Spatial-temporal variations of kelp 129I contents in coastal waters of China before and after the Fukushima Daiichi Nuclear Power Plant accident

Radioactive ¹²⁹I isotope, as one of the main products of the nuclear fission process, can be applied to track radioactive substances in the environment. So far, limited studies have investigated the spatial-temporal distribution of ¹²⁹I in marine ecosystems including the ¹²⁹I isotope released via nuclear activities. This study reports the ¹²⁹I concentrations of kelps collected from the shallow coastal Yellow Sea and East China Sea from 2009 to 2021. The results show that the kelp ¹²⁹I concentrations increased by 5 times in our studied areas in 2011 right after the Fukushima Daiichi Nuclear Power Plant (FDNPP) accident and then decreased back to the pre-accident level in the following years. Meanwhile, the kelp ¹²⁹I concentrations in the Yellow Sea decreased much faster than those in the East China Sea between 2012 and 2021, which could be attributed to large river inputs that sustain a high supply of ¹²⁹I to coastal areas. Our observations suggest that the FDNPP accident may not be the cause of the increase in ¹²⁹I in coastal kelps in 2011. Instead, the ¹²⁹I emitted by nuclear fuel reprocessing plants (NFRPs) and being flushed into coastal areas by rivers could be main source of ¹²⁹I to coastal kelps.