Residues of polycyclic aromatic hydrocarbons (PAHs), polychlorinated biphenyls (PCBs) and organochlorine pesticides in organically-farmed vegetables

The residues of polyaromatic hydrocarbons (PAHs), polychlorinated biphenyls (PCBs) and organochlorine pesticides (OCPs) in soils from organic farms and their uptake by four varieties of organic-produced potatoes and three varieties of organic carrots from England were investigated. Samples of the soils, crop peels and cores were all Soxhlet-extracted in triplicate, cleaned up by open-column chromatography and analysed by a multi-residue analytical method using gas chromatography with mass selective detection. The concentrations of PAHs, PCBs and OCPs in soils from organic farms ranged from 590 ± 43 to 2301 ± 146 μg/kg, 3.56 ± 0.73 to 9.61 ± 1.98 μg/kg and 52.2 ± 4.9 to 478 ± 111 μg/kg, respectively. Uptake by different crop varieties were 8.42 ± 0.93 to 40.1 ± 4.9 μg/kg ΣPAHs, 0.83 ± 0.19 to 2.68 ± 0.94 μg/kg ΣPCBs and 8.09 ± 0.83 to 133 ± 27 μg/kg ΣOCPs. Residue uptake from soils depended on plant variety; Desiree potato and Nairobi carrot varieties were more susceptible to PAH contamination. Likewise, uptake of PCBs and OCPs depended on potato variety. There were significant positive correlations between the PCB and OCP concentrations (P < 0.05) in soils and carrots but no significant correlation was found between the concentrations of any contaminants in soils and potatoes. Peeling carrots and potatoes was found to remove 52–100% of the contaminant residues depending on crop variety and the properties of the contaminants. Soil–crop bioconcentration factors (BCFs) decreased with increasing log Kow for PAHs up to about 4.5 and for PCBs up to about 6.5, above which no changes were discernible for either class of contaminants. No relationship was observed between soil–crop BCFs and log Kow for OCPs, most likely because their concentrations were low and variable.