Organophosphorus Pesticide Volatilization - ACS Symposium Series

17 Organophosphorus Pesticide Volatilization Model Soil Pits and Evaporation Ponds

Downloaded by NANYANG TECHNOLOGICAL UNIV on September 23, 2017 | http://pubs.acs.org Publication Date: August 15, 1984 | doi: 10.1021/bk-1984-0259.ch017

PAUL F. SANDERS and JAMES N. SEIBER Department of Environmental Toxicology, University of California at Davis, Davis, CA 95616

A simple environmental chamber was used to measure v o l a t i l i z a t i o n of mevinphos, diazinon, methyl parathion, malathion, and parathion from model s o i l pit and evaporation pond disposal systems, and experimental results were compared to mathematical model predictions. Experimental v o l a t i l i z a t i o n rate constants were determined for the pesticides from water. Henry's law constants gave good estimates of their relative v o l a t i l i t y , and absolute volatilization rates could be predicted from measured water loss rates or wind speed measurements. For pesticides with binding constants to s o i l greater than one, v o l a t i l i z a t i o n was much more rapid from the evaporation pond than from the s o i l p i t . The EXAMS computer program gave good estimates of volatilization rates from water and water-soil systems. Triton X-100 decreased v o l a t i l i z a t i o n rates of low solubility pesticides from water.

It has been estimated that over 400,000 m3 of dilute waste pesticide solution are generated in the United States annually (1). While the bulk of these waste solutions are used legally as spray diluent, some are disposed of by chemical or biological treatment, incineration, or in soil pits and evaporation ponds (1-3). Because of the large volume of water involved, incineration is not a preferred method. Adsorption of pesticides onto media such as activated charcoal, as well as biological and chemical treatment, are feasible methods, but they require frequent monitoring and maintenance. Evaporation ponds and soil pits have the advantages of less maintenance, applicability to a broad range of chemicals, and the ability to reduce the volume of waste via water evaporation. (1-3). In addition, these latter two methods have been estimated to be the least expensive on a per gallon basis of waste (1). This is of considerable importance because the wastes are 0097-6156/84/0259-0279$06.00/0 © 1984 American Chemical Society

Krueger and Seiber; Treatment and Disposal of Pesticide Wastes ACS Symposium Series; American Chemical Society: Washington, DC, 1984.


280

TREATMENT AND

DISPOSAL OF PESTICIDE WASTES

g e n e r a l l y disposed of by the farmer or a p p l i c a t o r on s i t e by the cheapest and simplest method a v a i l a b l e . Despite the advantages, there i s concern over the use of such containment methods because the f a t e of p e s t i c i d e s put i n t o such s i t e s i s not w e l l known ( 1 ) . One such f a t e process i s v o l a t i l i z a t i o n from the d i s p o s a l s i t e . Organophosphorus p e s t i c i d e v o l a t i l i z a t i o n from water and s o i l i s r e l a t i v e l y u n i n v e s t i g a t e d , and i f t h i s route of l o s s occurs to an a p p r e c i a b l e extent from d i s p o s a l s i t e s , a l o c a l r e s p i r a t o r y hazard may e x i s t . In t h i s paper, the v o l a t i l i z a t i o n of f i v e organophosphorus p e s t i c i d e s from model s o i l p i t s and evaporation ponds i s measured and p r e d i c t e d . A simple environmental chamber i s used to o b t a i n v o l a t i l i z a t i o n measurements. The use of the two-film model f o r p r e d i c t i n g v o l a t i l i z a t i o n r a t e s of organics from water i s i l l u s t r a t e d , and agreement between experimental and p r e d i c t e d r a t e con s t a n t s i s evaluated. Comparative v o l a t i l i z a t i o n s t u d i e s are described u s i n g model water, s o i l - w a t e r , and s o i l d i s p o s a l sys tems, and the r e s u l t s are compared to p r e d i c t i o n s of EXAMS, a popular computer code f o r p r e d i c t i n g the f a t e of organics i n aquatic systems. F i n a l l y , the experimental e f f e c t of T r i t o n X100, an e m u l s i f i e r , on p e s t i c i d e v o l a t i l i z a t i o n from water i s presented. Model P e s t i c i d e s F i v e organophosphorus p e s t i c i d e s were chosen that could be i s o thermally and simultaneously analyzed by gas chromatography u s i n g an N-P TSD d e t e c t o r . They are a l l c u r r e n t l y commercially used and e x h i b i t a wide range of physicochemical p r o p e r t i e s (Table I ) . A l s o i n f l u e n c i n g the choice of these p e s t i c i d e s was the f a c t that v o l a t i l i z a t i o n data measured from s o i l and water under c o n t r o l l e d l a b o r a t o r y c o n d i t i o n s are scarce f o r methyl p a r a t h i o n , p a r a t h i o n , and d i a z i n o n (14-17), and are not a v a i l a b l e f o r malathion and mevinphos. T e c h n i c a l mevinphos (60% Ε-isomer, S h e l l Development Co.), d i a z i n o n (87.2%, Ciba-Geigy Corp.), and malathion (93.3%, American Cyanamid), and a n a l y t i c a l grade methyl p a r a t h i o n (99%, Monsanto) and p a r a t h i o n (98%, S t a u f f e r Chemical Co.) were used. Laboratory Model Model D i s p o s a l System. The s p e c i f i c d i s p o s a l systems modeled use l i n e d p i t s as d e s c r i b e d by others (1-3). The l i n i n g i s u s u a l l y rubber or concrete, and i s used to prevent p e s t i c i d e s o l u t i o n from l e a c h i n g to the surrounding area. Because of the impervious l i n e r , the only t r a n s p o r t route f o r parent p e s t i c i d e i s v o l a t i l i z a t i o n , p r o v i d i n g the l i n e r remains i n t a c t . The s i m p l i c i t y of these systems allowed the use of a c r y s t a l l i z i n g d i s h as a model d i s p o s a l p i t . The d i s h (50 χ 100 mm; i n s i d e depth, 0.044 m; i n s i d e diameter, 0.095 m; c a p a c i t y , 310 ml) was f i l l e d to the brim with water or s o i l c o n t a i n i n g the d e s i r e d amount of p e s t i c i d e .


