2 Approaches to Decontamination or Disposal of Pesticides: Photodecomposition JACK R. PLIMMER Organic Chemical Synthesis Laboratory, Federal Research, Science, and Education Administration, USDA, Beltsville, MD 20705
The g u i d e l i n e s f o r the d i s p o s a l o f s m a l l q u a n t i t i e s o f unused p e s t i c i d e s i s s u e d b y the Environmental P r o t e c t i o n Agency i n 1975 make it clear that there is still a great need f o r satisf a c t o r y d i s p o s a l techniques f o r a variety o f pesticides. Specifically the g u i d e l i n e s s t a t e " s a f e d i s p o s a l procedures are most u r g e n t l y needed f o r those p e s t i c i d e s t h a t do not have a c c e p t a b l e d i s p o s a l procedures a t present and a r e e i t h e r : (a) extremely dangerous to man and wildlife because o f their h i g h toxicity; (b) not, o r o n l y s l o w l y degraded to nontoxic products in t h e environment; o r (c) produced in the l a r g e s t q u a n t i t i e s . P e s t i c i d e s in these c a t e g o r i e s i n c l u d e the organomercury and organoa r s e n i c compounds, t h a l l i u m sulfate, d i a z i n o n , methyl p a r a t h i o n , p a r a t h i o n , phorate, maneb, alachlor, CDAA, p r o p a c h l o r , a t r a z i n e , DDT, h e p t a c h l o r , toxaphene, l i n d a n e , chloramben, 2,4-D, 2 , 4 , 5 - T , aldrin, chlordane, e n d r i n , pentachlorophenol and 2,4,6-trichlorophenol" (1). Photochemical d e s t r u c t i o n o f organic m a t e r i a l has not achieved the s t a t u s o f a t e c h n o l o g i c a l process t h a t is a p p l i c a b l e on a l a r g e s c a l e ; indeed, its potential f o r d e t o x i c a t i o n o f wastes o r r e n d e r i n g them more s u s c e p t i b l e t o m i c r o b i a l degradat i o n has been l i t t l e explored. There i s an important need t o develop more data on r a t e s and e f f i c i e n c i e s o f photochemical r e a c t i o n s . Without t h i s b a s i c d a t a , there i s l i t t l e p o i n t i n d i s c u s s i n g the q u e s t i o n o f i n s t a l l a t i o n d e s i g n and c a l c u l a t i o n of o p e r a t i n g c o s t s . I n t h i s d i s c u s s i o n I would l i k e t o o u t l i n e some l i m i t i n g f a c t o r s and i n d i c a t e areas where progress i s desirable. M i c r o b i a l a c t i o n and the e f f e c t o f s u n l i g h t are two major f a c t o r s r e s p o n s i b l e f o r t r a n s f o r m a t i o n of p e s t i c i d e s i n the environment. I f the p e s t i c i d e i s a p p l i e d as a spray, a subs t a n t i a l p r o p o r t i o n o f the a p p l i e d m a t e r i a l may not reach the t a r g e t s i t e and an a p p r e c i a b l e amount may be l o s t by v o l a t i l i z a t i o n . P e s t i c i d e s v a p o r i z i n g from s u r f a c e s o r d u r i n g spray a p p l i c a t i o n may be transformed by p h o t o l y s i s i n the vapor phase; s i m i l a r l y p e s t i c i d e s i n water o r present on environmental 0-8412-0433-0/78/47-073-013$05.00/0 This chapter not subject to U.S. copyright. Published 1978 A m e r i c a n C h e m i c a l Society
14
DISPOSAL AND
DECONTAMINATION OF PESTICIDES
surfaces may be a l t e r e d c h e m i c a l l y by s o l a r r a d i a t i o n . I f s m a l l q u a n t i t i e s of p e s t i c i d e s are exposed to the prolonged a c t i o n of a i r , s u n l i g h t and m i c r o b i a l degradation, i t i s to be a n t i c i p a t e d t h a t i n most cases there w i l l be r a p i d breakdown t o simpler molecules. The problems i n v o l v e d i n i n t e n t i o n a l decontamination and d i s p o s a l of concentrated p e s t i c i d e wastes are somewhat d i f f e r e n t . I n c i n e r a t i o n appears to have g r e a t e s t p r a c t i c a l p o t e n t i a l as a d i s p o s a l technique when s u b s t a n t i a l q u a n t i t i e s of s u r p l u s combustible m a t e r i a l s are concentrated a t a s i n g l e l o c a t i o n . I t p r o v i d e s a complete s o l u t i o n to many problems of chemical d i s p o s a l , but i t i s important t h a t the c o n d i t i o n s r e q u i r e d f o r the combustion of each chemical be p r e v i o u s l y determined and t h a t the f l u e gases be e f f i c i e n t l y cleaned and monitored to ensure that no t o x i c m a t e r i a l s are r e l e a s e d ( 2 ) . Such c o n d i t i o n s demand equipment t h a t i s c o s t l y to i n s t a l l and operate. I f l a r g e volumes of m a t e r i a l s are to be handled, other options may be p r e f e r a b l e . S o i l d i s p o s a l o f f e r s a f e a s i b l e and economically a t t r a c t i v e a l t e r n a t i v e , but s u i t a b l e s i t e s are l i m i t e d and the c o r r e c t choice of s i t e i s of c r i t i c a l importance (3). D i l u t e aqueous wastes may be a p p l i e d to s u i t a b l y c o n s t r u c t ed s o i l d i s p o s a l areas or p u r i f i e d by passage through p e r c o l a t i o n beds and h o l d i n g tanks. S o i l d i s p o s a l r e l i e s on m i c r