Photoactivated toxicity in amphipods collected from polycyclic aromatic hydrocarbon-contaminated sites

The risk of photoactivated PAH toxicity in contaminated aquatic systems has not been well characterized. To document risk, amphipods (Gammarus spp.) were collected from two polycyclic aromatic hydrocarbon (PAH)-contaminated sites in the lower St. Louis River and Duluth Harbor, USA (Hog Island and USX) as well as a reference site (Chipmunk Cove) and were exposed in two separate, replicate tests to controlled intensities of solar radiation for 3 d. Contaminated site organisms died significantly faster compared to control site organisms. In all tests, mortality was strongly related to ultraviolet-A (UV-A; 320-400 nm) dose. Ultraviolet-B (280-320 nm) radiation did not increase mortality. To compare susceptibility among populations, regressions of arcsine-transformed, proportionate mortality versus UV dose were completed for each, and the slopes were statistically compared. Response slopes for the two contaminated site populations were both significantly greater than the reference site population (p = 0.0001 for test 1; p = 0.0002 for test 2). These results indicate that organisms residing in PAH-contaminated environments can accumulate PAH concentrations sufficient to be at risk for photoactivated toxicity. Although amphipods are not typically at risk of PAH-photoactivated toxicity because they are largely protected from exposure to sunlight, they are representative surrogates for species that may be similarly protected at some life stages (and thus able to accumulate significant PAH tissue concentrations) but not at others.