Methodologies for evaluating planar chlorinated hydrocarbon, PCH, and polycyclic aromatic hydrocarbon, PAH, exposure and bioconcentration in fish

Abstract

The accumulation of complex chemical mixtures in aquatic organisms and their resultant effects are difficult to estimate due the wide range of physical and biological properties of the chemi8cals and the potential interactions among them. In this thesis several techniques were integrated and compared to determine their utility in assessing chemical mixture 4exposure and effects. Two specific families of chemicals were examined, the planar halogenated hydrocarbons (PCHs) and polycyclic aromatic hydrocarbons (PAHs).

Chapter 1 describes the determination of 2, 3, 7, 8-tetrachlorodibenzo-p-dioxin (TCDD)-equivalent concentrations (TECs) in four ways in livers of lake trout from three Great Lake sites. Bioassay-derived (BD) TECs were measured with rat (H4IIE) and rainbow trout (RTL-W1) cell lines and chemistry-derived (CD) TECs were calculated with TCDD equivalency factors (TEFs) derived with H4IIE and RTL-W1. Generally, BD-TECs and CD-TECs for individual samples did not differ significantly for either H4IIE or RTL-W1 indicating that all of the AhR-active compounds in a sample were accounted for by the congener analysis and that these compounds in a sample were accounted for by the congener analysis and that these compounds in a sample were accounted for by the congener analysis and that these compounds acted in an additive fashion in both mammalian and piscine systems. However, contributions of individual PCHs to overall CD-TECs differed with H4IIE and RTL-W1 TEFs, and for some individual samples, TECs did depend on the method used. Hepatic TECs and ethoxyresorufin-O-deethylase (EROD) levels differed significantly between sites. For TECs the order was Glenora > Jackfish Bay > Back Bay; for EROD activity the order was Jackfish Bay > Glenora = Black Bay. No correlation was found between hepatic TECs and EROD activity, which suggests that the two measurements are evaluating different but related consequences of containment exposure.

In Chapter 2, a three-step approach was employed to assess the exposure of rainbow trout to polycyclic aromatic hydrocarbons (PAHs) in standardized creosote contaminated microcosms. Bioconcentration of PAHs was approximated using semipermeable membrane devices (SPMDs) and compared to levels seen in the trout. Large differences in concentrations of PPPAHs in the two matrices were seen, with SPMDs accumulating higher levels of analytes compared to the fish. Increases in hepatic EROD levels and bile metabolites with creosote dose indicate the difference is mainly due to biotransformation of accumulated PPPPAHs in the trout. Species-specific response to PPPAHs extracted from trout and SPMDs was assessed by calculating 2,3,7,8-tetrachlorodibenzo-p-dioxin equivalent concentrations (TECs) using mammalian and piscine cell line bioassays. The use of RTL-W1 or H4IIE did lead to different TECs, but the magnitude of the differences was not great and depended on whether SPMD or liver extracts were being examined. Possible reasons for the disparity include subtle differences in the AhR signal transduction system, PAH metabolism between fish and mammals or TEF derivation methods. This dissimilarity may indicate that RTL-W1 is more appropriate than H4IIE for assessing the toxic impact of PAHs to rainbow trout. The integration of the exposure assessment methodologies provided evidence of concentration-dependent PPPAH uptake in rainbow trout, despite low levels detected in the liver.

Chapter 3 examined the time-dependent uptake of priority pollutant polycyclic aromatic hydrocarbons (PPPAHs) in both semipermeable membrane devices (SPMDs) and rainbow trout exposed to creosote-dosed microcosms. SPMDs rapidly accumulated PPPAHs over time while rainbow tout maintained steady, low levels throughout the exposure period. In contrast, rainbow trout hepatic EROD was elevated by the first collection point, indicating exposure to CYPIA inducing compounds. It is hypothesized that this elevated activity lead to the metabolism and elimination of PPPAHs from the rainbow trout livers. A rainbow trout liver cell line, RTL-W1, was exposed to PPPAH extracts from both SPMDs and trout livers to determine bioassay-derived 2,3,7,8-tetrochlorodibenzo-p-dioxin equivalent concentrations (BD-TECs). BD-TECs followed the levels of chemical concentrations measured in both matrices. Using RTL-W1 2,3,7,8-tetrachlorodibenzo-p-dioxin equivalency factors (TEFs), chemically-derived (CD) TECs were determined for SPMDs and trout livers. Elevated BD-TECs compared to CD-TECs suggests the presence of an unknown EROD inducing compound(s) in the microcosms. This study demonstrates the importance of examining PPPAH uptake over time, its relationship to biological response, and the utility of a multilevel analysis for a more complete representation of the actual events that occur upon chemical exposure.