17.

SANDERS AND SEIBER

Pesticide

Organophosphorus Pesticide Volatilization

281

Table I . Physicochemical P r o p e r t i e s of Model P e s t i c i d e s a t 22°C Hydrolysis Vapor ^ Water Molecular Rate Constant Pressure Solubility Weight


a

Mevinphos Diazinon Me Parathion Malathion Parathion

b

224 304 263 330 291

miscible^ 68.8 37,7 143 12.4 d

e

d

e

f

2200 162 , 11.2 8.24? 6.05

1

34.5 .

g

h

h

2

5 8

- k 2 97 250 . 5.08 K

t

3

F H m

6 mm Hg χ 10 hr χ 10 , pH 8.5 Bowman e t a l . (4) Bowman e t a l . (5) Freed e t a l . (6) Êstimated from Spencer (7) .Calculated from Spencer e t a l . (8) .Calculated from Worthing (9) ^ C a l c u l a t e d from H a r r i s (10) and Faust e t a l . (11) C a l c u l a t e d from Smith et a l . (12) C a l c u l a t e d from H a r r i s (10) and Wolfe e t a l . (13) d

f

Environmental Chamber. The model d i s p o s a l system was placed i n an environmental chamber (Figure 1). D e t a i l s of the chamber and i t s use are discussed elsewhere (18). The chamber was designed so that i t was easy t o switch model waste dumps by simply changing c r y s t a l l i z i n g d i s h e s . I t was constructed from two f i v e - g a l l o n Pyrex b o t t l e s w i t h t h e i r bottoms c u t o f f . The c r y s t a l l i z i n g d i s h r e s t e d i n a Pyrex t r a y contained i n s i d e the chamber. An a i r d i s p e r s i o n tube s u p p l i e d a v a r i a b l e laminar a i r flow across the surface of the d i s h . The a i r , c o n t a i n i n g v o l a t i l i z e d p e s t i c i d e (and water), e x i t e d from the chamber through XAD-4 r e s i n , which trapped v o l a t i l i z e d p e s t i c i d e . To determine the amount v o l a t i l i z e d , the r e s i n was e x t r a c t e d w i t h e t h y l a c e t a t e , the solvent volume reduced, and the p e s t i c i d e s were analyzed by gas chromatog raphy. V o l a t i l i z a t i o n data reported from the environmental chamber were not c o r r e c t e d f o r v o l a t i l i z e d p e s t i c i d e r e c o v e r i e s . Recovery s t u d i e s p r e v i o u s l y run (18) gave percent r e c o v e r i e s as f o l l o w s : mevinphos, 72±6%, d i a z i n o n , 83±5%, methyl p a r a t h i o n , 77±5%, malathion, 76±8%, and p a r a t h i o n , 76±6%. I n l e t a i r was h u m i d i f i e d by passing i t through a column which had water t r i c k l i n g down i t over g l a s s r i n g s (18). By c o n t r o l l i n g the f r a c t i o n of a i r that passed through the column, the r e l a t i v e humidity could be v a r i e d and c o n t r o l l e d . Although i t could a l s o be v a r i e d , the a i r flow r a t e through the chamber was always s e t a t 20 1pm, which gave an a i r turnover time o f 1.7 minutes. Wind speed measurements were taken u s i n g a



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T R E A T M E N T A N D DISPOSAL O F PESTICIDE WASTES

c

Figure 1. Environmental chamber. A, a i r entrance; B, a i r e x i t ; C, hygrotherm; D, temperature and humidity probe; E, Pyrex t r a y ; F, c r y s t a l l i z i n g d i s h ; G, a i r d i s p e r s i o n tube; H, #12 rubber stoppers (covered with aluminum f o i l ) ; I , p e s t i c i d e vapor t r a p s ; J , flow meter. Reproduced with permission from Ref. 18. Copyright 1983, Pergamon P r e s s .


17.

S A N D E R S A N D SEIBER


283

Datametrics Model 100VT A i r Flow Meter. Measurements were taken at v a r i o u s l o c a t i o n s above the s o i l or water s u r f a c e a t a height of 0.8 cm, where the laminar a i r flow v e l o c i t y was g r e a t e s t . Depending on the probe l o c a t i o n r e l a t i v e to the a i r d i s p e r s i o n tube, the measured wind speed v a r i e d from 0.5 to 1.5 m/s, with an average of 1 m/s. At g r e a t e r heights above the s u r f a c e , the a i r flow r a t e was much lower and the a i r flow p a t t e r n s were unknown.


