Occurrence of natural organic chlorine in soils for different land uses

Consideration of natural formation of organochlorine compounds in soils is necessary in radioecology in order to understand chlorine radioisotope (36Cl) cycling in various environments for safety assessment purposes, but also in ecotoxicology because certain chlorinated organics in soils are toxic compounds. On the other hand, occurrence of organic chlorine in soils is poorly documented, especially in non-forest ecosystems. We measured total and organic chlorine concentrations in 51 French surface soils sampled from grassland, arable and forest sites on a national scale (French soil quality monitoring network) in order to characterize the variability of organic chlorine concentrations for these different land uses. While previous studies reported that the chlorination of soil organic matter is responsible for chlorine retention in temperate forest ecosystems, this study shows that the non-extractable organohalogen pool accounts for the majority (>80 % on an average) of the total measurable chlorine in grassland and agricultural soils. This suggests that natural chlorination is a widespread phenomenon in all kinds of soils. A multiple linear regression analysis performed on the dataset indicated that retention of organochlorine in soils is related to the organic carbon content, Cl input and soil pH