A Critique of the Status of Knowledge about Chemosensory Effects of Metals

Many metals interfere with the fish olfactory system, however, there are important differences in the internal processing between metals so potential effects cannot be described by one common mechanism. In addition to binding to the olfactory epithelium and accumulation in the olfactory bulb, metals interfere with neuroendocrine and endocrine processes in the brain. Metals also affect the mechanosensory system of ciliated hair cells along the body axis of the fish that respond to physical displacement of water. Organic matter and Ca ions decrease metal effects on the olfactory system as expected from the free ion activity model, although hardness and alkalinity have no effect, and Na and pH effects have not been studied. Most olfactory toxicity studies use short-term exposure regimes, while under natural conditions, exposure is of a more permanent nature. Fish that spend multi-generations in contaminated environments do not show as dramatically negative olfactory responses to metals as laboratory-reared fish, suggesting that caution should be taken when extrapolating results from the laboratory to the field. Although other aquatic species and processes included in setting water criteria are more sensitive than fish olfaction to metal exposure, multispecies field tests may be needed to appropriately test behavioral thresholds.