Two-Film Model f o r V o l a t i l i z a t i o n of Organics from Water V o l a t i l i z a t i o n of a chemical from water i s a f i r s t order process (19): Rate = kC

(1)

where k i s the f i r s t order r a t e constant (time and C i s the c o n c e n t r a t i o n of chemical i n water. Models used to p r e d i c t v o l a t i l i z a t i o n r a t e s have been based on the two-film theory (19), the Knudsen equation (15), and on p r i n c i p l e s based on evaporation from surface d e p o s i t s ( 2 ) . The two-film theory i s a simple and widely used k i n e t i c model f o r c a l c u l a t i o n of v o l a t i l i z a t i o n r a t e cons t a n t s o f organic chemicals from water, o r i g i n a l l y a p p l i e d to environmental v o l a t i l i z a t i o n by L i s s and S l a t e r (20) and l a t e r by Mackay and Leinonen (21) and Smith e t a l . (19). According to the two-film theory, v o l a t i l i z a t i o n from a water body depends on molecular d i f f u s i o n of a chemical through t h i n f i l m s of a i r and water on e i t h e r s i d e of the i n t e r f a c e . I t i s assumed that the chemical i s a t e q u i l i b r i u m across the i n t e r f a c e as determined by the Henry's law constant f o r the chemical. C o n s i d e r a t i o n of the above concepts leads to the f o l l o w i n g equation f o r the f i r s t order r a t e constant: k = ( l / L K U / k p + (RT/H k ) )

- 1

g

(2)

where L i s the s o l u t i o n depth (m), k and k are the l i q u i d and gas f i l m mass t r a n s f e r c o e f f i c i e n t s , r e s p e c t i v e l y (m/s), R i s the gas constant (atm m K mol"" ),«T is_çhe temperature (Κ), and Η i s the Henry's law constant (atm m mol ) . The Henry's law constant i s d e f i n e d as the r a t i o of the p a r t i a l pressure of a s o l ute above water t o i t s s o l u t i o n c o n c e n t r a t i o n a t e q u i l i b r i u m , and f o r low s o l u b i l i t y compounds can be estimated by the r a t i o of i t s vapor pressure to i t s water s o l u b i l i t y (22). Values f o r k- and k can be thought of as the v e l o c i t i e s of chemical movement through the water and a i r f i l m s , r e s p e c t i v e l y . They vary with environmen t a l c o n d i t i o n s , such as wind speed, water c u r r e n t s , and tempera t u r e , and w i t h the d i f f u s i o n c o e f f i c i e n t of the chemical (23). Henry's law constants f o r the p e s t i c i d e s used i n t h i s study were a l l l e s s than 10" atm m mol (Table I I ) . I t has been shown (19) that i n t h i s case, the l i q u i d f i l m of Equation 2 i s i n s i g n i f i c a n t and 1

g


284

TREATMENT AND DISPOSAL O F PESTICIDE WASTES


k = Hk /LRT g

(3)

Furthermore, as long as environmental c o n d i t i o n s remain constant, kg w i l l be n e a r l y constant ( d i f f u s i v i t y d i f f e r e n c e s between p e s t i c i d e s w i l l have only a minor e f f e c t ) and v a r i a t i o n s i n the r a t e constant should be l a r g e l y c o n t r o l l e d by the Henry's law constant (19). A common method f o r e s t i m a t i n g kg values i s t o f i r s t estimate kg f o r water, a w e l l c h a r a c t e r i z e d r e f e r e n c e compound, and then adjust t h i s to the kg of the compound of i n t e r e s t u s i n g the molec u l a r weight adjustment o f L i s s and S l a t e r (20): k

= k (18/M)** (4) c w where M i s the molecular weight of the p e s t i c i d e , and c and w r e f e r to the chemical of i n t e r e s t and water r e s p e c t i v e l y . T h i s adjustment c o r r e c t s f o r d i f f u s i v i t y d i f f e r e n c e s between compounds, which a r e i n v e r s e l y p r o p o r t i o n a l to the square root of t h e i r molecular weights. The kg value f o r water can be c a l c u l a t e d u s i n g a measured water evaporation r a t e and an equation given by Smith (19): g

g

k

= NRT/(P°-P) (5) w where P° and Ρ are the saturated and a c t u a l p a r t i a l pressure (atm) οξ wate^ vaçor a t temperature Τ (°K), R i s t h e ^ g a s ^ o n s t a n t (atm m mol Κ ) , and Ν i s the water f l u x (mol m hr ). Alterna t i v e l y , kg may be estimated by use of an e m p i r i c a l equation, such as that i n c o r p o r a t e d i n the EXAMS computer code (24), that e s t i mates k f o r water (m/hr) from the wind speed (m/s) a t 10 cm height : g

g

k

= 0.1857 + 11.36 χ WIND SPEED (6) w Wind speeds measured a t other heights may be adjusted by assuming a l o g a r i t h m i c wind p r o f i l e : g

U

2

= U^logiZ^Z^/log^/Z^]

(7)

where and U. a r e wind speeds a t h e i g h t s Z- and Z^, and Ζ i s the roughness Height. Although not i l l u s t r a t e d here, p e s t i c i d e k^ and k values may be c a l c u l a t e d d i r e c t l y from wind speed measurements and t h e i r r e s p e c t i v e d i f f u s i o n c o e f f i c i e n t s (23). In the present work, i t was d e s i r e d to 1) v e r i f y the p r e d i c t i o n that the Henry's law constant c o n t r o l l e d v a r i a t i o n s i n the experimental v o l a t i l i z a t i o n r a t e constants under constant e n v i r o n mental c o n d i t i o n s , and 2) compare experimental v o l a t i l i z a t i o n r a t e constants to p r e d i c t e d constants using the two methods f o r e s t i mating kg f o r water and the molecular weight adjustment procedure of L i s s and S l a t e r as discussed above. g


