Effect of plastic film mulching and film residues on phthalate esters concentrations in soil and plants, and its risk assessment

The application of plastic film mulching can greatly improve dryland productivity, while the release of toxic phthalate esters (PAEs) from the plastic film has generated concern. This study investigated the effects of mulched plastic film and residual plastic film on the PAE concentrations in the soil-crop system and assessed the risks to people eating crop products. The PAEs concentration in the 0–25 cm soil layer of plastic mulched farmland was 0.45–0.81 mg/kg, while the average PAEs concentration of 0.37–0.73 mg/kg in non-mulched farmland decreased by 19%. The PAEs concentration in mulched soil reached the highest in July, being 0.80–0.84 mg/kg, while in the non-mulched soil, the PAEs also appeared and gradually decreased from May at 0.62–0.74 mg/kg to October, and the PAEs concentrations were almost the same in the mulched and non–mulched soils at the harvest time in October at 0.37–0.44 mg/kg. With the amounts of residual film in farmland increasing from 0 kg/ha to 2700 kg/ha (equivalent to the total amount of residual film after 60 years of continuous plastic film mulching), the PAEs concentrations were no significant changes, being 0.54–0.93 mg/kg. Maize (Zea mays L.) roots could absorb and accumulate PAEs, and the bio-concentration factor (BCF) was 1.6–2.3, and the average PAEs concentrations in stems, leaves, and grains were 79%–80% of those in roots at 0.77–1.47 mg/kg. For the ingestion of maize grains or potato (Solanum tuberosum L.) tubers grown in plastic film mulched farmland or farmland containing residual film of 450–2700 kg/ha, the hazard index (HI) were less than 1, the carcinogenic risks (CRs) were 2.5 × 10−7–2.2 × 10−6, and the estrogenic equivalences were 6.17–17.73 ng E2/kg. This study provides important data for the risk management of PAEs in farmlands.