Relationship between radiocesium contamination and the contents of various elements in the web spider Nephila clavata (Nephilidae: Arachnida)

• Accumulation of 137Cs and various elements in web spiders was investigated.
• 137Cs accumulation positively correlated with that of K, Rb, Na, and Cu.
• Accumulation of alkali metals determined the level of 137Cs contamination.
• K–, Rb–, Cu–137Cs relationships were, however, site specific.

The accident at the Fukushima Dai-ichi nuclear power plant seriously contaminated a large area in northeast Japan with a large amount of radioactive material. Consequently, various organisms, including arthropods, in the ecosystem have been contaminated with radiocesium (137Cs) through the food chain. We previously showed that the web spider Nephila clavata was contaminated with 137Cs and that the level of contamination, which varied among spider individuals, was independent of the amount of prey consumed. The present study aimed to clarify the mechanisms that could determine the level of 137Cs contamination in N. clavata. We first demonstrated the patterns of contents of over 30 elements in N. clavata that were collected at two forest sites (PS and ES) in Fukushima and then focused on the relationships between the contents of the alkali metals Li, Na, K, and Rb and the accumulation of 137Cs in the spiders; Cs is an alkali metal and is expected to act similarly to Li, Na, K, and Rb. We also focused on the content of the non-alkali element, Cu, which is an essential element for oxygen transport in spiders. We found that Na content correlated positively with 137Cs accumulation at both sites, which suggested that 137Cs accumulation in N. clavata was related with the dynamics of Na. The K–, Rb–, and Cu–137Cs relationships were site specific; the relationships were significant at site PS, but not significant at site ES. Factors causing the site specific relationships and the probable pathway for 137Cs transfer from soil to plants and then to higher trophic levels are discussed in terms of the transfer processes of the alkali metals.