Herbicidal Residues in Pond Water and Hydrosoil

Abstract

Herbicidal residues in water and soil were determined after treating eight ponds with six herbicides. Relatively high concentrations of 2,6-dichlorobenzonitrile (dichlobenil), 2,3,6-trichlorophenylacetic acid (fenac), and 2,4-dichlorophenoxyacetic acid (2,4-D) were present in the upper 1-in of the hydrosoil following treatments with granular formulations of these herbicides. Fenac and dichlobenil residues persisted in both water and soil for periods exceeding 160 days. Low concentrations of 2,4-D were found in water for 24 days and in the soil for 55 days following treatment. The mono-N,N-dimethylcocoamine salt of 7-oxabicyclo(2.2.1)heptane-2,3-dicarboxylic acid (amine salt of endothall), 1,1′-dimethyl-4,4′-bipyridinium salt (paraquat), and 6,7-dihydrodipyrido(1,2-a:2’,1′-c)-pyrazidiinium salt (diquat) were relatively less persistent in water and were no longer found after 24, 8, and 4 days, respectively. However, paraquat and diquat were held by the hydrosoils and persisted in high concentrations for more than 85 and 160 days, respectively. In ponds with dense weed infestations, a large fraction of the herbicide may be held by the plants for some time.