Distribution of heavy metals and related health risks through soil ingestion in rural areas of western Japan

The distribution of heavy metal concentrations and related human health risks were investigated for Shimabara City, Nagasaki Prefecture. The purpose was to clarify the potential for heavy metal contamination in an area already known to be affected by nitrate pollution. A total of 188 soil samples was collected at 47 sites. The heavy metal content of the soil was measured in laboratory using an X-ray analyzer. The highest contents of heavy metals exceeded common background concentration in Japanese soils. The highest concentrations of Cu and Zn appear to be related to application of livestock waste in agriculture. Principal component and cluster analyses were performed to classify the sampling sites based on soil content of heavy metals. Three principal components (PCs) were extracted with the first PC explaining crustal constituents, the second explaining application of livestock waste, and the third explaining other types of anthropogenic pollutants. The cluster analysis resulted in 5 groups regarding the sampling locations. In total, 44% of sampling locations belonged to Group 1 and 46% to Group 2, distributed over the agricultural land in the northern part of the city and the urban area in the southern part of the city, respectively. There is a potential temporal health risk for the Pb content at specific locations in the area.