老化作用对微塑料与镉在运河沿岸土壤中共迁移影响

Effect of aging on co-transport of microplastics and cadmium in canal soils

通过柱淋溶实验结合数值模拟,研究了老化作用对不同粒径微塑料(MPs)及其与Cd(II)在运河沿岸土壤中共迁移的影响.结果表明,老化作用促进了MPs在土壤中迁移.相较于原始MPs,老化MPs在土壤中的迁移能力提高了28.3%~184%.主要因为老化作用增加了MPs表面的负电荷,进而提高MPs悬浮液的稳定性,以及增强MPs与土壤颗粒之间的排斥势垒,最终促进MPs在土壤中迁移.相较于单独MPs迁移,在共迁移体系中,Cd(II)抑制MPs在土壤中迁移(降低了0.20~0.33倍),并且Cd(II)对老化MPs在土壤中迁移的抑制作用更强(降低了0.21~0.59倍).此外,MPs作为载体促进吸附的Cd(II)在土壤中迁移.老化作用强化了MPs对Cd(II)在土壤中迁移的促进作用(提高了0.56~3.2倍).主要因为老化作用不仅提高了MPs对Cd(II)的吸附能力,而且还增强了MPs的迁移能力.两点动力学滞留模型较好拟合MPs与Cd(II)在土壤中共迁移的穿透曲线,解释老化作用对MPs与Cd(II)在土壤中共迁移的影响,且进一步表明了老化MPs增大Cd(II)在土壤中的迁移通量和潜在风险.

Packed column experiments and numerical simulations were conducted to investigate the effect of microplastics(MPs)aging on their co-transport with cadmium Cd(II)in canal soils.The aging of MPs facilitated their transport in soils.Compared with pristine(unaged)MPs,the transportability of aged MPs in soils increased by 28.3%~184%.This is likely because of the enhanced negative charges of MPs after aging,resulting in enhanced stability of MP suspensions and stronger repulsive energy barrier between aged MPs and soil particles.For the co-transport of MPs and Cd(II),compared with MPs-alone,the presence of Cd(II)inhibited the transport of MPs in soils,decreasing by 0.20~0.33 times.The aging effect of MPs further reinforced the inhibited transport of MPs by Cd(II),decreasing by 0.21~0.59times.In contract,MPs acted as carriers that enhance the transport of adsorbed Cd(II)in soils.Furthermore,the aged MPs exhibited greater enhancement effect on Cd(II)transport,increasing by 0.56~3.2 times,mainly due to the increased transport of aged MPs that can carry more adsorbed Cd(II).A two-site kinetic retention model was successfully employed to simulate the co-transport of MPs and Cd(II)in soils.The modeling results illustrate the effect of the aging on co-transport of MPs and Cd(II)and further indicate that the aged MPs increased the transport solute flux and potential risks of Cd(II)in soils.