Although it is widely recognized that lead affects children′s cognitive function even at lower blood lead level (<10 μg/dL), systematic studies on the source of lead for Japanese children have been limited. A case study for 3 Japanese children having higher blood lead level (∼3 μg/dL) was performed to identify the source of lead. Some potential sources (soil, indoor dust, outdoor dust, diet and tobacco) were collected from the environment of each child. After digestion with acid and extraction with artificial gastric juice, lead concentration and lead isotope ratio (207Pb/206Pb, 208Pb/206Pb) were measured by ICP-MS. Children were estimated to be exposed to 2.5∼5.0 μg of lead on daily basis that was much less than the value estimated from their blood lead level. Isotope ratio analysis indicated that indoor dust was the dominant exposure source (65∼88 % lead uptake basis) in one case, of which result was similar to those in other countries in spite of great differences in life styles. In another case, higher blood 208Pb/206Pb compare to those of environmental samples indicated the presence of unknown lead source(s) for this child.
