Original article Selenium source in the selenosis area of the Daba region, South Qinling Mountain, China Luo Kunli Æ Xu Lirong Æ Tan Jian’an Æ Wang Douhu Æ Xiang Lianhua Abstract Naore Village in the Shuang’an Introduction countryside, Ziyang County, Shaanxi Province is Selenium is closely related to the well being of organic life located in the Daba region of South Qinling generally, and to human health specifically. A narrow Mountain. It is one of two selenosis or selenium range of concentration exists between toxicity and defi- poisoning areas in China. Crops grown in the area ciency (Rosenfeld and Beath 1964; Thornton and others are enriched in selenium. The soil is derived from 1983; Yang and others 1983). The selenium content in the high-selenium, pyritic, black carbonaceous slate and Earth’s crust and mantle is quite low, about 0.05 mg/kg volcanic tuff of the Lujiaping Formation, Early (Liu and others 1984). China has two known selenosis Cambrian and Late Neoproterozoic in age, which is (selenium poisoning) areas; the first is Enshi, Hubei exposed in this area. The Lujiaping Formation is Province (Yan 1991; Yan and Wu 1993); the other is the more than 40-m thick. Selenium content of the Shuang’an countryside in Ziyang County, Shaanxi Prov- volcanic tuff averages 32 mg/kg Se and the black ince, in the Daba region of South Qinling Mountain, carbonaceous slate averages 22 mg/kg Se, which Central China (Mei 1985) (Fig. 1). The most concerning represent the highest concentrations recorded area of selenosis in the Shuang’an countryside of Ziyang among all the strata and rocks sampled in the Daba County is very small, limited to Naore village (Mei 1985; region of South Qinling Mountain. This series of Edit Committee on Ziyang County Annals 1989). The selenium-enriched rocks is also found in other selenium content of corn in some fields of Naore village is places in the Daba region, South Qinling Mountain, 6.6 mg/kg (Luo and Qiu 1995), and horsebeans reach where the soil contains about 10 to 30 mg/kg Se. 48.84 mg/kg Se (Mei 1985). The selenium content of soil in These zones are latent selenosis zones in the Daba these fields is 15.74 mg/kg (Mei 1985) and 26 mg/kg (Zhao region. In addition, a selenium-enriched black and others 1993). Village people consume the selenium- carbonaceous shale, of Early Cambrian age, and enriched crops from these fields. It is clear that the sele- containing 10 to 40 mg/kg Se, occurs in several other nium in the crops came from local selenium-enriched soil provinces in the south of China. (Mei 1985; Edit Committee on Ziyang County Annals 1989; Keywords Selenosis Æ Selenium enrichment Æ Early Zhao and others 1993), but what is the source of the Cambrian Æ China Æ Shaanxi Province selenium in the soil? Mei (1985) suggested that the selenium in this selenosis area may come from a selenium-enriched coal bed and Ziyang County is cited as a selenium-rich region in his introduction and summary, but he did not explain what Received: 19 December 2002 / Accepted: 21 August 2003 kind of coal caused the selenosis or where the selenium Published online: 4 September 2003 came from in this selenium-rich region. When more recent ª Springer-Verlag 2003 papers or reports mention the selenosis in Ziyang, most of them cite Mei’s contention that the selenium is from L. Kunli (&) Æ X. Lirong Æ T. Jian’an burning Se-enriched coal. CAS, Institute of Geographical Sciences and Natural Resource In the Daba region, the biggest stone coal mine (Silurian in Research, Building 917, 3 Datun Road, age) is at Haoping (Edit Committee on Ziyang County 100101 Beijing, China E-mail: [email protected] Annals 1989; Luo and others 1995), located about 10 km Tel.: +86-010-64856503 southeast of Naore village (Fig. 1); it has large reserves and Fax: +86-010-64851844 its coal is very commonly used in the Daba region. At W. Douhu Naore village, there is a small deposit of stone coal, but it is Xi’an University of Science and Technology, not used because the quality is poor and the reserve is 710054 Xi’an, China small since it is enclosed in the volcanic tuff (Fig. 2). As X. Lianhua there is no highway between Naore village and the Ha- Ziyang Bureau of Mineral Development Supervision, oping stone coal mine, this stone coal is more expensive 725300 Ziyang, Shaanxi, China than the local cornstalks used as fuel by most villagers in 426 Environmental Geology (2004) 45:426–432 DOI 10.1007/s00254-003-0893-z Original article Fig. 1 In 1982, Luo began to study the strata sequences and Map showing the study area and the geologic setting of Naore village geochemical character of Cambrian and Silurian rocks in in Ziyang County. Please note: 1 stratigraphic boundary, 2 fault, 3 river, 4 Early Paleozoic