The element arsenic occurs naturally in dif-ferent forms, which may be classifiedeither as organic or inorganic. Arsenic is

distributed widely in rocks, soil, water and air—andin living things. Arsenic can be released to the envi-ronment as a result of natural events or its releasecan be caused by human activities. Natural concen-trations of arsenic in soil typically range from 0.1 to40 parts per million (ppm), with an average concen-tration of 5 to 6 ppm. Through erosion, dissolutionand weathering, arsenic can be released from theEarth’s crust into groundwater or surface water.Geothermal waters (e.g., “hot springs”) also canrelease arsenic into groundwater, particularly in theWestern United States. Other natural sources ofarsenic include volcanoes and forest fires.In nature, arsenic can be found in many forms, bothorganic and inorganic. Inorganic arsenic is generat-ed when arsenic binds with elements such as oxy-gen, chlorine and sulfur. Arsenic is usually found in inorganic forms inwater, the most predominant form being arsenate[As(V)], although arsenite [As(III)] may be presentunder some conditions. When arsenic is found inplants and animals, it bonds with carbon and hydro-gen, forming organic arsenic. Organic arsenic is usually less harmful than inor-ganic arsenic, although exposure to high levels ofsome organic arsenic compounds may cause similareffect to those from inorganic arsenic.

Drinking Water Problems: Arsenic

Bruce J. Lesikar, Professor and Extension Agricultural Engineer, Texas Cooperative Extension, Rebecca H. Melton, Extension Assistant, Texas Cooperative Extension,

The Texas A&M University SystemMichael F. Hare, Senior Natural Resources Specialist, Pesticide Programs Division,

Texas Department of AgricultureJanie Hopkins, Manager, Groundwater Monitoring Section,

Texas Water Development Board, Monty C. Dozier, Assistant Professor and Extension Specialist,

Texas Cooperative Extension,The Texas A&M University System

L-546711-05

'

In water, arsenic can undergo a series of changes,including oxidation-reduction reactions (an arsenicatom taking electrons from another atom or losingthem to another atom), ligand exchanges (electronexchanges involving other atoms which are com-bined with a central arsenic atom), and biotransfor-mations (chemical changes to arsenic atoms withinthe body of a living thing). For example, manyarsenic compounds can dissolve in water, so fishand shellfish can accumulate arsenic, but most ofthis arsenic will be bound in a form that is notharmful to other animals.An arsenic atom’s oxidation state (either its combi-nation with oxygen or its loss of electrons, makingthe atom positive in charge) and its oxidation-reduc-tion potential (its willingness to exchange electronswith other atoms) affect its fate and its transportprocesses in groundwater. The following character-istics of water also have been identified as affectingthe transport and disposition of arsenic:

• the acidity or alkalinity of the water (pH)• amount of iron in the water• amount of metal sulfide and sulfide in the

water• water temperature and salinity• distribution and composition of the living

things present in the waterOxidation state appears to be the most importantfactor determining arsenic’s fate and its transport

The resulting effects of arsenic exposure maydepend on a person’s sex, ethnicity, age, health andnutritional status and especially the concentration inthe water and duration of exposure. When high lev-els of arsenic (concentrations above 60milligrams/liter) are ingested over a short period,acute poisoning occurs. Acute poisoning can kill. Nonlethal symptoms of acute poisoning include:

• Gastrointestinal effects such as nausea, vomit-ing, abdominal pain and severe diarrhea

• Swelling of tissue around the eye • Decreased production of red and white blood

cells• Abnormal heart rhythms• Damage to blood vessels• Tingling in hand an feet (“pins and needles”)

Arsenic levels are rarely high enough in drinkingwater supplies to result in acute poisoning.Chronic ingestion of low levels of inorganic arseniccan cause skin to darken and small “corns” or“water” to form on palms, soles and torso. Long-term exposure can also lead to gastrointestinalsymptoms, diabetes, anemia, cardiovascular, pul-monary, neurological effects and liver disease.Manifestations of these effects can include noncir-rhotic portal hypertension (high blood presser in theblood vessels of the liver in the absence of the livediseases known as cirrhosis), bleeding esophagealvarices (bulging veins in the esophagus),splenomegaly (enlarged spleen), hyperspenism(spleen destroying more blood cells than usual),metallic taste in mouth, Mee’s lines in nail beds,bone marrow depression (less production of bloodcells) and peripheral neuropathy. Contact with inor-ganic arsenic may cause skin to turn red and swell.Workplace exposure or chronic ingestion of arsenic-contaminated water or medications containingarsenic also is associated with development of skin,lung and other cancers. Several studies have shownthat inorganic arsenic can increase risk of lung can-cer, skin cancer, bladder cancer, liver cancer, kidneycancer and prostate cancer. The World HealthOrganization (WHO), the United States Departmentof Health and Human Services (DHHS), and the EPAhave determined inorganic arsenic to be a humancarcinogen.It is not known if arsenic exposure causes birthdefects or other developmental effect in people,although birth defects have been observed in ani-mals exposed to high amounts of inorganic arsenic.It seems likely that health effects seen in childrenexposed to high amounts of arsenic will resembleeffects seen in adults exposed to high amounts.

