Influence of aged and pristine polyethylene microplastics on bioavailability of three heavy metals in soil: Toxic effects to earthworms (Eisenia fetida).

Virgin microplastics (MPs) would undergo aging process when entering environment, the adsorption capability of pollutants onto MPs may change during the aging process. To better understand the influence of aged polyethylene microplastics (PE-MP) on the bioavailability of three heavy metals (Zn, Pb, and Cd) in soil, hydrogen peroxide exposure (3% H2O2) and ultraviolet irradiation methods were employed to simulate the aging process. After aging process, different amount (0.1%, 1%, 10%) of PE-MP (pristine or aged) was added into soil to assess the ability of soil (containing PE-MP) adsorbing heavy metal. Moreover, different amount (0.01%, 0.1%, 1%) of PE-MP (pristine or aged) was added into soil to cultivate the earthworms to assess the impact of PE-MP on bioavailability of three heavy metals. Results indicated that the aged and virgin PE-MP had similar capability to adsorb heavy metal, the adsorption ability of Zn2+, Pb2+, and Cd2+ to pristine PE-MP were 2.42, 7.47, and 7.76 mg/g, respectively. The concentration of Zn or Pb in earthworms in treatments of metal +1% PE-MP was slightly higher than that in single metal (Zn or Pb) treatment, moreover, the concentration of Cd in earthworms in treatment of Cd + 1% PE-MP was significantly (p < 0.05) higher than that in single Cd treatment, exhibiting that 1% of PE-MP enhanced the bioavailability of heavy metals in soil. However, heavy metal concentrations in earthworms in treatments of metal + pristine PE-MP showed insignificant (p > 0.05) difference with those in treatments of metal + aged PE-MP, indicating that the aging process in this study did not change the environmental influence of PE-MP on heavy metals bioavailability. Superoxide dismutase activity, reactive oxygen species level, malondialdehyde content, and related gene expression in earthworms showed that PE-MP and heavy metals would bring toxic synergy to earthworms, therefore, the influence of MPs should be comprehensively considered when determining the environmental risk of heavy metals in soil.

Li M ，Jia H ，Gao Q ，Han S ，Yu Y ，Sun L ... -  《-》

Impacts of polyethylene microplastics on bioavailability and toxicity of metals in soil.

In this study, we investigated the bioavailability and toxicity of metals (Cu and Ni) in the soil containing polyethylene microplastics (PE-MPs). The bioavailability of the metals determined by the five-step chemical sequential extraction method increased with the addition of MPs (0.1%, 1%, 10%) in the soil, which was confirmed by the adsorption-desorption characteristics. To further examine the bioavailability and toxicity of metals, earthworms (Eisenia fetida) were exposed to soil containing Cu2+ (100 mg/kg) or Ni2+ (40 mg/kg) with different amounts (0.01%, 0.05%, and 0.1%) of PE-MPs for 21 days. The highest concentrations of Cu2+ and Ni2+ in earthworms reached to 73.3 and 36.3 mg/kg, respectively. Moreover, metal concentrations in earthworms increased with MP contents in the soil, which was consistent with the bioavailability measured by the sequential extraction method. Furthermore, changes in biomarkers including peroxidase (POD), catalase (CAT) and superoxide dismutase (SOD) activity, malondialdehyde (MDA) contents, and related gene expression levels in earthworms suggested that the pollutants caused toxicity to earthworms. Overall, MPs increased the bioavailability of metals in the soil and the toxic effects to earthworms. These findings provide insights regarding the impacts of MPs on the bioavailability of metals and the combined toxic effects of these two kinds of pollutants on terrestrial animals.

Li M ，Liu Y ，Xu G ，Wang Y ，Yu Y ... -  《-》

Influence of polyethylene-microplastic on environmental behaviors of metals in soil.

