Arsenic Concentration from Different Sources in the World - Term Paper Example

Assess the likely health impacts of the increased use of groundwaters in Peoples Republic of China – identify key geogenic and anthropogenic contaminants. By Alok Mohan ABSTRACT Pollution is another huge problem contributing to the larger crisis at hand. Over half of China’s population, about 700 million people and 11 percent of the world’s, only have access to drinking water of a quality below World Health Organization standards (WHO). The water is contaminated by a combination of industrial pollution and human and animal waste. Arsenic (As) is widely known for its adverse effects on human health, affecting millions of people around the world. In Asia the consumption of groundwater (through wells) in an attempt to replace polluted surface water supplies has resulted in widespread As poisoning. Both, the United States Environmental Protection Agency (US-EPA) and the World Health Organization (WHO) have established the As level for drinking water at 10 µg L. Chronic arsenic poisoning affects at least 3,000 people in Guizhou Province, southwest China. High As concentrations have been found in groundwater of Xinjiang and Shanxi Provinces, China. Integrated approach to arsenic investigation including geochemical modeling with adsorption modeling was presented by Welch and Lico (1998) which was used for the site of investigation was the Southern Carson Desert in arid zone of Nevada. The same method is recommended here. They used sequential extraction to determine carbonate and hydroxide fractions with arsenic in sediments. Speciation modeling was used to calculate saturation indices for minerals like siderite and rhodochrosite which can decrease concentrations of dissolved iron and manganese. The results have been mentioned as per the findings at various places of china under various studies. INDEX S. no. Content Page no. 1 Introduction 3 2 Arsenic Poisoning 6 3 Arsenic in drinking water 8 4 Arsenic cycling 9 5 Arsenic concentration from different sources in the world 10 6 Chemistry of Arsenic 11 7 Arsenic in naturel environment : Redox zones 12 8 Geochemical Modelling 12 9 Investigation of Arsenic 13 10 Result and conclusion 14 11 References 15 Introduction Back in 1999, Wen Jinbao, a Chinese deputy prime minister, warned of the dire water situation in China and of looming water shortages. Since then, Mr. Wen has assumed the post of prime minister and predgled to provide clean water for his people. His administration has guaranteed an additional $240 million this year to achieve this end. However, this amount may not be nearly enough to satisfy China’s massive demand. The country has long suffered from alternating periods of severe flooding and drought. Combined with high pollution levels and a history of heedless and haphazard policies, the country is witnessing a precipitous drop in this most essential supply. High ranking officials and international agencies alike are deeply concerned about the situation and with good reason. According to hydrologists, government officers and industrial leaders, water and waste pollution is the single most serious issue facing China. Presently, one in three rural inhabitants lacks access to safe drinking water. The urban situation is not any more heartening. More than a hundred large cities are short of water and half are considered to be seriously threatened by the shortage. In the northern region of the country, the water table has dropped more than a meter. Even in the capital city of Beijing, the water supply per individual is only 300 cubic meters (66,000 gallons) per year. The country’s water resources are among the lowest in the world per capita and concentrated in the south, so that the north and the west experience regular droughts. Due to inadequate investments in supply and treatment infrastructure, even where water is not scarce, it is rarely clean. Close to 600 million people have water supplies that are contaminated by animal and human waste. Pan Yue, the deputy head of the State Environmental Protection Administration (SEPA), China’s environmental watchdog ministry, has called the shortage and its associated problems ‘the bottleneck constraining economic growth.’ China does not have the water resources to sustain the rapid economic growth it aspires to. What is more, the nation’s current policies make future sustainability even less likely. September 21, 2001 Landsat image of Harbin, China The Songhua River flows north out of the Changbai Mountains, cutting across the Manchurian Plain of northern China. As China’s northernmost river system, the Songhua is an important artery in transporting agricultural products grown on the plain. On its northward course, the river wends its way past Harbin, the capital of China’s Heilongjiang Province, where it provides another lifeline. As much as 80 percent of the city’s public water supply comes directly from the river. That supply was cut off after an explosion at a petrochemical plant dumped 100 tons of benzene and other harmful chemicals into the river on November 13, 2005. As the chemical slick reached the city, officials turned off water supplies to prevent illness until the chemicals passed. According to the U.S. Environmental Protection Agency, the primary pollutant, benzene, is a clear liquid that has a strong smell. It is highly flammable and can affect the nervous and immune systems in the short term or cause cancer after long-term exposure. The World Health Organization recommends that no more than 10 micrograms of benzene be permitted in each liter of drinking water. The Chinese industrial accident put about 100 times that amount into the Songhua. Though the chemical can be cleaned from the water, benzene evaporates quickly on its own or it may be degraded by microbes in the water. NASA image by Robert Simmon, based on Landsat-7 data provided by the UMD Global Land Cover Facility. Text excepted from NASAs Earth Observatory website. Pollution is another huge problem contributing to the larger crisis at hand. Over half of China’s population, about 700 million people and 11 percent of the world’s, only have access to drinking water of a quality below World Health Organization standards (WHO). The water is contaminated by a combination of industrial pollution and human and animal waste. The lack of clean water for animals creates the threat of disease as livestock take in all types of pollutants and microbes. Disease is likely to pass from poultry to pigs to humans, and ultimately, the threat of Avian Bird Flu and similar diseases becomes very grave. WHO warns of the high risk of a global pandemic that is not a question of if but of when. In late July of 2004, a mysterious black and brown plume of toxic matter over 80 miles long swept along the Huai River, one of China’s seven major rivers, and killed millions of fish and devastated wildlife. There were differing explanations for the disaster, the two leading reasons being that either too much water had been taken from the river system and the Huai River had lost its ability to clean itself, or that numerous factories had dumped untreated waste directly into the water and the levels of toxicity had accumulated to an critical point. According to SEPA, more than 70 percent of China’s lakes and five of China’s seven largest river systems are polluted enough to be unsuitable for human contact. In Shangba, located in northern Guangdong, pollution in the local water supply is so bad that the small towns in the region are known as ‘cancer villages’ by locals. A large mineral mine owned by the provincial government and several other small mines have been spewing toxic waste into local rivers and raising lead levels to 44 times permitted rates. Water in area streams is rust-colored and water drawn from local sources has been known to corrode the metal of teapots. Poisons from the mines are also destroying local crops, which require clean water for irrigation. Rice yields in this region are one third that of the national average and no one wants to buy the crop. The solution to nearly all of Shangba’s problems would be a reservoir, but that idea was abandoned after various tiers of government bickered over the 8.4 million yuan cost. Human waste is its own serious form of pollution and economic liability for the country. China has a daily sewage creation rate of close to 3.7 billion tons. The country would need 10,000 waste water treatment plants at a cost of $48 billion to achieve even a 50 percent treatment rate, according to Frost and Sullivan, a water consulting firm. With increasing urban populations, the problem of handling household waste is becoming more severe. Of the 168 million tons of solid waste that China produces annually, only 20 percent is properly disposed of. The commonality between all water-saving initiatives is the significant amount of money required to implement any of them. Severe pollution contaminates the potable water supply, but treatment equipment is expensive. Likewise, traditional irrigation methods can be adjusted and improved to increase efficiency, but the best equipment still needs to be imported. The costs should not be ignored however, because