o b i a l a c t i o n to transform p e s t i c i d e s i n t o simple innocuous molecules. This process, i n v o l v i n g conversion of complex molecules to carbon d i o x i d e , water, c h l o r i d e i o n e t c . , i s g e n e r a l l y r e f e r r e d to as "mineralization". We can a l s o add chemical treatment and i r r a d i a t i o n to the processes of m i c r o b i a l a c t i o n and i n c i n e r a t i o n as ways to reduce the hazards of s u r p l u s p e s t i c i d e s . Chemical treatment of organic compounds may i n c l u d e r e a c t i o n s such as conversion t o carbon t e t r a c h l o r i d e by the process of c h l o r i n o l y s i s , which i m p l i e s r e a c t i o n w i t h gaseous c h l o r i n e under vigorous c o n d i t i o n s . Treatment w i t h other reagents such as sodium hydroxide may be used; f o r example, a strong base r a p i d l y increases the r a t e of h y d r o l y s i s of organophosphorus p e s t i c i d e s such as p a r a t h i o n . Thus t o x i c i t y may be s u b s t a n t i a l l y reduced. A v a r i e t y of chemical treatments have been i n v e s t i g a t e d . Kennedy et a l . (4) found t h a t s e v e r a l p e s t i c i d e s could be e f f e c t i v e l y degraded by d i s s o l v i n g metal r e d u c t i o n (sodium i n l i q u i d ammonia). Organochlorine compounds present a p a r t i c u l a r problem. The EPA g u i d e l i n e s s t a t e t h a t "the only acceptable d i s p o s a l procedure f o r these p e s t i c i d e s i s i n c i n e r a t i o n . However, i n most cases, complex i n c i n e r a t i o n equipment i s r e q u i r e d i n order t o assure that s u f f i c i e n t l y h i g h temperatures are developed, and to prevent atmospheric contamination by combustion products. Furthermore, i n c i n e r a t i o n i s p r a c t i c a l o n l y on a v e r y l a r g e s c a l e and i s uns u i t e d t o the s m a l l batch operations which c h a r a c t e r i z e most pesticide disposal situations. "We recommend t h a t a study be made of other techniques
2.
PLIMMER
15
Decontamination or Disposal of Pesticides
I n p a r t i c u l a r , we recommend t h a t a study be made of a d i s p o s a l procedure which employs both h y d r o l y s i s and o x i d a t i o n " ( 1 ) . I n such cases, I suggest t h a t the p o s s i b i l i t y of u s i n g i r r a d i a t i o n followed by m i c r o b i a l degradation should a l s o be examined as an a l t e r n a t i v e method t o reduce the hazard of d i l u t e aqueous wastes. Aqueous systems c o n t a i n i n g p a r t s per m i l l i o n or l e s s of c h l o r i n a t e d compounds or other t o x i c organic wastes may be i r r a d i a t e d to reduce t h e i r t o x i c i t y and a l s o to reduce t h e i r " r e c a l c i t r a n c e " . I f some p a r t s of the molecules can be modified i n t h i s way, they may be rendered more s u s c e p t i b l e to degradation by microorganisms. For example, a r e d u c t i o n i n the number of c h l o r i n e atoms attached to an aromatic r i n g w i l l g e n e r a l l y i n crease the r a t e of decomposition by microorganisms. The breakdown of (2,4-dichlorophenoxy)acetic a c i d by s o i l microorganisms i s much more r a p i d than t h a t of (2,4,5-trichlorophenoxy)acetic a c i d . S i m i l a r l y p o l y c h l o r i n a t e d biphenyls c o n t a i n i n g few halogen s u b s t i t u e n t s are more r e a d i l y degraded than the more h i g h l y s u b s t i t u t e d molecules ( 5 ) . P h o t o l y s i s as a method f o r the i n t e n t i o n a l d e s t r u c t i o n of p e s t i c i d e s would appear to have great p o t e n t i a l . S u n l i g h t as a source of r a d i a n t energy i s f r e e l y a v a i l a b l e , and s o l a r r a d i a t i o n i s a potent agent f o r the d e s t r u c t i o n of many man-made chemicals i n the environment. I n f a c t , i t i s v e r y d i f f i c u l t to s y n t h e s i z e organic chemicals t h a t can r e s i s t the a c t i o n of sun and a i r f o r long p e r i o d s . Water i s p u r i f i e d by the a c t i o n of a i r and s u n l i g h t . Many t o x i c chemicals, such as the c h l o r o d i o x i n s , may be decomposed by u l t r a v i o l e t r a d i a t i o n (6,7)· Most p e s t i c i d e s on u l t r a v i o l e t i r r a d i a t i o n u l t i m a t e l y a f f o r d products that are much l e s s t o x i c or hazardous to the e n v i r o n ment than the o r i g i n a l m a t e r i a l . I t may be p o s s i b l e t o take p r a c t i c a l advantage of t h i s f a c t i f we are w i l l i n g to examine the requirements and l i m i t a t i o n s of photochemical r e a c t i o n s . Questions that must be considered i n c l u d e the f o l l o w i n g : 1) How r a p i d l y do photochemical r e a c t i o n s occur and what energy input i s necessary? 2) What products are to be a n t i c i p a t e d and how are they a f f e c t e d by the p h y s i c a l s t a t e of the reactants? How R a p i d l y do Photochemical Reactions Occur and What are Energy Requirements?
