Shehong Li

Thallium pollution in China: A geo-environmental perspective

It is well known that thallium (Tl) is a non-essential and toxic metal to human health, but less is known about the geo-environmentally-induced Tl pollution and its associated health impacts. High concentrations of Tl that are primarily associated with the epithermal metallogenesis of sulfide minerals have the potential of producing Tl pollution in the environment, which has been recognized as an emerging pollutant in China. This paper aims to review the research progress in China on Tl pollution in terms of the source, mobility, transportation pathway, and health exposure of Tl and to address the environmental concerns on Tl pollution in a geo-environmental perspective. Tl associated with the epithermal metallogenesis of sulfide minerals has been documented to disperse readily and accumulate through the geo-environmental processes of soil enrichment, water transportation and food crop growth beyond a mineralized zone. The enrichments of Tl in local soil, water, and crops may result in Tl pollution and consequent adverse health effects, e.g. chronic Tl poisoning. Investigation of the baseline Tl in the geo-environment, proper land use and health-related environmental planning and regulation are critical to prevent the Tl pollution. Examination of the human urinary Tl concentration is a quick approach to identify exposure of Tl pollution to humans. The experiences of Tl pollution in China can provide important lessons for many other regions in the world with similar geo-environmental contexts because of the high mobility and toxicity of Tl.

Medical geology of arsenic, selenium and thallium in China

Arsenic (As), selenium (Se) and thallium (Tl) are three trace metals (metalloids) of high concern in China because deficiency or excess expose can cause a range of endemic diseases, such as endemic arsenism, selenosis, Keshan disease (KD), Kashin-Beck disease (KBD) and thallotoxicosis. These specific endemic diseases were attributable for overabundance or deficiency (mainly referring to selenium) of these three elements in the local environment as a result of natural geochemical processes and/or anthropologic activities. The geochemistry and human health impacts of these three trace elements have been intensively studied since the 1970s in China, in terms of geochemical sources, distribution, transportation, health impact pathways, and prevention/remediation measures. Endemic arsenism in China are induced from the exposures of high As in either drinking water or domestic combustion of As-rich coals. Both endemic selenium deficiency and selenosis occurred in China. The KD and KBD were related to the deficiency of Se in the low-Se geological belt with Se contents in soil less than 0.125mg/kg stretching from northeast to southwest of China. Endemic selenosis occurred in areas with high Se concentrations in soils derived from the Se-enriched black carbonaceous siliceous rocks, carbonaceous shale and slate. Endemic Tl poisoning occurred in southwestern China due to Tl contamination in local drinking water and vegetables surrounding the Tl-rich sulfide mineralized areas. Some measures have been taken to control and remedy the endemic diseases with significant effects in reducing health risk and damage of As, Se and Tl. However, the states of the endemic diseases of As, Se and Tl in China are still serious in some areas, and substantial research efforts regarding the health impacts of these elements are further required. This paper reviews the progress of medical geology of As, Se and Tl in China, and provides with some outlooks for future research directions.

Distribution and transport of selenium in Yutangba, China: Impact of human activities

Yutangba, one of the typical high-Se areas where a sudden incidence of Se poisoning occurred in 1963, is located in the northern part of Shuanghe town about 81 km SE of Enshi, Hubei Province, China. In this area, a comprehensive investigation was conducted on the distribution of Se in soils, plant species, stream water and sediment. The mean concentrations of Se were: total soil, 4.75+/-7.43 mg/kg (n=150); Corn seeds, 1.48+/-1.41 mg/kg (n=20); Agry wormwood, 1.68+/-1.27 mg/kg (n=30); Bracken fern, 0.63+/-1.61 mg/kg (n=57), and Central China dryoathyrium, 0.48+/-0.72 mg/kg (n=39); Stream water, 58.4+/-16.8 microg/L (n=12); stream sediment, 26.6+/-26.8 mg/kg (n=11). The spatial distribution of Se in soils and plants is significantly uneven and higher Se samples mainly distributed in the croplands and northwest Yutangba, while almost all the lower Se samples are located in undisturbed areas. 11 samples contained extremely high concentrations of Se, ranging from 346 to 2018 mg/kg with an average of 899+/-548 mg/kg, were found at croplands and discarded coal spoils in Yutangba. The distribution of Se in Yutangba is related to the pathways of Se transport, which was caused by human activities such as stone coal conveyance by local villagers, mining of stone coal for use as a fuel or fertilizer, and discharging lime into cropland to improve soil. These activities caused variable addition of Se to the soil and further accumulation of Se in food chain. Therefore, human activities have played an important role in the distribution, transport, and bioavailability of Se. Yutangba is still a high risk area where Se poisoning may occur again, and so are almost all high-Se areas in Enshi Prefecture.

