Abstract:

It has been 10 years since the Fukushima accident happened in March 2011. Japan proposed to discharge nuclear wastewater from the Fukushima Nuclear Power Plant to the ocean. Marine fish could absorb and concentrate on artificial radionuclides and thus become carriers and transmitters of artificial radionuclides. Therefore, it is important to monitor these artificial radionuclides (e.g., ¹³⁷Cs) in marine biotas to evaluate the influence of nuclear wastewater from Fukushima on marine environments. In order to understand the impact of ¹³⁷Cs on contamination in the East China Sea after the Fukushima nuclear meltdown and the release of diluted nuclear wastewater into the ocean, pomfret (Stromateidae), larimichthys polyactis (Pseudosciaena polyactis), hairtail (Trichiurus haumela), anglerfish (Lophiidae), lepidotrigla kishinouyi (Lepidotrigla), cynoglossus(Cynoglossus), farmed shrimp (Penaeus japonicus), scapharca subcrenata (Scapharca subcrenata) and mitten crab (Eriocheir sinensis) were collected from Zhoushan fishing ground in the East China Sea during 2011 and 2012 to determine ¹³⁷Cs by using high purity germanium gamma spectrometer in this study. The ¹³⁷Cs in these biotas was observed to be <0.11?1.2 Bq?kg^?1, which was slightly lower than that in the west coast of the USA and North Pacific fisheries (6?36 Bq?kg^?1) and significantly lower than the Fukushima adjacent sea (5?1200 Bq?kg^?1). The concentration factor of ¹³⁷Cs in the biotas of this study was (2.7?20)×10² L?kg^?1, which ranked second after ¹⁴C (~10⁴ L?kg^?1) among multiple artificial radionuclides from the nuclear wastewater of the Fukushima. Human consumers of fish would have received a total committed effective dose of 0.039?0.45 μSv?a^?1, which is clearly lower than that in the west coast of the USA, North Pacific fishing ground, and Fukushima adjacent sea. Considering the relatively higher concentration factor of ¹³⁷Cs in marine biotas, it is necessary to strengthen the monitor of artificial radionuclides (e.g., ¹³⁷Cs) in different species of marine lives to evaluate the influence of nuclear wastewater discharged by Japan on marine environments, biota, and human health. This study conducted a survey on the ¹³⁷Cs dose level of marine organisms in offshore fisheries just after the Fukushima nuclear accident, which provides the baseline data for the investigation of the Fukushima nuclear accident and the subsequent effects of artificial radioactive substances discharged from nuclear wastewater in Japan on offshore fisheries in the future. It is recommended that subsequent surveys be carried out in offshore China and in traditional North Pacific fishing grounds, especially in the North Pacific, which lies in the northeast of Fukushima, as the Kuroshio extension can directly transport Fukushima effluent to this area.

Key words: Fukushima accident, radionuclide, discharge wastewater to the ocean, radiological dose rates, marine biota

摘要：

2011年3月日本福岛发生核事故至今已有10余年，日本政府于近期决定将事故产生的核废水排入海洋，而海洋鱼类可以吸收和积累人工放射性核素而成为人工放射性物质的携带者与传播者，因此，对海洋鱼类中人工核素包括¹³⁷Cs的监测就十分重要。为了解福岛核泄漏发生以及日后核废水稀释排入海洋后¹³⁷Cs在中国东海的污染影响情况，于2011－2012年在东海舟山渔场海域采集了包括鲳属（Pampus）、小黄鱼（Pseudosciaena polyactis）、带鱼（Trichiurus haumela）、鮟鱇科（Lophiiformes）、红娘鱼属（Lepidotrigla）、舌鳎属（Cynoglossus）、日本对虾（Penaeus japonicus）、毛蚶（Scapharca subcrenata）和中华绒螯蟹（Eriocheir sinensis）在内的海洋生物样品，利用高纯锗伽马能谱仪对¹³⁷Cs进行分析。发现¹³⁷Cs的质量活度为<0.11－1.2 Bq?kg^?1，略低于美国西海岸和北太平洋渔场（6－36 Bq?kg^?1），明显低于福岛附近海域（5－1200 Bq?kg^?1）。¹³⁷Cs在研究区域生物样品中的生物浓缩系数为 (2.7－20)×10² L?kg^?1，是仅次于福岛排污废水中¹⁴C的生物浓缩系数（~10⁴ L?kg^?1）。居民食用中国东海的海产品带来的辐射剂量为0.039－0.45 μSv?a^?1，明显小于美国西海岸、北太平洋渔场和福岛附近海域。研究表明，¹³⁷Cs在鱼类中生物浓缩系数较高，因此，需要加强海洋中不同种群的鱼类中人工核素（包括¹³⁷Cs）含量的监测，以评估日本排放核废水对海洋环境、生物以及人类健康的影响。该研究是福岛核事故刚发生后对中国近海渔场海洋生物体内¹³⁷Cs剂量水平的一次调查，为今后调查福岛核事故以及核废水排放的人工放射性物质对中国近海渔场的后续影响提供了基础资料。建议对中国近海和中国传统的太平洋渔场进行连续性调查，特别是处于福岛东北部海域的北太平洋渔场的调查，因黑潮延伸体可以将福岛排污水直接输送至该区域。