Gill damage in Puget Sound fish: industrial chemicals associated with DNA changes.

Chemical pollutants in parts of Puget Sound appear to be damaging the DNA of fish that live there, according to findings published this month by Donald C. Malins of the Pacific Northwest Research Institute Biochemical Oncology Program and colleagues [EHP 112:511-515]. The researchers compared DNA extracted from the gills of English sole in the Duwamish River (which flows into the sound through a heavily industrialized area in south Seattle) to DNA taken from fish in the relatively clean Quartermaster Harbor. They found significantly more structural damage in the DNA of fish taken from the Duwamish compared to samples from Quartermaster Harbor.

For this study, the researchers used two chemical markers to characterize the levels of pollution in bottom sediments: polynuclear aromatic hydrocarbons (PAHs), by-products of fossil fuel combustion that are readily metabolized in fish, and polychlorinated biphenyls (PCBs), which were banned in the United States in 1979, but persist in the environment due to their slow rate of degradation. PCBs accumulate in fish tissue and have been responsible for many advisories to limit human consumption; the Washington State Department of Health warns of the possible adverse health risks of consuming English sole and other bottom-feeding fish from the lower Duwamish River due in the presence of PCBs, PAHs, and other toxic chemicals.

The team used expression of cytochrome P450 1A (CYP1A) as a measure of exposure to the contaminants of interest. CYP1A is involved in the oxidation of chemicals including PAHs and PCBs, and when it reacts with hydrocarbons, including PAHs, it can create metabolic by-products that can alter DNA. Also, certain PCBs can cause CYP1A to form reactive oxygen, which can damage DNA. Higher levels of CYP1A expression may lead to a greater risk of damage to DNA and more potential for mutations. The Duwamish is substantially more contaminated with PAHs and PCBs compared to Quartermaster Harbor, and the levels of toxic chemicals in the sediments at both sites were consistent with the degree of expression of CYPIA in the gills offish from the respective sites.

The researchers used Fourier transform infrared (FT-IR) spectroscopy statistical models to identify subtle structural changes in gill DNA including differences in base functional groups and conformational disruptions that have the potential to affect transcription and replication. This technology had been previously used to identify changes in the structure offish liver DNA and to predict prostate and breast cancer in humans. The researchers applied logistic regression analysis to these models to assess the effects of contaminants on fish gills. This yielded a "DNA damage index" based upon the different spectral properties of gill DNA from each fish group.

This index could be used in the future to gauge the effectiveness of cleanups at polluted sites. For example, if gill tissue from fish at a site undergoing remediation had a DNA damage index close to that of fish from a clean reference site, it would be an indication that remedial efforts had been successful. An added environmental benefit of the technique is that researchers can take small biopsies of gills in the target fish and return the fish to the water alive.

The researchers hypothesize that fish with gill DNA damage might also have damage to DNA in other parts of the body. They are presently examining the liver, gonads, and kidneys of the fish sampled in the current study to determine the potential correlation between gill DNA damage and internal organ damage. They are also applying the FT-IR models to fish from polluted and clean sites in California to see if the DNA damage index is equally useful in other contaminated environments. Further research is necessary to determine if a high DNA damage index score is an accurate predictor of health problems in fish and risks to people who consume them.