Li M ，Wu D ，Wu D ，Guo H ，Han S ... -  《-》

Combined ecotoxicological effects of different-sized polyethylene microplastics and imidacloprid on the earthworms (Eisenia fetida).

Microplastics (MPs) and pesticides frequently coexist in farmland soil; however, there are relatively few studies on the ecological risk assessment of soil animals attributed to the combined pollution caused by MPs and pesticides. Moreover, the influence of particle size on the combined toxic effects of MPs and pesticides remains poorly understood. In this study, different-sized polyethylene MPs (PE MPs; 10 μm, 500 μm, and 2 mm) were combined with a series of imidacloprid concentrations (IMI; 0.10, 0.50 and 1.00 mg/kg), and earthworms (Eisenia fetida) were exposed to these MP and IMI combinations for 28 d to explore the combined toxic effects and mechanisms. The results showed, compared with IMI or PE MPs exposure alone, the combined exposure of IMI and PE MPs did not substantially increase the acute toxicity of earthworms but significantly inhibited weight increase and induced more serious epidermal damage to earthworms with a size effect; among these 10 μm PE MPs combined with IMI exhibited the strongest toxic effects. In addition, the combined exposure decreased antioxidant enzymes activity and caused oxidative damage in earthworms. Transcriptome results demonstrated most of the treatment combinations affected the ferroptosis pathway, which was further verified by the increase in the total iron content, reactive oxygen species, and malondialdehyde content in earthworms. Combined with the analysis of key signalling pathways, the above results revealed that the combined exposure to IMI and PE MPs showed stronger toxicity to earthworms than exposure to either IMI or MPs alone, which was mediated by the superimposed effect of ferroptosis and oxidative damage. Moreover, the effect was size-dependent, with 10 μm PE MPs combined with IMI exhibiting the strongest toxic effects. This study aimed to provide data to support the ecological risk assessment of soil animals caused by the combined pollution of MPs and coexisting pesticides.

Fu H ，Zhu L ，Mao L ，Zhang L ，Zhang Y ，Chang Y ，Liu X ，Jiang H ... -  《-》

Effects of microplastics on the phytoremediation of Cd, Pb, and Zn contaminated soils by Solanum photeinocarpum and Lantana camara.

Microplastics are emerging pollutants and have become a global environmental issue. The impacts of microplastics on the phytoremediation of heavy metal-contaminated soils are unclear. A pot experiment was conducted to investigate the effects of four additions (0, 0.1%, 0.5%, and 1% w·w-1) of polyethylene (PE) and cadmium (Cd), lead (Pb), and zinc (Zn) contaminated soil on the growth and heavy metal accumulation of two hyperaccumulators (Solanum photeinocarpum and Lantana camara). PE significantly decreased the pH and activities of dehydrogenase and phosphatase in soil, while it increased the bioavailability of Cd and Pb in soil. Peroxidase (POD), catalase (CAT), and malondialdehyde (MDA) activity in the plant leaves were all considerably increased by PE. PE had no discernible impact on plant height, but it did significantly impede root growth. PE affected the morphological contents of heavy metals in soils and plants, while it did not alter their proportions. PE increased the content of heavy metals in the shoots and roots of the two plants by 8.01-38.32% and 12.24-46.28%, respectively. However, PE significantly reduced the Cd extraction amount in plant shoots, while it significantly increased the Zn extraction amount in the plant roots of S. photeinocarpum. For L. camara, a lower addition (0.1%) of PE inhibited the extraction amount of Pb and Zn in the plant shoots, but a higher addition (0.5% and 1%) of PE stimulated the Pb extraction amount in the plant roots and the Zn extraction amount in the plant shoots. Our results indicated that PE microplastics have negative effects on the soil environment, plant growth, and the phytoremediation efficiency of Cd and Pb. These findings contribute to a better knowledge of the interaction effects of microplastics and heavy metal-contaminated soils.

Yu Q ，Gao B ，Wu P ，Chen M ，He C ，Zhang X ... -  《-》