Chlorophenoxy and chlorobenzoic acid herbicides; their use in eleven agricultural watersheds and their loss to stream waters in Southern Ontario, Canada 1975–1977

Abstract

A survey in 1975 of eleven agricultural watersheds revealed that chlorophenoxy (CPOA) and chlorobenzoic acid (CBA) herbicides were used for weed control in cereals, corn, peas and beans on farm land and along right-of-ways and other sites on non-agricultural land. These land uses represented 52.6% of the eleven watersheds and 31.8% of this area received treatments of CPOA and CBA herbicides. The quantities and areas treated with chloramben, 2,4-D, 2,4-DB, dicamba, MCPA, mecoprop and 2,4,5-T were documented. Analysis of 949 initial stream waters revealed residues of 2,4-D in sixty-six, 2,4,5-T in twenty-one, MCPA in six and dicamba in one. Losses to stream water were correlated to spray activity adjacent to streams especially where careless use of equipment or material contaminated the water. In addition, storm runoff waters carried herbicide residues to streams, especially when occurring close to the time of application. Spraying of right-of-ways involved spraying of ditch banks with the inevitable contamination of stream water. Losses to water represented 0.03% of agricultural uses and 0.5% of non-agricultural uses. Concentrations found in water were well below currently accepted water quality objectives and therefore posed no known hazard.