Evaporation ponds volatilization

Mathematical models have also predicted a low volatility for methyl parathion (Jury et al. 1983 McLean et al. 1988). One study using a laboratory model designed to mimic conditions at soil pit and evaporation pond disposal sites (Sanders and Seiber 1983) did find a high volatility from the soil pit model (75% of the deposited material), but a low volatility for the evaporation pond model (3. 7% of the deposited material). A study of methyl parathion and the structurally similar compound ethyl parathion, which have similar vapor pressures, foimd that methyl parathion underwent less volatilization than ethyl parathion in a review of the data, the reduced level of volatilization for methyl parathion was determined to be due to its adsorption to the soil phase (Alvarez-Benedi et al. 1999). 

In this paper, the volatilization of five organophosphorus pesticides from model soil pits and evaporation ponds is measured and predicted. A simple environmental chamber is used to obtain volatilization measurements. The use of the two-film model for predicting volatilization rates of organics from water is illustrated, and agreement between experimental and predicted rate constants is evaluated. Comparative volatilization studies are described using model water, soil-water, and soil disposal systems, and the results are compared to predictions of EXAMS, a popular computer code for predicting the fate of organics in aquatic systems. Finally, the experimental effect of Triton X-100, an emulsifier, on pesticide volatilization from water is presented. 

It should be noted that hydrolysis of these pesticides is expected to occur simultaneously with volatilization for the pesticides studied (Table I). Over a 7 day experiment, however, only malathion and mevlnphos would be expected to hydrolyze to a significant extent. We determined the loss rate of mevlnphos to be 0.0016 0.0002 hr l (tjj = 18 days), and of malathion to be 0.011 0.001 hr-1 (t j = 2.6 days) at 22 2°C, at pH 8.2+0.2 for a model evaporation pond by daily sampling of duplicate pesticide solu-Xlons (covered to prevent volatilization) for 7 days and plotting log concentration versus time. For both of these pesticides, then, degradation was a much more important route of pesticide loss from water than volatilization. The relatively slow loss rate of the other pesticides could not be determined in our 7 day... 

The relative importance of the two processes in a model evaporation pond, along with the time lor 97% loss of the applied pesticide (system purification time), were calculated (Table V). This calculation confirmed that mevinphos and malathion dissipated primarily by hydrolysis, with malathion the more rapid of these two chemicals. For methyl and ethyl parathion, both processes were significant, although volatilization was the dominant dissipation route. However, since both processes were relatively slow for these pesticides, the purification time was fairly long. Diazinon was predicted to be lost primarily via volatilization, and the purification time was relatively short. 

In order to more closely represent the volatilization environment that would be encountered in an evaporation pond, Triton X-100, a non-ionic emulsifier similar to those used in some pesticide formulations, was added to prepared pesticide solutions at 1000 ppm. The presence of this emulsifier caused a decrease in the percent pesticide volatilized in one day in all cases except for mevinphos (Table VI). Three mechanisms are probably in operation here. First, Triton X-100 micelles will exist in solution because its concentration of 1000 ppm is well above its critical micelle concentration of 194 ppm (30). Pesticide may partition into these micelles, reducing the free concentration in water available for volatilization, which will in turn reduce the Henry s law constant for the chemical (31). Second, the pesticides may exhibit an affinity for the thin film of Triton that exists on the water surface. One can no longer assume that equilibrium exists across the air-water interface, and a Triton X-100 surface film resistance... 

A simple environmental chamber is quite useful for obtaining volatilization data for model soil and water disposal systems. It was found that volatilization of low solubility pesticides occurred to a greater extent from water than from soil, and could be a major route of loss of some pesticides from evaporation ponds. Henry s law constants in the range studied gave good estimations of relative volatilization rates from water. Absolute volatilization rates from water could be predicted from measured water loss rates or from simple wind speed measurements. The EXAMS computer code was able to estimate volatilization from water, water-soil, and wet soil systems. Because of its ability to calculate volatilization from wind speed measurements, it has the potential of being applied to full-scale evaporation ponds and soil pits. 

Diazinon released to water from both point and nonpoint sources may be emitted to the atmosphere by volatilization, sorbed to soils and sediments, or accumulated in aquatic organisms. While evaporation may not be expected to be significant based upon the Henry s law constant (see Table 3-2), volatilization of diazinon can be an important transport process. Sanders and Seiber (1983) reported that 17% of the diazinon added to a model pond volatilized in 24 hours. Diazinon released to water also may be adsorbed moderately by soils and sediments based on its organic carbon partition coefficient (K00) values measured in soil (Sharom et al. 1980a). Because this pesticide is only moderately adsorbed by some soils, leaching into groundwater can occur. 

Karlson, U. Frankenberger, W.T. Jr, (1990). Volatilization of selenium from agricultural evaporation pond sediments. The Science of the Total Environment, 92, 41-54. 

