A S y i e l d s a p r o t e c t i o n factor o f > 2 7 for C A S . Because o f the r a p i d A S biodégradation o b s e r v e d i n natural water a n d toxicity a m e l i o r a t i o n or attenuation r e s u l t i n g f r o m sorpt i o n to solids, this safety factor is expected to b e conservative. A d d i t i o n a l C A S c h r o n i c - t o x i c i t y studies w i t h f u l l analytical support to c o n f i r m exposure concentrations are suggested to validate the safety of C A S i n the aquatic e n v i r o n m e n t . 1 4

1 4

1 4

AES. E x p o s u r e concentrations for A E S are e x p e c t e d to b e 0.015 mg/ L , o n the basis o f U S T E S T p r e d i c t i o n s for m e a n - f l o w c o n d i t i o n s . Because U S T E S T - p r e d i c t e d concentrations are for the m i x i n g z o n e i n rivers d o w n stream from S T P effluents, the m o d e l p r e d i c t i o n s do not take i n t o account r e m o v a l b y sorption or biodégradation i n the r e c e i v i n g stream. T h e r e f o r e , the p r e d i c t e d A E S exposure concentrations are the highest expected e n v i r o n m e n t a l concentrations. T h e average A E S c h a i n l e n g t h u s e d i n c l e a n i n g p r o d u c t s is a p p r o x i m a t e l y C E S . T h e c h r o n i c - t o x i c i t y i n f o r m a t i o n was generated w i t h C E S. However, the results can b e extrapolated to d e t e r m i n e the c h r o n i c toxicity o f C E S b y u s i n g the L A S quantitative s t r u c t u r e - a c t i v i t y r e l a t i o n s h i p ( Q S A R ) . T h e extrapolated c h r o n i c toxicity N O E C s for C E S are t h e n 0.53, 1.5, a n d 79 for fish, invertebrates, a n d algae, r e s p e c t i v e l y . T h e toxicity v a l u e u s e d i n the risk assessment represents the N O E C f r o m a test o n the most sensitive species, the fathead m i n n o w . T h e ratio of the effect-level c o n c e n tration to the e x p o s u r e - l e v e l concentration y i e l d s a a p r o t e c t i o n factor o f 35 u n d e r m e a n - f l o w conditions. A s is the case w i t h L A S a n d A S , this risk assessment is c o n s i d e r e d conservative because of the a m e l i o r a t i o n o f toxicity r e s u l t i n g from sorption to effluent a n d surface water s u s p e n d e d solids. I n a d d i t i o n , A E S are expected to u n d e r g o an i n i t i a l h y d r o l y s i s l i k e A S . T h i s 1 3

3

1 3

3

1 4 7

1 3

3

3


17.

FENDINGER ET AL.


Surfactants

555

m e c h a n i s m w o u l d r a p i d l y r e m o v e A E S f r o m n a t u r a l waters a n d w o u l d result i n a m u c h l o w e r exposure. H o w e v e r , a d d i t i o n a l studies o n t h e fate a n d effects o f A E S are p l a n n e d to f u r t h e r s u p p o r t these conclusions.


Conclusions Integration o f use, biodégradation o r r e m o v a l d u r i n g sewage treatment, e n v i r o n m e n t a l concentrations, a n d aquatic effect data i n t o a n aquatic risk assessment demonstrates the safety o f L A S , A S , a n d A E S i n c o n s u m e r p r o d ucts. F i e l d investigations collaborate the risk assessments based o n laboratory a n d m o d e l measurements. A d d i t i o n a l investigations are u n d e r w a y to gain a d d i t i o n a l confidence i n the risk assessments m a d e for A S a n d A E S .

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ACCEPTED

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