M2 AM Aquatic Ecotoxicology (Part 1)
Monday, 14 November 2005: 8:00 AM - 11:40 AM in Ballroom 2

(DIA-1117-647706) Lab to field extrapolation for PAH phototoxicity risk assessment.

Diamond, S¹, Mount, D¹, Erickson, R¹, Heinis, L¹, Hockett, J¹, Highland, T¹, Jensen, C¹, ¹ USEPA, NHEERL, MED, Duluth, MN, USA

ABSTRACT- Photoactivated toxicity (PAT) of polycyclic aromatic hydrocarbons (PAH) has been quantified in laboratory and limited outdoor experiments. These results are critical for assessing risk of PAT at PAH-contaminated sites. However, extrapolation of these laboratory results introduces uncertainty for several reasons. Laboratory exposures involve use of artificial ultraviolet radiation (UVR) sources, water that does not attenuate UVR, and single PAHs. In natural settings the source of UVR is solar radiation, water columns can strongly attenuate UVR, and PAHs are typically comprised of complex mixtures. These sources of uncertainty were investigated using laboratory and field exposures of fathead minnows, extensive measurement and modeling UVR exposure, and evaluation of the relative toxicity of single PAH and complex mixtures. Based on fathead minnow exposures, the initial ratio of field and laboratory LD50s was 11.6:1, based on the multiple of UVR and tissue concentration of PAH. Quantification of differences between the experimental and field-UVA exposures, based on pyrene and anthracene, indicate that 30% of the uncertainty of lab to field extrapolation in this example is due to spectral differences. Quantification of spectral attenuation within the field-site water column explains an additional 10% of the uncertainty. The 11.6:1 potency ratio was calculated based on tissue pyrene, or the sum of tissue pyrene, fluoranthene, and anthracene in laboratory and field experiments, respectively. Of the 16 PAHs measured, evidence or modeling suggests that 9 are potentially photoactive. Based on QSAR models, the potency of all the measured PAHs is approximately 1.5 times greater than the combined pyrene, anthracene, and fluoranthene potency. When these factors are all quantified, the uncertainty in lab to field extrapolation, expressed as the original 11.6:1 potency ratio, can be reduced to a ratio of 3.48:1. These estimates, and their importance relative to other studies and the estimation of PAT risk will be discussed.

Key words: polycyclic aromatic hydrocarbons, phototoxicity, risk assessment, ultraviolet radiation