Simultaneous stabilization of Pb, Cd, and As in soil by rhamnolipid coated sulfidated nano zero-valent iron: Effects and mechanisms.

Sulfidation effectively improves the electron transfer efficiency of nanoscale zero-valent iron (nZVI), but decreases the specific surface area of nZVI. In this study, sulfidated nZVI (S-nZVI) coated with rhamnolipid (RL-S-nZVI) was synthesized and used to stabilize Pb, Cd, and As in combined polluted soil. The stabilization efficiency of 0.3% (wt) RL-S-nZVI to water soluble Pb, Cd, and As in soil reached 88.76%, 72%, and 63%, respectively. Rhamnolipid coating inhibited the reduction of specific surface area and successfully encapsulated nZVI, thus reducing the oxidation of Fe0. The types of iron oxides in RL-S-nZVI were reduced compared to S-nZVI, but the content and strength of Fe0 iron were obviously enhanced. Furthermore, rhamnolipid functional groups (-COOH and -COO-) were also involved in the stabilization process. In addition, the stabilization efficiency of RL-S-nZVI to the bioavailable Pb, Cd, and As in soil increased by 41%, 41%, and 50%, respectively, compared with nZVI. The presence of organic acids, especially citric acid, improved the stabilization efficiency of RL-S-nZVI to the three metals. The result of BCR sequential extraction indicated that RL-S-nZVI increased the residual state of Pb, Cd, and As and reduced the acid-soluble and reducible state after 28 days of soil incubation. XRD and XPS analyses showed that the stabilization mechanisms of RL-S-nZVI on heavy metals involved in ion exchange, surface complexation, adsorption, co-precipitation, chemisorption, and redox.

Polyamide microplastics as better environmental vectors of Cr(VI) in comparison to polyethylene and polypropylene microplastics.

The adsorption, desorption, and their influence factors of Cr(VI) by microplastics (MPs) in the solution was investigated in this study. The results demonstrated that UV aging promoted adsorption, while the increase of salinity and natural organic matter (NOM) inhibited adsorption. The particle size affected the total Cr(VI) active adsorption sites on MPs, while the pH changed the electrostatic force. The Cr(VI) adsorption by MPs conformed to the pseudo-first and pseudo-second order kinetic models, and was monolayer and inhomogeneous. SEM-EDS, XPS and ATR-FTIR analyses demonstrated that the physical adsorption dominated the adsorption process. Especially, the highest adsorption capacity of Cr(VI) by polyamide (PA) MPs was attributed to their hydrophilic amide groups. However, Cr(VI) was only released from PA MPs, of which desorption rate followed the sequence of seawater (79.5 %) > fresh water (66.6 %) > deionized water (34.8 %). Thus, PA MPs might be non-negligible environmental vectors for the transport of Cr(VI).

Exogenous iron alters uptake and translocation of CuO nanoparticles in soil-rice system: A life cycle study.

The abundant iron in farmland soil may affect the environmental fate of metal-based nanoparticles (MNPs). In this study, the effect of FeSO4 and nano-zero-valent iron (nZVI) as exogenous iron on the uptake and translocation of CuO nanoparticles (NPs) in soil-rice system was performed in a life cycle study. The results show that exogenous iron basically elevated the soil pH and electrical conductivity but lowered the redox potential. Moreover, the Cu bioavailability in soil was significantly increased by 86-269% with exogenous iron at the tillering stage, while was reduced by 15-45% with medium and high concentrations of Fe(II) at the maturation stage. Meanwhile, the addition of exogenous iron resolved the unfilling of grains caused by CuO NPs. Notably, except for highest Fe(II) treatment, both Fe(II) and nZVI reduced Cu accumulation from 31% to 84% in roots and leaves due to more iron plaque. Especially, medium Fe(II) level markedly decreased the Cu content in the brown rice. µ-XRF analysis suggests that high intensity of Cu was primarily located in the rice hull and embryo under Fe(II) treatment. The reduction of CuO NPs to Cu2O caused by Fe(II) can explain the positive effect of exogenous iron on controlling the environmental risk of MNPs.