17. SANDERS A N D SEIBER


285


Experimental and P r e d i c t e d V o l a t i l i z a t i o n Kate Constants P e s t i c i d e s o l u t i o n s were prepared i n tap water (pH 8.110.1) as reported p r e v i o u s l y (18). I n i t i a l p e s t i c i d e concentrations were 180 ppm f o r mevinphos, 14 ppm f o r d i a z i n o n and methyl p a r a t h i o n , 24 ppm f o r malathion, and 3.5 ppm f o r p a r a t h i o n . V o l a t i l i z a t i o n of the p e s t i c i d e s was measured each day f o r 7 days. The s o l u t i o n pH was 8.5±0.2, the r e l a t i v e humidity of the chamber a i r was c o n t r o l l e d a t 85±1%, and the chamber temperature average was 22± 2°C. Water (2 or 4 ml) was sampled, the r e s i n i n the trap was changed, and the water l o s t to evaporation ( p r e v i o u s l y determined by weighing, 27±2 ml out of 310 ml) was replaced each day. Samples were prepared and analyzed as reported p r e v i o u s l y (18). Because of slow c o n c e n t r a t i o n decreases with time, low v o l a t i l i z a t i o n r a t e s r e l a t i v e to h y d r o l y s i s r a t e s i n some cases, and small a r t i f i c i a l l o s s e s of p e s t i c i d e due to repeated water sampling, the most accurate method of determining v o l a t i l i z a t i o n r a t e constants was to d i v i d e the average p e s t i c i d e c o n c e n t r a t i o n f o r that day i n t o the average v o l a t i l i z a t i o n r a t e over the same p e r i o d (Equation 1). Rate constants f o r the seven days were averaged. The e n t i r e experiment was performed i n t r i p l i c a t e . Although a l o g a r i t h m i c wind speed p r o f i l e d i d not e x i s t i n our chamber, the measured wind speed was adjusted to an a r t i f i c i a l wind speed of 2.21 m/s a t 10 cm height u s i n g Equation 7. Experimental and p r e d i c t e d v o l a t i l i z a t i o n r a t e constants f o r the f i v e p e s t i c i d e s are l i s t e d i n Table I I . I t should be noted t h a t , d e s p i t e low H values f o r the p e s t i c i d e s , experimental v o l a t i l i z a t i o n r a t e s f o r d i a z i n o n and p a r a t h i o n a r e f a i r l y r a p i d from water under the c o n d i t i o n s of our t e s t s ( t of 4.2 and 9.6 days, r e s p e c t i v e l y ) . When compared to t h e i r h y d r o l y s i s r a t e constants (Table I ) , v o l a t i l i z a t i o n can be seen to be a more important route of l o s s than h y d r o l y s i s f o r d i a z i n o n , p a r a t h i o n , and methyl p a r a t h i o n . The r e l a t i v e v o l a t i l i z a t i o n r a t e s reported here f o r d i a z i n o n and p a r a t h i o n are i n good agreement w i t h those reported by L i c h t e n s t e i n (14). I t i s apparent from Table I I that v a r i a t i o n s i n the e x p e r i mental r a t e constants (k) a r e e s s e n t i a l l y c o n t r o l l e d by the Henry's law constant, i n agreement w i t h the two-film theory p r e d i c t i o n . A p l o t of k y s . H f o r the f i v e p e s t i c i d e s gave an i n t e r c e p t of 5.4 χ 10 hr , a slope of 6.9 χ 10 mol/(hr atm m ) , and a c o r r e l a t i o n c o e f f i c i e n t of 0.969. Thus, i t seems that Henry's law values could be used to p r e d i c t r e l a t i v e v o l a t i l i z a t i o n r a t e s of the p e s t i c i d e s , and an absolute v o l a t i l i z a t i o n r a t e f o r one p e s t i c i d e can be c a l c u l a t e d i f the v o l a t i l i z a t i o n r a t e i s known f o r another and Henry's law constants a r e known f o r both: t

rate

2

= rate

x

χ (H^H^

(8)

Except f o r mevinphos, agreement between experimental v o l a t i l i z a t i o n r a t e constants and r a t e constants p r e d i c t e d u s i n g k


286

TREATMENT AND


Table I I . V o l a t i l i z a t i o n of F i v e Organophosphates from Water Pesticide

H

a

Experimental ±1 Std. Dev.

P r e d i c t e d k^ 11 Std. Dev. Method I

C


e

Mevinphos 0.0518 Malathion 2.51 Me Parathion 10.3 Parathion 18.7 Diazinon 94.0

g

0.3610.06 2.210.1 1311 3013 6815

0.07610.006 3.010.2 14+1 2412 11819

Predicted k , 11 Std. Dev. Method 2 f

0.0410.02 1.410.5 613 1115 54127

.atm.m mol χ 10 ( c a l c u l a t e d from Table I) hr χ 10 ^From u n c e r t a i n t y i n water l o s s r a t e ^From u n c e r t a i n t y i n measured wind speed Ûsing measured water l o s s r a t e and Equation 5 Using measured wind speed and Equation 6 Vapor pressure was d i v i d e d by d e n s i t y of mevinphos (5.58 χ 10^ mol/m^) D

