Uptake and Excretion of Chemicals by Aquatic Fauna

Factors influencing the movement of chemicals across biological membranes are: solubility in lipids and in water, chemical stability, ionization, and molecular weight of the chemical. On the part of aquatic fauna, the transport of chemicals is affected by metabolic activity and by the physiological state of the animals. Additional factors include water temperature, hardness or salinity, and presence of other chemicals. The effects of these factors will be discussed and illustrated by examples. The uptake of highly lipid-soluble compounds by fish appears to be determined by their solubility in water, and compounds with extremely low solubility in water are not taken up in spite of their high solubility in lipids. Examples are hexabromo-benzene, highly brominated biphenyls, C24 chlorinated paraffins, and some flame retardants of the Dechlorane series. In addition to solubility in water, there may be a high molecular weight threshold, beyond which compounds are not taken up, and factors based on the chemical structure of the compounds may play a role as well. For example, Dechlorane 604, a tetrabromophenyl norbornene, is accumulated by fish to a much lesser degree than a tribromophenyl norbornene, present as a minor impurity in Dechlorane 604. Chemical and biochemical stability of compounds are additional factors determining the extent of environmental contamination. Examples are the widespread contamination of aquatic biota by two nonachlors, present originally as relatively minor components in technical chlordane, and the contamination by some components of toxaphene. The use of a one compartment model in studies of accumulation and excretion of chemicals by aquatic fauna, and its extension to the determination of lethality curves, will be mentioned.