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

The effect of soil pH on the disappearance of 14 C ring-labeled atrazine (2-chloro-4-(ethylamino)-6-(isoProDvlami- no)-s-triazinel, hydroxyatrazine 12-hydroxy-4-(ethylamino)-6- (isopropylamino)-s-triazinel, and prometryne (2,4-bis(isopro- pylamino)-6-(methylthio)-s-triazineI were studied over a 5- month period in a Bladen silt loam soil under greenhouse con- ditions. Employment of an integrated system allowed simul- taneous monitoring of degradation, volatilization, respiration, plant uptake, and leaching processes. A resulting balance-sheet indicated that a range of 87 to 99% of the ? 4 C added could be accounted for after 5 months. Degradation was found to be the primary mode of dissipation. The pattern of atrazine deg- radation 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 hydroxy- propazine (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

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