1

4

g

values from measured water l o s s r a t e s i s w i t h i n a f a c t o r of two (Table I I ) . T h i s c l o s e agreement i n d i c a t e s that v o l a t i l i z a t i o n of low s o l u b i l i t y organophosphates from water can be estimated from water l o s s r a t e s . The poor c o r r e l a t i o n f o r mevinphos i s a t t r i b u ted to the method f o r e s t i m a t i n g Henry's law constant, which i s only a p p l i c a b l e to low s o l u b i l i t y compounds. For compounds such as mevinphos, a d i r e c t measurement of Η i s recommended. The gas s t r i p p i n g apparatus of Mackay may be appropriate (25). Except f o r mevinphos, agreement between experimental r a t e constants and r a t e constants p r e d i c t e d u s i n g kg f o r water, as estimated from wind speed measurements, was w i t h i n a f a c t o r of three or b e t t e r (Table I I ) , although the l a b o r a t o r y measurements were higher i n a l l cases. At a given wind speed, i t has been observed that v o l a t i l i z a t i o n r a t e s vary w i t h the l a b o r a t o r y system used, and are u s u a l l y somewhat higher than those i n the e n v i r o n ment (23). Equation 6 was derived from wind tunnel experiments, which mimic the r e a l environment b e t t e r than our chamber, so i t s kg p r e d i c t i o n s might be expected to be lower than those we measured. The u n c e r t a i n t y i n the wind speed i s another important c o n s i d e r a t i o n . As mentioned p r e v i o u s l y , the wind speed a t 0.8 cm height v a r i e d by 150% depending on the probe l o c a t i o n , and the c a l c u l a t e d wind speed at 10 cm height was an a r t i f i c i a l v a l u e , much higher than the a c t u a l wind speed at t h i s h e i g h t . Nonethe l e s s , t h i s approach was f e l t to be j u s t i f i e d s i n c e a i r movement immediately above the water surface would be expected to c o n t r o l v o l a t i l i z a t i o n r a t e s . Considering the above, the agreement between experimental and p r e d i c t e d values i s q u i t e good.It appears


17.

SANDERS AND SEIBER


287

that methods to p r e d i c t v o l a t i l i z a t i o n r a t e s from wind speeds can be used to estimate v o l a t i l i z a t i o n r a t e s f o r a simple l a b o r a t o r y system. In t h i s case, a method that r e q u i r e d the assumption of a l o g a r i t h m i c wind speed p r o f i l e (Equation 7) was a p p l i c a b l e to a chamber that provided c o n t r o l l e d a i r flow only immediately above the water s u r f a c e .


Volatilization

from Water, Soil-Water, and S o i l Systems

In order to a s c e r t a i n the i n f l u e n c e o f s o i l on v o l a t i l i z a t i o n , p e s t i c i d e s were incorporated i n t o water, a w a t e r - s o i l mixture, wet s o i l , and dry s o i l (1.7 (w/w) hygroscopic water s t i l l p r e s e n t ) , and the percent v o l a t i l i z a t i o n that occurred i n one day was measured. For a l l four media, the i n i t i a l p e s t i c i d e amounts were h e l d n e a r l y constant, and were approximately equal to the l e v e l s given i n the previous s e c t i o n . The s o i l used was R e i f f sandy loam (78% sand, 16% s i l t , 6% c l a y , 2.8% organic matter, and bulk d e n s i t y of 1.3 g/ml). For s o i l samples, the d e s i r e d amount of p e s t i c i d e d i s s o l v e d i n e t h y l acetate (ca. 5 ml) was slowly dripped onto dry s o i l w i t h frequent shaking. For wet s o i l , the s o i l was then blended a t low speed w i t h a Waring blender w i t h enough water to s a t u r a t e i t (36% w/w) f o r one minute. For the water and s o i l mixt u r e , 73 g of dry s o i l were added to 286 ml of prepared p e s t i c i d e s o l u t i o n i n the c r y s t a l l i z i n g d i s h . The chamber c o n d i t i o n s were the same as i n the previous s e c t i o n . S o i l samples (ca. 4 g) were e x t r a c t e d f o r 1 minute with 250 ml e t h y l acetate u s i n g a Waring e x p l o s i o n proof blender, equipped w i t h P o l y t r o n blades, a t 80 v o l t s . The e x t r a c t s were f i l t e r e d through Whatman #1 f i l t e r paper and concentrated f o r GLC a n a l y s i s . R e s u l t s are uncorrected f o r s o i l r e c o v e r i e s , which from t r i p l i c a t e determinations a t 5 and 500 ppm s p i k i n g l e v e l s were found to be as f o l l o w s : saturated s o i l , 87±4% ( a l l p e s t i c i d e s ) ; dry s o i l 76±4% (mevinphos), 91±6% ( a l l other p e s t i c i d e s ) . Water samples from the w a t e r - s o i l system were c e n t r i f u g e d to remove suspended m a t e r i a l before e x t r a c t i o n . Simultaneous b i n d i n g constants of the p e s t i c i d e s to R e i f f sandy loam a t the concentrations used i n t h i s study were measured by shaking 200 ml of prepared p e s t i c i d e s o l u t i o n with 100 grams of the s o i l f o r s u f f i c i e n t time to allow e q u i l i b r a t i o n to occur (4 hours f o r mevinphos, 1 hour f o r the other p e s t i c i d e s ) . The sand was allowed to s e t t l e , and the s i l t and c l a y were removed from the a l k a l i n e s o l u t i o n (pH 7.9) by c e n t r i f u g a t i o n on a t a b l e t o p c e n t r i fuge. The r e s u l t a n t decrease i n the water c o n c e n t r a t i o n of the p e s t i c i d e was then measured by a n a l y z i n g water samples taken before and a f t e r mixing with s o i l . Experimental b i n d i n g constants were as f o l l o w s (ug/g s o i l ) / ( u g / m l water): mevinphos, 1.110.1; d i a z i n o n , 4.3±0.4; methyl p a r a t h i o n , 4.0±0.3; malathion, 1.6±0.2; p a r a t h i o n , 9±2. D i a z i n o n , methyl p a r a t h i o n , and p a r a t h i o n , with b i n d i n g constants to s o i l c o n s i d e r a b l y greater than 1, showed a decrease i n the percent p e s t i c i d e v o l a t i l i z e d i n one day as the s o i l / w a t e r



