Abstract
Farmland soil and leafy vegetables accumulate more polycyclic aromatic hydrocarbons (PAHs) in suburban sites. In this study, 13 sampling areas were selected from vegetable fields in the outskirts of Xi’an, the largest city in northwestern China. The similarity of PAH composition in soil and vegetation was investigated through principal components analysis and redundancy analysis (RDA), rather than discrimination of PAH congeners from various sources. The toxic equivalent quantity of PAHs in soil ranged from 7 to 202 μg/kg d.w., with an average of 41 μg/kg d.w., which exceeded the agricultural/horticultural soil acceptance criteria for New Zealand. However, the cancer risk level posed by combined direct ingestion, dermal contact, inhalation of soil particles, and inhalation of surface soil vapor met the rigorous international criteria (1×10−6). The concentration of total PAHs was (1052±73) μg/kg d.w. in vegetation (mean±standard error). The cancer risks posed by ingestion of vegetation ranged from 2×10−5 to 2×10−4 with an average of 1.66×10−4, which was higher than international excess lifetime risk limits for carcinogens (1×10−4). The geochemical indices indicated that the PAHs in soil and vegetables were mainly from vehicle and crude oil combustion. Both the total PAHs in vegetation and bioconcentration factor for total PAHs (the ratio of total PAHs in vegetation to total PAHs in soil) increased with increasing pH as well as decreasing sand in soil. The total variation in distribution of PAHs in vegetation explained by those in soil reached 98% in RDA, which was statistically significant based on Monte Carlo permutation. Common pollution source and notable effects of soil contamination on vegetation would result in highly similar distribution of PAHs in soil and vegetation.
Highlights
Incomplete combustion, pyrolysis of organic materials by industry, agriculture and traffic, diagenetic alteration of natural organic matter (OM), long-term wastewater irrigation, reused sewage sludge, and fertilizer use in agricultural production result in high concentrations of polycyclic aromatic hydrocarbons (PAHs) in farmland soil [1,2,3]
The cancer risks posed by exposure pathways of direct ingestion and dermal contact PAHs in soil, inhalation of soil particles and surface soil vapor met the rigorous acceptable cancer risk level (1×10−6)
The Bap toxic equivalent quantity (TEQ) values of PAHs in soil were higher than agricultural/horticultural soil acceptance criteria provided for surface (
Summary
Incomplete combustion, pyrolysis of organic materials by industry, agriculture and traffic, diagenetic alteration of natural organic matter (OM), long-term wastewater irrigation, reused sewage sludge, and fertilizer use in agricultural production result in high concentrations of polycyclic aromatic hydrocarbons (PAHs) in farmland soil [1,2,3]. Other PAHs may contribute to carcinogenic risk [4] and should not necessarily be assumed to be noncarcinogens. When a mixture of chemicals with the same mechanism of action is encountered, the concentration of each chemical is measured and multiplied by its TEF value. The results are added to give the toxic equivalent quantity (TEQ) value of the mixture. Regulatory agencies in the United States [5], Europe [6], New Zealand [7] and Canada [8] have advocated use of the TEQ approach. PAH soil quality criteria/guidelines based on Bap TEQ have been issued by New Zealand [7] and Canada [8]. Excess lifetime risk limits for carcinogens typically range from 10–6 to 10–4 [8,9]
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