Submitted to: Chemosphere
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: July 7, 2003
Publication Date: January 15, 2004
Citation: Neurath, S., Sadeghi, A.M., Shirmohammadi, A., Isensee, A.R., Torrents, A. 2004. Atrazine distribution measured in soil and leachate following infiltration conditions. Chemosphere. 54:489-496.
Interpretive Summary: Understanding pesticide interactions and movement is important in predicting environmental fate and transport. The interactions of the upper 10 cm of soil profile are of particular importance for compounds such as atrazine, one of the most widely used herbicides. A series of detailed laboratory experiments were conducted to evaluate the influence of rainfall intensity and delay time between application time and the rain event. Results showed that for delayed rain events, atrazine movement was independent of infiltration rate (rain intensity) and was significantly lower than expected. These findings suggest that atrazine movement through the soil cores was dependent on interactions of the infiltrating water with the soil surface or plant material on the soil surface. Thus, both rain intensity and the time at which the rain event occurs after pesticide application need to be considered when predicting atrazine fate.
Atrazine transport through packed 10 cm soil columns representative of the 0-10 cm soil horizon was observed by measuring the atrazine recovery in the total leachate volume and in the upper and lower soil layers following infiltration of 7.5 cm water using a mechanical vacuum extractor. Measured recoveries were analyzed to understand the influence of infiltration rate and delay time on atrazine transport and distribution in the column. Four time periods (0.28, 0.8, 1.8, and 5.5 hr) representing very high to moderate infiltration rates (26.8, 9.4, 4.2, and 1.4 cm/hr) were used. Replicate soil columns were tested immediately and following a 2-d delay after atrazine application. Results indicated that atrazine recovery in leachate was independent of infiltration rate, but significantly lower for infiltration following a 2-d delay. Atrazine distribution in the 0-1 and 9-10 cm soil layers was affected by both infiltration rate and delay. These results are in contrast with previous field and laboratory studies that suggest that atrazine recovery in the leachate increases with increasing infiltration rate. The difference in atrazine recovery measured using rain simulation equipment and the mechanical vacuum extractor on intact soil cores and previous leaching experiments illustrates the effect of infiltrating water interacting with the atrazine present on the soil surface. Thes results suggest that atrazine mobilization from the soil surface is dependent on interactions of the infiltrating water with the soil surface, in addition to the rate of infiltration through the surface soil.