288

TREATMENT AND DISPOSAL OF PESTICIDE WASTES

r a t i o was increased (Figure 2). T h i s was due to b i n d i n g of the p e s t i c i d e s by the s o i l causing a decrease i n the f r e e p e s t i c i d e c o n c e n t r a t i o n i n water a v a i l a b l e f o r v o l a t i l i z a t i o n . L i c h t e n s t e i n showed a s i m i l a r decrease i n v o l a t i l i z a t i o n f o r d i a z i n o n and parathion i n the presence of s o i l (14). Mevinphos, with a b i n d i n g constant of about 1, had a greater a f f i n i t y f o r water than f o r s o i l (on a volume b a s i s ) . As the s o i l / w a t e r r a t i o increased, i t was crowded i n t o a p r o g r e s s i v e l y smaller volume of water. Thus, i t s c o n c e n t r a t i o n i n water and t h e r e f o r e i t s v o l a t i l i z a t i o n r a t e increased, although i t was very low i n a l l cases. Malathion, with a b i n d i n g constant of s l i g h t l y over 1, showed t r a n s i t i o n a l behavior. V o l a t i l i z a t i o n r a t e s from dry s o i l were by f a r the lowest i n a l l cases, because of the high b i n d i n g c a p a c i t y that dry s o i l has f o r p e s t i c i d e s i n the absence of water (26). The percent p e s t i c i d e v o l a t i l i z e d i n one day from wet s o i l c o r r e l a t e d p o s i t i v e l y with the f a c t o r [vapor pressure/(water s o l u b i l i t y χ b i n d i n g c o n s t a n t ) ] . T h i s f a c t o r has been reported to be l i n e a r l y r e l a t e d to the v o l a t i l i z a t i o n r a t e of chemicals from s o i l surfaces (27). For p e s t i c i d e s with Henry's law constants and s o i l b i n d i n g constants w i t h i n the range s t u d i e d , the f a c t o r i s a l s o approximately p r o p o r t i o n a l to the f r a c t i o n of chemical i n s o i l a i r a t e q u i l i b r i u m (28). In the present study, i t was found that four of the p e s t i c i d e s had low f a c t o r s , and l e s s than 1% v o l a t i l i z e d i n 1 day (Table I I I ) . Diazinon, on the other hand, had a higher f a c t o r , and 2% of i t v o l a t i l i z e d . The use of t h i s f a c t o r t h e r e f o r e does seem to have some merit f o r q u a l i t a t i v e prediction.

Table I I I . P e s t i c i d e V o l a t i l i z a t i o n from Wet S o i l C o r r e l a t e d with a S o i l V o l a t i l i z a t i o n F a c t o r a

Pesticide Mevinphos Malathion Parathion Me Parathion Diazinon

% Volatilized** ±1 Std. Dev. 0.48±0.06 0.3110.01 0.8±0.2 0.710.1 2.010.6

Volatilization Factor atm m m o l " χ Ι Ο 3

1

0.0471 1.57 2.08 2.58 21.9

^ D u p l i c a t e determinations In the f i r s t day Vapor pressure/(water s o l u b i l i t y χ b i n d i n g constant)


8

0


17.

SANDERS AND SEIBER


I

I

DIAZINON

I

1

HE PARATHION PARATHION

Γ MEVINPHOS

MALATHION

WATER

WET SOIL

WATER AND SOIL

DRY SOIL

Figure 2. Experimentally determined and EXAMS p r e d i c t e d percents v o l a t i l i z e d ( i n one day) f o r f i v e organophosphorus p e s t i c i d e s incorporated i n t o water, w a t e r - s o i l , and s o i l systems. Computer p r e d i c t i o n s are not shown f o r mevinphos or f o r dry s o i l .


289

290

T R E A T M E N T AND DISPOSAL O F PESTICIDE WASTES


Use of EXAMS w i t h Model D i s p o s a l Systems EXAMS (Exposure A n a l y s i s Modeling System) i s an e l a b o r a t e computer program that p r e d i c t s the f a t e o f organic chemicals i n aquatic systems (24). Most input data can be e a s i l y measured, c a l c u l a t e d , or obtained from l i t e r a t u r e sources. For t h i s reason, the program i s r e a d i l y a c c e s s i b l e to chemists f o r use as a p r e d i c t i v e t o o l . In the present study, EXAMS was used to c a l c u l a t e v o l a t i l i z a t i o n r a t e constants from water, wet s o i l , and a w a t e r - s o i l mix t u r e . EXAMS uses the two-film theory to c a l c u l a t e v o l a t i l i z a t i o n r a t e s from the 10 cm wind speed as discussed above. EXAMS r e q u i r e s as a minimum environment a t l e a s t one l i t t o r a l (water) and one b e n t h i c (sediment) compartment. A very small benthic com partment f o r the water system and a very small l i t t o r a l compart ment f o r the wet s o i l system (7.09 χ 1 0 " m volume and 1 χ 10~8 m depth i n both cases) was used, so that these compartments and t h e i r input parameters had a n e g l i g i b l e e f f e c t on the c a l c u l a t e d r a t e s . For the w a t e r - s o i l system, the same p r o p o r t i o n s were used as i n the l a b o r a t o r y experiment. T r a n s f e r r a t e s between s o i l and water were assumed to be r a p i d r e l a t i v e to v o l a t i l i z a t i o n r a t e s , and were s e t as recommended i n the EXAMS manual (24). The input data needed by EXAMS i n order t o c a l c u l a t e v o l a t i l i z a t i o n r a t e s from a w a t e r - s o i l system, u s i n g p a r a t h i o n as an example, a r e shown i n Table IV. Percents v o l a t i l i z e d i n one day f o r the v a r i o u s media were c a l c u l a t e d u s i n g i n i t i a l p e s t i c i d e amounts and the o v e r a l l v o l a t i l i z a t i o n r a t e constants, obtained from the h a l f l i f e f o r v o l a t i l i z a t i o n as output by EXAMS. Mevinphos r e s u l t s a r e not i n c l u d e d here, f o r as discussed p r e v i o u s l y , methods f o r c a l c u l a t i o n used i n EXAMS are not a p p r o p r i a t e f o r water m i s c i b l e compounds. The experimental and computer p r e d i c t e d percents v o l a t i l i z e d i n one day are q u a l i t a t i v e l y s i m i l a r ( F i g u r e 2). Q u a n t i t a t i v e l y , exper imental and p r e d i c t e d percents v o l a t i l i z e d agreed w i t h i n a f a c t o r of three f o r d i a z i n o n , methyl p a r a t h i o n , and malathion, and w i t h i n a f a c t o r of f i v e f o r p a r a t h i o n . C o n s i d e r i n g the f a c t that EXAMS was not intended f o r use w i t h wet s o i l systems, these r e s u l t s are encouraging. I t should be noted that h y d r o l y s i s of these p e s t i c i d e s i s expected to occur simultaneously w i t h v o l a t i l i z a t i o n f o r the pes t i c i d e s s t u d i e d (Table I ) . Over a 7 day experiment, however, only malathion and mevinphos would be expected to hydrolyze to a s i g n i f i c a n t extent. We determined the l o s s r a t e of mevinphos to be 0.0016±0.0002 hr-1 (tJj = 18 days), and of malathion to be 0.0111 0.001 h r " ( t ^ = 2.6 days) a t 2212°C, a t pH 8.210.2 f o r a model evaporation pond by d a i l y sampling of d u p l i c a t e p e s t i c i d e s o l u t i o n s (covered to prevent v o l a t i l i z a t i o n ) f o r 7 days and p l o t t i n g log c o n c e n t r a t i o n versus time. For both of these p e s t i c i d e s , then, degradation was a much more important route of p e s t i c i d e l o s s from water than v o l a t i l i z a t i o n . The r e l a t i v e l y slow l o s s r a t e of the other p e s t i c i d e s could not be determined i n our 7 day 1 1