through drinking-water treatment systems. Arsenateis removed more easily than arsenite, because of itsgreater ionic charge. Treatment procedures usingactivated alumina, ion exchange, and reverse osmosistechnologies can achieve relatively high arsenateremoval rates. However, these technologies do notachieve comparable removal rates for arsenite,although its oxidization to arsenate (removal of twomore electrons from each atom) can improveremoval efficiencies. If arsenite is found in thesource water, an oxidation step should be added tothe treatment system before the arsenic removalunit.

What are the agricultural usesof arsenic?

Most agricultural uses of arsenic have been bannedin the United States. The last agricultural use of inor-ganic arsenic, arsenic acid on cotton, was canceledvoluntarily in 1993. Inorganic arsenic compounds(arsenic acid, arsenic trioxide and sodium arsenate)currently are used only in sealed ant baits and inwood preservatives. Organic arsenic is found in the organic herbicidesmonosodium methanearsonate (MSMA) and disodi-um methanearsonate (DSMA), which currently areapplied to cotton fields or used for the postemer-gence control of crabgrass, Dallisgrass and other turfweeds. Organic arsenic also is found in feed addi-tives for poultry and swine and appears to concen-trate in the wastes of these animals. Soil bacteriaturn organic arsenic compounds in soil into alky-larsines and arsenate; no published data currentlyare available on the leaching or transport of MSMAor DSMA from soil.

How can arsenic affect health? Rats require tiny amounts of arsenic for normaldevelopment of their fetuses, and there is limitedevidence that trace amounts of arsenic may be bene-ficial for humans and animals. In most cases, infre-quent ingestion of water containing relatively lowlevels of arsenic can be converted by the body toorganic forms and passed through the body withoutan adverse impact. However, exposure to elevated levels of inorganicarsenic can be harmful to the body. Although thenew Maximum Contaminant Level (MCL) for arsenicis 10 micrograms /liter, the United StatesEnvironmental Protection Agency (EPA) estimatesthat about 350,000 people in the United States maydrink water containing more than 50micrograms/liter of arsenic, and nearly 25 millionpeople may drink water containing more the 25micrograms/liter.

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Tests can measure arsenic levels in blood, urine, hairor fingernails, with urine tests the most reliable indi-cator of arsenic exposure within the last few days.Tests on hair and fingernails can measure exposureto high levels of arsenic over the post 6 to 12months. These tests can determine exposure toabove-average levels of arsenic but cannot predicthow such arsenic levels will affect health.

What is the standard for arsenic levels in drinking water?On January 22, 2001, the EPA lowered the amountof allowable arsenic in public drinking water from50 micrograms/liter to 10 micrograms/liter. U.S. pub-lic water systems must comply with this new stan-dard beginning January 23, 2006. With this decreasein the Maximum Contaminant Level (MCL), the like-lihood of exceeding the new standard increases.Public systems with arsenic levels exceeding thenew MCL will be required either to treat their wateror to find alternative sources of supply. Compliancewith this 80 percent decrease in MCL presents achallenge to water treatment systems because of itstoxicological, economic and infrastructure implica-tions. While compliance will decrease consumers’exposure to arsenic, it will increase their watercosts. MCLs apply only to public water supplies. Home-owners’ private wells are not regulated, which meansthat such homeowners may be consuming water witharsenic concentrations exceeding official standards.Private well owners must decide whether to test theirwell water, then treat it if necessary. Testing wellwater for arsenic typically costs about $25. Wells with high arsenic levels sometimes aregrouped in a particular area, so the Texas WaterDevelopment Board (TWDB) recommends that youinform your neighbors if tests of your water revealhigh levels of arsenic and that all residents in thearea with private water supplies send samples oftheir water to state-certified laboratories to be testedfor arsenic contamination. A list of labs certified bythe Texas Commis-sion on Environmental Quality(TCEQ) for testing public drinking-water suppliescan be found at http://www.tnrcc.state.tx.us/permit-ting/waterperm/ pdw/chemlabs.pdf.

