Accumulation of polycyclic aromatic hydrocarbons and heavy metals in lettuce grown in the soils contaminated with long-term wastewater irrigation

Accumulation of polycyclic aromatic hydrocarbons (PAHs) and heavy metals (HMs) by crop plants from contaminated soils may pose health risks. A greenhouse pot experiment using lettuce (Lactuca satuva L.) as a representative vegetable was conducted to assess the concentrations of PAHs and HMs in vegetables grown in wastewater-contaminated soils. The concentrations of total PAHs were ranged from 1.5 to 3.4 mg kg−1 in the contaminated soils, while 1.2 mg kg−1 in the reference soil. Linear regression analyses showed that the relationships between soil and shoot PAH concentrations were stronger for LMW-PAHs (R2 between 0.51 and 0.92) than for HMW-PAHs (R2 0.02 and 0.60), suggesting that translocation for LMW-PAHs is faster than HMW-PAHs. Furthermore, the data imply that root uptake was the main pathway for HMW-PAHs accumulation. The plant shoots were also highly contaminated with HMs, particularly Cd (0.4-0.9 mg kg−1), Cr (3.4-4.1 mg kg−1), Ni (11.7-15.1 mg kg−1) and Pb (2.3-5.3 mg kg−1), and exceed the guidance limits set by State Environmental Protection Administration (SEPA), China and the World Health Organization (WHO). This study highlights the potential health risks associated with cultivation and consumption of leafy vegetables on wastewater-contaminated soils.