Disappearance ofs-Triazines as Affected by Soil pH Using a Balance-Sheet Approach

Abstract

The effect of soil pH on the disappearance of14C ring-labeled atrazine [2-chloro-4-(ethylamino)-6-(isopropylamino)-s-triazine], hydroxyatrazine [2-hydroxy-4-(ethylamino)-6-(isopropylamino)-s-triazine], and prometryne [2,4-bis(isopropylamino)-6-(methylthio)-s-triazine] were studied over a 5-month period in a Bladen silt loam soil under greenhouse conditions. Employment of an integrated system allowed simultaneous monitoring of degradation, volatilization, respiration, plant uptake, and leaching processes. A resulting balance-sheet indicated that a range of 87 to 99% of the14C added could be accounted for after 5 months. Degradation was found to be the primary mode of dissipation. The pattern of atrazine degradation was characteristic of nonbiological processes, while prometryne degradation was probably by microbial action. Hydroxyatrazine was the major metabolite from the atrazine treatments while prometryne yielded an unknown and hydroxypropazine [2-hydroxy-4,6-bis(isopropylamino)-s-triazine]. Ex-tractable atrazine after 5 months amounted to 35% of the initial amount added in the pH 7.5 soil and 11% in the pH 5.5 soil, while prometryne occurred as 10% in the pH 7.5 soil and 42% in the pH 5.5 soil. Plant uptake and leaching occurred to a greater extent in the more alkaline soil with each chemical, but these pathways along with volatilization and respiration were minor contributors toward the disappearance of these herbicides.