Sorption of polycyclic aromatic hydrocarbons to carbohydrates and lipids of ryegrass root and implications for a sorption prediction model.

Plant lipids were considered as the main storage sites for hydrophobic organic contaminants while carbohydrates were generally underestimated, and the lipid-water partition coefficients (Klip) of contaminants were assumed to be the same as the corresponding octanol-water partition coefficients (Kow). Sorption of five polycyclic aromatic hydrocarbons (PAHs) to ryegrass root and its carbohydrates and lipids was investigated to evaluate the role of carbohydrates and lipids on sorption of organic contaminants to plant Results revealed that sorption of PAHs to ryegrass root was actually regulated by both carbohydrates and lipids rather than lipids individually, as generally assumed. Kch (carbohydrates-water partition coefficient) and Klip could be estimated with the corresponding Kow values: log Kch = 1.23 log Kow - 2.42 and log Klip = 1.23 log Kow - 0.78. Although the affinity of PAHs for lipids appears to be about 1.64 orders of magnitudes higher than that for carbohydrates, sorption of PAHs to carbohydrates could not be neglected because of its predominant weight fraction in plants (about 98 times of lipids for ryegrass root). An improved model containing integral roles of carbohydrates and lipids was established, which showed excellent accuracy for predicting the sorption of organic contaminants to plants.