the cost of not taking action and not putting conservation measures into place will be significantly higher down the road. The World Bank has concluded that pollution is costing the country 8-12 percent of its 1.4 billion GDP in direct damage annually and the water issue is a large part of this. The Chinese Academy of Engineering predicts that the amount of water available per person per year will drop to 1760 cubic meters by 2030. With a swelling population and economy requiring more and more water, China’s water needs will soon likely hit the limits of what is available. How the country’s government officials and citizens alike will respond is unknown. Many argue that rational pricing of water and recycling for reuse can help avert catastrophe. People are aware of what needs to be done, but whether it gets done remains an unanswerable question. 1 About 300 million Chinese drink unsafe water tainted by chemicals and other contaminants according to a new report from the Chinese government. A leading government official said the greatest non-drought threat to Chinas water resources, is chemical pollutants and other harmful substances that contaminate drinking supplies for 190 million people. A recent nationwide survey found that about 90% of Chinas cities have polluted ground water, while millions of rural Chinese face risks from naturally occurring contaminants like arsenic and excess fluorine. The report follows a massive chemical spill in northeastern China which dumped 100 tons of benzene and other carcinogenic chemicals into the Songhua River following an explosion at a petrochemical plant. Initially local officials tried to cover up the toxic spill which eventually forced shutoff of water in the major city of Harbin and later flowed into Russian territory. 2 Arsenic Poisoning Chronic arsenic poisoning affects at least 3,000 people in Guizhou Province, southwest China (Zheng and others, 1996). Those affected exhibit typical symptoms of arsenic poisoning including hyperpigmentation (flushed appearance, freckles), hyperkeratosis (scaly lesions on the skin, generally concentrated on the hands and feet), Bowen’s disease (dark, horny, precancerous lesions of the skin), and squamous cell carcinoma. Zheng and others, (1996) have shown that chili peppers dried over open coal-burning stoves may be a principal vector for the arsenic poisoning. Fresh chili peppers have less than one part-per-million (ppm) arsenic. In contrast, chili peppers dried over high-arsenic coal fires can have more than 500 ppm arsenic. Significant amounts of arsenic may also come from other tainted foods, ingestion of dust (samples of kitchen dust contained as much as 3,000 ppm arsenic), and from inhalation of indoor air polluted by arsenic derived from coal combustion. The arsenic content of drinking water samples was below the current EPA drinking water standard of 50 ppb and does not appear to be an important factor. Detailed chemical and mineralogical characterization of the arsenic-bearing coal samples from thisregion recently was conducted by Finkelman, Belkin, Ding and coworkers (cited below). They analyzed about 50 coal samples that they had collected from several locations within Guizhou Province. Instrumental neutron activation analyses of the coal indicate arsenic concentrations as high as 35,000 ppm! The magnitude of this concentration can be seen by comparison with U.S. coals. The mean concentration for arsenic in nearly 10,000 U.S coal samples is approximately 22 ppm, with a maximum value of about 2000 ppm. In these studies polished blocks of the coal were examined using a scanning electron microscope equipped with energy-dispersive x-ray analyzer (SEM - EDS) and an electron microprobe (EMP). A wide variety of As-bearing mineral phases in the coal samples were observed. Pyrite is the most common sulfide, occurring as framboids, euhedral crystals, and irregular shapes. The range of As in pyrite determined by EMP analyses is from the detection limit (~100 ppm) in unaltered framboids to about 4.5 weight percent in grains adjacent to arsenopyrite crystals. Arsenopyrite occurs in a variety of habits, including large 150-250 m crystals, narrow, 1 to 5 m veins, and small crystals. A third As-bearing sulfide, composed of As, Pb, and S, is present rarely. Another group of As-bearing minerals contains arsenic in the 5+ valence state as arsenate commonly substituting for the phosphate group. An unidentified As-bearing iron phosphate, usually associated with banded iron oxide. Jarosite [K2Fe6 3+(SO4)4(OH)12] was present as an alteration product of sulfides or as mixtures