ASSESSING THE LONG-TERM TOXICITY OF CRUDE-OIL IMPACTED WATERS; THE ROLE OF SECONDARY CONTAMINANTS AND THE BIOLOGICAL EFFECTS OF HYDROCARBON DEGRADATION PRODUCTS

The quality of water affected by crude-oil spills depends not only on the original compounds released, but also on hydrocarbon degradation products and toxic metals such as As, Co, Cr and Ni released during iron reduction. Water samples from a 40-year-old hydrocarbon plume resulting from a crude-oil release near Bemidji, MN, USA were characterized for redox-sensitive chemical species, trace elements, nonvolatile dissolved organic carbon (NVDOC) and total petroleum hydrocarbons in the diesel range (TPHd). Within the plume, degradation products constitute a major fraction of the dissolved organic matter, far exceeding TPHd. To evaluate toxicity of diesel-range hydrocarbons and their degradation products, plume water samples were processed to remove volatile organics and As. The remaining fraction was screened for biological activity (46 human nuclear receptors and 40 transcriptional pathways). Results show upregulation of peroxisome proliferator-activated receptors, estrogen receptor, and pregnane X receptor, with higher levels of activity in more contaminated samples. Such activation has been associated with adverse effects on development and endocrine and liver function. To investigate whether commonly used sample preparation protocols result in differing chemical/biological profiles we evaluated samples prepared using three common procedures: 1) a solid phase extraction targeting a range of polar and nonpolar compounds (HLB); 2) a dichloromethane (DCM) extraction typically used for TPHd analyses; and 3) DCM followed by silica gel cleanup (SGC) to remove polar compounds. Upregulation of biological activity in the HLB extracts consistently exceeded that of the DCM extracts. The biological activity of the hydrocarbon fraction isolated with the SGC was indistinguishable from background, indicating the polar degradation products caused the measured biological effects.