Influence of the nature of particulate organic matter on the sorption of cypermethrin: implications on K_OC correlations

The sorption of the pyrethroid insecticide, cypermethrin, on clean mineral particles, mineral particles coated with aquatic humic substances, and suspended particles from the Tees Estuary was studied. The sorption process was dominated by the organic carbon or organic matter on the particle surfaces, as shown by the significant increase in the sorptive capacity of montmorillonite after being coated with aquatic humic material. Humic acid, the most aromatic coating, was the strongest sorbent, followed by fulvic acid, hydrophilic macromolecular acid, then natural coatings on estuarine suspended particles. After deduction of the contribution from the clean mineral, K_oc values ranged from 160 000 to 810 000; they decreased with increasing mass fraction organic carbon (f_oc) and increasing polarity in natural organic matter. A good correlation between K_oc and f_oc was found for both hydrophilic macromolecular acid coatings and natural coatings on estuarine particles, suggesting that hydrophilic macromolecular acid may be used to model organic coatings on estuarine suspended particles and their sorption behaviour.