Summary and Conclusions

Assessing the toxic potential for PAHs is a complicated process. Species exhibit wide variation in susceptibility and response. Currently, the most appropriate method for protecting against adverse effects from toxicant exposure is to test many species and construct species-sensitivity distributions (SSDs), which are basically empirical cumulative frequency distributions. By testing a number of species from a variety of taxa, the distribution of responses can be examined and an appropriate level of protection (e.g., 5th percentile) can be set.

PAH contamination is a problem worldwide, occurring almost universally in urban areas and occasionally in nonurban areas due to oil spills, forest fires, and atmospheric fallout. Surprisingly, for such a common and abundant class of contaminants, there is a paucity of toxicity information for species exposed to PAHs. Considering that very low concentrations can lead to serious adverse effects, many populations are simply not protected. Surprisingly, there are few environmental statutes that contain regulatory values for protecting ecosystems from PAH exposure. Within the United States, ambient water quality criteria are promulgated by the US EPA under the Clean Water Act to protect aquatic life. Under this statute, several criteria values have been developed for various toxicants; however, none are currently in place for any of the PAHs. Canada has issued interim aquatic life guidelines for several PAH compounds in freshwater and many have been set at very low concentrations (0.012-0.04 ppb). The Netherlands also has guidelines for several PAH compounds in freshwater that are very low (most between 0.001 and 0.05 ppb).

In the US, the EPA is actively working to develop sediment criteria for PAHs, and at least one state,

Washington, has codified sediment guidelines. Canada has interim sediment guidelines for several individual PAHs, many set at relatively low values (6.2-111 ng/g dry sediment). In most cases, if ecotoxicologists want to assess the toxic potential for PAH contamination in a given system, they must turn to the sparse literature that is available. Of course, most sites contain multiple toxicants that can interact and cause effects at lower than expected concentrations. Only after significant progress is made in understanding how individual PAHs act on myriad biological systems can we begin to tackle the problem of complex mixtures containing PAHs and other toxicants.

See also: Bioaccumulation; Body Residues; Crude Oil, Oil, Gasoline and Petrol; Dose-Response; Ecological Risk Assessment; Ecotoxicology Nomenclature: LC, LD, LOC, LOEC, MAC; Ecotoxicology: The Focal Topics; Ecotoxicology: The History and Present Directions; Estuaries; Estuary Restoration; Reproductive Toxicity.

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