Soil Science and Plant Nutrition (2010) 56, 344–356
Heavy metal contamination of agricultural soils around a chromite mine in Vietnam Chu N. KIEN1, Nguyen V. NOI2, Le T. SON2, Ha M. NGOC2, Sota TANAKA3, Takuro NISHINA4 and K oz o IWASAKI4 1
United Graduate School of Agricultural Sciences, Ehime University, Ehime 790-8566, 2Faculty of Chemistry, Hanoi University of Science, Hanoi, Vietnam, 3Graduate School of Kuroshio Science and 4Faculty of Agriculture, Kochi University, Kochi 783-8502, Japan
Abstract In Vietnam, the Co Dinh mine is the largest chromite mine in the country. Mining, ore dressing and disposal of the tailings provide obvious sources of heavy metal contamination in the mine area. The present study examined the influence of chromite mining activities on the adjacent lowland paddy field by investigating heavy metal and As levels in the mine tailings, sediments, paddy soils and water. At paddy fields located near the mine tailings, the total contents of Cr, Co and Ni were 5,750, 375 and 5,590 mg kg)1, and the contents of their water-extractable form were 12.7, 1.16 and 32.3 mg kg)1, respectively. These results revealed severe contamination of lowland paddy soils with Cr, Co and Ni as a result of mining activity, suggesting serious health hazards through agricultural products, including livestock in this area. The principal source of the pollution was sediment inflow owing to the collapse of the dike, which was poorly constructed by heaping up soil. Moreover, water flowing out from the mining area was also polluted with Cr and Ni (15.0–41.0 and 20.0–135 lg L)1, respectively). This might raise another problem of heavy metal pollution of watercourses in the area, indicating the need for further investigation and monitoring of fluctuations of water quality with seasonal changes. Key words:
contamination, heavy metal, mine, soil, Vietnam.
INTRODUCTION Mining activities produce large quantities of waste materials, such as waste rock, tailings and slag, leading to metal contamination of the environment (Adriano 2001; Chopin and Alloway 2007; Jung 2001). Elevated levels of toxic metals are often reported in agricultural soils, food crops and stream systems as a result of the discharge and dispersion of mine wastes into the environment (Jung 2001; Lee 2006; McGowen and Basta 2001). A number of studies have investigated the spatial distribution and behavior of heavy metals in and around mining areas to assess the potential health risks and environmental hazards caused by polluted agricultural products. For example, enrichment of Cr and Ni (86–358 and 21.2– 126 mg kg)1, respectively) as a result of mine tailings was reported for surface soils taken from the Almade´n mining Correspondence: C. N. KIEN, United Graduate School of Agricultural Sciences, Ehime University, 3-5-7, Tarumi, Matsuyama, Ehime 790-8566, Japan. Email: [email protected]
Received 25 September 2009. Accepted for publication 20 December 2009.
district in Spain (Bueno et al. 2009). Elevated levels of Cr and Ni (182–1,029 mg Cr kg)1 and 15–432 mg Ni kg)1) were also found in soils collected from mining areas in southern Togo (Gnandi and Tobschall 2002). Bi et al. (2006) reported Cr contamination of agricultural soils (71–240 mg kg)1), resulting from zinc smelting activities in Hezhang County, western Guizhou, China. High levels of heavy metals in paddy fields nearby the Daduk Au–Ag– Pb–Zn mining area of Korea were caused by dispersion of the metals from the tailings by sedimentation and watercourses (Lee et al. 2001). In addition, a number of studies have investigated the vertical distribution of heavy metals in soil profiles in and round mining areas, and changes in the geochemical processes throughout the profile (Adriano 2001; Johnson et al. 2000; Kim and Jung 2004; Otero et al. 2000). According to these studies, it appears that the profile distribution patterns of each heavy metal are site specific, with no consistent distribution pattern correlating with soil depth. The toxicity and bioavailability of heavy metals in soils are influenced by the metal’s mobility and reactivity with various environmental factors. Therefore, information about metal speciation as well as its total content is neces 2010 Japanese Society of Soil Science and Plant Nutrition
Soil contamination by a chromite mine in Vietnam
sary for the assessment of heavy metal toxicity and bioavailability. The proportion of a metal that is mobile and bioavailable will provide practical information for evaluating its potential environmental risks. Kien et al. (2009) studied and reported the form and horizontal distribution of Cu and As in paddy soils and watercourses resulting from the exploitation of tin and tungsten ores in Daitu district, in the northern part of Vietnam. However, in Vietnam, few studies on the form and distribution of heavy metals and metalloids have been carried out for agricultural soils affected by mining activities. In Vietnam, a wide variety of minerals have been found to contain various elements (e.g. antimony, chromite, copper, tin, tungsten), and a lot of metalliferrous mines have been established over the country. Some are currently being mined, whereas others have been abandoned. Many of these mines are located in mountainous areas or in the upper reaches of lowland streams, where various types of crops are cultivated, including lowland rice, which is the major crop. Although dikes are usually constructed around mine areas to prevent the release of tailings, waste water and solid waste into the surrounding environment, frequent occurrences of flooding during the rainy season have caused some of these dikes to collapse and not function properly, resulting in heavy metal pollution in lower streams and farmland areas. Therefore, it is impera-
Figure 1 Location of the sampling sites. 2010 Japanese Society of Soil Science and Plant Nutrition
tive that we accumulate more data related to heavy metal contamination around mining sites where various types of metals are extracted. In the present study, we assessed the influence of heavy metal contamination on lowland paddy fields in the downstream areas of the Co Dinh chromite mine and clarified possible pathways that the contaminants might take. The chemical forms of the contaminants were also determined to evaluate their mobility and any potential risks to the surrounding environment.
MATERIALS AND METHODS Co Dinh chromite mine Mining activity at the Co Dinh chromite mine (19o43¢N, 105o36¢E; Fig. 1) was initiated in the early 20th century (1930) with ore extraction from the ground surface, followed by open-pit mining. Large-scale and intensive mining activities commenced in the 1990s. Recently, the Co Dinh Chromite Mining Company temporarily closed the mine with the aim of re-construction and installation of new technology. However, local people living in the vicinity of the mine continue small-scale activities using small adits and open pits. The chromite concentrate produced from this mine contains 46% Cr2O3 and