Fates of cadmium introduced into channels microcosm

Abstract

Five 10 μg Cd·l −1 were continuously input to aquatic microcosm channels for one year. Cadmium accumulation in both biotic and abiotic components was determined. Cadmium inputs and outputs equilibrated within approximately 20 days of initial Cd inputs. Most community components accumulated Cd proportional to Cd water concentrations. Equilibrium Cd concentrations of sediments, aufwuchs, macrophytes, chironomids, and mosquito fish exposed to 10 μg Cd·l −1 were 0.59, 55, 250, 40, and 40 μg Cd·g −1, dry weight, respectively. Cadmium was rapidly eliminated from all biotic components when Cd inputs were terminated. Cadmium concentrations were similar to those in control channels within a few weeks in the aufwuchs community to a few months in macrophytes after Cd inputs were terminated. Cadmium uptake fluxes by the aufwuchs community and mosquito fish were first order, with respect to Cd concentration in the water. The rate constants for uptake and depuration for the aufwuchs community were 0.42 and 0.66 d −1, respectively (concentration basis). The rate constants for uptake and depuration of Cd by mosquitofish were approximately 25 and 0.004 d −1, respectively (concentration basis). Cadmium concentrations in organic headpool sediments had not significantly decreased six months after cessation of Cd inputs, which indicates that the abiotic half time for contaminated organic sediments is very long. Half times for elimination from channel sand sediments were 72 and 38 d for 5 and 10 μg·l −1 exposure, respectively, after Cd inputs were terminated Cd concentrations in macroinvertebrates varied seasonally. The carrying capacity of the channels microcosm limited the number of samples of secondary and tertiary consumers which could be sampled. It was concluded that concluded that experimental channels of the size described here were not appropriate as screening tools for the fates of trace contaminants, but were effective for the study of trace contaminants, especially in conjunction with mathematical modeling efforts and less complex laboratory studies.