Photoenhanced toxicity of a weathered oil on Ceriodaphnia dubia reproduction

Traditionally, the toxic effects of petroleum have been investigated by con ducting studies in the absence of ultraviolet radiation (UV). Photomediated toxicity is often not considered, and the toxic effects of an oil spill ca n be grossly underestimated. The toxicity of a weathered oil collected from a monitoring well at an abandoned oil field to Ceriodaphnia dubia was exam ined in the presence of UV A solar simulator equipped with WE, UVA, and coo l white lamps was used to generate environmentally comparable solar radiati on intensities. C. dubia were exposed to six concentrations of water accomm odated fractions (WAF) of weathered oil in conjunction with three levels of laboratory simulated UV (Reference = < 0.002 mu W/cm(2) UVB; 3.0 mu W/cm(2 ) UVA; Low = 0.30 mu W/cm(2) UVB; 75.0 mu W/cm(2) UVA; High = 2.0 mu W/cm(2 ) UVB; 340.0 mu W/cm(2) UVA) and visible light. Seven day static renewal bi oassays were used to characterize WAF/UV toxicity. WAF toxicity significant ly (p < 0.05) increased when the organisms were exposed to WAF in the prese nce of UV. The photoenhanced toxicity of the WAF increased with WAF concent ration within each UV regime. Relative to the reference light regime, the a verage number of neonates from adults exposed to 1.6 mg TPH/L decreased sig nificantly by 20% within the low light regime, and by 60% within the high l ight regime. These results indicate that or ganisms exposed to dissolved-ph ase weathered oil in the presence of environmentally realistic solar radiat ion, exhibit 1.3-2.5 times greater sensitivity, relative to organisms expos ed under traditional laboratory fluorescent lighting.