The literature concerning toxicity of PAHs indicates that these compounds are toxic to plants only at very high concentrations and there are several examples of plants accumulating high concentrations. Photoactivation of PAHs is likely to be an important process for plants due to their high exposure to UV radiation and high tissue concentrations. One review cites a number of studies that demonstrate a substantial increase in toxicity to plants when photoactivation is considered. Several bioassays have been developed that are based on physiological and biochemical processes, including chlorophyll (Chl a) fluorescence, which appears to be a very useful bioindi-cator ofPAH toxicity because it has been linked to altered growth. As an example, one study reported aqueous EC50 values for several plant functions in the low mg ml_ range when aquatic macrophytes where exposed to creosote, a PAH-rich mixture. It should be noted that these values are relatively high compared to the EC50 values observed for many faunal species.
A substantial body of literature concerns the remediation of soils and aquatic sediments by plants. Several plant species appear to be effective for removing these contaminants from areas where concentrations are likely toxic for some faunal species but not so for plants. One facet of this research that has received little attention is the increase in availability of soil or sediment PAHs to animals. When certain plant species are introduced to an area for PAH remediation, an increase in animal abundance, especially wildlife, may follow. By accumulating and concentrating PAHs in their tissues, especially the very toxic photoactivated PAHs, animals that graze on these plants may be acquiring a higher dose of these compounds than they normally would in areas not densely populated by these plants.
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