ABSTRACT
One of the more important issues concerning ground water remediation is to set the reasonable target in the remediation work. Persuasive target is to reproduce the pre-remediated condition which means zero
contaminant concentrations. However, this target is always impossible to achieve because of the high cost involved. In Japan, there are no comparable standard for allowable concentrations in contaminated groundwater. Human health risk assessment approach is a tool that permits establishment of remediation levels (target) that are protective of human health, depend on site conditions, remediation techniques, chemical characteristics, and utilize “acceptable” risk levels that can be selected to be more or less restrictive. Human risk assessment considers for main steps: 1) hazard identification, 2) dose-response or toxicity assessment, 3) exposure assessment and 4) risk characterization. The hazard identification is an identification of potentially harmful chemicals present in different media at a site. The toxicity assessment examines the toxicity, or harmfulness of each chemical found at the site. The exposure assessment step consists of identifying conditions under which people come in contact with the chemicals and characterizing the magnitude of exposure (exposure dose, mg/kg/day). In the risk characterization step, information from the above three steps is combined to estimate an additional risk to human health caused by exposure to the toxic chemicals assessed. For chemicals causing cancer, risk is understood to be the likelihood of cancer resulting from exposure to a chemical and is expressed as a probability. If the risk obtained from the risk assessment is larger than that established as “acceptable”(usually set 1 × 10−5 of drinking water in Japan), then it is said that the population is at risk and it’s necessary to reduce media concentrations to “Acceptable levels”. For noncarcinogen chemicals, the Hazard Quotient (HQ) is calculated, which is the ratio of the exposure dose for that chemical to the RfD (Reference Dose). If HQ > 1, it means that the population is receiving a dose larger than the RfD (maximum dose at which it is known that no adverse effects occurs) and, consequently, there is a possibility that the population will experience adverse effects.