with iron oxide and commonly contained a few weight percent As. An additional As-rich phase was only observed as scattered micron-sized grains that contained only Fe and As (± O), as identified by SEM-EDS. The atomic ratio of Fe/As in this mineral is about 1 and the mineral may be scorodite, FeAsO4 •2H2O. Three samples from the same location had As concentrations in excess of 3 weight percent and were mineralogically unusual. Although they contain small grains and veins of arsenopyrite and Asbearing pyrite, the concentration of these phases is completely inadequate to account for the As abundance on a whole coal basis. However, in SEM back-scattered electron images, a distinct banding characterized by differing image brightness is easily observed. Some of this banding forms box-like arrangements but in all cases the bands appear to have sharp edges. The bands range from a few m to tens and a few hundreds of m in thickness. SEM-EDS results show that these bright bands are highly enriched in As. In fact, there is a relationship between the EDS count intensity for As and apparent brightness of the SEM image. Semi-quantitative analysis by SEM-EDS demonstrate that the bright bands contain As at levels 3 weight percent. Fe concentrations in the bands are low but always present at levels from 0.2 to 0.4 weight percent, S is the only other major element found. Using an SEM, no discrete As-bearing phases could be resolved in these bands at 50,000 times magnification. Thin fragments of one sample were examined by an advanced fieldemission transmission electron microscope. No discrete As-bearing phase could be observed using this instrument at magnifications of 1 million times. Thus, finely-dispersed arsenopyrite, Asbearing pyrite, or any other As-phase can be ruled out as the source of the As. To define the nature of bonding in the arsenic-bearing phases, a reconnaissance study of two higharsenic samples was conducted using high-energy X-rays from a synchrotron source. Collection of diffraction spectrum intensity across the XANES (X-ray absorption near-edge structure) and EXAFS (extended X-ray absorption fine structure) regions of an absorption spectrum can provide three-dimensional information on the electronic state and chemical coordination for each crystallographic site of the chosen element. Results from this work demonstrate that ~ 100 percent of the As in one sample is AsO4 and that about 75 percent of the As in the other sample is AsO4 with the balance (25 percent) as sulfide-bound As. Thus, for the two coals examined, the preponderance of the As is in the 5+ valence state. Mineralogical characterization of the coals from Guizhou Province may help elucidate the geologic process that created the high-arsenic coals and the relationship of the high-arsenic coals to the gold. Knowledge of these processes and relationships may help determine the regional distribution of these environmentally dangerous coals. Information on the arsenic mineralogy may also help us to anticipate the behavior of arsenic during coal combustion. Preliminary characterization of residual ash in coal-burning stoves indicates high retention of arsenic. Mineralogical characterization in conjunction with combustion tests may determine if one or more of the arsenic-bearing phases is primarily responsible for adsorption of arsenic on the chili peppers.3 Arsenic in drinking water Widespread high concentrations of As generally result from natural processes, although human activities can increase arsenic concentrations. The most prevalent causes of widespread high concentrations are release from iron oxide and sulfide mineral oxidation. Up flow of geothermal water and evaporative concentration also can produce high arsenic concentrations in ground water. Arsenic can be released to ground water by desorption from, and dissolution of, iron oxide. Aquifers with toxic ground water commonly contain iron oxide with arsenic as an impurity. Desorption of arsenic can be promoted by either an increase in pH or the concentration of a competing ion, such as phosphorous. Arsenic also can be released from iron oxide because of chemical reduction of the oxide. Deposition of Fe-coated sediment along with organic matter can lead to the dissolution of the oxide coating with consequent release of arsenic to ground water. Introduction of synthetic organic compounds into aquifers also can lead to reductive dissolution of iron oxide and arsenic release. Pyrite commonly contains arsenic in trace amounts, although arsenic concentration can exceed five percent. The rate of sulfide-mineral oxidation is limited