Evaluation of a Reporter Gene System Biomarker for Detecting Contamination in Tropical Marine Sediments.

A major challenge in conducting field assessments of potential ecological impacts is optimizing the number of samples and the costs. This is especially important in light of the growing concern over the presence of persistent organic contaminants, such as PCBs, dioxins, furans, and PAHs in sediments. A reporter gene system (RGS) assay that measures induction of the CYP1A1 gene and transcription of P450 enzyme systems is often used to assess potential toxicity of these compounds in environmental samples (1, 2, 3). RGS has gained acceptance as an inexpensive, rapid method for screening environmental samples for contaminants (4, 5). The RGS approach has been validated in the laboratory with pure compounds, known chemical mixtures, and from field-collected sediments by comparing RGS system response and chemical concentrations (1, 2, 3, 6). Our study differed from other validation studies in two respects: we used field-collected sediments over a wide range of contaminant concentrations and evaluated RGS response to sediment samples containing a mixture of dioxins, furans, and PAHs. With few exceptions, the previous validation studies using field-collected samples used fairly small sample sizes and generally evaluated one chemical group (3, 6). Few studies have compared large numbers of samples containing both PAHs and 2,3,7,8 tetrachlorodibenzo-p-dioxin (TCDD) over the range reported here. The purpose of this study was to determine if there is a high correlation between RGS response and chemistry results from the same samples. If this proves to be the case, the assay could be used to screen large areas at a relatively low cost. Samples exhibiting high responses could be targeted for further characterization using more precise, but costly, GC/MS methods. Matched sediment samples (n = 31) were collected off the northwestern shore of Johnston Island, adjacent to potential sources of PAHs and 2,3,7,8 tetrachlorodibenzo-p-dioxin (TCDD) (Site 1), and at sites farther removed from the potential contaminant sources (Sites 3, 4). To ensure blind analysis of the samples, P450 RGS assays were conducted by MEC Analytical Systems (Carlsbad, California) and Columbia Analytical Services (Vista, California) while chemical analyses were completed by the Toxic Contaminant Research Laboratory at Wright State University (Dayton, Ohio). The RGS assay used in this study was developed by Anderson et al. (1) and detailed methods have been described (1, 7). Induction in the assay is dependent upon the aryl hydrocarbon receptor (AhR) activation pathway. AhR ligands, including planar PCBs, PAHs, and TCDD, bind to AhR, activating it and resulting in its translocation to the nucleus of the cell. In the nucleus, the activated