volcanic rock, 5 Upper Neoproterozoic, the Daba region. She and her research group (Luo and 6-Early Paleozoic syenite porphyry, 7 Daguiping Formation (Silurian), others 1994, Luo and Jiang1995, Luo and others1995, 8 Lower Neoproterozoic, 9 Meiziya Formation (Silurian), 10 Lujiaping 2001, 2002) studied the selenium content and its distri- Formation (Cambrian), 11 Donghe Group, 12 Jianzhuba Formation bution pattern in early Paleozoic rocks and stone coal, (Lower Cambrian), 13 siliceous escarpment, 14 Naore village and the relationship between selenium content of the rocks and their mineral and chemical composition. Naore. Only a few families use the Haoping stone coal as Recently, they studied the elemental activity of different fuel. early Paleozoic rocks in the supergene environment of If the selenium in this selenosis area comes from burning the Daba region, South Qinling Mountain. In this paper, selenium-enriched coal, why are there no selenosis prob- the relation of the selenium content of the soil and lems reported in the town of Haoping and other places bedrock in Ziyang County, especially at Naore village is where the citizens use more stone coal for warmth and discussed. The selenium content in soil and rock in other cooking than in Naore village, and why is the only sele- parts of the Daba region are reported, particularly at nosis occurrence in a small area of the Naore valley? Why Tieluba-Zuolong (Langao County, Fig. 3), at Lujiaping- is there no selenosis in other valleys adjacent to the Naore Jianzhuba (Ziyang County, (Fig. 3) and at Suang’an- village where the geographical conditions and living habits Xinglong (Fig. 3), where geological conditions are similar are the same? to Naore village. In addition to the known selenosis Li and others (1982) first reported that there were big dif- areas, latent selenosis regions in the Daba area, South ferences in selenium content in water, soil, crops, and hu- Qinling Mountain are outlined in this paper, which is the man hair in different localities of the Daba region, but they first such report. offer no explanation for the wide differences in selenium content encountered. Zhao and others (1993) made a systematic study of soil in Ziyang County and found great differences in selenium content, which varied from Materials and Methods 0.324 mg/kg to 23.53 mg/kg. Luo and others (1994, 2001) analyzed the selenium content of the bedrock strata in the The selenosis area at Naore village, where the selenium Daba region and demonstrated that there were great dif- content of the farmland soil is the highest in Ziyang ferences in selenium content of different types of rocks. County, was the first selected for surveying and sampling Previously, the researchers studying the selenosis prob- of the strata. When surveying and sampling in Naore or lems in China were mainly physicians, ecologists or other areas, we took ten rock samples from each type of agriculturalists; few geologists have paid attention to the rock bed, such as black shale, carbonaceous slate, lime- selenosis problem. Field geological work in the Daba stone, etc. At the same time, samples of the natural or region is complicated by poor communication since most cultivated soil (at a depth of 0–30 cm) were collected at places have no highway access. In addition, the strati- the points where bedrock is exposed. The soil at the graphic sequence in the Daba region is complicated by bottom of the Naore village valley and on the sloping faulting. Previously, no detailed geological fieldwork has fields on both sides is mainly weathered from local been done in the Naore village. bedrock. The soil at the bottom of the valley is thick, Environmental Geology (2004) 45:426–432 427 Original article Fig. 2 The geology of the selenosis area at Naore village, Ziyang County: M1 plan geological map, M2 measured cross section, M3 soil profiles. The measured section started at the top of the mountain to the north of Naore village, and the strike of the section is N190°, nearly parallel to the direction of dip. Please note: 1 Neoproterozoic dolomite, 2 siliceous rock, 3 stone coal, 4 volcanic tuff, 5 black carbonaceous slate, 6 gray-green silty shale, 7 limestone of Jianzhuba Formation, 8 resi- dential area; 9 Se-enriched area, l0 location of soil test pit about 0.3 m, while the soil on the sloping fields is thin, Results varying from 0.1 m to 0.3 m. All samples were analyzed by the Northwest Geological The study area Testing Center which is a first class analytical laboratory The Daba region of South Qinling Mountain is located in of CNNC (China National Non-Ferrous Metals Industry the southern part of Shaanxi Province, in Central China Corporation), accredited by China National Metrology (Fig.