by the supply of an oxidizing agent, most commonly molecular oxygen. High nitrate concentrations from agricultural activities also can oxidize sulfide minerals. Human activities that increase the supply of oxygen, or another oxidizing agent such as nitrate, to ground water can lead to increased mineral oxidation and, consequently, high arsenic concentrations. Irrigation in arid and semi-arid regions can increase evaporative concentration, which can lead to high arsenic concentrations.4 ARSENIC CYCLING ARSENIC CONCENTRATION FROM DIFFERENT SOURCES IN THE WORLD High As concentrations have been found in groundwater from Inner Mongolia, Xinjiang and Shanxi Provinces, China (Smedley, et al., 2001; Niu, et al., 1997). The first cases were recognized in Xinjiang Province in the early 1980s (Smedley and Kinniburgh, 2002). Wang (1984) found As concentrations up to 1200 µg L in groundwater from the province. Wang and Huang (1994) reported As concentrations of between 40 and 750 µg in deep artesian groundwater from Dzungaria Basin on the north of the Tianshan Mountains. Artesian groundwater has been used for drinking in the region since 1960, and chronic health problems have been identified as a result (Wang and Huang, 1994). It is reported that in the vicinity of an As mine in Hinan, China, nearly 35% of the local population had severe arsenism, and that percentage increased with age (Geng, et al., 2005). It is believed that the soil-plant transfer pathway is mainly responsible for human exposure to As (Geng, et al., 2005).5 Chemistry of Arsenic Arsenic is present in aqueous environment in +III and +V oxidation states. Principle source of arsenic is the oxidation of sulfidic minerals like arsenopyrite, FeAsS. In oxidizing environment the principle attenuation mechanism of arsenic migration is its adsorption on Fe(OH)3. Adsorption affinity is higher for As5+ than for As3+ and both are pH-dependent. Maximum adsorption for As5+ occurs at pH about 4.0 and for As3+ about 7.0 (Pierce and Moore, 1982). However, Fe(OH)3 is unstable mineral phase which dissolves when Eh and pH decrease and releases adsorbed arsenic. Decreasing values of Eh are generally related to high organic matter content in sediments or to anthropogenic contamination by organic contaminants like BTEX (Benzen, Toluen, Ethylbenzen, Xylen) group. Organic matter in sediments or dissolved organic contaminants are electron donors during reductive dissolution of Fe(OH)3. This process is responsible for high dissolved arsenic concentrations in Bangladesh and West Bengal, India (Nickson et al. 1998). Reduction of pH is often related to penetration of acid contamination like acid mine drainage to an aquifer. There is dissolution of Fe(OH)3 at pH0. Typical examples of forward codes are MINTEQA2 (Allison et al. 1995) and PHREEQC (Parkhurst, 1995). Coupled transport and chemical models are being developed and some of them like mixing cells models PHREEQC-2, (Parkhurst and Appelo, in press), can be used to determine number of flushing cycles necessary for desorption of arsenic. Investigation of Arsenic Integrated approach to arsenic investigation including geochemical modeling with adsorption modeling was presented by Welch and Lico (1998). Site of investigation was the Southern Carson Desert in arid zone of Nevada. They used sequential extraction to determine carbonate and hydroxide fractions with arsenic in sediments. Speciation modeling was used to calculate saturation indices for minerals like siderite and rhodochrosite which can decrease concentrations of dissolved iron and manganese. Code WHAM (Tipping, 1994) with organic data base was used to estimate complexation of iron with organic matter. Forward adsorption modeling was used to model adsorption of arsenic in competition with other dissolved species like phosphate and silica. Results of the investigation indicated a significant role of evaporation and reductive dissolution of ferric oxyhydroxides in high dissolved arsenic concentrations.6 Result and conclusion A potential hazard to Beijing was revealed due to the accumulation trend of heavy metals in agricultural soils with sewage irrigation, which results in metal contamination and human exposure risk. Samples including soils and plants were collected to assess the impacts of sewage irrigation on the irrigated farming area of Beijing. Concentrations of the five elements Cd, Cr, Cu, Zn, and Pb were determined in samples to calculate the accumulation factor and to establish a basis for environmental protection and the suitability of sewage irrigation for particular land use in the urban-rural interaction