Effects of water management on arsenic and cadmium speciation and accumulation in an upland rice cultivar

Pot and field experiments were conducted to investigate the effects of water regimes on the speciation and accumulation of arsenic（As） and cadmium（Cd） in Brazilian upland rice growing in soils polluted with both As and Cd. In the pot experiment constant and intermittent flooding treatments gave 3–16 times higher As concentrations in soil solution than did aerobic conditions but Cd showed the opposite trend. Compared to arsenate, there were more marked changes in the arsenite concentrations in the soil solution as water management shifted, and therefore arsenite concentrations dominated the As speciation and bioavailability in the soil. In the field experiment As concentrations in the rice grains increased from 0.14 to 0.21 mg/kg while Cd concentrations decreased from 0.21 to 0.02 mg/kg with increasing irrigation ranging from aerobic to constantly flooding conditions. Among the various water regimes the conventional irrigation treatment produced the highest rice grain yield of 6.29 tons/ha. The As speciation analysis reveals that the accumulation of dimethylarsinic acid（from 11.3% to 61.7%） made a greater contribution to the increase in total As in brown rice in the intermittent and constant flooding treatments compared to the intermittent-aerobic treatment. Thus, water management exerted opposite effects on Cd and As speciation and bioavailability in the soil and consequently on their accumulation in the upland rice. Special care is required when irrigation regime methods are employed to mitigate the accumulation of metal（loid）s in the grain of rice grown in soils polluted with both As and Cd.

Emerging contaminants: Evaluation of degradable chelators towards enhancing cadmium phytoextraction efficiency of bioenergy crop grown on polluted soil

Exogenous application of chelators towards enhancing heavy metals extraction efficiency of bioenergy crop has received considerable attention in recent time.However,little is known about optimal application rate,comparative evaluation of degradable versus non-degradable chelators and their impact on cadmium(Cd)speciation and uptake,physiological and biochemical activity of sweet sorghum grown under Cd stress.Four chelators namely,Nitrilotriacetic acid(NTA),tetrasodium N,N-diacetate(TDA),Ethylenediamine tetraacetic acid(EDTA),iminodisuccinic acid(IDA)and control(CK)were applied and compared at rates of 2,5,and 10 mmol kg^(-1) towards augmenting phytoextraction efficiency of sweet sorghum for Cd remediation in a screen house study.Results showed that sweet sorghum augmented with TDA significantly(P<0.05)increased biomass,enhanced Cd uptake and accumulation when compared to EDTA at application rate of 2-5 mmol kg1.TDA influenced Cd speciation via increasing acid-soluble,reducible,oxidizable,and residual fractions of Cd,thus increasing Cd bioavailability.NTA and TDA increased proline concentrations,antioxidant enzymes and net photosynthetic activity rate(Pn)comparably to EDTA in sweet sorghum,thus enhancing stress tolerance and stabilizing photosynthetic activities.Overall,exogenous application of degradable TDA at 2-5 mmol kg^(-1) could be recommended as replacement for non-degradable EDTA in a chelate assisted approach towards augmenting bioenergy crop for phytoremediation of Cd polluted soil.