Effect of poly-γ-glutamic acid on the phytoremediation of ramie (Boehmeria nivea L.) in the Hg-contaminated soil

Low-molecular-weight organic acids-mediated transport of neonicotinoid pesticides through saturated soil porous media: Combined effects of the molecular structures of organic acids and the chemical properties of contaminants

Empirical information about the transport properties of neonicotinoid pesticides through the soil as affected by the ubiquitous low molecular weight organic acids (LMWOAs) is lacking. Herein, the impacts of three LMWOAs with different molecular structures, including citric acid, acetic acid, and malic acid, on the mobility characteristics of two typical neonicotinoid pesticides (Dinotefuran (DTF) and Nitenpyram (NTP)) were explored. Interestingly, under acidic conditions, different mechanisms were involved in transporting DTF and NTP by adding exogenous LMWOAs. Concretely, acetic acid and malic acid inhibited DTF transport, ascribed to the enhanced electrostatic attraction between DTF and porous media and the additional binding sites provided by the deposited LMWOAs. However, citric acid slightly enhanced DTF mobility due to the fact that the inhibitory effect was weakened by the steric hindrance effect induced by the deposited citric acid with a large molecular size. In comparison, all three LMWOAs promoted NTP transport at pH 5.0. Because the interaction between NTP with soil organic matter (e.g., via π-π stacking interaction) was masked by the LMWOAs coating on soil surfaces. Nevertheless, LMWOAs could promote the mobility of both neonicotinoid pesticides at pH 7.0 due to the steric hindrance effect caused by the deposited organic acids and the competitive retention between LMWOAs and pesticides for effective surface deposition sites of soil particles. Furthermore, the extent of the promotion effects of LMWOAs generally followed the order of citric acid > malic acid > acetic acid. This pattern was highly related to their molecular structures (e.g., number and type of functional groups and molecular size). Additionally, when the background solutions contained Ca2+, the bridging effect of cations also contributed to the transport-enhancement effects of LMWOAs. The findings provide valuable information about the mobility behaviors of neonicotinoid pesticides co-existing with LMWOAs in soil-water systems.

Effects of Transporter Inhibitors and Chemical Analogs on the Uptake of Antimonite and Antimonate by Boehmeria nivea L

Antimony (Sb) is a non-essential metalloid that can be taken up by plants from contaminated soils and thus enter the food chain and threaten human health. Boehmeria nivea L. (ramie) is a promising phytoremediation plant for Sb-polluted soils. However, the mechanisms of antimonite (SbIII) and antimonate (SbV) uptake by ramie remain unclear. In this study, a hydroponic system was established to investigate how different substances affect the uptake of SbIII or SbV by ramie, including an energy inhibitor (malonic acid), an aquaglyceroporin inhibitor (silver nitrate), an SbV analog (phosphate-PV), and SbIII analogs (arsenite-AsIII, glycerol, silicic acid-Si, and glucose). The results indicated that ramie primarily transported Sb by increasing the Sb concentration in the bleeding sap, rather than increasing the weight of the bleeding sap. After 16 h of Sb exposure, the absolute amount of transported Sb from the roots to the aboveground parts was 1.90 times higher under SbIII than under SbV. The addition of malonic acid significantly inhibited the uptake of SbV but had limited effects on SbIII, indicating that SbV uptake was energy dependent. PV addition significantly reduced SbV uptake, while the addition of AsIII, glycerol, and Si obviously inhibited SbIII uptake. This suggested that the uptake of SbV might be via low-affinity P transporters and SbIII might use aquaglyceroporins. These findings deepen the understanding of Sb uptake pathways in ramie, contribute to a better comprehension of Sb toxicity mechanisms in ramie, and establish a foundation for identifying the most effective Sb uptake pathways, which could further improve the efficiency of phytoremediation of Sb-polluted soils.