Avoidance response bioassays were conducted with eight aquatic contaminants, including cadmium, copper, mercury, zinc, chloroform, dioctyl phthalate (DOP), trisodium nitrilotriacetic acid (NTA), and phenol. Tests were performed in a dual-channel fluviarium system, and the toxicant injection procedure used provided good regulation of exposure concentrations. Juvenile stages of largemouth bass (Micropterus salmoides), bluegill sunfish (Lepomis macrochirus), and rainbow trout (Salmo gairdneri), and tadpoles of the American toad (Bufo americanus) proved to be suitable animals for evaluating avoidance or attraction responses. The trout was the most sensitive species tested.
Avoidance was significant in tests with cadmium, phenol, and zinc, and significant attraction resulted from exposures to chloroform, COP, and mercury. Animals generally avoided lower concentrations of copper but were attracted to higher exposure levels. NTA produced variable responses. In tests With trout, threshold concentrations for avoidance or attraction were estimated to fall at 0.0002 mg/1 mercury, 0.047 mg/1 zinc, 0.052 mg/1 cadmium, 0.074 mg/1 copper, 11.9 mg/1 chloroform, and 56.6 mg/1 NTA. The threshold for phenol, determined using bluegill, was 39.0 mg/1. Results from fish embryo-larval toxicity tests were used to gauge sensitivity of the avoidance response bioassay. Toxicant concentrations which produced embryo-larval lethality or teratogenesis at frequencies of 10% (LC10) and 1% (LC1) were compared to behavioral threshold concentrations. The avoidance test was observed to be a less sensitive procedure for evaluating the effects of all the selected toxicants, except zinc. However, the behavioral test provided valuable information which was not obtainable using other bioassay methodologies
