Herbicide and estrogen effects on the metabolic activity of Elliptio complanata measured by calorespirometry

Herbicides and estrogen are important contaminants of world water systems with effects on aquatic organisms. The effects of short-time exposure to atrazine, 2,4-Dichlorophenoxyacetic acid (2,4-D), paraquat, and estrogen on the metabolic activity of gill tissue from the freshwater bivalve Elliptio complanata were investigated by isothermal calorimetry and respirometry. Metabolic heat rates were altered following short-time exposure of gill tissue to these compounds over the concentration range from 10(-6) to 10(-3) M. The effects of herbicides and estrogen on metabolic heat rates were compound specific and time and concentration dependent. Treatment of tissue with estrogen caused stimulation of metabolic heat rates. In general, treatment with herbicides at low concentration or short times of exposure caused stimulation of metabolic heat rates, possibly due to uncoupling. Longer exposures and higher concentration subsequently caused inhibition of metabolic activity and decreased metabolic heat rates. Treatment of mitochondria isolated from gill and muscle tissues showed a similar pattern of respiratory rate stimulation at concentrations of 10(-4) M 2, 4-D and inhibition at higher concentration. Analysis of CO2 and O2 from the headspace gases in the calorimeter ampule showed an increase in the respiratory quotient indicating a shift in metabolism following addition of 2,4-D or paraquat.