Lead concentration in blood of Asian black bears in two areas of Central Japan

To measure blood lead level, we collected a total of 88 blood samples from 66 Asian black bears (Ursus thibetanus japonicus) that were live-trapped in two study areas in Japan. In both areas, extensive sika deer (Cervus nippon) and wild boar (Sus scrofa) control programs and sport hunting using lead-based ammunition have been conducted. The area in the Ashio-Nikko Mountains is located near a former copper mine and smelter. The Okutama Mountains are situated in the suburbs of Tokyo, a mega-city with a population of nearly 14 million. In both study areas, the use of leaded gasoline was permitted until 1975 for regular gasoline vehicles. Our analysis revealed that Japanese black bears had higher lead compared to American black bears (U. americanus) and brown bears (U. arctos) in North America. Blood lead concentrations were higher in the Ashio-Nikko Mountains (110.4 ± 38.3 SD μg/L) than in the Okutama Mountains (49.3 ± 46.2 SD μg/L). The blood lead concentrations were particularly high in lactating females compared to most males and females. White blood cell count was decreased with increasing blood lead concentration. The source of lead contamination remains unknown at this time. However, Japanese black bears in our study areas commonly scavenge on large mammals, and lead-based ammunition could constitute a significant portion of the contamination in both areas. In addition, former mining activities could elevate the lead concentrations of bears in the Ashio-Nikko Mountains. Atmospheric lead depositions originating from former leaded gasoline use in Japan and current air pollution from the Asian continent are also potential factors in both areas. Future identification of exposure sources is necessary.