Biological Significance and Fate of Atrazine under Aquifer Conditions

Abstract

Concentrations of atrazine [2-chloro-4-(ethylamino)-6-(isopropylamino)- s -triazine] in contaminated groundwater recovered from 41 monitoring wells in Hall and Buffalo counties, Nebraska range from 0.01 to 8.29 μg/L. Over a 1-year period concentrations fluctuated sufficiently in a seasonal pattern to indicate that atrazine dissipation occurs. This reduction in concentration can be attributed to adsorption, dispersion, and degradation. A limited amount of atrazine degraded chemically to hydroxyatrazine [2-hydroxy-4-(ethylamino)-6-(isopropylamino)- s -triazine] under simulated aquifer conditions; microbial degradation could not be detected. A geometrical progression model for predicting long term residue accumulation indicates that current contamination levels probably reflect a steady-state situation between the amount that yearly enters into, and the partial degradation that occurs within, the aquifer. Oat ( Avena sativa L. ‘Neal’) bioassays indicate that present levels of groundwater contamination remain well below the threshold necessary for phytotoxicity.