Journal of Geochemical Exploration 139 (2014) 97–108 Contents lists available at ScienceDirect Journal of Geochemical Exploration journal homepage: www.elsevier.com/locate/jgeoexp The origin and geochemical cycle of soil selenium in a Se-rich area of China Tao Yu a, Zhongfang Yang a,b,⁎, Yaoyao Lv a,QingyeHoua, Xueqi Xia a, Haiyan Feng a,MengZhanga, Lixin Jin c, Zezhong Kan c a China University of Geosciences, Beijing 100083, PR China b Key Laboratory of Ecological Geochemistry, Ministry of Land and Resources, Beijing 100037, PR China c Sichuan Institute of Geological Survey, Chengdu 610081, Sichuan, PR China article info abstract Article history: Mianyang City, located in the Fujiang River Basin, Sichuan Province, is a Se-rich area of China. The distribution of Received 29 January 2013 Selenium (Se) in the Mianyang area was studied based on assay data obtained from soil, irrigation water, fertil- Accepted 30 September 2013 izer, and rice (grain and stem) samples. The ratio between natural and anthropogenic sources in the area was de- Available online 9 October 2013 rived by analyzing the concentrations and spatial distributions of multiple elements (such as Se, cadmium, arsenic, and mercury) in the soil. The controlling factors affecting Se concentration in the soil were also investi- Keywords: Selenium gated. We established a geochemical model of the Se cycle among the different media (i.e., the atmosphere, fl Origin water, soils, and plants). We then calculated the annual Se ux caused by various inputs' (such as precipitation, Geochemical cycle fertilization, and irrigation) and outputs' (such as infiltration, crop harvest, removal of straws from cropland, and Se-rich area volatilization) pathways in the topsoil. We discuss the contribution of different pathways to the Se cycle and pro- China vide evidence for exploring Se-rich land in the study area. © 2013 Elsevier B.V. All rights reserved. 1. Introduction element in plants; however, whether this element is essential for plants remains debatable (Bañuelos et al., 1997; Lyons et al., 2009; Mateja Selenium (Se) is an important trace element in the ecological envi- et al., 2007). ronment. This element has been studied for more than 190 years since In the soil–plant–animal/human food system, the soils supply Se Swedish chemists discovered it in 1817. Excessive exposure to Se and to satisfy the requirement for plants, humans, and livestock. Human lack of Se in the environment both cause health problems to humans and natural activities constantly change Se concentration in soils. There- and animals (Wang, 1993). The excessive exposure of livestock to Se, fore, the sources, existing forms, and bioavailability of Se in soils play which caused alkaline disease and blind stagger in Europe and the decisive roles in the geochemical cycle of Se. Se concentration ranges United States, had been recognized in the 1930s (Moxon, 1937). This from 0.01 mg/kg to 2.0 mg/kg in the vast majority of soils in the world, finding highlighted concerns regarding Se poisoning; and thus, Se with an average concentration of 0.4 mg/kg and a very uneven dis- was considered as an important environmental contaminant until the tribution (Fordyce, 2007). To date, several countries have successively 1950s (Mayland, 1994). In 1957, Schwarz and Foltz proved for the reported soils with an excessive or deficient amount of Se (Dhillon first time that animals need Se as a nutrient (Schwarz and Foltz, and Dhillon, 2003; Ermakov and Jovanovic, 2010; Fleming, 1980; 1957). Se was subsequently determined to be an important component Fordyce et al., 2010; Ihnat, 1989; Jacobs, 1990; Lakin, 1972; Neal, of glutathione peroxidase (Awasthi et al., 1975; Rotruck et al., 1973). 1995; Wang and Gao, 2001). On a worldwide scale, the areas of soils Moreover, Se deficiency may cause white muscle disease among live- with low Se concentration or which lack Se are relatively larger than stock. Se has received universal attention in several fields, including those with potentially harmful high concentrations of Se (Girling, plant growth, human health, agricultural production, and ecology 1984). China is located in a low Se area, with more than approximately (Combs and Combs, 1986; Fordyce et al., 2000; Huang et al., 2013; 10 provinces (municipalities) exhibiting varying degrees of Se deficien- Johnson et al., 2010; Levander and Burk, 2006; Mayland, 1994). The cy. The region with Se deficiency accounts for approximately 72% of the World Health Organization (WHO) has also confirmed that Se is a nec- national land area. Such arithmetic indicates that Se concentration of essary nutritional element for animals (WHO, 1987). Se is a beneficial soils in low-Se areas is 0.13 mg/kg (Hu et al., 2000; Tan, 1989; Tan et al., 2002). Endemic diseases, such as Kashin–Beck disease and Keshan disease, are prevalent where Se is relatively deficient in soils (Gao et al., 2011; Lv et al., 2012). These diseases seriously affect the physical health of local residents. Therefore, studying the source and geochemical ⁎ Corresponding author at: China University of Geosciences, No. 29, Xueyuan Road, fi Haidian District, Beijing 100083, PR China. Tel./fax: +86 10 82322079. behavior of Se in soils from China with relative Se de ciency is highly E-mail address: [email protected] (Z. Yang). significant. 