Polycyclic aromatic hydrocarbons in paddy soils: Distribution, source apportionment, and risk assessment in major rice-growing regions of China

Polycyclic aromatic hydrocarbons (PAHs) in agricultural environments and their potential health impacts have raised significant concern, particularly due to their substantial emissions from biomass and coal combustion. However, the environmental fate and human exposure risks of PAHs in flooded paddy soils, which are characterized by unique anaerobic conditions, remain poorly understood. To address this, we analyzed PAHs in flooded soils from three typical rice-growing regions in China, including Taihu Plain (TP), Hani Terrace (HT), and Sanjiang Plain (SP), covering a 4000 km transect with varying climatic and soil conditions. The concentrations of 16 U.S. Environmental Protection Agency priority PAHs ranged from 87.5 to 5820 ng/g in the TP, 56.6 to 707 ng/g in the HT, and 98.6 to 1480 ng/g in the SP. Notably, we found that 4–6-ring PAHs dominated in the TP, whereas 3- and 4-ring compounds were more prevalent in the HT and SP. Molecular diagnostic ratios, positive matrix factorization, and principal component analysis identified biomass combustion as the primary source of PAHs. Although 7 carcinogenic PAHs represented less than one-third of the total PAH concentrations, their toxic effects accounted for over 90 % of the overall toxicity, with cancer risks from daily rice consumption exceeding 60 %. Most samples showed PAH intake levels below permissible limits, and no samples posed unacceptable non-carcinogenic risk. These findings highlight the urgent need for a deeper understanding of PAH risks in paddy fields, providing multi-regional insights into the environmental and health impacts of rice cultivation and contributing to sustainable agricultural practices.