Where have high levels ofarsenic been found in Texas?

The TWDB collects groundwater samples through itsGroundwater Quality Sampling Program. Between1983 and 2004, the agency analyzed nearly 15,000samples from more than 10,000 wells for arsenic con-tamination (some wells were sampled more than

once); 69 percent of the 15,000 samples had unde-tectable levels of arsenic. For the 4,642 water samples with detectable arsenicconcentrations, the median arsenic level was 5 micro-grams/liter, meaning that half the samples had con-centrations greater than 5 micrograms/liter and halfthe samples had concentrations less than 5 micro-grams/liter. Twenty-seven percent of these samplescontained arsenic in excess of 10 micrograms/liter,the new EPA standard. Of the nearly 900 water wellswith concentrations exceeding the new primary stan-dard of 10 micrograms/liter, approximately 30 percentprovided water to households, 24 percent to publicsupply facilities, 18 percent to irrigation wells, 16 per-cent to stock wells, and 5 percent to other uses,including industrial and commercial facilities; 7 per-cent of these wells were unused. High arsenic con-centrations that are believed to be naturally occurringhave been found in the southern High Plains(Ogallala aquifer), in several West Texas counties (var-ious aquifers) and in south Texas (Gulf Coast aquifer)(Fig. 1). Some data reported to the TCEQ about public drink-ing-water systems (not shown in Fig. 1) also indicatehigh arsenic concentrations, mainly in the Ogallalaand the Gulf Coast aquifers. For example, Harris-Brazoria-Galveston-area public water systems usingsignificant proportions of groundwater report arseniclevels in excess of 10 micrograms/liter (Regner et al.,2004).

What can water well owners doabout arsenic contamination?

Well owners need to consider the following options iftheir well water is found to contain excessive levelsof arsenic:

• Purchase bottled water for drinking andcooking. Unless their water source has arseniclevels greater than 500 micrograms/liter, theymay safely use their well water for non-con-sumption activities such as showering, bathing,and washing clothes.

• Connect to a public water system. All com-munity water-supply systems are tested regular-ly for arsenic and other contaminants, and suchsystems should be in compliance with EPA regu-lations in 2006.

• Extend the existing well’s casing or drill anew well into different water-bearing for-mations, possibly reducing arsenic levels.Well designs may lower arsenic concentrations ifthey access a different aquifer or allow mixingof water from different levels in an aquifer.

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• Purchase treatment systems. Well ownerschoosing this option should test their wateragain to determine if other constituents dis-solved in their water also exceed drinking-water standards. Even if levels of other con-stituents are found to comply with drinkingwater standards, these constituents may inter-fere with proposed arsenic remediation sys-tems. Iron and manganese, for example, hindereffective arsenic treatment and should beremoved before arsenic treatment begins. Wellowners also must consider whether treatmentshould occur at each tap (point-of-use) orbefore entry to the residence (point-of-entry),given the different treatment systems availablefor each option.

What treatment methods arecommonly used by

private well owners? (Adapted from USEPA, 2003)

Common treatment methods used to remove arsenicfrom well water include adsorption columns, reverseosmosis, distillation and ion exchange. Before install-ing a particular treatment system, well ownersshould be certain that it will meet their needs. Theyshould work with reputable dealers familiar withthe areas where their wells are located and find outthe amount of arsenic a treatment system willremove, its maintenance requirements and its costs.Treatment systems certified by an independentagency such as the National Sanitation Foundation(NSF) usually effectively live up to manufacturer’sclaims. After well owners install a treatment system,they should test their water periodically to ensurethat arsenic is being removed.

Adsorption ColumnModified activated alumina and iron-based sorbentsare among the adsorptive materials that can be usedto remove arsenic from water. The advantages of

using an adsorption column operationinclude simple operation,

low maintenance,low relative costdepending upon car-tridge replacementfrequency, smallunder-the-counter

footprint, hightreatment capac-ity and slowbreakthrough

kinetics. Arsenicthat has passeduntreated

through anadsorption column

unit is detected morereadily by routine monitor-

ing than in systems with rapidbreakthrough. To prevent untreat-

ed arsenic from leaking into drinkingwater, well owners can use metered car-

tridges that will shut off the system outletonce a designated volume of water haspassed through the treatment unit.Initial capital cost of an adsorption unitranges from $100 to $300. Operation andmaintenance costs will include water

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Figure 1. Arsenic content in groundwater sampled from1983 to 2004 by the TWDB.

sampling and laboratory analysis and replacementof pre-filters and membrane cartridges, as well asother regular maintenance.

