Salinity elevates Cd bioaccumulation of sea rice cultured under co-exposure of cadmium and salt

Salt-tolerant rice (sea rice) is a key cultivar for increasing rice yields in salinity soil.The co-existence of salinity and cadmium (Cd) toxicities in the plant-soil system has become a great challenge for sustainable agriculture,especially in some estuaries and coastal areas.However,little information is available on the Cd accumulating features of sea rice under the co-stress of Cd and salinity.In this work,a hydroponic experiment with combined Cd(0,0.2,0.8 mg/L Cd^(2+)) and saline (0,0.6%,and 1.2%NaCl,W/V) levels and a pot experiment were set to evaluate the Cd toxic risks of sea rice.The hydroponic results showed that more Cd accumulated in sea rice than that in the reported high-Cd-accumulating rice,Chang Xianggu.It indicated an interesting synergistic effect between Cd and Na levels in sea rice,and the Cd level rose significantly with a concomitant increase in Na level in both shoot(r=0.54,p<0.01) and root (r=0.66,p<0.01) of sea rice.Lower MDA content was found in sea rice,implying that the salt addition probably triggered the defensive ability against oxidative stress.The pot experiment indicated that the coexistent Cd and salinity stress further inhibited the rice growth and rice yield,and the Cd concentration in rice grain was below 0.2 mg/kg.Collectively,this work provides a general understanding of the co-stress of Cd and salinity on the growth and Cd accumulation of sea rice.Additional work is required to precisely identify the phytoremediation potential of sea rice in Cd-polluted saline soil.

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 acid dissolution characteristics of cadmium fixed by a novel Ca-Fe-Si composite material

Ca-Fe-Si material(CIS),a novel composite material rich in calcium,iron,manganese and silicon showed marvelous immobilization properties for heavy metal(loid)s in soils.To elucidate the acid stability of Cd fixed by CIS(CIS-Cd)and the underlying immobilizationmechanisms,the acid dissolution characteristics of CIS-Cdwere investigated by using acid titration method and X-ray diffraction(XRD)technique.The results showed that CIS-Cd had distinctive acid buffering capacity in different pH ranges.Based on the titration curve between dissolution rate of CIS-Cd and pH,CIS-Cd can be divided into non acid-stable Cd(9.4%),moderately acid-stable Cd(22.5%)and acid-stable Cd(68.1%).XRD analysis of CIS-Cd at different pH intervals and the correlation curves of dissolution rates of Cd and concomitant elements indicated that non acid-stable Cdwas mainly bound by carbonate,silicate and sulfate(CdCO_(3),Cd_(2)SiO_(4) and CdSO_(4))or co-precipitated with the corresponding calcium salts.Moderately acid-stable Cd was mainly bound by magnesium-aluminum-silicon containing minerals or electrically bound bymanganese iron minerals.Acid-stable Cd remaining undissolved at pH<2.42 included CdFe_(2)O_(4) and ferromanganese minerals strongly bound Cd.It was by multilateral fixation mechanisms that Ca-Fe-Si material possessed marvelous immobilization capability for Cd and strong resilience to environmental acidification as well.The findings implicated that proper combination of calcium-iron-silicon containing minerals could develop novel promising amendments with high efficiency in heavy metal(loid)s immobilization and strong resilience to environmental change.