Persistence of Four Herbicides in Pond Water

Abstract

This study, which was made in collaboration with the Army Corps of Engineers' Expanded Project for Aquatic Weed Control (Public Law 85‐500), reports the persistence of four herbicides in water and soils. The study considered only persistence as indicated by sampling and analytic techniques having a combined sensitivity of about 0.01 ppm. Fenac appeared to have the least potential for use in sources of potable water because of its long survival. The effects of heavy weed infestations on residue persistence were not evaluated. The analytic methods used for 3‐AT would not differentiate between 3‐AT and a principal metabolite (ATX). Although ATX is not phytotoxic, it is incorporated into the cellular protein of Esch. coli. This has not been demonstrated for mammals. Until the effects of ATX on mammalian biochemistry are determined, its presence in potable water is undesirable. As is the case with fenac, the survival of 3‐AT and ATX in water has to be evaluated in weed‐choked environments. Excluding toxicologic considerations, paraquat and diquat appear to have the greatest potential for use in sources of potable water supply. Both disappear rapidly in water and do not appear to be desorbed from bottom sediments. Because paraquat and diquat are strongly sorbed on certain clays, the introduction of such sorbents to the coagulation‐sedimentation phase of conventional water treatment might remove residues during the short period they remain in water.