area of Beijing. Using reference values provided by the Beijing Background Research Cooperative Group in the 1970s, the pollution load index (PLI), enrichment factor (EF), and contamination factor (CF) of these metals were calculated. The pollution load indices (sewage irrigation land 3.49) of soils indicated that metal contamination occurred in these sites. The metal enrichment (EF of Cd 1.8, Cr 1.7, Cu 2.3, Zn 2.0, Pb 1.9) and the metal contamination (CF of Cd 2.6, Cr 1.5, Cu 2.0, Zn 1.7, Pb 1.6) showed that the accumulation trend of the five toxic metals increased during the sewage irrigation as compared with the lower reference values than other region in China and world average, and that pollution with Cd, Cu, Zn, and Pb was exacerbated in soils. The distributions of these metals were homogeneous in the irrigation area, but small-scale heterogeneous spatial distribution was observed. Irrigation sources were found to affect heavy metal distributions in soils. It was suggested that heavy metal transfer from soils to plants was a key pathway to human health exposure to metal contamination. However, with the expansion of urban areas in Beijing, soil inhalation and ingestion may become important pathways of human exposure to metal contamination. The rapid economic development in the Pearl River Delta (PRD) region in South China in the last three decades has had a significant impact on the local environment. Estuarine sediment is a major sink for contaminants and nutrients in the surrounding ecosystem. The accumulation of trace metals in sediments may cause serious environmental problems in the aquatic system. Thirty sediment cores were collected in the Pearl River Estuary (PRE) in 2000 for a study on trace metal pollution in this region. Heavy metal concentrations and Pb isotopic compositions in the four 210Pb-dated sediment cores were determined to assess the fluxes in metal deposits over the last one hundred years. The concentrations of Cu, Pb and Zn in the surface sediment layers were generally elevated when compared with the sub-surface layers. There has been a significant increase in inputs of Cu, Pb and Zn in the PRE since the 1970s. The results also showed that different sampling locations in the estuary received slightly different types of inputs. Pb isotopic composition data indicated that the increased Pb in the recent sediments was of anthropogenic origin. The results of trace metal influxes showed that about 30% of total Pb and 15% of total Zn in the sediments in the 1990s were from anthropogenic sources. The combination of trace metal analysis, Pb isotopic composition and 210Pb dating in an estuary can provide vital information on the long-term accumulation of metals in sediments.8 REFERENCE 1 China’s Imminent Water Crisis (news.mongabay.com,May 30, 2005 ) 2 China Faces Water Crisis -- 300 million drink unsafe water Tina Butler, mongabay.com December 30, 2005 (news.mongabay.com) 3 Arsenic poisoning caused by residential coal combustion in Guizhou Province, China Robert B. Finkelman1, Harvey E. Belkin, Baoshan Zheng, and Jose A. CentenoU.S. Geological Survey, Reston, VA, 2Institute of Geochemistry, Guiyang, P.R. China, Armed Forces Institute of Pathology, Washington, DC 4 Arsenic in Ground Water: A Perspective from the United States of America Alan H. Welch U.S. Geological Survey, 333 W. Nye Lane, Carson City, NV 89706 5 Recent Developments on Arsenic: Contamination and Remediation M.E. Ortiz Escobar N.V. Hue and W. G. Cutler. Department of Tropical Plant and Soil Sciences, University of Hawaii; Environmental Resources Management and University of Hawaii 6 Geochemical modeling applications in investigation of arsenic behavior A. Sracek, P. Bhattacharya, G. Jacks, J.P. Gustafssonand M. von Brömssen Department of Hydrogeology, Eng. Geology and Applied Geophysics, Faculty of Science, Charles University, Prague, Czech Republic, Department of Civil Engineering, Pontificial Catholic University, Rio de Janeiro, RJ Brazil,. 3Division of Land and Water Resources, Kungliga Tekniska Högskolan, SE-100 44 Stockholm, Sweden, Scandiaconsult Sverige AB, Stockholm, Sweden. 7 Impacts of sewage irrigation on heavy metal distribution and contamination in Beijing, China. Lin WH, Zhao JZ et al Research Center for Eco-Environment Sciences, Chinese Academy of Sciences, Beijing, China. 8 Over one hundred years of trace metal fluxes in the sediments of the Pearl River Estuary, South China. Ip CC, Li XD, Zhang G, Farmer JG, Wai OW,Li YS Department of Civil and Structural Engineering, The Hong Kong Polytechnic University, Hung Hom, Kowloon, China. Read More