Effects of Water Management on Cadmium and Arsenic Accumulation and Dimethylarsinic Acid Concentrations in Japanese Rice

Abstract

Rice consumption is a major source of cadmium and arsenic for the population of Asia. We investigated the effects of water management in rice paddy on levels of cadmium and arsenic in Japanese rice grains. Flooding increased arsenic concentrations in rice grains, whereas aerobic treatment increased the concentration of cadmium. Flooding for 3 weeks before and after heading was most effective in reducing grain cadmium concentrations, but this treatment increased the arsenic concentration considerably, whereas aerobic treatment during the same period was effective in reducing arsenic concentrations but increased the cadmium concentration markedly. Flooding treatment after heading was found to be more effective than flooding treatment before heading in reducing rice grain cadmium without a concomitant increase in total arsenic levels, although it increased inorganic arsenic levels. Concentrations of dimethylarsinic acid (DMA) in grain were very low under aerobic conditions but increased under flooded conditions. DMA accounted for 3-52% of the total arsenic concentration in grain grown in soil with a lower arsenic concentration and 10-80% in soil with a higher arsenic concentration. A possible explanation for the accumulation of DMA in rice grains is that DMA translocates from shoots/roots to the grains more readily than does inorganic arsenic.

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

“…The aerobic treatment resulted in higher Cd concentrations in the soil solution but the flooding treatment gave lower Cd concentrations during the growing season. Arao et al (2009) also reported that Cd concentrations in the soil solution were below the detection limit during the time of flooding but increased during aerobic conditions. These results can be explained by the combining of Cd with S to form CdS at low redox potential under flooding conditions (Bingham et al, 1976).…”

“…Selection and breeding of rice cultivars with low As and Cd accumulation have been practiced to reduce As and Cd in the rice grains (Zhang and Duan, 2008;Li et al, 2012;Ye et al, 2012). Water management is another promising method that affects Cd and As bioavailability in soils and their subsequent uptake by rice (Arao et al, 2009;Rahaman et al, 2011;Hu et al, 2013b). When a paddy field is flooded and the soil has a low redox potential, any Cd present in the soil combines with sulfur (S) to form CdS which has low solubility in water (Bingham et al, 1976).…”

“…When a paddy field is flooded and the soil has a low redox potential, any Cd present in the soil combines with sulfur (S) to form CdS which has low solubility in water (Bingham et al, 1976). Thus, flooding during the growing season, especially during later stages of plant growth, can effectively reduce Cd concentrations in rice grains (Arao et al, 2009;Hu et al, 2013a). In contrast, anaerobic conditions in paddy soils usually lead to the reduction of arsenate (As(V)) to arsenite (As(III)) which enhances the bioavailability of As to the rice plants (Masscheleyn et al, 1991;Marin et al, 1993;Takahashi et al, 2004).…”

“…IAPAQ-9), an important upland rice cultivar, was introduced to China during the 1990s and currently thousands of hectares of this variety are cultivated in the central and northern regions to combine water saving with high grain yields (Cheng et al, 2000). To the best of our knowledge all previous reports on the effects of water management practices or experiments on Cd and/or As accumulation have involved lowland rice cultivars (Arao et al, 2009;Li et al, 2009b;Hua et al, 2011;Somenahally et al, 2011) with few studies on upland rice cultivars. In the present study pot and field experiments were therefore conducted to investigate the effects of water management regimes on both As and Cd speciation and bioavailability in the soil and their accumulation in the grains of Brazilian upland rice.…”

Mitigation of cadmium and arsenic in rice grain by applying different silicon fertilizers in contaminated fields

“…This inhibitory effect of Si is supported by many laboratory experiments (Bogdan and Schenk 2008;Li et al 2009;Fleck et al 2013;Tripathi et al 2013). Areao et al (2009) reported that the soil Eh value decreased rapidly during the flooded period. In this case, arsenite as the predominant form of As species in paddy soils (reducing environments) is actually present in solution predominantly as an undissociated molecule at pH <8.…”