AQUATIC DISSIPATION OF TRICLOPYR IN LAKE SEMINOLE, GEORGIA

A field study was conducted to evaluate the environmental dissipation of triclopyr herbicide under aquatic-use conditions. Three 4-h plots i n Lake Seminole, Georgia, were selected for use: one control, one aeri al plot, and one subsurface plot; both applications were at the maximu m aquatic-use rate of 2.5 mg/L. Water, sediment, plants, fish, clams, and crayfish were all analyzed for residues, and water temperature, ox ygen levels, pH, and conductivity were monitored. The half-life for aq ueous-phase triclopyr ranged from 0.5 to 3.6 days, and the dissipation in surface and bottom waters was equivalent. The intermediate decay p roduct of triclopyr, 3,5,6-trichloro-2-pyridinol (TCP), had an observe d aquatic half-life of less than 1 day. No accumulation of triclopyr o r TCP on sediment was observed. The half-life of triclopyr metabolized by aquatic plants averaged 4 days. Fish species did not exhibit any b ioconcentration of triclopyr or TCP, with only trace amounts of either compound found in fish tissue. Both clams and crayfish contained dete ctable residues of triclopyr. The elimination of triclopyr from clam t issue was more rapid, with an observed half-life of 1.5 days, vs 12 da ys for crayfish; retention of triclopyr in the crayfish carcass (carap ace, chelopeds, and gills) may have been an important mechanism. There was no detectable decline in water quality in either treatment plot.