Partition coefficients of organic contaminants with carbohydrates

In view of the current lack of reliable partition coefficients for organic compounds with carbohydrates (K_ch), carefully measured values with cellulose and starch, the two major forms of carbohydrates, are provided for a wide range of compounds: short-chain chlorinated hydrocarbons, halogenated benzenes, alkyl benzenes, polycyclic aromatic hydrocarbons (PAHs), polychlorinated biphenyls, and organochlorine pesticides. To ensure the accuracy of the K_ch data, solute concentrations in both water and carbohydrate phases are measured by direct solvent extraction of the samples. For a given compound, the observed partition coefficient with cellulose (K_cl) is virtually the same as that with starch (K_st). This finding expedites the evaluation of organic contamination with different forms of carbohydrates. The presently determined K_ch values of 13 PAHs are substantially lower (by 3−66 times) than the literature data; the latter are suspect as they were obtained with (i) presumably impure carbohydrate samples or (ii) indirectly measured equilibrium solute concentrations in carbohydrate and water phases. Although the K_ch values are generally considerably lower than the respective K_ow (octanol−water) or K_lipid (lipid−water), accurate K_ch data are duly required to accurately estimate the contamination of carbohydrates by organic compounds because of the abundance of carbohydrates over lipids in crops and plants. To overcome the current lack of reliable K_ch data for organic compounds, a close correlation of log K_ch with log K_ow has been established for predicting the unavailable K_ch data for low-polarity compounds.