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UPTAKE OF IONIZABLE ORGANIC CHEMICALS AT FISH GILLS
Citation:
Erickson, R J. UPTAKE OF IONIZABLE ORGANIC CHEMICALS AT FISH GILLS. Presented at 22nd Annual SETAC Meeting, Baltimore, MD, November 1-15, 2001.
Description:
Uptake of organic acids by fish, and their toxicity, generally decrease with increasing pH above the pK, presumably due to neutral forms of such chemicals being more readily adsorbed than their ionized forms. However, uptake usually exceeds that expected based just on the concentration of the neutral form. This excess uptake might be due to some adsorption of iodized forms, but also might be due to conversion of ionized form to neutral form because of reduced pH or depletion of the neutral form at the gill surface. To better establish mechanisms regulating accumulation of ionizable organic chemicals, uptake and elimination of several chlorinated phenols and dichlorobenzylamine by large rainbow trout were studied in metabolism chambers. These experiments demonstrated the importance of shifts in chemical equilibrium at the gill surface for determining chemical uptake and elimination. The pH dependence of chemical uptake in these large fish was observed to deviate substantially from that reported to small fish and suggested very little dependence on the hydrophobiciy or pK o the chemical. Results could be explained by a mechanistic model for chemical exchange at fish gills which accounted for the interactions of flows, diffusion, chemical speciation, and gill pH alterations.