Monitoring Lead (Pb) Pollution and Identifying Pb Pollution Sources in Japan Using Stable Pb Isotope Analysis with Kidneys of Wild Rats

Abstract

Although Japan has been considered to have little lead (Pb) pollution in modern times, the actual pollution situation is unclear. The present study aims to investigate the extent of Pb pollution and to identify the pollution sources in Japan using stable Pb isotope analysis with kidneys of wild rats. Wild brown (Rattus norvegicus, n = 43) and black (R. rattus, n = 98) rats were trapped from various sites in Japan. Mean Pb concentrations in the kidneys of rats from Okinawa (15.58 mg/kg, dry weight), Aichi (10.83), Niigata (10.62), Fukuoka (8.09), Ibaraki (5.06), Kyoto (4.58), Osaka (4.57), Kanagawa (3.42), and Tokyo (3.40) were above the threshold (2.50) for histological kidney changes. Similarly, compared with the previous report, it was regarded that even structural and functional kidney damage as well as neurotoxicity have spread among rats in Japan. Additionally, the possibility of human exposure to a high level of Pb was assumed. In regard to stable Pb isotope analysis, distinctive values of stable Pb isotope ratios (Pb-IRs) were detected in some kidney samples with Pb levels above 5.0 mg/kg. This result indicated that composite factors are involved in Pb pollution. However, the identification of a concrete pollution source has not been accomplished due to limited differences among previously reported values of Pb isotope composition in circulating Pb products. Namely, the current study established the limit of Pb isotope analysis for source identification. Further detailed research about monitoring Pb pollution in Japan and the demonstration of a novel method to identify Pb sources are needed.

Keywords: developed country; metal contamination; source identification; stable Pb isotope; wild rodent.

Figure 1

Distribution and number of rat samples by region.

Figure 2

Pb-IRs (²⁰⁸Pb/²⁰⁶Pb and ²⁰⁷Pb/²⁰⁶Pb) in kidneys of wild rats from various regions in Japan.

Figure 3

Pb-IRs in kidneys of wild rat from various regions in Japan. Pb level in kidney < 2.5 mg/kg (a); 2.5 ≤ Pb level in kidney < 5.0 (b); 5.0 ≤ Pb level in kidney < 15.0 (c); 15.0 ≤ Pb level in kidney (d). A = Aichi, C = Chiba, F = Fukuoka, G = Tochigi, H = Hyogo, I = Ibaraki, K = Kanagawa, M = Saitama, N = Niigata, O = Okinawa, S = Osaka, T = Tokyo, Y = Kyoto. Circle = solder circulated in Japan [39], square = paint [39], triangle = battery [40], inverted triangle = airborne particulate matter [39]. Figure 3a was shown with simple dots due to too many individuals.

Figure 4

Pb levels (mg/kg, dry weight) in kidneys of wild rats from various regions in Japan and other countries. Data are shown in box and whisker plots: box limits represent 25th and 75th percentiles; lines within the boxes indicate the medians; whisker ends indicate minimum and maximum values. The red line indicates the previously reported renal Pb level (2.5 mg/kg) above which histopathological changes should be expected. Black and white inverted triangle = rats from polluted and control area in Poland [32], black and white square = rats from polluted and control area in Italy [30], black and white triangle = rats from polluted and control area in Belgium [41], black and white circle = rats from polluted and control area in Zambia [33].