Arsenic Poisoning

Arsenic is a common natural and anthropogenic contaminant in sediments, surface waters, and ground waters. In Taiwan, Bangladesh, and the United States arsenic poisoning has been linked to disorders such as hyperpigmentation (Black-foot disease), Peripheral Vascular Disease, skin and bladder cancer, and gangrene ^2,3. Sporadic occurrences of Black-foot disease occurred in southwest Taiwan in the early twentieth century with a peak incidence in the late fifty’s ². The cause of this arsenic poisoning was due to resident’s use of contaminated artesian wells ². Arsenic poisoning incidents reduced significantly when residents began switching to tap water in the endemic villages ². Awareness of this outbreak caused the EPA cancer risk assessment to use the cancer data from Southwest Taiwan to predict the cancer risk assessment in the United States ^4,6. Recently changes in water quality standards in America along with greater understanding of arsenic toxicity have increased the necessity for methods of determining potentially bioavailable arsenic in field environments as well as characterization in natural environments.

Complex geochemical and biological mechanisms control the distribution of arsenic within repositories in the biosphere, hydrosphere, and lithosphere. Arsenic in water is primarily found in two oxidation states, As (III) and As (V) ¹. As (III) is considered more toxic than As (V), and is generally less mobile. Therefore, under many conditions As sequestion is undergone through reduction. This, however, is problematic because reducing environments release arsenic from arsenic bearing minerals such as oxyhydroxides. This is exactly what happened in Bangladesh when buried deposits of peat acted as electron donors for the reduction of arsenic bearing Goethite into the groundwaters^3. Controls on the distribution of arsenic include: redox conditions, pH, presence of Iron and Manganese Oxyhydroxides, and metabolic activities of microorganisms. Iron oxides, however, generally control arsenic speciation in near-surface environments ¹. Iron, when present, in the environment, controls the mobility, fate, and bioavailability of aqueous arsenic species by converting bioavailable arsenite (AsO₃^3-) and arsenate (AsO₄^3-) species to immobilized forms adsorbed or coprecipitated in iron oxides ¹. Chemical availability of As is an indirect measure of bioavailability. Bioavailability refers to the concentration of a target chemical that actually enters the systemic circulation of an organism from an administered dose⁵. (commonly considered the total concentration of the chemical present in the organism’s environment). It is generally assumed that dissolved phases are most bioavailable ⁵. Chemical availability of As is dependent on speciation. Therefore, when the speciation of arsenic in a soil system is known the chemical availability becomes a good indicator of bioavailability.

The World Health Organization estimates that 41 million people worldwide (some sources estimate 57 million) are drinking groundwater contaminated by arsenic at unsafe levels ¹⁰. In Taiwan alone approximately 2 million people are potentially exposed to polluted water ⁹. Arsenic, although rare in natural abundance in the lithosphere, is common in sulfides such as chalcopyrite, realgar, orpiment, galena, marcasite, arsenopyrite, enargite, and it has a strong affinity for pyrite, one of the world’s most common minerals ⁹. It is also common in other minerals through substitution. Arsenic in groundwater is often the result of dissolving weathered rock and soils or through reduction of iron oxides. In the case of the massive epidemic in Bangladesh the arsenic is released to the groundwater through goethite (FeOOH) reduction ⁴. Which is driven by microbial degradation of buried deposits of peat. The peat acts as an electron donor so that iron oxide reduction can take place.

Arsenic is often added to groundwater through anthropogenic sources such as use in alloying agents, wood preservatives, mineral extraction and processing wastes, poultry and swine feed additives, pesticides, and highly soluble arsenic trioxide stockpiles ^1,9. The most globally significant anthropomorphic source of arsenic is probably through combustion of fossil fuels ¹². The arsenic mainly appears as arsenite in the dust and travels through the atmosphere releasing arsenic throughout the globe. In 1988 Nriagu and Pacyna estimated that as much 70% of the global atmospheric As flux is anthropogenic. In the past arsenic acid was even used as a cotton defoliant in the southern part of the United States ¹¹.