Their
Most organic compounds can be decomposed by thermal energy, a process that u s u a l l y takes p l a c e r a p i d l y . How u s e f u l i s u l t r a v i o l e t i r r a d i a t i o n , i f we w i s h to achieve a s i m i l a r e f f e c t ? F i r s t , the rupture of a chemical bond r e q u i r e s a d e f i n i t e amount of energy. Because the d i s s o c i a t i o n of a carbon-carbon bond r e q u i r e s an input of about 100 k i l o c a l o r i e s per mole, we must use l i g h t possessing a t l e a s t t h a t amount of energy. The energy of electromagnetic r a d i a t i o n i s i n v e r s e l y p r o p o r t i o n a l to i t s wavelength so the source must provide a s a t i s f a c t o r y output of energy a t low wavelengths. A f r e q u e n t l y used source f o r
16
DISPOSAL AND DECONTAMINATION OF PESTICIDES
photochemical r e a c t i o n s i s the medium p r e s s u r e mercury a r c , w i t h maximum energy d i s t r i b u t i o n around 254 nm. T h i s source must be housed i n quartz to permit the passage of low wavelengths. Secondly, the r a t e of p h o t o l y s i s depends on s e v e r a l f a c t o r s . D i r e c t p h o t o l y s i s of an o r g a n i c compound i n s o l u t i o n r e q u i r e s that l i g h t must be absorbed f o r r e a c t i o n to occur. L i g h t energy i s measured i n quanta. The number of l i g h t quanta absorbed by the r e a c t a n t d i v i d e d i n t o the number of molecules of p h o t o l y s i s product formed measures the e f f i c i e n c y , or 'quantum y i e l d ' , of the p r o c e s s . However, the quantum y i e l d of a photochemical r e a c t i o n does not p r o v i d e a good i n d i c a t i o n of the r e a c t i o n r a t e because i t i s o n l y one f a c t o r i n determining the r a t e , which a l s o depends on the r a t e of a b s o r p t i o n of l i g h t by the system and the f r a c t i o n of absorbed l i g h t t h a t produces the r e a c t i v e s t a t e (8). Therefore the source of l i g h t must not o n l y possess s u f f i c i e n t energy i n terms of wavelength d i s t r i b u t i o n , i t must a l s o supply s u f f i c i e n t i n t e n s i t y i n terms of r a d i a n t energy output over u n i t time. A b s o r p t i o n o f l i g h t by the molecule i s d e f i n e d a t any wavel e n g t h by the shape of i t s a b s o r p t i o n curve. Benzenoid compounds g e n e r a l l y absorb l i g h t weakly around 300 nm, which corresponds to the r e g i o n of the s o l a r spectrum p r o v i d i n g most energy. Cyclodiene i n s e c t i c i d e s such as a l d r i n or d i e l d r i n do not absorb l i g h t except a t wavelengths below 250 nm. Such r a d i a t i o n r e q u i r e s an u n f i l t e r e d mercury a r c source. I used the term 'quantum y i e l d ' to i n d i c a t e the e f f i c i e n c y of the photodecomposition p r o c e s s . I t must be r e c o g n i z e d t h a t the a b s o r p t i o n of l i g h t does not l e a d t o decomposition i n every case, even though the l i g h t may have s u f f i c i e n t energy to break chemical bonds. The energy absorbed by the molecule l e a d s to e x c i t a t i o n . I n a d d i t i o n to decomposition, l o s s of energy from the e x c i t e d s t a t e may occur by f l u o r e s c e n c e , e x c i t a t i o n of another molecule, e t c . D i s s o c i a t i o n o f a bond r e p r e s e n t s o n l y one of the p o s s i b l e modes of energy l o s s . How Can Some of the L i m i t a t i o n s be Overcome? The requirement t h a t the r a d i a t i o n c o n t a i n energy o f s u f f i c i e n t l y short wavelengths t o cause d i s s o c i a t i o n of a chemical bond a p p l i e s o n l y to the d i r e c t a b s o r p t i o n of energy by the r e a c t i n g molecule; a l t e r n a t i v e processes can f a c i l i t a t e the i n d u c t i o n of photochemical r e a c t i o n by l i g h t of longer wavelengths. S e n s i t i z a t i o n r e p r e s e n t s an example o f such a p r o c e s s . A m i t r o l e i s r e s i s t a n t to the d i r e c t a c t i o n of l i g h t of wavelengths g r e a t e r than 260 nm, i t begins t o absorb l i g h t a t s h o r t e r wavel e n g t h s , and i t i s p h o t o c h e m i c a l l y s t a b l e . However, i n the presence of r i b o f l a v i n , a m i t r o l e i n aqueous s o l u t i o n i s r a p i d l y degraded by l i g h t of wavelengths above 300 nm ( 9 ) . S i m i l a r l y , the c y c l o d i e n e i n s e c t i c i d e s i n the presence o f acetone, which absorbs l i g h t a t 290 nm, undergo photochemical r e a c t i o n s .
