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Arsenic

Overview
 
CAS Number: 7440-38-2
Synonyms: Arsenate, Arsenite, As(3), As(5)
Contaminant Type: Chemical

Arsenic occurs naturally in rock, soil and biota, all of which release it to water. In water, inorganic forms are more common in than organic forms. [595]

Most (90 percent) arsenic use in the US is for the wood preservative chromated copper arsenate (CCA). Other uses include paint, pharmaceuticals, dyes and semi-conductors. [592] Improper discharges can release arsenic into water. Other releases may come from industrial process including burning of fuels, mining, smelting and paper production. [595]

As(3) is the predominant ground water form. In surface waters, As(5) is the predominant form as surface aeration oxidizes As(3) to As(5). [591] Factors affecting the fate and transport of arsenic in water include its oxidation state, oxidation-reduction potential, pH, the levels of iron and sulfide, temperature, salinity and biota. [595] Arsenic is also impacted by the presence of suspended solids. In surface water, arsenic is more likely sorbed to particulates than dissolved. [595]

Arsenic is linked to cancer of the bladder, lungs, skin, kidneys, liver and prostate and has non-carcinogenic cardiovascular, pulmonary, neurological and endocrine effects. [592] The maximum contaminant level (MCL) is to protect against effects of bladder and lung cancers, and to reduce the non-carcinogenic effects. [594]

Total arsenic is regulated in drinking water in the US with a MCL of 0.10 mg/L or 10 ug/L. USEPA has identified several treatment processes as Best Available Technologies (BATs)for control of arsenic in drinking water. They are: ion exchange, activated alumina, reverse osmosis, coagulation/filtration, lime softening (pH exceeding 10.5), electrodialysis reversal, and oxidation/filtration or iron removal (Fe:As greater than 20:1). [597] The BATS are based on the removal of As(5).

For purposes of research and design of treatment processes, the speciation of As(5) and As(3) needs to be known as do the soluble and particulate fractions. Measuring total arsenic, and passing the sample through a 0.45 micron filter to collect the soluble fraction, and passing the soluble fraction through an ion exchange column which retains As(5) allows for speciation and fractionation.

Arsenic in both surface water and in ground water is typically less than 10 ug/L. [591] A 1995 survey of arsenic in California waters found a median of 2 ug/L, and found that arsenic exceeded 5 ug/L or greater in 12 percent of wells. [591] Estimates of requirements to meet the 10 ug/L MCL are 7.6 percent of US ground water supplies [596] and 5.5 percent of community water systems (3,000 of the nation's 54,000). [592]

Because of the relatively large number of water systems that will have to meet the 10 ug/L MCL, the USEPA has established an Arsenic Demonstration Program involving 50 locations across the US and numerous treatment technologies including ion exchange, adsorptive media, coagulation/filtration, activated alumina, and oxidation/filtration. [593]

Date of Literature Search: March 2007



591 California EPA; 2004; Public Health Goal For Arsenic in Drinking Water; Public Health Goal For Arsenic in Drinking Water; Office of Environmental Health Hazard Assessment, California Environmental Protection Agency, Sacramento, CA.
592 USEPA; 2007; Technical fact sheet: final rule for arsenic in drinking water; http://www.epa.gov/safewater/arsenic/regulations_techfactsheet.html; As posted on August 28, 2007. EPA 815-F-00-016. Office of Ground Water and Drinking Water, USEPA, Washington, DC.
593 USEPA Office of Research and Development; 2007; Arsenic Research; http://www.epa.gov/nrmrl/wswrd/dw/arsenic/; As posted on August 28, 2007. Office of Research and Development, USEPA, Cincinnati, OH.
594 USEPA; 2001; Arsenic and Clarifications to Compliance and New Source Monitoring Rule: A Quick Reference Guide; Arsenic and Clarifications to Compliance and New Source Monitoring Rule: A Quick Reference Guide; EPA 816-F-01-004. Office of Ground Water and Drinking Water, USEPA, Washington, DC.
595 USEPA; 2000; Arsenic Occurrence in Public Water Supplies; Arsenic Occurrence in Public Water Supplies; EPA-815-R-00-023. Office of Ground Water and Drinking Water, USEPA, Washington, DC.
596 Focazio, M., Welch, A., Watkins, S., Helsel, D. and Horn, M.; 2000; A retrospective analysis on the occurrence of arsenic in ground water resources of the United States and limitations in drinking water supply; A retrospective analysis on the occurrence of arsenic in ground water resources of the United States and limitations in drinking water supply; WRIR 99-4279, US Geological Survey, Reston, VA.
597 USEPA; 2002; Implementation Guidance for the Arsenic Rule; Implementation Guidance for the Arsenic Rule; EPA-816-K-02-018. Office of Ground Water and Drinking Water, Washington, DC.



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