Enhanced organic contaminants accumulation in crops: Mechanisms, interactions with engineered nanomaterials in soil

The mechanism of enhanced accumulation of organic contaminants in crops with engineered nanomaterials (ENMs) were investigated by co-exposure of crops (Ipomoea aquatica Forsk (Swamp morning-glory), Cucumis sativus L. (cucumber), Zea mays L. (corn), Spinacia oleracea L. (spinach) and Cucurbita moschata (pumpkin))to a range of chemicals (polycyclic aromatic hydrocarbons (PAHs), organochlorine pesticides (OCPs) and polybrominated diphenyl ether (PBDE)) and ENMs (TiO2, Ag, Al2O3, graphene, carbon nanotubes (CNTs)) in soil. Induced by 50 mg kg−1 graphene co-exposure, the increase range of BDE-209, BaP, p,p′-DDE, HCB, PYR, FLU, ANT, and PHEN in the plants were increased in the range of 7.51–36.42, 5.69–32.77, 7.09–59.43, 11.61–66.73, 4.58–57.71, 5.79–109.07, 12.85–109.76, and15.57–127.75 ng g−1, respectively. The contaminants in ENMs-spiked and control soils were separated into bioavailable, bound and residual fractions using a sequential ultrasonic extraction procedure (SUEP) to investigate the mechanism of the enhanced accumulation. The bioavailable fraction in spiked soils showed no significant difference (p > 0.05) from that in the control, while the bound fraction increased in equal proportion (p > 0.05) to the reduction in the residual fraction. These results implied that ENMs can competitively adsorbed the bound of organic contaminants from soil and co-transferred into crops, followed by a portion of the residual fraction transferred to the bound fraction to maintain the balance of different fractions in soils. The mass balance was all higher than 98.5%, indicating the portion of degraded contaminants was less than 1.5%. These findings could expand our knowledge about the organic contaminants accumulation enhancement in crops with ENMs.