2.
PLIMMER
Decontamination or Disposal of Pesticides
17
S e n s i t i z e d processes i n v o l v e the t r a n s f e r of energy from a molecule t h a t has absorbed l i g h t and become e x c i t e d to a h i g h e r energy s t a t e ( u s u a l l y a " t r i p l e t " s t a t e ) . C o l l i s i o n s t h a t t a k e place during t h i s r e l a t i v e l y long-lived " t r i p l e t " state r e s u l t i n t r a n s f e r of energy from the e x c i t e d molecule t o a second molecule, which becomes the r e a c t a n t . Thus, photochemical r e a c t i o n occurs w i t h o u t d i r e c t a b s o r p t i o n of l i g h t by the r e a c t i n g molecule. Another type of energy t r a n s f e r i n v o l v e s "charge t r a n s f e r " mechanisms. For example, the photodecomposition of halogenated aromatic compounds such as DDT i s f a c i l i t a t e d i n the presence of amines. Halobenzenes f u n c t i o n as e l e c t r o n acceptors i n the formation of e x c i t e d c h a r g e - t r a n s f e r complexes w i t h amines, and p h o t o l y s i s of the c h a r g e - t r a n s f e r complexes may occur a t much lower wavelengths than a r e r e q u i r e d f o r the halogenated compounds alone. S e n s i t i z e r s a r e abundant i n " n a t u r a l " waters and account f o r the enhanced r a t e s of p h o t o l y s i s of p o l l u t a n t s i n streams and r i v e r s . Even though the body of water may appear opaque or darkc o l o r e d t o the o b s e r v e r , r a t e s of p h o t o l y s i s near the s u r f a c e are more r a p i d than i n d i s t i l l e d water. The n a t u r e of " n a t u r a l " p h o t o s e n s i t i z e r s has r e c e i v e d a t t e n t i o n . Ross and Crosby (10) examined the p h o t o o x i d a t i o n of a l d r i n and found t h a t i n the presence o r absence of l i g h t of wavelengths g r e a t e r than 300 nm, a l d r i n (10 p g / l . ) was s t a b l e t o l i g h t i n d e m i n e r a l i z e d water. A l d r i n does not absorb l i g h t above 250 nm, but i n the presence of 0.1% of the t r i p l e t s e n s i t i z e r s , acetone or acetaldehyde, a l d r i n was p h o t o o x i d i z e d t o d i e l d r i n . S i n g l e t oxygen d i d not appear t o be i m p l i c a t e d i n t h i s c o n v e r s i o n , nor were photoi s o m e r i z a t i o n products detected i n these experiments. I t was suggested t h a t the f o r m a t i o n of a p h o t o c h e m i c a l l y generated o x i d a n t such as p e r a c e t i c a c i d might be r e s p o n s i b l e f o r the conversion. The a b i l i t y of r e l a t i v e l y i n v o l a t i l e o x i d a n t s t o b r i n g about such r e a c t i o n s was suggested by experiments i n s t e r i l i z e d water obtained from r i c e paddies. I t appeared unl i k e l y i n t h i s case t h a t v o l a t i l e compounds would remain a f t e r vacuum evaporation; n e v e r t h e l e s s 25% of the a l d r i n was converted to d i e l d r i n i n 36 hours i r r a d i a t i o n . The e f f e c t of p h y s i c a l s t a t e has a l s o been s t u d i e d t o some extent. The i n t e r a c t i o n of a molecule w i t h a s u r f a c e m o d i f i e s the p h y s i c a l and chemical p r o p e r t i e s of the molecule through the e f f e c t s of p o l a r o r nonpolar groups a t the i n t e r f a c e . I f the molecule i s i r r a d i a t e d , i t w i l l d i s p l a y m o d i f i e d photochemical behavior because the energy r e l a t i o n s between e x c i t e d e l e c t r o n i c s t a t e s w i l l have been changed. As examples, the u l t r a v i o l e t s p e c t r a of a n i l i n e s and phenols i n hexane were measured i n the presence and absence of s i l i c a . The s h i f t s i n a b s o r p t i o n maxima can be r a t i o n a l i z e d i n terms of hydrogen bonding (11). The changes i n a b s o r p t i o n spectrum produced when a molecule i s adsorbed on a s o l i d w i l l a l s o change i t s |hotochemical b e h a v i o r .
