A MODEL FOR EXCHANGE OF ORGANIC-CHEMICALS AT FISH GILLS - FLOW AND DIFFUSION LIMITATIONS

A mathematical model for the exchange of neutral organic chemicals at fish gills was formulated based on limitations imposed by flows of water and blood to the gills, diffusion barriers defined by gill morphology, and chemical binding relationships within water and blood. This model was parameterized independently of exchange measurements and validated against datasets on the relationship of chemical uptake rates for large rainbow trout and small guppies to chemical hydrophobicity. This model was found to closely predict the magnitude and trends of observed gill uptake rates in these datasets, predictions deviating from observed values by no more than a factor of two over a range of octanol:water partition coefficients from 2 to > 10(6). Elimination rates for small guppies were also predicted. This analysis suggests that gill exchange can be understood and predicted on the basis of fundamental physiological and morphological variables.