Enrichment of Arsenic in Surface Water, Stream Sediments and Soils in Tibet

Groundwater in sedimentary deposits in China, Southern, and Southeast Asia down gradient from the Tibetan plateau contain elevated As concentrations on a regional scale. To ascertain the possibility of source region As enrichment, samples of water (n=86), stream sediment (n=77) and soil (n=73) were collected from the Singe Tsangpo (upstream of the Indus River), Yarlung Tsangpo (upstream of the Brahmaputra River) and other drainage basins in Tibet in June of 2008. The average arsenic concentration in stream waters, sediments and soils was 58±70 μg/L (n=39, range 2-252 μg/L), 42±40 mg/kg (n=37, range 12-227 mg/kg), and 44±27mg/kg (n=28, range 12-84 mg/kg) respectively for the Singe Tsangpo and was 11±17 μg/L (n=30, range 2-83 μg/L), 28±11 mg/kg (n=28, range 2-61 mg/kg), and 30±34 mg/kg (n=21, range 6-173 mg/kg) respectively for the Yarlung Tsangpo. A dug well contained 195 μg/L of As. In addition to elevated As levels in surface and shallow groundwater of Tibet, hot spring and alkaline salt lake waters displayed very high As levels, reaching a maximum value of 5,985 μg/L and 10,626 μg/L As, respectively. The positive correlation between [As] and [Na]+[K] in stream waters indicates that these surface water arsenic enrichments are linked to the hot springs and/or salt lakes. Further, 24% of As in stream sediment is reductively leachable, with bulk As displaying a positive correlation with stream water As, suggesting sorption from stream water. In contrast, the fraction of reductively leachable As is negligible for soils and several rock samples, suggesting that As in them are associated with unweathered minerals. Whether the pronounced As anomaly found in Tibet affects the sedimentary As content in deltas downstream or not requires further study.

Distribution of uranium and thorium in Irtysh River and the upriver wastewater from a rare metal mine impact on it

lag/g) was about 3 times higher than in the control (0.60 lag/g). Conclusions: This study indicated that smelters in a Chinese mercury mine were exposed to extremely high levels of Hg0 vapor, and that miners were estimated to be also exposed to higher levels of MeHg than those in controls. Further study is needed to determine the origin of such the comparatively high hair MeHg concentrations in the exposed group.

Fluoride in Chilies from Southwestern China

The purpose of this research is to investigate the fluoride contents in the chilies from southwest China and other countries in order to calculate the difference in fluoride levels in the fresh chilies. The standard method in China for analysis of fluoride in food (GB/T 5009.18‐2003) was applied to determinate the fluoride content in chilies. By determining the fluoride content in 176 fresh chili samples from 77 counties in southwest China and 31 chili samples from other countries, the research not only aims to find the regularity of fluoride distribution in fresh chili, but also to determine the origin of fluoride in fresh chili in China compared with the foreign samples. The geometric mean of fluoride content in the fresh chili was 8.9 mg kg−1 (dry weight, 176 samples, confidence level: 95%). According to the study on the contents of fluoride in fresh chili, it seems that the fluoride content standard for vegetables in GB2762‐2005 in China is inappropriate for chili, and 24.7 mg kg−1(dry weight) and 5.2 mg kg−1 (fresh weight) in recommend as the fluoride contaminated discrimination values for fresh chili.