Mobility and degradation of pesticides and their degradates in intact soilcolumns

Laboratory studies were conducted to determine the mobility of parent pesti cides and degradation products through the use of large undisturbed soil co lumns. The influence of vegetation on the mobility of pesticide adjuvants w as also investigated. Modifications to the laboratory setup of soil columns for studying various pesticides, degradation products, and adjuvants were done to fit the needs of the particular compound being studied. To improve mass balances of volatile parent compounds, such as methyl bromide, as well as biodegradable (mineralizable) pesticide degradation products such as de ethylatrazine, modifications of columns to accommodate isolation of volatil e degradation products were accomplished by enclosure of the column head sp ace and use of flow-through systems. Evidence of preferential flow of atraz ine, deethylatrazine, metolachlor, and methyl bromide were indicated by the presence of either the C-14-compound or Br- (in the case of methyl bromide -applied soil columns) after the first leaching event. Diffusion through th e soil matrix was also evident with apeak of C-14 in the leachate several w eeks after pesticide (or degradate) application to the soil column. Deethyl atrazine, a major degradate of atrazine, was more mobile than the parent co mpound. Vegetation had a significant positive effect on reducing the mobili ty of the adjuvants propylene glycol and ethylene glycol.