AN INTEGRATED ASSESSMENT OF THE BIOLOGICAL EFFECTS OF BORON TO THE RAINBOW-TROUT

Acute and chronic toxicity tests have been performed in a number of independent laboratories to assess the effects of boron on aquatic life. Among the lowest effect concentrations were those determined in investigations on embryo-larval stages of the rainbow trout (Oncorhyncus mykiss) in reconstituted water. To gain a more precise definition of effect levels with rainbow trout, additional studies were performed with this species in both laboratory and natural dilution waters. Consistent lowest observed effect concentrations (LOECs) ranged from 0.1 to > 18 mg/L boron. The flat concentration-response curve observed for boron (i.e., small changes in effects relative to large increases in boron concentrations) sometimes affected precision in the determination of no-effect or threshold concentrations. Other factors that may have contributed to the wide range of LOEC values related to the effects of different types of dilution water on boron toxicity and the differential sensitivity of the trout strains evaluated. The impact of these variables on defining effect levels is discussed in detail in this paper. Based on the results of the rainbow trout tests, together with data from field surveys, a concentration of between 0.75 and 1.0 mg/L is determined to be a reasonable, environmentally acceptable limit for boron in aquatic systems. This conclusion is consistent with limits proposed by other investigators.