|Gan, J - UNIVERSITY OF MINNESOTA|
|Becker, R - UNIVERSITY OF MINNESOTA|
Submitted to: Journal of Environmental Quality
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: March 9, 1996
Publication Date: N/A
Interpretive Summary: Herbicide contamination of ground water from spills is often much more severe than contamination caused by normal agricultural practices. The objective of this study was to determine the effect of high concentration on the persistence and movement of the herbicide atrazine in two Minnesota soils. The rate of atrazine dissipation when present at high rates in the field was slow during the initial 6 months following application and then dissipated rapidly during the following spring. There was no evidence of substantial leaching with relatively low levels of atrazine detected below 12 inches. It is noteworthy, however, that higher levels of atrazine were present in the soil profile with the higher initially applied concentrations. Considering the relatively low levels currently used for regulatory purposes, atrazine present in surface soil did pose more environmental risk for water contamination than atrazine present at commonly used field rates. The overall behavior of atrazine in the soils tested in the laboratory was not greatly affected by concentration but was affected by soil type. Our results show that while a spill of atrazine on a clay loam soil would not pose a threat to water resources, atrazine spills on coarser textured soils would require immediate action. From our data, it appears that land spreading of the contaminated soil would be a viable option for remediation provided the atrazine were diluted to less than 100 ppm.
Technical Abstract: Dissipation of atrazine in a Webster clay loam and an Estherville sandy loam was determined over a concentration range of 5 to 5,000 mg kg**-1 in field and laboratory experiments. Over the first six months in the Webster soil, the persistence of atrazine (based on percent of applied) was greater for the high-rate treatments than the low-rate treatments. However, in the laboratory, there was no effect of concentration on dissipation; the amount of atrazine degraded increased proportionally with the increase of concentration. In the Estherville sandy loam, persistence was greater at high concentration in both field and laboratory studies. Mineralization was the most important pathway for the dissipation of atrazine at all concentrations in the Webster soil and from 5 to 500 mg kg**-1 in the Estherville soil. It was postulated that some soil microorganisms were able to use the N or C from the s-triazine ring. Atrazine may have stimulated soil microbial growth and activity and thus stimulated the degradation of atrazine based on increased soil respiration in the Webster clay loam treated at 500 and 5,000 mg kg**-1. Degradation pathways in both soils apparently were not influenced by concentration. Ring cleavage and hydrolysis were the major metabolic pathways in both soils, with dealkylation of less importance. Soil factors such as the type and content of organic matter, clay content, and soil pH could be important in determining the persistence and degradation of elevated levels of atrazine. Addition of a dairy manure amendment was shown to have the potential for detoxifying atrazine in contaminated soil. Manure increased the rate of atrazine mineralization, whereas corn meal decreased mineralization and (NH4)2HPO4 inhibited it.