Globally, millions of people are at risk for the adverse effects of arsenic exposure. Contaminated drinking water is usually contaminated through inorganic arsenic. Inorganic arsenic is more acutely toxic that organic arsenic species ^2,3. Other countries than Taiwan and Bangladesh that currently face arsenic exposure include: Argentina, Cambodia, Chile, China, Ghana, Hungary, India, Mexico, Vietnam, Tibet, Thailand, as well as the United States ^1,2,3,9. As the world population increases beyond 6 billion clean drinking water is quickly becoming one of globe’s most valuable resources. In order to protect our drinking water we must continue to study and understand contaminants of all varieties. This is a fundamental mission and goal of the applicant’s research group at Texas A&M University. This project will directly aid in this endeavor. Additionally, the international component to the proposed research will serve as a reminder to the scientific community of the importance in scientific collaboration and goodwill across global borders in solving the world’s environmental issues.

 This post is an excerpt from a copywritten article written by Clint Miller. All quotes must be cited to me.

Evaluating Arsenic Availability in Taiwanese Soils using DOWEX M4195, Fe³⁺ Substituted, Resin; Clint Miller; NSF EAPSI Grant Application; 2007

References

1. A review of the source, behaviour and distribution of arsenic in natural waters; P.L. Smedley*, D.G. Kinniburgh, Applied Geochemistry 17 (2002) 517-568

2. Long-term arsenic exposure and ischemic heart disease in arseniasis-hyperendemic villages in Taiwan, Chin-Hsiao Tseng, Choon-Khim Chong, Ching-Ping Tseng, Yu-Mei Hsueh, Hung-Yi Chiou, Ching-Chung Tseng, and Chien-Jen Chen; Toxicology Letters, Volume 137, Issues 1-2, 31 January 2003, Pages 15-21

3. Arsenic poisoning in groundwater: Health risk and geochemical sources in Bangladesh, H. M. Anawar, J. Akai, K. M. G. Mostofa, S. Safiullah, and S. M. Tareq; Environment International, Volume 27, Issue 7, February 2002, Pages 597-604

4. Significance of Exposure Assessment to Analysis of Cancer Risk from Inorganic Arsenic in Drinking Water in Taiwan; Kenneth G. Brown and Chien-Jen Chen; Risk Analysis, Volume 15 Issue 4 Page 475-484, August 1995

5. An In Vitro Gastrointestinal Method To Estimate Bioavailable Arsenic in Contaminated Soils and Solid Media; Rodriguez, R. R.; Basta, N. T.; Casteel, S.; S. W.; Pace, L. W.; Environmental Science & Technology, 1999, 33, 642-649

6. Inorganic arsenic: a need and an opportunity to improve risk assessment; W R Chappell, B D Beck, K G Brown, R Chaney, R Cothern, C R Cothern, K J Irgolic, D W North, I Thornton, and T A Tsongas; Environ Health Perspect. 1997 October; 105(10): 1060-1067.

7. Quantification of Potential Arsenic Bioavailability in Spatially Varying Geologic Environments at the Watershed Scale using Chelating Resins; Lake, G. E.; M.A. Thesis, Texas A&M University, 2002), 227 pp

8. Assessment of the phytotoxicity of chromium in soils using the selective ion exchange resin extraction method; Pei-Fang Yu, Kai-Wei Juang and Dar-Yuan Lee; Plant and Soil 258: 333-340, 2004.

9. Contamination of drinking-water by arsenic in Bangladesh: a public health emergency; Allan H. Smith; Elena O. Lingas; Mahfuzar Rahman; Bulletin of the World Health Organization; Print ISSN 0042-9686; Bull World Health Organ vol. 78 no. 9 Genebra 2000

10. Worldwide Occurrences of Arsenic in Ground Water; D. Kirk Nordstrom, SCIENCE VOL 296, 21 JUNE 2002; 2143-2145

11. Occurrence and Distribution of Arsenic in Soils and Plants; Leo M. Walsh; Malcolm E. Sumner; Dennis R. Keeney; Environmental Health Perspectives, Vol. 19. (Aug., 1977), pp. 67-71

12. Quantitative assessment of worldwide contamination of air, water, and soils by trace metals; Nriagu, J.O., Pacyna, J.M., Nature 333, 134-139; 1988