Environmental complex mixture toxicity assessment

Trichloroethylene (TCE) was found as a contaminant in the well supplying water to an aquatic testing laboratory. The groundwater was routinely screened by a commercial laboratory for volatile and semivolatile compounds, metals, herbicides, pesticides, and polychlorinated biphenyls using U.S. Environmental Protection Agency methods. Although TCE was the only reportable peak on the gas chromatograph, with average concentrations of 0.200 mg/l, other small peaks were also present, indicating the possibility that the contamination was not limited to TCE alone. A chronic 6-month carcinogenicity assay was conducted on-site in a biomonitoring trailer, using the Japanese medaka fish (Oryzias latipes) in an initiation-promotion protocol, with diethylnitrosamine (DEN) as the initiator and the TCE-contaminated groundwater as a promoter. Study results indicated no evidence of carcinogenic potential of the groundwater without initiation. There was, however, a tumor-promotional effect of the groundwater after DEN initiation. A follow-up laboratory study was conducted using reagent grade TCE added to carbon-filtered groundwater to simulate TCE concentrations comparable to those found in the contaminated groundwater. Study results indicated no promotional effects of TCE. These studies emphasize the necessity for on-site bioassays to assess potential environmental hazards. In this instance, chemical analysis of the groundwater identified TCE as the only reportable contaminant, but other compounds present below reportable limits were noted and may have had a synergistic effect on tumor promotion observed with the groundwater exposure. Laboratory toxicity testing of single compounds can produce toxicity data specific to that compound for that species but cannot take into account the possible toxic effects of mixtures of compounds.