Wild Japanese monkeys inhabiting the forest area of Fukushima City have lower blood cell counts than monkeys from Northern Japan, a paper in Scientific Reports finds. The research suggests that exposure to radioactive materials following the Fukushima Daiichi nuclear disaster may have contributed to blood changes in these primates, although the precise cause of these changes remains to be proven.

Shin-ichi Hayama and colleagues compared 61 monkeys located 70 km from the Fukushima Daiichi nuclear power plant with 31 monkeys from the Shimokita Penisula, approximately 400 km from the nuclear power plant. Red and white blood cell counts, haemoglobin and haematocrit levels were all significantly lower in the Fukushima monkeys than in the Shimokita monkeys. Muscle radiocesium levels - a measure of radiation exposure - varied in Fukushima monkeys in relationship to the levels of contamination detected in the soil from their habitat, whereas radiocesium levels were undetectable in all Shimokita monkeys. White blood cell counts were negatively correlated with muscle radiocesium concentrations in immature - but not mature - Fukushima monkeys, which indicates that younger monkeys may be more vulnerable to radioactive materials, the authors propose. They suggest that the low blood cell counts may be a sign of a compromised immune system, which could potentially make the monkeys susceptible to epidemic infectious disease.

The researchers rule out infectious disease or malnutrition as an alternative cause of low blood cell counts in Fukushima monkeys, but note that further studies are needed to confirm whether the low blood counts are caused by radiation damage.