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Figure 2. Adsorption Treatment (Adapted from USEPA,2003).

Figure 3. Reverse Osmosis Treatment Unit (Adaptedfrom Kneen et al., 1995 and USEPA, 2003).

poses each day. Typical treatment-unit productionrates range from 5 to 15 gallons of water per day.The typical cost range of RO devices is from $300 to$1,000. The RO unit’s membrane should be replacedaccording to the manufacturer’s recommended sched-ule. New membranes cost about $150, and a carbon-based pre-filter typically costs between $15 and $50.Depending on the system, based on a 10-year average,cost of water production ranges from 5 to 10 cents/gal-lon, not including the cost of water wasted or the cost,if any, of treating wastewater from the RO unit.

Reverse Osmosis (RO)RO treatment units are recommended for use witharsenic-rich water containing high levels of sulfates,phosphates or dissolved solids. When operated attypical tap pressures, some RO devices remove morethan 95 percent of the arsenate present (90 percentof arsenite). An RO unit passes water under pressurethough a semi-permeable membrane. This mem-brane allows water to pass through but preventsarsenic from doing so. Most units will have

• A pre-filter to remove solids and extend mem-brane life.

• An activated carbon filter to remove odors,taste and chlorine.

• A semi-permeable membrane.• A tank to hold the treated water.• A drain connection for discharging wastewater

generated.However, RO units achieve relatively poor waterrecovery. Most units are designed to recover 20 to 30 percent of the water treated. For example, if 100 gallons are treated, only 20 to 30 gallons will beuseable; the rest of the water will be sent to thewastewater treatment system. Homeowners using on-site wastewater treatment systems should considerthe impact additional loading from an RO unit mayhave on their septic systems. Because of RO systems’inefficiency, such units typically are used to treat onlydrinking and cooking water, so system size should bebased on the number of gallons used for these pur-

DistillationDistillation reduces arsenic levels from a watersource. In the distillation process, water is heated toboiling in an enclosed container, with impurities leftbehind as the water evaporates. The resulting steamthen cools and condenses back into a liquid. Thus,dissolved gases and compounds that volatilize nearthe boiling point of water will be carried with thesteam and end up in the treated water. Such contami-nants can be removed by passing the distilled waterthrough a post-filter. Most distillation units can treat5 to 11 gallons of water a day. Distillation units can be purchased for between $300and $1200. However, operating costs for distillationsystems may be higher than for other treatmentmethods due to the large amounts of electricityrequired to operate the distiller. Energy costs can beestimated using the following formula:

Wattage of unitCost/gal = 0.024 X X cost of electricity ($/kWh)

Production (gal/day)

other breakthrough events can occur very quickly,effluent from an IE treatment unit should be moni-tored frequently to ensure the unit is operating prop-erly. In addition to ongoing costs of monitoring and forresin replacement, an ion exchange unit initiallycosts somewhere between $400 and $1500.

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Figure 5. Ion Exchange Process (Adapted fromRobillard et al., 2001).

Arseniccontaminated

waterTreatedwater

Arsenic

Chloride or hydroxide

Exchange resin

Figure 4. Distillation Process (Adapted from Kocher etal., 2003).

Ion Exchange (IE)Ions are charged particles. Because arsenate forms ananion (negatively charged ion), it can be removedfrom water through an ion exchange process (IE). Thisprocess removes arsenic from a water source by pass-ing the water under pressure through one or morecolumns packed with an exchange resin. The resintypically used for arsenic treatment is a strong-baseion exchange resin in either a chloride or a hydroxideform. As an arsenic ion (arsenate) moves across theresin, a chloride or a hydroxide ion is released fromthe resin and the arsenate takes its place, because theresin exchange site attracts the arsenic ion morestrongly than the ion it replaced. Replacement of allthe original ions saturates the resin column, and itmust be regenerated or replaced.For treatment ofarsenic, resin recharging can be done only at specialfacilities, making IE treatment expensive.If the water source contains iron, more than 500 mg/Lof total dissolved solids (TDS), more than 50 mg/L ofsulfate (SO4

2-) or high levels of nitrate, ion exchangemost likely is not the best treatment option. Arseniccombined with iron may pass through the columnuntreated. Arsenic breakthrough also can occur whennitrate and sulfate ions compete with arsenate forplaces on the resin. If nitrate and sulfate ions displacearsenic ions, arsenate will pass untreated through theIE unit. As the resin column becomes saturated withions, sulfate-rich water fed through the system maycause chromatographic peaking, making concentra-tions of arsenic and nitrate in the effluent from thecolumn higher than they were in the water enteringthe column. Because chromatographic peaking and

How should a well owner select a treatment unit?

