Linear and non-linear relationships between soil sorption and hydrophobicity

Abstract

The relationship between log K (oc) and log P was examined by use of a large dataset. For most of the hydrophobic compounds (e.g. 0.5 < log P < 7.5), the organic carbon content plays a dominant role in soil sorption and the sorption coefficient is linearly related to the octanol/water partition coefficient. For hydrophilic compounds (e.g. log P < 0.5), hydrophobic sorption becomes less significant. The hydrophilic contribution to sorption is equal to, or higher than, the hydrophobic contribution to sorption, resulting in the observed K (oc) values being higher than those predicted from their log P values. For highly hydrophobic compounds (e.g. log P > 7.5), log K (oc) decreases with increasing hydrophobicity because of a lack of chemical availability due to low solubility. A linear solvation energy relationship shows that the sorption potential increases with increasing molecular size by increasing the dispersion interactions between the chemical and soil organic phase. The sorption potential decreases with increase in the basicity of hydrophobic compounds by increasing the H-bonding of chemicals with water. Principal component analysis shows that the octanol/water system is the closest system, but not an ideal surrogate, to describe the soil sorption for hydrophobic compounds as compared with other solvent/water partition systems.

Can the Use of Coccidiostats in Poultry Breeding Lead to Residues in Vegetables? An Experimental Study

“…Because uptake by the roots is related to the partitioning of the component in the soil water, too high of log K ow values would result in less uptake by the plant. 24 Several lettuce samples from the salinomycin, nicarbazin/ narasin, and diclazuril manure treatments also appeared to contain monensin (same mass spectrometric transitions, retention times, and relative ion intensities), but these levels of contamination never exceeded the LOQ. Lettuce samples originating from the monensin treatments (manure as well as premix) had levels well above the LOQ.…”

“…As the log K ow value increases, sorption to the soil will increase and smaller amounts will be found in the soil water. Because uptake by the roots is related to the partitioning of the component in the soil water, too high of log K ow values would result in less uptake by the plant …”