18
DISPOSAL AND DECONTAMINATION OF PESTTCTDES
S o i l appears to e x e r t a p r o t e c t i v e e f f e c t , but s i l i c a may en hance p h o t o l y s i s . Korte and h i s coworkers (12,13) r e p o r t e d the m i n e r a l i z a t i o n of a number of compounds exposed t o u l t r a v i o l e t i r r a d i a t i o n i n an oxygen stream. The source of l i g h t was a h i g h pressure lamp (125 W) housed i n a pyrex c o l d f i n g e r . I t was found t h a t the r a t e of c o n v e r s i o n was g r e a t e r i f the compounds were adsorbed on p a r t i c u l a t e matter than i f they were deposited as s o l i d s or t h i n f i l m s . The experimental arrangement permitted i r r a d i a t i o n of the m a t e r i a l adsorbed on s i l i c a g e l ; the s i l i c a g e l was mixed c o n t i n u o u s l y by a r o t a t i n g drum surrounding the lamp housing. I n i t i a l l y , i t was found t h a t c e r t a i n c y c l o d i e n e p e s t i c i d e s and t h e i r pho t ο i somer i ζ a t ion products were completely decomposed (12) on i r r a d i a t i o n i n the s o l i d s t a t e . Hexachlorobenzene, pentachlorobenzene, pentachlorophenol, 1 , 1 , l - t r i c h l o r o - 2 , 2 - b i s (£chlorophenyl)ethane (DDT), 1,l-dichloro-2,2-bis(£-chlorophenyl)ethylene (DDE), 2,2^4,4',5,5'-hexachlorobiphenyl, and 2,2 ,4,5 t e t r a c h l o r o b i p h e n y l were adsorbed on quartz and i r r a d i a t e d (Table I ) . ,
t
Table I . I r r a d i a t i o n of pentachlorophenol, DDT and DDE on 100 g s i l i c a g e l (wavelength > 290 nm) (12).
Compound PCP DDT DDE *
Initial Quantity mg 102 385 362
Amount Recovered 7 days 4 days % mg me % 26 298 91
25 77 25
12 66 19
12 255 69
* A l s o detected dichlorobenzophenone, 38 trichlorobenzophenone, 7 mg
mg;
The r a t e of disappearance o f the compounds was measured, and i n some cases the q u a n t i t y o f CO- and HC1 evolved was a l s o determined. I t was considered t h a t the r a t e o f disappearance was not accounted f o r by the f o r m a t i o n of o r g a n i c photoproducts, nor could i t be a t t r i b u t e d to v o l a t i l i z a t i o n . These f i n d i n g s may have an important b e a r i n g on the f a t e of p e s t i c i d e s adsorbed on p a r t i c u l a t e matter. What Products are Formed i n Photochemical Reactions of P e s t i c i d e s ? In p r a c t i c e , we are concerned w i t h the r a t e of pho to decom p o s i t i o n and a l s o w i t h the n a t u r e of the products. P h o t o l y s i s of halogenated compounds o f t e n leads to dehalogenated p r o d u c t s , presumably v i a a process of hydrogen a b s t r a c t i o n from the s o l v e n t by a completely d i s s o c i a t e d molecule or e x c i t e d complex
2.
19
Decontamination or Disposal of Pesticides
PLIMMER
between s o l u t e and s o l v e n t . The t a b l e s show some r e s u l t s o f our own i n v e s t i g a t i o n s o f the p h o t o l y s i s of s e v e r a l c h l o r i n a t e d aromatic compounds (14,15) (Tables I I - V ) . Table I I . P h o t o l y s i s of chlorophenol methyl ethers i n methanol ( l g / L , wavelength > 260 nm) (14,15). Recovery of C I C ^ O C ^ Time
4 h 8 h
Y i e l d of
(%)
C^OC^
(%)
2.
