The role of organic matter quality and mineral surfaces for the sorption of chlorpyrifos and diazinon on soils, sediments, and suspended estuary sediment

This study examines the relative significance of natural organic matter (NOM) quality and mineral surfaces for the sorption of chlorpyrifos (phosphorothioic acid, O,O-diethyl O-[3,5,6-trichloro-2-pyridnyl] ester) and diazinon (phosphorothioic acid, O,O-diethyl O-[6-methyl-2-(1-methylethyl)-4-pyrimidinyl] ester) on eight California soils, sediments, and suspended estuary sediment. Their aggregate behavior reveals some sorption behaviors of semi-polar contaminant with environmental sorbents.; NOM was characterized with pyrolysis-gas chromatography-mass spectrometry (py-GC-MS) into biological source and chemical class groupings. X-ray diffraction was used to quantitate the minerals present and N2-BET isotherms were used to determine mesopore structure. NOM was removed with hypochlorite oxidation and combustion.; The change in diazinon Kd values depended on sample type. Organic matter thresholds for NOM predominance depended on sample type and organic carbon loading. The order from smallest to largest was: sediments < agricultural soils < forest soils. Chlorpyrifos sorption depended primarily on organic carbon loading and secondarily on NOM saccharide content, non-aromatic, non-heteroatom substituted components of NOM, and kaolinite content. Diazinon n values were negatively correlated with kaolinite content.; Suspended sediments were collected from the Sacramento River, Freeport, CA, and characterized by particle size distribution and pyrolysis-GC-MS. Chlorpyrifos desorption kinetics were measured using TenaxRTM beads as a desorption driving force. The measured Kd was 345 L kg -1. Uptake data fit the Elovich equation and had a lower limit of 10,000 for the ratio of maximum and minimum diffusion constants. The release data fit a two-phase model with a fast release fraction of 0.806 and fast and slow rate constants of 0.943 h-1 and 5.92 x 10-3 h-1, respectively.; These values were use in a coupled hydrodynamic and environmental fate model that evaluated chlorpyrifos release and persistence during tidal resuspension events in the Napa-Sonoma slough network, San Pablo Bay, CA. The modeled release was most sensitive to the depth of the active bed and the KF value. A doubling of the active bed depth increased release by more than 50%. A tripling of chlorpyrifos KF caused release to be essentially limited by equilibrium sorption rather than desorption kinetics.