Effects of organic carbon quality on the sorption behavior of pesticides in Japanese soils

We analyzed the factors influencing pesticide sorption to soils by testing 17 pesticides with different polarity and chemical structures in 8 soils, including major types in Japan. The soil–water distribution coefficients (Kd) were significantly positively correlated with organic carbon (OC) content. However, the OC-normalized sorption coefficients (Koc) of many pesticides exhibited high variability among soils. Solid-state 13C nuclear magnetic resonance (NMR) was performed to elucidate the effect of OC quality on Koc variability. The NMR results indicated that the aromatic carbon content in soil was positively correlated with the Koc values of pesticides. The sorption pattern of pesticides to soils containing abundant aromatic carbon was influenced by the differences in the molecular structures of pesticides, similar to that to activated carbon and graphite. The results indicate the aromatic carbon in soils, particularly black carbon, is an important factor influencing the sorption of pesticides to soils.