m
£
o_
m
£
45 13
+ -
7 +
54 83
54 54
70 76
Table I I I . P h o t o l y s i s o f c h l o r o t o l u e n e s wavelength > 260 nm) (14,15). Recovery of C1C H CH 6
Time
4
3
i n methanol ( l g / L ,
Y i e l d of C ^ C I L j
(%)
£. 4 h 8 h
(%)
m
5
13
+
+
Ε 61 37
o^
m
67 60
61 66
Ε 21 37
Table IV. P h o t o l y s i s o f c h l o r o b e n z o n i t r i l e s i n methanol ( l g / L , wavelength > 260 nm) (14,15). Amount Recovered (%)
Product * (%)
4 h
8 h
4 h
8 h
57
36
27
37
82
80
13
17
2,6-Dichlorobenzonitrile 2-Chlorobenzonitrile
*Formed by l o s s o f 1 C l atom. Table V. P h o t o l y s i s o f chlorobenzoic a c i d s i n methanol (0.5 g/L, wavelength > 260 nm, 8 h i r r a d i a t i o n ) (14,15). Amount Recovered (%)
Y i e l d o f C^COOH (%)
ο
-
100
m
9
52
£
37
60
DISPOSAL AND DECONTAMINATION OF PESTICIDES
I t i s not easy t o p r e d i c t photochemical r e a c t i v i t y i n terms o f the known e l e c t r o n i c e f f e c t s o f s u b s t i t u e n t groups* The e x c i t e d s t a t e i n halogen l o s s i s probably a s i n g l e t , and l i t t l e informat i o n e x i s t s concerning e l e c t r o n d i s t r i b u t i o n i n t h i s s t a t e . S e v e r a l workers have i n v e s t i g a t e d t h e r a t e s o f f o r m a t i o n and t h e products formed by t h e n u c l e o p h i l i c displacement of halogens and other s u b s t i t u e n t s under t h e i n f l u e n c e o f l i g h t . One o f t h e e a r l i e s t s t u d i e s was concerned w i t h the enhancement o f the r a t e o f replacement o f c h l o r i n e by the h y d r o x y l group of c h l o r a c e t i c a c i d under u l t r a v i o l e t l i g h t — i n v e s t i g a t e d by von E u l e r i n 1916 (16). Crosby (17 , and t h i s Symposium) has d i s c u s s e d examples of p h o t o n u c l e o p h i l i c r e a c t i o n s of p e s t i c i d e s and has c i t e d t h e photodecomposition o f n i t r o f e n , fenaminosulf and o t h e r p e s t i c i d e s i n water among a number o f examples. Because l i g h t f a c i l i t a t e s such displacement r e a c t i o n s , t h e i r study should be extended t o determine whether the enhancement o f r e a c t i o n r a t e s can be put t o p r a c t i c a l use. There i s now a s u b s t a n t i a l volume o f l i t e r a t u r e d e s c r i b i n g the i s o l a t i o n and i d e n t i f i c a t i o n of i r r a d i a t i o n products o f p e s t i c i d e s . Many e a r l i e r s t u d i e s were performed under i l l - d e f i n e d c o n d i t i o n s . Subsequent s t u d i e s were c a r r i e d out t o determine products under "environmental" c o n d i t i o n s , i n order t o p r o v i d e i n f o r m a t i o n f o r r e g u l a t o r y agencies. Other l a b o r a t o r y s t u d i e s o f photochemical r e a c t i o n s o f p e s t i c i d e s were conducted f o r "academic" reasons. However, we r e c o g n i z e that t h e processes are complex. I n i t i a l photochemical r e a c t i o n s y i e l d one or more products t h a t may undergo subsequent photochemical o r thermal reactions„ so a complex m i x t u r e of products r e s u l t s . There may be an accumulation o f p h o t o s t a b l e m a t e r i a l s . I n v e r y d i l u t e s o l u t i o n i n t h e presence o f oxygen i t i s l i k e l y t h a t s u b s t a n t i a l degradation o f t h e molecule w i l l occur. M e c h a n i s t i c o r g a n i c photochemistry i s an i n t e l l e c t u a l l y stimulating pursuit. Unfortunately i t i s s t i l l i n a r e l a t i v e l y p r i m i t i v e s t a t e . To quote from a review by H. E. Zimmerman (18): "Despite the i n c r e a s i n g number of known photochemical r e a c t i o n s the t o t a l number o f w e l l - e s t a b l i s h e d photochemical t r a n s f o r m a t i o n s i s i n f i n i t e s i m a l compared w i t h t h a t i n ground s t a t e chemistry .... f u r t h e r , our understanding o f the f a c t o r s which c o n t r o l photochemical r e a c t i o n s i s s t i l l q u i t e p r i m i t i v e . . . more complex c a l c u l a t i o n s a r e not needed, a new approach i s needed. F i n a l l y , t o t a l l y new methods o f determining photochemical r e a c t i o n mechanisms a r e needed; t h e number i s r e a l l y q u i t e s m a l l when compared w i t h those developed f o r use i n ground s t a t e o r g a n i c chemistry." M e c h a n i s t i c s t u d i e s o f p e s t i c i d e photochemistry a r e sparse; the major e f f o r t has u s u a l l y been t o i s o l a t e and i d e n t i f y photoproducts. T h i s can r e a d i l y be understood i n terms o f immediate o b j e c t i v e s , s i n c e concern t h a t t h e photoproducts may become environmental p o l l u t a n t s o r demonstrate t o x i c i t y has been a major
2.
