Effects of Dichlobenil on Two Fishpond Environments

Abstract

Pond studies were conducted at Tishomingo, Oklahoma with wettable powder 2,6-dichlorobenzonitrile (dichlobenil) and at Denver, Colorado with granular dichlobenil to measure chronic effects on fish and other effects on the ecosystem. Decline of the herbicide was rapid at Tishomingo, with only about 3% of the material remaining after 11 days, while at Denver the herbicide took 3 weeks to reach peak concentration in the water and was still measurable in the water after 189 days. Dichlobenil was present in bottom sediments after 312 days at Tishomingo and after 166 days at Denver. Weeds were controlled at both locations, but regrowth occurred after 3 months in ponds treated at 10 and 20 ppm dichlobenil. No immediate mortality was sustained by fish at either locality, but day-to-day mortality was serious at higher concentrations at Tishomingo. Reproduction apparently was affected by higher dichlobenil levels at Tishomingo. Growth of fish was fastest in ponds treated with highest rates of dichlobenil at Tishomingo, and slowest in the untreated ponds. Residues of dichlobenil developed in fish from all ponds, but faster at Tishomingo than at Denver, and larger in high-treatment ponds than in low-treatment ponds. Some pathology was seen in liver, kidney, and pancreas of Tishomingo fish.