Haematological analysis of Japanese macaques (Macaca fuscata) in the area affected by the Fukushima Daiichi Nuclear Power Plant accident

Abstract

Several populations of wild Japanese macaques (Macaca fuscata) inhabit the area around Fukushima Daiichi Nuclear Power Plant (FNPP). To measure and control the size of these populations, macaques are captured annually. Between May 2013 and December 2014, we performed a haematological analysis of Japanese macaques captured within a 40-km radius of FNPP, the location of a nuclear disaster two years post-accident. The dose-rate of radiocaesium was estimated using the ERICA Tool. The median internal dose-rate was 7.6 μGy/day (ranging from 1.8 to 219 μGy/day) and the external dose-rate was 13.9 μGy/day (ranging from 6.7 to 35.1 μGy/day). We performed multiple regression analyses to estimate the dose-rate effects on haematological values in peripheral blood and bone marrow. The white blood cell and platelet counts showed an inverse correlation with the internal dose-rate in mature macaques. Furthermore, the myeloid cell, megakaryocyte, and haematopoietic cell counts were inversely correlated and the occupancy of adipose tissue was positively correlated with internal dose-rate in femoral bone marrow of mature macaques. These relationships suggest that persistent whole body exposure to low-dose-rate radiation affects haematopoiesis in Japanese macaques.

Figure 1

Map of the sampling point. The black circle indicates the location of Fukushima Daiichi Nuclear Power Plant (FNPP). X-marks and cross-marks indicate the sampling points of Japanese macaques in the exposed and the non-exposed areas, respectively.

Figure 2

Correlation between dose-rate and haematological values in bone marrow of the exposed group. White circles: immature macaques (N = 20), black circle: mature macaques (N = 18). Cell number is presented per 115,600 μm² of bone marrow. Solid lines and dashed lines indicate linear trend lines which were drawn by the scatter plots of mature and immature animals, respectively. r and p indicate Pearson’s correlation coefficient and p value, respectively. All Pearson’s correlation coefficients and p values are shown in Supplementary Table S2.

Figure 3

Representative histology of bone marrow of the exposed macaques. (a) A 9-year-old male captured on August 27, 2013 with 479 Bq/kg (¹³⁴Cs + ¹³⁷Cs) of the skeletal muscle, of which the estimated internal dose-rate was 4.90 μGy/day and the external dose-rate was 24.8 μGy/day. (b) An 8-year-old female captured on January 24, 2014 with 11,400 Bq/kg (¹³⁷Cs + ¹³⁴Cs) of the skeletal muscle, of which the estimated internal dose-rate was 74.5 μGy/day and the external dose-rate was 24.9 μGy/day.