Atrazine precipitation

In recent studies, pesticides such as atrazine have been found in precipitation. Therefore volatilization and subsequent transport in the gaseous phase is an important environmental pathway. Vaporization rates of pesticides deposited on surface of soil and plant leaves depend on the physical-chemical properties of the substance. A useful physicochemical criterion is Henry s constant, Ku, which is defined as the equilibrium air-to-water partial pressure ratio of the substance (see Chapter 7). 

During the late spring and summer of 1990 and 1991, a USGS study focused on herbicide transport into the atmosphere by various processes. This study was conducted prior to significant label rate reductions for atrazine-containing products. Once in the atmosphere, these compounds can be dispersed by air currents and redeposited by precipitation, snow, and dry deposition on the land surface, lakes, and streams. 

The overall objective of the precipitation study was to (1) determine the occurrence and temporal distribution of herbicides and their degradation products in precipitation, (2) estimate the amounts of atrazine deposited by precipitation annually in individual states and over a large part of the United States, (3) relate annual deposition of atrazine to amounts applied annually, and (4) compare annual herbicide deposition by precipitation within the Mississippi River Basin to the estimated annual amount transported out of the basin in streamflow. 

Precipitation-weighted atrazine concentration, in micrograms per liter... 

Figure 30.10 Precipitation-weighted concentrations of atrazine in water samples from northern and northeastern United States during mid-April and mid-July in 1990 and 1991 (Goolsby etal., 1997). (See Color Plate Section)...

Plate 11 Estimated deposition of atrazine in precipitation from northern and northeastern United States during March through December 1990 and January through December 1991 (Goolsby et al., 1997). 

Oxidation, 445-449 Reduction, 445-449 Toxicity, 484 Precipitation, 446-448 Atrazine, 355-362 Adsorption, 359-361 Desorption, 361... 

Immunization and Fusion Protocol. Groups of five BALB/c female mice (4-6 weeks old), were given series of three injections every two weeks, with KLH-conjugated atrazine or hydroxyatrazine (50 ug/injection) mixed with Freund s adjuvant. After a rest period of two months, the mice were boosted with 500 ug of the conjugate. Three to four days later, the mice were sacrificed and the spleen cells were fused with the murine myeloma cell line Sp 2/0.Agl4 (12,13). The positive hybridomas were cloned and expanded in mice and the MAbs were purified from the ascitic fluid by ammonium sulfate precipitation, and DEAE-cellulose anion-exchange chromatography (14). 

The BCD complex of atrazine was prepared by adding technical grade atrazine to a solution of an equimolar amount of BCD in water at 60-80 C and then refluxing under an argon atmosphere until all solid had dissolved. The reaction mixtures were allowed to cool to room temperature, and any precipitate was filtered. The solid BCD complex was isolated from the filtrate by removal of water at 1-2 torr and 30-40 C) for characterization purposes. Reaction times varied, with longer periods of time required for more concentrated solutions. 

Temple and Hilton [253] determined the solubilities of ametryne, diuron, and atrazine in a wide range of 0.5 % surfactant solutions. Weight for weight the solubility is greatest in the cationic Nalquat and Aliquat series. The Carbowaxes and dimethylformamide have no effect on the solubility of these herbicides (Table 10.28). These authors point out that when no surfactant is present, saturated solutions applied to the foliage will precipitate as the spray evaporates. When a solubilized preparation is used, two effects should be considered firstly the increased amount of surfactant in the initial spray, and secondly, the solubility of the herbicide in the remaining surfactant after the water has evaporated. It has been found that the solubility (4 to 15%) of ametryne, diuron, and atrazine in some pure surfactants is sufficient to keep all of the herbicide present in a saturated spray solution in solution on the leaf surface but it is possible that solubilized preparations are more readily lost from leaf surfaces in rainwater. 

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