Iodine enrichment in the groundwater in South China and its hydrogeochemical control

In North China,iodine-rich groundwater has been extensively studied,but few in South China.This study aimed to investigate the characteristics of iodine-rich groundwater in South China and identify potential contamination sources.The results revealed that the average concentration of iodine in groundwater was 890μg/L,with a maximumconcentration of 6350μg/L,exceeding the permitted levels recommended by the World Health Organization(5–300μg/L).Notably,the enrichment of iodide occurred in acidic conditions(pH=6.6)and a relatively low Eh environment(Eh=198.4 mV).Pearson correlation and cluster analyses suggested that the enrichment of iodide could be attributed to the intensified redox process involving Mn(II),iodine(I_(2)),or iodate(IO_(3)^(−))in the soil.The strong affinity between Mn(II)and I_(2)/IO_(3)^(−)facilitated their interaction,resulting in the formation and mobilization of I^(−)from the soil to the groundwater.Leaching experiments further confirmed that reducing substances(such as sodium sulfides,ascorbic acids,and fulvic acids)in the soil with low dissolved oxygen(DO)levels(<1.0 mg/L)enhanced the dissolution of iodine species.Conversely,higher DO content(>3.8 mg/L)promoted the oxidation of I^(−)into I_(2)or IO_(3)^(−),leading to its stabilization.This research provides new insights into the characteristics and mechanisms of I^(−)enrichment in groundwater in South China,and emphasizes the significance of the redox reactions involving Mn(II)and I_(2)/IO_(3)^(−),as well as the influence of soil properties in regulating the occurrence and transportation of iodine species within groundwater systems.

The effect of interaction between Bacillus subtilis DBM and soil minerals on Cu(Ⅱ) and Pb(Ⅱ) adsorption

The effects of interaction between Bacillus subtilis DBM and soil minerals on Cu(Ⅱ)and Pb(Ⅱ)adsorption were investigated.After combination with DBM,the Cu(Ⅱ)and Pb(Ⅱ)adsorption capacities of kaolinite and goethite improved compared with the application of the minerals independently.The modeling results of potentiometric titration data proved that the site concentrations of kaolinite and goethite increased by 80%and 30%,respectively after combination with DBM.However,the involvement of functional groups in the DBM/mineral combinations resulted in lower concentrations of observed sites than the theoretical values and led to the enhancement of desorption rates by NH_4NO_3 and EDTA-Na_2.The DBM-mineral complexes might also help to prevent heavy metals from entering DBM cells to improve the survivability of DBM in heavy metal-contaminated environments.During the combination process,the extracellular proteins of DBM provided more binding sites for the minerals to absorb Cu(Ⅱ)and Pb(Ⅱ).In particular,an especially stable complexation site was formed between goethite and phosphodiester bonds from EPS to enhance the Pb(Ⅱ)adsorption capacity.So,we can conclude that the DBM–mineral complexes could improve the Cu(Ⅱ)and Pb(Ⅱ)adsorption capacities of minerals and protect DBM in heavy metal-contaminated environments.

Phenomic and metabolomic responses of roots to cadmium reveal contrasting resistance strategies in two rice cultivars(Oryza sativa L.)

To cope with heavy metal stress,plant root systems undergo root structure modification and release of multifarious metabolites.Elucidation of the resistance strategies to heavy metals mediated by the root system is crucial to comprehend the resistance mechanisms of plants.Here two rice cultivars with contrasting grain cadmium(Cd)accumulation traits were selected and the responses of their root systems to Cd stress were evaluated by morphological and metabolomics analysis.The phenomic and metabolomic responses of the root system varied between the two cultivars under Cd stress.The low-Cd accumulation rice cultivar(TY816)had a more highly developed root system that coped with Cd stress(10μM)by maintaining high root activity,while the root cells of the high-Cd accumulation cultivar(JY841)lost viability due to excessive Cd accumulation.TY816 upregulated lipids and fatty acids to reduce Cd uptake,whereas JY841 upregulated phenylethanoid glycosides to cope with Cd-induced oxidative stress.The combination of metabolomics and phenomics revealed that rice roots employ multiple strategies to increase their tolerance of Cd-induced oxidative stress.Differing capacities to shape the root system architecture and reprogram root exudate metabolites may contribute to the contrasting Cd accumulation abilities between JY841 and TY816.

Responses of ramie(Boehmeria nivea L.)to increasing rare earth element(REE)concentrations in a hydroponic system

A number of studies have focused on the effects of rare earth elements(REEs) on crop plants,while little attention has been paid on how tolerant plant species respond to increasing mixed REE concentrations.In this study,ramie(Boehmeria nivea L.) was exposed to a series of REE concentrations prepared with equimolar mixtures of 16 REEs(i.e.0,1.6,8,16,80,160,400,800 μmol/L) in order to explore REE accumulation and fractionation characteristics in ramie and the responses of this plant to mixed REEs.Results show that ramie root and shoot biomasses are unaffected under lower REE concentrations(1.6-80 μmol/L),while the growth of ramie and the uptake of nutrients especially Ca and Mn are largely inhibited under higher REE concentrations(160-800 μmol/L).The P and Mo concentrations in the roots increase with the increasing REE concentrations in the solution,suggestive of an involvement of P and Mo in dealing with the high concentrations of REEs in this plant.The preferential uptake of Ce and heavy REEs(HREEs) and the preferential transport of HREEs within the plant lead to a positive Ce anomaly and a HREE enrichment in ramie leaves.Our study suggests that ramie could be a good candidate for the phyto re mediation of heavily REE-contaminated soils(e.g.,REE mine tailings in southern China).Our results also shed light on points of taking into account phytoremediation management strategies of REEcontaminated soils(e.g.,P and Mo fertilization).