Thorium accumulation in the sedimentary environment of the Vigo Ria (NW Iberian Peninsula)

Thorium levels and their association with Fe, Sc, Ca, and Particulate Organic Carbon (POC) were researched in sediments of the Vigo Ria in order to assess the influence of radioactive gneisses from the neighbouring continental Galiñeiro Complex. Sediment of 50 surface samples and 1 core was analysed by ICP-MS and the results were validated with certificate reference material from marine sediment. It was found that Th accumulates in the middle Ria zone (9-15 mg kg−1) as a result of the terrestrial source. The thorium concentration in the Ria (average: 9.4 ± 5.1 mg kg−1) is not anthropogenically impacted in accordance with its own regional background level (11.4 ± 3.5 mg kg−1), which is two times higher than the content in earth's crust. Throughout the relationship Th/Fe, Th may be associated with the iron cycle in the Ria, probably through iron oxy-hydroxide scavenging.