There have been a number of closed and abandoned mines since 1990s. Many of them have not been appropriately managed, and brought about heavy metal contamination in nearby soil and water. The results of detailed investigation on surrounding environments of those mines conducted by Ministry of Environment (MOE) on 2009 revealed that there have been serious environmental contamination within almost 95% of abandoned mines (105 among 110 mines). For the sake of quantitative environment risk assessment, the MOE set up a guideline on human risk assessment of soil contamination and a number of researches have been actively undertaken for developing more effective and efficient methodologies of human and ecological risk assessments. Generally, the human risk assessment of soil contamination is composed of 4 steps: hazard identification, exposure assessment, toxicity assessment, and risk determination. Among those steps, the result of exposure assessment totally depends on the quality of exposure parameters used, and advanced countries have made their great efforts on preparing reliable values of exposure parameters. However, there have been definitely lack of such endeavors and foreign values are used in Korea. For this reason, this study was initiated to propose a suitable methodology for human risk assessment of heavy metal contamination nearby abandoned metal mine areas. In particular, a number of exposure parameters were extracted from diverse references to be specified to residents near mine areas.
In addition, a variety of soil analytical methods were compared to select the most relevant one for computing average daily dose of crop-intake pathway using soil exposure concentrations and soil-crop bioconcentration factors (BCF). For attaining the goals of the study, rice was the crop of concern because it is one of representative crops in Korea and was cultivated within all the area of 5 mines targeted in this study. The 5 soil analytic methods (0.1/1 N HCl, 1 M NH4NO3, 0.1 M NaNO3, 0.01 M CaCl2, and total digestion using aqua regia) were compared.
First, five heavy metals (As, Cd, Cu, Pb, and Zn) were determined as major hazardous contaminants in this human risk assessment. In addition, 6 exposure pathways (soil-intake, soil-dermal contact, soil-inhalation, groundwater-dermal contact, groundwater-intake, and crop-intake) were selected for this study. Three types of receptors (male and female adults and child) were taken into account. More importantly, a number of exposure parameters related to the characteristics of receptors were obtained from comprehensive survey of reference data and the guideline of MOE to specify those parameters to residents near mines. The computed total excess carcinogenic risks for all mine areas of concern exceeded the acceptable carcinogenic risk (1 × 10?6), indicating that these areas are likely unsafe due to a carcinogenic hazard. Meanwhile, the hazard indices were higher than the unit risk (1) for all receptors, except for children in Yanggok and Bong mines, suggesting that there are non-carcinogenic risks for these groups in the study areas. Consumption of groundwater and crops grown in the area were identified as major exposure pathways for carcinogenic and non-carcinogenic hazards in areas of concern. Finally, the dominant contaminant contributing to carcinogenic and non-carcinogenic risks was arsenic.
Based on the results of comparison between diverse soil analytical methods, the lowest errors between crop exposure concentrations and soil exposure concentrations multiplied by soil-crop BCFs were obtained from 0.01 M CaCl2 for As, 1 M NH4NO3 for Cd, 0.1/1 N HCl for Cd, 0.1 M NaNO3 for Pb, and total digestion for Zn. The results indicate that the partial extraction using 0.1/1 N HCl was superior or equivalent to total digestion. In addition, 0.1 M NaNO3 method for As, Cd, Cu and Pb combined with total digestion for Zn is recommended for improving the reliability of human risk assessment for crop-intake pathway.