The toxicity of fluoranthene to Hyalella azteca in sediment and water-only exposures under varying light spectra

In the US Environmental Protection Agency methods for sediment toxicity testing, the light regimen is specified as a 16:8 light dark cycle with 500–1000 lx. The potential for photoinduced toxic effects from this requirement is evaluated. Hyalella azteca were exposed to fluoranthene in both water only and sediment to examine the impact of light spectra on the toxicity of fluoranthene. The light sources included gold fluorescent light (λ>500 nm), cool white fluorescent light, and UV-enhanced fluorescent light. Toxicity was determined as mortality after 10 days of exposure. The extent of mortality was determined both as LC50 and LR50 (median lethal body residue). In water-only exposures, the toxicity of fluoranthene was greatest under the UV-enhanced spectra, followed by fluorescent light, and least toxic under the gold light. Both the LC50 and LR50 values exhibited the same pattern. The toxicity under gold light gave an LR50 of 0.81 mmolkg−1 (0.82–0.79, 95% CI) similar to values expected for the acute toxicity of nonpolar narcotic (anesthetic) compounds. The LR50 values under the other two light sources were substantially lower, 4 and 58 times lower for the fluorescent and UV-enhanced exposures, respectively. In sediment, toxicity was not significantly affected by the light source. Toxicity occurred only when the body residue concentration approached that of the LR50 under gold light from the water-only exposures. Thus, H. azteca were significantly protected from the light by burrowing into the sediment.