Sanders, P.F., Seiber, J.N. (1984) Qrganophosphorus pesticides volatilization. Model soil pits and evaporation ponds. In Treatment and Disposal of Pesticide Wastes. Krueger, R.F., Seiber, J.N. Editors, Am. Chem. Soc. Sym. Series 259, 279-295. 

Gao S, Tanji KK. 1995. Model for biomethylation and volatilization of selenium from agricultural evaporation ponds. J Environ Qual 24 191-197. 

All passive systems rely on the natural hydraulic gradient to transport LNAPL to the recovery location. Under most circumstances, the flow of LNAPL into this type of system is very slow. At open surface recovery sites (trenches and ponds) constructed in low-permeability soils, the LNAPL migrates in so slowly that free volatile product often evaporates before it accumulates sufficiently to be collected. High-permeability soils typically are subject to a low hydraulic gradient, which limits the rate of flow into the system. Conditions that are more favorable to passive recovery, shown schematically in Figure 7.1, include ... 

Once In an evaporation bed, a pesticide can adsorb to a soil colloid, undergo chemical or microbial degradation, or escape from the bed by volatilization. An evaporation bed has the potential advantage over an open pond of decreasing pesticide volatilization while allowing for Increased degradation through microbial and soil-catalyzed reactions. 

Freshwater mammals such as heaver may leave odors on the surface of their ponds and olfactorily sample the water or layer of air immediately above it. Lipids on water may form micelles, small blobs of molecules (from Latin mica, a grain, crumb, morsel) that enhance evaporation into the air layer by increased chemical potential. Some seahirds hunt hy odor (e.g. Hutchison and Wenzel, 1980 Nevitt, 1999). They may respond to prey volatiles (from krill, squid, or fish) that rise to the water surface and evaporate into the air. The air-water equilibrium for dilute solutions can be expressed by using partition coefficients, relative volatility, or Henry s law (Thibodeaux, 1979). 

In water, DEHP is predominantly sorbed to suspended particulates and sediments, but some remains dissolved in the aqueous phase. Volatilization is not a dominant transport process. Volatilization from water and soil is not expected to be important, based on the bw Hairy s law constant (estimated value 1.71xl0 5 atm-m3/mol Staples et al. 1997). It has been estimated that the evaporative half-life of DEHP from water would be about 15 years (EPA 1979), and that only about 2% of DEHP loading of lakes and ponds would be volatilized (Wolfe et al. 1980a). 

Fig. 14. SF(C3-nC5) versus saturation pressures for the oils and gas-condensates of this study. Three data regions are distinguishable, that of the Maturation Sequence of oils (MI, M2), that of Gas-Enriched Oils, including Brazeau River Cardium (C), and that of Evaporative Gas-Condensates. An area between the first two regions also hosts data representing volatile oils, e.g. Robinson Creek (Rob.), often of high maturity, i.e. oils close to their critical points, and similar gas-condensates, some believed to be of thermal origin, e.g. Hatter s Pond (H).

PROBABLE FATE photolysis-, information lacking, photodissociation to chloroacetyl chloride in stratosphere is predicted oxidation-, photooxidation in troposphere may be the predominant fate, photooxidation in aquatic environments probably occurs at a slow rate hydrolysis-. unimportant compared to volatilization volatilization due to high vapor pressure, volatilization to the atmosphere should be the major transport process, if released in water, will be removed by volatilization with a half-life of 6-9 days, 5-8 days, and 23-32 hr, in a typical pond, lake, or river respectively, will be removed quickly by volatilization if released on land biological processes data is lacking, bioaccumulation not expected, biodegradation may be possible evaporation from water 25°C of 1 ppm solution 50% after 22 min, 90% after 109 min. 

PROBABLE FATE photolysis not significant in aquatic environment, photodissoeia-tion in stratosphere probably a significant fate oxidation not important in aquatic environment, oxidation is rapid above 110°C, photooxidation in the troposphere probably important hydrolysis too slow to be consequential, rapid above 110°C, expected to hydrolyze under alkaline conditions first-order hydrolysis half-life 45 days volatilization probable primary transport process, release to water will primarily be lost by volatilization in days to weeks, volatilization half-life in a model river and pond is estimated to be 6.3 hr and 3.5 days respectively, volatilization from dry soil will be fairly rapid biological processes NA evaporation from water 25°C of 1 ppm solution is 50% after 56 min. and 90% after less than 120 min., evaporation rate 0.65 oxidative decomposition occurs by UV radiation... 

This is becoming truer since the cheapest way of removing many low-boiling solvents from waste water has been by air stripping or evaporation from effluent ponds or interceptor surfaces. Such avoidable contributions to VOC will become increasingly unacceptable as standards for air quality are raised. This also applies to marine dumping since volatile solvents are mostly evaporated before degradation takes place. 

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