Ecological risk assessment on a cadmium contaminated soil landfill--a preliminary evaluation based on toxicity tests on local species and site-specific information.

In recent years, methodology of ecological risk assessment has been developed and applied frequently for addressing various circumstances where ecological impacts are suspected or have occurred due to environmental contamination; however, its practice is very limited in Taiwan. In 1982, brown rice from rice paddy fields in Da-Tan, Tau-Yuan, was found to be contaminated with Cd and Pb due to illegal discharges of wastewater, known as the "Cd rice" incidence. Cadmium laden soil was transferred to a constructed landfill in an industrial park 15 years after the incident. Possible leakage of the landfill was suspected by committee members of a supervising board for the remediation process, and a preliminary ecological risk evaluation was requested. A possible risk scenario was that groundwater contamination due to the leachate containing Cd and Pb from the landfill could result in pollution of coastal water, and subsequently produce toxic effects to aquatic organisms. Chemical dissipation in groundwater systems was simulated and short-term chronic toxicity tests on larvae of three local aquatic species were also performed to determine the no-observed adverse-effect concentrations (NOAECs), as well as the predicted no effect concentrations (PNECs), of the two metals in the organisms tested. The hazard quotient (HQ), the ratio of predicted environmental concentrations (PECs) to PNECs, was used for risk characterization. A worst-case-scenario calculation showed that the maximum Cd concentration at 60 m and farther downstream from the site in the groundwater system would be 0.0028 mg l(-1) with a maximum initial concentration of 0.65 mg l(-1) in the leachate, while for Pb, the highest concentration of 0.044 mg l(-1) would be reached at a distance of 40 m and farther, which was based on an initial concentration of 4.4 mg l(-1) in the leachate; however, both cases would only occur 80 years after the initiation of leakage. A presumed dilution factor of 100 was used to calculate the PECs based on the maximum initial concentrations. The Cd and Pb's PNECs for three aquatic animals were 0.01 to approximately 0.1 mg l(-1), higher than their PECs in coastal water, resulting in HQs less than 1 for the scenario described. We concluded that if a leakage does occur, the ecological impact would be minimal because a majority of the metals will be retained in the soil phase and the remaining, if released into the aquatic system, cannot reach high enough concentrations to produce toxicity to marine animals.