PLIMMER
Decontamination or Disposal of Pesticides
21
reason f o r undertaking t h e i r i d e n t i f i c a t i o n . Some i n d i c a t i o n of the q u a l i t a t i v e s i g n i f i c a n c e of these photoproducts may have been obtained, but more p r e c i s e q u a n t i t a t i v e i n f o r m a t i o n has been obtained i n o n l y a few cases. K i n e t i c a n a l y s i s presents an extremely important and comp l e x problem. However, few photochemical s t u d i e s of p e s t i c i d e s have been concerned w i t h the measurement of r e a c t i o n r a t e s . For t h i s reason the work of the EPA group i n Athens, Georgia, has been p a r t i c u l a r l y v a l u a b l e i n e s t a b l i s h i n g a q u a n t i t a t i v e t r e a t ment t h a t a l l o w s p r e d i c t i o n of p h o t o l y s i s r a t e s under s o l a r i r r a d i a t i o n (19). This group has approached the problem of determining the l i f e t i m e of organic p o l l u t a n t s i r r a d i a t e d i n a q u a t i c systems. Dealing w i t h the process of d i r e c t p h o t o l y s i s , they have d e r i v e d mathematical expressions as a b a s i s f o r judgment as to whether a g i v e n compound w i l l appear as a s i g n i f i c a n t r e s i d u e i n the a q u a t i c environment and have computed " p h o t o l y s i s r a t e s " of a number of compounds. ( " P h o t o l y s i s r a t e " here i m p l i e s the p h o t o l y t i c conversion of the s t a r t i n g m a t e r i a l over u n i t time.) S o l a r i n t e n s i t y and the a t t e n u a t i o n of l i g h t i n n a t u r a l waters were used to c a l c u l a t e energy i n p u t s . Quantum y i e l d data and a b s o r p t i o n c o e f f i c i e n t s of the m a t e r i a l i n q u e s t i o n were used i n a computer-based c a l c u l a t i o n of photol y s i s r a t e s . The f i g u r e s shown i n Table VI i n d i c a t e the v a l u e s obtained f o r DDE (19). Table V I . P h o t o l y s i s h a l f - l i f e c a l c u l a t e d f o r DDE near the s u r f a c e of water body (19). Season Spring Summer Fall Winter
Half-life 1.4 days 0.94 2.4 61
These c a l c u l a t i o n s were v e r i f i e d e x p e r i m e n t a l l y f o r d i l u t e s o l u t i o n s . In h i g h c o n c e n t r a t i o n s the computed h a l f - l i v e s are longer as one approaches the s i t u a t i o n i n which a l l the i n c i d e n t l i g h t i s absorbed. The s o l v e n t i s r e s p o n s i b l e f o r some energy a b s o r p t i o n , so h a l f - l i f e i n c r e a s e s w i t h i n c r e a s i n g depth. W i t h i n the range of assumptions, there was reasonable correspondence between e x p e r i m e n t a l l y determined r a t e s and those obtained by computation (+ 30%). Even i n the absence of quantum y i e l d d a t a , minimum h a l f - l i v e s can be c a l c u l a t e d from the a b s o r p t i o n spectrum. Many environmental v a r i a b l e s l i m i t the v a l u e of the comp u t a t i o n . However, i n a w a s t e - d i s p o s a l f a c i l i t y , most of these v a r i a b l e s c o u l d be c o n t r o l l e d . Thus, the data and computations present a b a s i s f o r a f e a s i b i l i t y study, because necessary energy input and p h o t o l y t i c h a l f - l i v e s can be c a l c u l a t e d from data obtained i n the l a b o r a t o r y . T h i s approach m e r i t s a t t e n t i o n ,
22
DISPOSAL AND
DECONTAMINATION OF PESTICIDES
and i n i t i a l data must be accumulated t o make f u r t h e r e v a l u a t i o n possible» Costs P r a c t i c a l attempts t o e v a l u a t e the techniques are few. The c o s t f i g u r e s provided are of i n t e r e s t but a r e u s u a l l y out of date. In a r e p o r t i s s u e d by the Atomic Energy Commission, B a l l a n t i n e et a l . (20) d i s c u s s e d the p r a c t i c a l i t y of u s i n g atomic r a d i a t i o n f o r wastewater treatment. The a p p l i c a t i o n s t h a t they suggested were the improvement of sludge h a n d l i n g , t o t a l d e s t r u c t i o n of o r g a n i c s , d i s i n f e c t i o n , and the s e l e c t i v e removal of r e f r a c t o r i e s or s p e c i f i c compounds. The l a s t a p p l i c a t i o n i s of p a r t i c u l a r i n t e r e s t i n t h i s symposium. The r e f r a c t o r i e s i n waste water a r e o r g a n i c compounds not e f f i c i e n t l y removed by primary treatment. They c o u l d i n c l u d e c h l o r i n a t e d phenol, l i g n i n e , and o t h e r s l o w l y biodegradable compounds. T h e i r c o n c e n t r a t i o n i n m u n i c i p a l wastewaters ranges from 10 PPM t o o c c a s i o n a l h i g h v a l u e s of 100 PPM. In i n d u