An accident in a nuclear power plant can cause radioactive contamination to the environment. On March 2011, the radioactive cesium-137 (137Cs) was released into the environment from an accident at the Fukushima Daiichi Nuclear Power Plant[1]. Consequently, the radioactive cesium-137 with a half-life of 30 years caused contamination that was a serious concern because of the deleterious effect of radioactive cesium-137 on the environment or on humans[2–4]. Radioactive cesium-137 has been found in contaminated soil[5], forest[6], seawater[7–9], and freshwater[10], In addition, there are several reports that showed that radioactive cesium-137 has contaminated seawater fisheries. Wada et al.2013 determined that radioactive cesium contamination had occurred in marine products that took place during April 2011 to October 2012. The authors showed that the exceeded regulatory limit of contaminants in Japan was found in the several commercial fishes that were caught in coastal shallow waters[11]. Consistent with Wada et al. 2013[11], other authors monitored the radioactive cesium contamination in marine products during 2011 to 2015. The authors showed that the contamination in several fishes had been found in the Fukushima Prefecture[12]. Radioactive cesium have not only contaminated seawater fish, but have also contaminated freshwater types. The authors showed that during 2015–2016, the freshwater fish found in water around the Fukushima Dai-ichi Nuclear Power Plant had been contamination with radioactive cesium[13]. Kurikami et al. 2019 have also mentioned that during October 2018, freshwater fish in rivers at Fukushima Prefecture had been found to be contaminated with radioactive cesium. This radioactive cesium was higher than the Japanese regulatory limit of 100 Bq.kg− 1 for general foodstuffs[14]. The contamination of fishes is termed an aquatic bioaccumulation; an important pathway for the transfer of radioactive cesium from fishes to humans. Therefore, humans can potentially receive radioactive cesium by directly contact or by consumption of contaminated fresh fishes or contaminated fish products. In addition, Kana Yamamoto et al. 2019 evaluated the radioactive cesium contamination of pregnant women over a 5-year period after the Fukushima Daiichi Nuclear Power Plant accident at Minamisoma City which was an area that was included the evacuation zone. Authors reported that a maximum annual effective dose was found in these individuals by radioactive cesium-134 and − 137 that was estimated to be at 16 µSv/year[15]. Moreover, Masahiko Matsuo et al. 2019 evaluated radioactive contamination in an evacuation area called Tomioka Town located in the Fukushima Prefecture after six years after the Fukushima Daiichi Nuclear Power Plant accident. The authors reported that the median air dose rates both for indoors and outdoors were 0.20 µSv/h and 0.26 µSv/h, respectively. The indoor radiation exposure dose rate in the area that residents had returned home to was 1.6 mSv/y. However, the median air dose rate measured outdoors in this difficult to return area was 2.3 µSv/h (20 mSv/y)[16].
It should be noted that the environmental and human contamination from radioactive cesium after several years since the Fukushima Daiichi Nuclear Power Plant accident have still been found to be in the low-dose radiation range. It is known that high doses of radiation induce damage to cells or tissues[17–21]. However, information on the potential health risks from exposure to low-dose radiation is still unclear[22].
There are works that have studied the effect of gamma ray at the radiation dose level that might be found in a radiation accident or environmental radiation dose. Rithidech et al. 2005 studied the effect of 137Cs gamma ray on bone marrow cells of mice after an in vivo exposure to 0.05, 0.1, or 1.0 Gy. The authors found that NF-κB activation occurred in bone marrow cells of mice after an in vivo exposure to 0.1 and 1.0 Gy (but not 0.05 Gy) of 137Cs gamma ray[23]. Similar findings came from another publication, Jangiam et al. 2018 determined the late effects of 137Cs gamma ray on the bone marrow, lungs, and testis of mice after an in vivo exposure to 0.05, 0.1, or 1.0 Gy. The authors found that the number of cell death, DNA damage, and inflammation response did not significantly change in bone marrow, lungs, and testis of mice that were exposed to 0.05 Gy of 137Cs gamma rays, when compared to a sham control. In contrast, significant changes in the number of cell death, DNA damage, and inflammation responses were shown in bone marrow, lungs, and testis of mice that had been exposed to 0.1 and 1.0 Gy of 137Cs gamma rays[24]. It should be noted that there was a difference in biological response to 0.05 Gy of gamma rays, when compared to 0.1 or 1.0 Gy exposure.
This current study has focused on the effect of low-dose gamma rays that might result in radioactive cesium contamination in humans. Red blood cells and plasma were used to study radiation effects because red blood cells and plasma are major components of blood. In addition, the damage of red blood cells might cause insufficient oxygen consumption in tissue or organs, resulting in increases in the risk of deleterious effects on the human body[25]. Moreover, there were evidences suggested the effect of low-dose fast neutrons on the blood components[26–28]. The objective of this current study was to determine the effects of in vitro exposure to radioactive cesium-137 on some human blood components.