The Process of Methylmercury Accumulation in Rice (Oryza sativa L.)

Abstract

Recent studies have shown that rice consumption can be an important pathway of methylmercury (MeHg) exposure to humans in Hg mining areas and also in certain inland areas of Southwestern China. The seed of rice has the highest ability to accumulate MeHg compared to other tissues. The main objective of this study was to investigate the process of (MeHg) accumulation in rice seed (Oryza sativa L.) by monitoring MeHg levels in specific tissues of rice plants experiencing various levels of Hg multisource pollution during a full rice growing season. Four groups of experimental plantations were utilized, distributed among a rural artisanal Hg production site and a regional background control site. Our results suggest that the newly deposited Hg is more readily transformed to MeHg and accumulated in rice plants than Hg forms with an extended residence time in soil, and soil is the potential source of MeHg in the tissues of rice plants. MeHg in soil was first absorbed by roots and then translocated to the above-ground parts (leaf and stalk). During the full rice growing season only a very small amount of MeHg was retained in the root section. In the premature plant, the majority of MeHg is located in the leaf and stalk; however, most of this MeHg was transferred to seed during the ripening period.

Rice consumption contributes to low level methylmercury exposure in southern China

“…The THg and MeHg concentrations in the rice samples reported in this study were significantly lower than that from the Hg mining areas in Guizhou Province Horvat et al, 2003;Meng et al, 2010Meng et al, , 2011Qiu et al, 2008;Zhang et al, 2010a,b). The THg concentrations were comparable with that from 20 provinces in China (with a mean of 5.8 ng·g −1 , Qian et al, 2010) and that reported in the third national Total Diet Study conducted in China in 2000 (with a mean of 9.0 ng·g −1 ), which was considered to be an average concentration for THg in rice collected in China (Li et al, 2006).…”

“…Highly elevated THg concentrations (up to 1120 ng·g −1 ) were reported Horvat et al, 2003;Meng et al, 2010Meng et al, , 2011Qiu et al, 2008;Zhang et al, 2010a,b). More importantly, the highly toxic MeHg concentrations can reach as high as 174 ng·g −1 .…”

Methylmercury accumulation in rice plants (Oryza sativa L.) In low Hg areas and the potential health - Risk exposing in extreme micro-environments

“…THg distribution in rice tissues exhibited the following distribution patterns: leaf > stalk > soil> root >stem>rice>hull at the CPF in Xinyang city. The results were consistent with the THg distribution at the control site, but varied from THg distribution at the artisanal Hg mining site and the abandoned Hg mining sites [25].…”

“…The lowest one was found in hull (6.22 ± 2.9 µg kg -1 ), with the range 3.63-8.81 µg kg -1 . Meng et al [25] regarded that the THg in hull might also originate from air.…”

Spatial distribution of mercury in topsoil from five regions of China

“…Thus, soil becomes an important source of Hg. Recent studies in Guizhou Province, southwestern China, have showed that rice is the major pathway for methylmercury (MeHg) exposure to humans, in which MeHg is mainly accumulated from soil (Meng et al 2010(Meng et al , 2011Qiu et al 2008;Zhang et al 2010). Therefore, monitoring the concentrations of Hg in soil is important for understanding the geochemical cycle of Hg in the environment.…”