3

1


17.

SANDERS AND SEIBER


291

Table IV. EXAMS V o l a t i l i z a t i o n Rate Constant C a l c u l a t i o n f o r a Water-Soil System: Input Data f o r P a r a t h i o n


Parameter Molecular Weight (MWTG) Water S o l u b i l i t y (S0LG(1)) Vapor Pressure (VAPRG) H y d r o l y s i s Rate Constants: B a s i c (KBHG(1,1)) N e u t r a l (KNHG(1,1), KNHG(2,1)) A c i d i c (KAHG(1,1)) Binding Constant (KPSG) No. of Compartments (KOUNT) Type of Compartment 1 (TYPEE(l)) Type of Compartment 2 (TYPEE(2)) Compartment Connection V a r i a b l e (JTURBG(l)) Compartment Connection V a r i a b l e (ITURBG(l) L i t t o r a l Compartment Depth (DEPTHG(l)) Benthic Compartment Depth (DEPTHG(2)) L i t t o r a l Compartment Volume (V0LG(1)) Benthic Compartment Volume (V0LG(2)) Surface Area (AREA(*), XSTURG(*)) Bulk Density of Benthic Compartment (SDCHRG(2)) Benthic S a t u r a t i o n Factor (PCTWAG(2)) Suspended Sediment (SDCHRG(l)) Temperature (TCELG(*)) pH (PHG(*)) pOH (P0HG(*)) Wind Speed a t 10 cm Height (WINDG(l)) Oxygen Exchange Constant (K02G(1)) Mixing Length (CHARLG(l)) D i s p e r s i o n C o e f f i c i e n t (DSPG(l))

Value 291.27 12.4 ppm 6.05 χ 10 mm Hg _6

M-•1* 99 .4 h r 1 94 χ 1 0 " h r - l 0 9 (ug/g)/(ug/ml) 2 L (Littoral) Β (Benthic) 1 2 0.034 m 0.0074 in 0.000254 m 0.000056 m 0.00709 m 1.8 g/ml 136 5 mg/1 22°C 8.5 5.5 2.21 m/s 3.17 cm7hr 0.021 m*" 1.5 χ 10* m/hr

^Free chemical only (29) Bound and f r e e chemical (29) Âs c a l c u l a t e d i n e a r l i e r s e c t i o n As suggested i n EXAMS manual (24)


_ 1

4

b

3

3

2

c

d

4

d


292

TREATMENT AND


experiment. However, l i t e r a t u r e h y d r o l y s i s r a t e constants f o r a l l p e s t i c i d e s (from Table I) could be put i n t o the EXAMS program. The r e l a t i v e importance of the two processes i n a model evapora t i o n pond, along w i t h the time Ζοτ 97% l o s s of the a p p l i e d p e s t i cide (system p u r i f i c a t i o n time), were c a l c u l a t e d (Table V). This c a l c u l a t i o n confirmed that mevinphos and malathion d i s s i p a t e d p r i m a r i l y by h y d r o l y s i s , with malathion the more r a p i d of these two chemicals. For methyl and e t h y l p a r a t h i o n , both processes were s i g n i f i c a n t , although v o l a t i l i z a t i o n was the dominant d i s s i p a t i o n route. However, since both processes were r e l a t i v e l y slow f o r these p e s t i c i d e s , the p u r i f i c a t i o n time was f a i r l y long. Diazinon was p r e d i c t e d to be l o s t p r i m a r i l y v i a v o l a t i l i z a t i o n , and the p u r i f i c a t i o n time was r e l a t i v e l y short.

