Figure 1Conceptual model to explain the effect of atmospheric Hg on Se uptake by rice (Image by IGCAS)

Selenium (Se) is an important trace element for human nutrition, and is known to reduce Hg toxicity in animals. Se also has a recognized interactive effect on mercury (Hg) uptake in plants.

Rice (Oryza sativa L) is the dominant cereal crop for the population of China, and the grain is an important source of dietary Se. The environment in some parts of China contains a high Hg concentration due to historic or current-day mining activities. Notable studies have been published on the distribution of Hg and Se in rice plants in Hg mining areas. However, the potential effects of Hg on the Se concentration in rice in mining environments have not been previously assessed.

Prof. FENG Xinbin’s Mercury Research Group from the Institute of Geochemistry, CAS (IGCAS) has investigated the process of Se uptake in rice plants.  During the rice harvest season, the whole rice (Oryza sativa L) plant samples and corresponding soils were collected from across both an active artisanal mercury mining area and an abandoned commercial mercury mining area in Guizhou Province, China.

The Se concentration in soil was similar across the two mining areas, but the Se concentration in the grain of paddy rice was found dramatically different (artisanal area 51±3 ng g^-1 and abandoned area 235±99 ng g^-1, mean and standard error). The artisanal mining area was characterized by a significantly greater total gaseous mercury (TGM) concentration in ambient air than the abandoned area (231 ng m^-3 and 34 ng m^-3 respectively).

The researchers discovered a negative correlation (R2=0.242, P=0.074) between the TGM concentration in ambient air and the concentration of Se in grain for the artisanal area only.  Principal component analysis (PCA) indicated that the source of Se in rice was the atmosphere for the artisanal area (no contribution from soil), and both the atmosphere and soil for the abandoned area.

They have proposed that TGM falls to soil and reacts with Se, inhibiting the translocation of Se to rice grain. Their data has suggested that Se intake by the artisanal mining community is insufficient to meet Se dietary requirements, predisposing this community to greater risk from Hg poisoning.

Based on the former research results, the researchers proposed a conceptual model (see Figure 1) to explain the effect of atmospheric Hg on Se uptake by rice.

The research was financed by the National Key Basic Research Program of China (973 Program 2013CB430004), Natural Science Foundation of China (41073098, 41203091, 41073062, 41173126, and 11105172), and also financed by the 135 project of IGCAS.

The study entitled “Effect of atmospheric mercury deposition on selenium accumulation in rice (Oryza sativa L.) at a mercury mining region in Southwestern China” was recently published in Environmental Science and Technology.

Contact:
FENG Xinbin
Institute of Geochemistry, Chinese Academy of Sciences
E-mail: fengxinbin@vip.gyig.ac.cn

(By ZHANG Chao)