PAH concentrations and to compare this with laboratory results. Results of these efforts will 
contribute to development of ELS fish bioaccumulation models for PBTs under project B2. 
2. Dosimetry Relationships for PAH Toxicity to ELS Fish. 
Effective assessment of the risk of PAHs to fish populations requires improved understanding of 
the relationship of PAH accumulation, UV intensity and spectmm, and fish age to various effects 
in ELS fish. Dosimetry relationships will be developed in the laboratoiy for selected individual 
PAHs. Experimental methods will be developed to allow continuous exposure of ELS fish to 
various levels of both PAHs and UV radiation. Tests will be conducted to address the effects of 
PAH levels, the duration/nature of prior exposure to PAHs, fish age, and UV intensity, duration, 
and variability. 
A major impediment to PAH risk assessments is the complex mixtures that occur in most PAH- 
contaminated natural systems. Even if such mixtures could be completely characterized, the 
potencies of most constituents would be unknown and the combined toxicity could be 
significantly underestimated. The unaccounted-for toxicity could be addressed with an index 
which compares total measured photo-activated toxicity from a complex mixture to the expected 
toxicity based on measured accumulations of a subset of mixture constituents for which photo- 
activated potencies are known. Such an index could be based on the oligochaete Lumbriculus 
variegatus, for which phototoxicity bioassays are relatively simple and precise, and can involve 
either water or sediment exposures. The phototoxicity of complex PAH mixtures from selected 
sites and of reference PAHs to both L. variegatus and ELS fish will be tested to determine the 
utility of such an index. 
3. Assessment of PAH effects in Natural Systems and the Use of Photo-activated Potency as an 
Ecological Indicator. 
The effects of PAHs on ELS fish in selected natural systems will be evaluated using floating 
experimental platforms containing chambers in which fish can be exposed to site water and to 
various levels of UV radiation through selective wavelength screening. Such systems will 
provide a direct test of the legitimacy of concerns about photo-activated toxicity for natural levels 
of PAHs and UV radiation, and provide data for testing the applicability of laboratory data and 
methods to the prediction of these effects. 
MED scientists will also work cooperatively with researchers from the Great Lakes Ecological 
Indicators (GLEI) project to evaluate photo-activated PAH toxicity potency in sediments as an 
ecological indicator. GLEI staff will collect sediments samples from a stratified random set of 
coastal wetlands and tributaries to the Great Lakes. Samples will be shipped to MED and 
evaluated for photo-activated PAH toxicity potency using the oligochaete L. variegatus as 
described above. The measured potency of PAHs in these sediments will be compared to 
chemical characterization being conducted by the University of Minnesota cooperators, and 
indices of UV transmission in the water column, to estimate relative risk from this pathway at 
each site, using the photo-activated PAH toxicity models developed by MED in this and previous 
research. Additionally, estimated risk from photo-activated toxicants with be examined relative 
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