田中 亜紀

We examined the conception rate of wild Japanese monkeys (Macaca fuscata) in Fukushima City that were exposed to radiation as a result of the Fukushima Daiichi Nuclear Power Plant accident in March 2011. The conception rate in the year of delivery from 2009 to 2022 was estimated by dissecting individuals that were euthanized by the government for population control as a countermeasure against crop damage. To evaluate the effects of exposure, the cumulative exposure dose for each individual was calculated using the concentration of radiocesium deposited in the soil at the capture site and the concentration of radiocesium in muscle estimated from the aggregated transfer factor. There were no significant differences in conception rates across all age classes over time. In terms of conception rates by age class, there was a significant decrease post-exposure compared with pre-exposure in the age class ≥ 8 years, but no significant differences in the age class 5-7 years. The non-ovulation rate did not significantly differ between the pre- and post-exposure periods for any age class. Body fat index, which can affect fertility, was compared between the pre- and post-exposure periods, and no significant differences were found in either age class. In contrast, the median total cumulative exposure (cumulative internal exposure + cumulative external exposure) was significantly higher in the age class ≥ 8 years compared with the age class 5-7 years. These results suggest that the total cumulative exposure dose may be one of the reasons for the lower conception rate in the post-exposure period among the age class ≥ 8 years.

Wild Japanese monkeys (Macaca fuscata) were exposed to radiation after the Fukushima Daiichi nuclear accident in 2011. To clarify the biological effects of radiation exposure on their fetal growth, pregnant monkeys and their fetuses were analyzed. These animals were collected between 2008 and 2020 (before and after the accident in 2011) living in Fukushima City, approximately 70 km from the nuclear power plant. Multiple regression analyses were conducted with fetal body weight (FBW) and fetal head circumference (FHS) as objective variables, and maternal and fetal factors as explanatory variables. The maternal factors were relative exposure dose rate (REDR), age, body weight, body length, fat index, and parity. The fetal factors were crown ramp length (CRL) and sex. Multiple regression analyses showed that FBR and FHS growth were positively associated with CRL, maternal body length, and negatively associated with REDR. Since the relative growth of FBR and FHS to CRL decreased with increasing REDR, radiation exposure due to the nuclear accident may have contributed to the delayed fetal growth observed in Japanese monkeys.

In forensic pathology, it is important to detect and recover as evidence residual metal particles and projectiles when evaluating potential gunshot wounds. This process can be challenging when the bullets are fragmented. This report presents our experience using multiple modalities to analyze the wound of an illegally killed Japanese serow (Capricornis crispus) found in a mountainous region without its head and hind limbs. We performed postmortem computed tomography (PMCT) and necropsy that showed a distant-range gunshot wound of the neck likely created by a centerfire rifle. A postmortem cut through the neck and absent head precluded a complete evaluation. To determine the composition of the metal-like fragments in the neck, sampling and metal analysis were performed in two ways. Samples extracted from the exposed wound surface without CT guidance were analyzed directly using inductively coupled plasma mass spectrometry (ICP-MS). Samples from the bone, muscles, and cervical cord extracted under CT guidance were analyzed using x-ray analytic microscopy (XGT-9000, HORIBA, Kyoto, Japan). In wound surface samples, silicon and iron were detected as the main components on ICP-MS, suggesting that the materials were gravel. The samples taken under CT guidance and analyzed with XGT-9000 revealed that the high-density CT areas were mainly composed of lead. Combining CT-guided sample extraction and XGT-9000 can be useful for retrieving true projectile fragments and avoiding the confusion created by erroneously sampling non-projectile surface materials.

Abstract Over the 10 years immediately after the Fukushima Daiichi nuclear accident, we measured the changes in the muscle ¹³⁷Cs concentration (Bq/kg) of wild Japanese monkeys living in Fukushima City, which is located approximately 70 km from the Fukushima Daiichi Nuclear Power Plant. The muscle¹³⁷Csconcentration, which was observed at a maximum of 13,500 Bq/kg immediately after the accident, had decreased to several hundred Bq/kg 10 years later. The muscle ¹³⁷Cs concentration was significantly related to the soil contamination levels (10,000–30,000, 30,000–60,000, 60,000–100,000, and 100,000–300,000 Bq/m²), sex, age class (immature, mature), body weight (> 5000 g, 5000–10,000 g, < 10,000 g), and seasons (the cold period from December to April, the warm period from May to November).The value of muscle ¹³⁷Cs concentration and the aggregated transfer factor (T_ag: calculated by dividing muscle ¹³⁷Cs concentration [Bq/kg] by soil ¹³⁷Cs deposition density at the capture site [Bq/m²]) apparently decreased with time for several years. However, post hoc pairwise comparisons showed no difference from 2017 to 2020, and the accumulation of ¹³⁷Cs in muscle may continue for some time.