s t r i a l wastes, h i g h e r v a l u e s a r e encountered. The c a l c u l a t e d c o s t of r a d i a t i o n treatment f o r 1000 g a l l o n c o n t a i n i n g 10 PPM was $0.11; t h i s i n c r e a s e d t o $1.10 i f the c o n c e n t r a t i o n of p o l l u t a n t was 1000 PPM. These c o s t s were based on disappearance of the r e f r a c t o r y compound, not on t o t a l o x i d a t i o n , which must be accomplished by f u r t h e r treatment. The q u e s t i o n of u s i n g u l t r a v i o l e t i r r a d i a t i o n f o r the r e moval of r e f r a c t o r y compounds from water was addressed by B u l l a and Edgerley (21). They found t h a t a l d r i n , d i e l d r i n and e n d r i n i n d i l u t e aqueous s o l u t i o n s were degraded by l i g h t of 253.7 nm wavelength. Time, depth and i n t e n s i t y of r a d i a t i o n were r e l a t e d to the degradation of i n d i v i d u a l compounds, and c o s t estimates were made f o r 50 percent degradation of p e s t i c i d e s a t 10 cm depth. These were $24 f o r a l d r i n s o l u t i o n s , $74 f o r d i e l d r i n and $57 f o r e n d r i n per m i l l i o n g a l l o n s , f o r c o n c e n t r a t i o n s of 20 t o 25 ug per l i t e r . These f i g u r e s c o u l d p o s s i b l y be reduced i f the r e a c t o r design were improved, and many compounds l e s s r e s i s t a n t t o p h o t o l y s i s could be processed a t lower c o s t . I r r a d i a t i o n i n the presence of o x i d a n t s such as c h l o r i n e or oxygen may be more e f f e c t i v e ; however, the f o r m a t i o n of c h l o r i n a t e d o r g a n i c molecules as end products i s u n d e s i r a b l e . There i s need f o r f u r t h e r study of the comparative c o s t s of waste d i s p o s a l by i n c i n e r a t i o n , b i o l o g i c a l treatment, s o i l d i s p o s a l , ocean d i s p o s a l and i r r a d i a t i o n . I n a d d i t i o n to d o l l a r c o s t s , other f a c t o r s , p a r t i c u l a r l y environmental impacts, must a l s o be taken i n t o account. U l t i m a t e l y , i t i s to be hoped t h a t t e c h n o l o g i c a l developments w i l l permit the e f f i c i e n t u t i l i z a t i o n of s o l a r energy to degrade chemical wastes; such a process might i n v o l v e the use of p h o t o l y s i s alone o r as a p r e p a r a t o r y step to achieve p a r t i a l breakdown of r e f r a c t o r y molecules b e f o r e wastes are subjected t o m i c r o b i o l o g i c a l degradation.
2. PLIMMER
Decontamination or Disposal of Pesticides
Literature
1.
2. 3. 4. 5. 6. 7. 8. 9. 10. 11.
12. 13. 14. 15. 16. 17. 18. 19. 20. 21.
23
Cited
Lawless, E. W., Ferguson, T. L . , and Meiners, A. F. "Guide lines for the Disposal of Small Quantities of Unused Pesti cides'." EPA-67012-75-057, National Environmental Research Center, U. S. Environmental Protection Agency, Cincinnati, Ohio. 1975. Kennedy, M. V., Stojanovic, B. J., and Shuman, F. L . , Jr., Residue Rev. (1967) 29, 89-104. Plimmer, J. R., and Kearney, P. C. 165th Natl. Mtg. Amer. Chem. Soc., Dallas (April 1973). Kennedy, M. V., Stojanovic, B. J., and Shuman, F. L . , Jr., J. Environ. Qual (1972) 1, 63-65. Peakall, D. Β., and Lincer, J. L . , BioScience (1970) 20, 958-964. Plimmer, J. R., Klingebiel, U. I., Crosby, D. G., and Wong, A. S. Advances in Chemistry No. 120. pp. 44-54. American Chemical Society, Washington, D.C. 1973. Crosby, D. G., and Wong, A. S., Science (1977) 195, 13371338. Turro, N. J., J. Chem. Ed. (1967) 44, 536-537. Plimmer, J. R., Kearney, P. C., Kaufman, D. D., and Guardia, F. S., J. Agr. Food Chem. (1967) 15, 996-997. Roos, R. D., and Crosby, D. C., Chemosphere (1975) 5, 277282. Plimmer, J. R., in "Fate of Pesticides in Environment", Vol. 6 of "Pesticide Chemistry", A. S. Tahori, ed. pp. 47-76. Gordon and Breach Science Publishers, New York and London. 1972. Gäb, S., Parlar, H., Nitz, S., Hastert, Κ., and Korte, F., Chemosphere (1974) 3, 183-186. Gäb, S., Nitz, Η., Parlar, Η., and Korte, F., Chemosphere (1975) 4, 251-256. Plimmer, J. R., Residue Rev. (1971) 33, 47-74. Plimmer, J. R., and Hummer, Β. Ε., 155th Am. Chem. Soc. Nat. Meeting, San Francisco (1968). von Euler, Η., Chem. Ber. (1916) 49, 1366-1371. Crosby, D. G., Moilanen, K. W., Nakagawa, Μ., and Wong, A. S., U.S.-Japan Seminar on the Environmental Toxicology of Pesticides, Ioso, Japan, Oct. 1971. Zimmerman, Η. Ε., Science (1976) 191, 523-528. Zepp, R. Α., and Clive, D. Μ., Environ. Sci. Technol. (1977) 11, 359-366. Ballantine, D. S., Miller, L. Α., Bishop, D. F., and Rohrman, F. A. Atomic Energy Commission Report. 1970. Bulla, C. D., III, and Edgerley, E., Jr., J. Water Pollut. Contr. Fed. (1968) 40, 546-556.
MARCH 9,
1978
