WA7 Agrochemicals, Pesticides, Pharmaceuticals
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() The nitrogen hurdle: Inhibition of atrazine biodegradation in soil and consequences for groundwater contamination.
van Afferden, M.1, Hansen, A.1, 1 Mexican Institute of Water Technology, Jiutepec, Morelos, Mexico
ABSTRACT- Atrazine is included in the annex of the Stockholm Convention as Persistent Organic Pollutant (POP) and prohibited in various countries of the European Community. In Mexico and United States atrazine still represents one of the most used herbicides in the control of broad-leaved weeds, although restrictions have currently been defined by EPA's "Interim Reregistration Eligibility Decision". Atrazine is considered to be mobile and persistent in the environment and, as such, is widely found in ground- and surface water. Biodegradation can be regarded as the main route of dissipation under aerobic conditions. For aerobic soil environments reported half-lives vary from a few days to several years, which even makes it difficult applying environmental risk assessment prognosis. The purpose of the presented work is to characterize the environmental fate and transport of atrazine in Mexican agricultural soils and thereby contribute to Mexican atrazine regulation. Radiotracer studies using 14C-ring-atrazine showed that half-lives in soil samples vary significantly with soil type. The fastest mineralization was determined with a half-live of 3.25 days, one of the lowest reported for atrazine in soil, the slowest degradation with a half live of 173 days. It is shown that soil nitrate concentration controls the degree and kinetics of atrazine biodegradation. Mineralization of atrazine is completely inhibited by N-concentrations that reflect real field fertilizer concentrations in the first centimeters of soil layer after applying atrazine and fertilizers at the same time. A microbial consortium was isolated and characterized showing the same N-control in liquid culture as in soil microcosms. The consequences of fertilization on biodegradation and consequently infiltration of atrazine have been modeled numerically. The results demonstrate that inhibition of atrazine biodegradation by N-fertilizing can be assumed to play an important role in the fate and transport of the herbicide and may explain high local concentrations of surface and groundwater contamination.
Key words: mineralization, Atrazine, inhibition, soil