Table V. R e l a t i v e V o l a t i l i z a t i o n and Reaction Rates as P r e d i c t e d by EXAMS f o r a Model Evaporation Pond Pesticide

Malathion Diazinon Mevinphos Parathion Me P a r a t h i o n

% Hydrolysis

99 4.6 99.7 31 31

% Volatilization

0.6 95 0.1 68 68

P u r i f i c a t i o n Time (days) 6 26 42 89 152

I t i s c l e a r that computer codes such as EXAMS can be q u i t e u s e f u l f o r i n v e s t i g a t i n g the r e l a t i v e importance of f a t e processes i n evaporation ponds and s o i l p i t s . E m u l s i f i e r E f f e c t on V o l a t i l i z a t i o n of P e s t i c i d e s from Water In order to more c l o s e l y represent the v o l a t i l i z a t i o n environment that would be encountered i n an evaporation pond, T r i t o n X-100, a non-ionic e m u l s i f i e r s i m i l a r to those used i n some p e s t i c i d e f o r mulations, was added to prepared p e s t i c i d e s o l u t i o n s at 1000 ppm. The presence of t h i s e m u l s i f i e r caused a decrease i n the percent p e s t i c i d e v o l a t i l i z e d i n one day i n a l l cases except f o r mevinphos (Table V I ) . Three mechanisms are probably i n o p e r a t i o n here. F i r s t , T r i t o n X-100 m i c e l l e s w i l l e x i s t i n s o l u t i o n because i t s c o n c e n t r a t i o n of 1000 ppm i s w e l l above i t s c r i t i c a l m i c e l l e con c e n t r a t i o n of 194 ppm (30). P e s t i c i d e may p a r t i t i o n i n t o these m i c e l l e s , reducing the f r e e c o n c e n t r a t i o n i n water a v a i l a b l e f o r v o l a t i l i z a t i o n , which w i l l i n turn reduce the Henry's law constant f o r the chemical (31). Second, the p e s t i c i d e s may e x h i b i t an a f f i n i t y f o r the t h i n f i l m of T r i t o n that e x i s t s on the water sur face. One can no longer assume that e q u i l i b r i u m e x i s t s across the air-water i n t e r f a c e , and a T r i t o n X-100 surface f i l m r e s i s t a n c e


17.

S A N D E R S A N D SEIBER


293

Table VI. Percent V o l a t i l i z a t i o n of F i v e Organophosphorus P e s t i c i d e s i n the Presence and Absence of T r i t o n X-100


Pesticide

Diazinon Parathion Me Parathion Malathion Mevinphos

% V o l a t i l i z e d ±1 Std. Dev. T r i t o n Present T r i t o n Absent 12±1 6±2 2.610.2 0.2810.03 0.1210.02

5*1 1.9*0.6 1.3+0.1 0.21^0.02 0.13*0.02

Note:l000 ppm T r i t o n X-100, t r i p l i c a t e 24 hour experiments, chamber c o n d i t i o n s same as previously must be added to the two-film equation (32). T h i r d , the f i l m of T r i t o n X-100 reduces the turbulence a t the air-water i n t e r f a c e , thus reducing k-^ and/or k values (31). L i c h t e n s t e i n a l s o noted an i n h i b i t i o n of v o l a t i l i z a t i o n of d i a z i n o n , as w e l l as s e v e r a l other p e s t i c i d e s , when LAS detergent was added to b u f f e r e d water (14). However, he found that the detergent increased v o l a t i l i z a t i o n o f p a r a t h i o n and d i e l d r i n , i n d i c a t i n g that s u r f a c t a n t e f f e c t s may be more complex than discussed here. I t i s c l e a r that the presence of formulation components i n water complicates the e s t i mation of p e s t i c i d e v o l a t i l i z a t i o n from evaporation ponds. g

Conclusions A simple environmental chamber i s q u i t e u s e f u l f o r o b t a i n i n g v o l a t i l i z a t i o n data f o r model s o i l and water d i s p o s a l systems. I t was found that v o l a t i l i z a t i o n of low s o l u b i l i t y p e s t i c i d e s occurred to a greater extent from water than from s o i l , and could be a major route of l o s s of some p e s t i c i d e s from evaporation ponds. Henry's law constants i n the range s t u d i e d gave good estimations of r e l a t i v e v o l a t i l i z a t i o n r a t e s from water. Absolute v o l a t i l i z a t i o n r a t e s from water could be p r e d i c t e d from measured water l o s s r a t e s or from simple wind speed measurements. The EXAMS computer code was able to estimate v o l a t i l i z a t i o n from water, w a t e r - s o i l , and wet s o i l systems. Because of i t s a b i l i t y t o c a l c u l a t e v o l a t i l i z a t i o n from wind speed measurements, i t has the p o t e n t i a l of being a p p l i e d to f u l l - s c a l e evaporation ponds and s o i l p i t s . Whether one would want to maximize or minimize v o l a t i l i z a t i o n r a t e s from these systems i s open to debate. The user may want t o maximize t h i s r a t e , f o r i t can help decontaminate the system and keep p e s t i c i d e concentrations under c o n t r o l . A l t e r n a t i v e l y , the user or the p u b l i c may want to minimize v o l a t i l i z a t i o n , to reduce r e s p i r a t o r y r i s k s i n the v i c i n i t y of the s i t e s . The approach taken here was simply to document what happens, so that the proper


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294

choice of a d i s p o s a l system can be made to f i t the needs of a s p e c i f i c user and s i t e . Acknowledgments


T h i s work was supported i n p a r t by the N a t i o n a l I n s t i t u t e of Health t r a i n i n g grant #PHS ES07059-06. Thanks go to EPA (Mr. L a r r y Burns) f o r f u r n i s h i n g a copy of the EXAMS computer program.

Literature Cited 1.

2.

3.

4. 5. 6. 7.

8. 9. 10.

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