0375-6742/$ – see front matter © 2013 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.gexplo.2013.09.006 98 T. Yu et al. / Journal of Geochemical Exploration 139 (2014) 97–108 Mianyang City is located in the Fujiang River Basin, Sichuan Province using a bamboo spade, and each of the four sub-samples was in the southwestern of China where Se is relatively deficient in soils. A composited for analysis. In this study, totally 2601 composite multi-objective regional geochemical survey of the Chengdu Economic samples of topsoil and 650 composite samples of subsoil Zone of Sichuan Province was conducted from 2002 to 2008 (Chen were collected. After the sampling site was selected, we used et al., 2008). The survey revealed that Se-rich soils in Mianyang are sediment sampling equipment to load equal amounts of characteristically distributed along the riverbanks. An enrichment of coarse active sediments from three to five points of the section toxic heavy metals, such as cadmium (Cd), lead (Pb), and zinc (Zn), in plastic buckets, with the excess water drained off. The was also found in the soil. We conducted a systematic study of the collected samples were loaded into a clean sack and kept in a sources and pathways of the geochemical cycle of Se in soils from this cool, dry place. The dried samples were sieved by using a 20- area, with the aim of providing a case study of a geochemical cycle in mesh (b0.84 mm) nylon sieve. The sieved samples were kept a Se-rich area. in clean Teflon bags and sent to the laboratory for analysis. The samples to be analyzed included 5% national standard 2. Material and methods material. (2) We collected rice grains, stems, and the corresponding sam- 2.1. Study area ples of the topsoil during the harvest season in the rice- growing regions. The method of topsoil collection was the The research area is located in Mianyang City in the midstream of same as the first procedure. We first analyzed the entire area the Fujiang River Basin. The area measures 10,404 km2 with the geo- at each sampling site to determine the cropland, terrain, and graphic coordinates of 105°2′26″ to 105°43′25″ (E) and 30°0′18″ to fertility status. Those plots with area about 3500 m2 and 31°1′52″ (N). This area has a subtropical humid monsoon climate, well-growing rice were chosen as sampling sites based on with neither cold winters nor hot summers. The annual average tem- the summary investigation about plots area, landform and perature is 17.3°C, and the frost-free season is long. The annual average rice growing conditions of study region. In each plot, 4–5sam- precipitation is 602 mm to 1389 mm. The annual sunshine hours are pling units were taken. The unit scale is 50cm×(sowing width 1042 h to 1665 h. The topography of the entire area is dominated by + row spacing) cm. The sampling sites were more than 1 m hills. The terrain shows a discrepancy between the north and south: from the edge of the land. We collected 124 samples of rice high in the north and lower in the south, with an elevation of 290 m grains and their corresponding topsoil, and 50 samples of to 650 m. Nine major soil types can be found in the study area based stems. The rice grain and stem samples were washed with on the Chinese soil taxonomy classification (CRG-CST, 2001), i.e., Calcaric tap water and then with deionized water to remove soil parti- Purple-Udic Cambosols, Calcaric Purple-Orthic Primosols, Carbonatic cles and dust. Subsequently, we dried the samples with tissue Udi-Orthic Primosols, Recalcaric Gleyi-Stagnic Anthrosols, Typic Fe- paper. The rice grains were dehulled. All the plant samples accumuli-Stagnic Anthrosols, Typic Fe-leachi-Stagnic Anthrosols, Albic were then oven-dried at 45 °C for 72 h to a constant weight. Fe-leachi-Stagnic Anthrosols, Typic Aquic-Alluvic Primosols, and Lithic The dried plant samples were ground into fine powder Haplic-Perudic Ferrosols. (b0.074 mm) using a stainless steel mill and were kept in Two crops of rice are planted in most parts of the research area: one clean Teflon bags prior to chemical analysis (Yang et al., crop of rice and one crop of wheat. Besides, maize is planted in a 2005). small portion of the area.