No single technology will treat all water contami-nants. Before selecting a treatment option, wellowners should test the water source, using a labora-tory qualified to determine water quality. A list oflabs certified by the Texas Commission on Environ-mental Quality (TCEQ) for testing drinking watercan be found at: http://www.tnrcc.state.tx.us/permitting/waterperm/pdw/chemlabs.pdf. Once you have established the constituents presentin your water supply, research different productsand find one suitable for treating these constituents.Note systems’ co-treatment compatibility if morethan one contaminant must be treated. For example,although ion exchange can be used to treat bothnitrate and perchlorate, a system must be set upspecifically to treat both. Compare initial costs, oper-ation and maintenance costs and requirements, con-taminant removal efficiency, warranties, lifeexpectancy of the system and company reputation.Before making your final decision, also considerwastewater or solid wastes generated by a system.Home water-treatment systems are not regulated byfederal or state laws, but some national organizationsoffer product certifications. The Water Quality

Association (WQA) offers a validation program andadvertising guidelines. Products that receive theWQA’s Gold Seal Product Validations are certified asto mechanical performance but not for ability toremove harmful contaminants. The NationalSanitation Foundation (NSF) certifies products’ abili-ty to remove contaminants affecting health. A list ofdrinking-water treatment units with NSF certifica-tion can be found on the World Wide Web at:http://www.nsf.org /Certified/DWTU/. For questionsregarding a particular product’s certification, contactthe NSF Consumer Hotline at 877-8-NSF-HELP orinfo@nsf.org or by writing to NSF International, P.O.Box 130140, 789 N. Dixboro Road, Ann Arbor, MI48113-0140. An EPA registration number on a prod-uct indicates merely that the unit is registered withthe EPA; this registration number does not implyEPA approval or certification.

How can well owners keeptheir systems working?

No matter what treatment technology you use,maintenance is required to keep the system operat-ing properly, and the first step to proper operationand maintenance is proper installation. Qualifiedinstallers

• carry liability insurance for property damageduring installation;

• are accessible for service calls;• accept responsibility for minor adjustments

after installation; and • give a valid estimate of installation costs.

After system installation, water treatment unitsmust be maintained properly. RO membranes andresin in ion exchange units must be replaced as nec-essary. All systems should be operated according tomanufacturer’s specifications. Treating more waterin a certain period of time than a system is design-ed for may lower treatment effectiveness andadversely impact effluent water quality. Water out-put by treatment units should be tested regularly toensure proper system operation.

Useful LinksEnviroTools, 2002, Arsenic, adapted from ATSDRFactsheet, at: http://www.envirotools.org/factsheets/contaminants/arsenic.shtml; Illinois Department of Public Health, Arsenic inGroundwater, at: http://www.idph.state.il.us/envhealth/factsheets/arsenicwater.htmMaine Drinking Water Program, Arsenic Treatment,at: http://www.maine.gov/dhhs/eng/water/ArsenicTreatment.htm (February 25, 2004)

Minnesota Department of Health, Arsenic in WellWater, at: http://www.health.state.mn.us/divs/eh/wells/arsenic.html (December 27, 2004)Massachusetts DEP, Drinking Water—Arsenic inPrivate Well Water, at: http://www.mass.gov/dep/brp/dws/files/arswell.htmNatural Resources Defense Council, Arsenic inDrinking Water, at:http://www.nrdc.org/water/drinking/qarsenic.asp (March 21, 2001)Public Health, Seattle and King County PublicHealth, Arsenic Facts, at http://www.metrokc.gov/health/tsp/arsenic.htm (July 6, 2004)Regner, G, Court, M., and Kreig, K, 2004, Healtheffects and occurrence of arsenic in Texas’ water sup-plies, Texas Commission on Environmental Quality,at: http://www.tnrcc.state.tx.us/permitting/waterperm/pdw/tf2004_arsenic.pdfUniversity of Wisconsin Water Resources Institute,Arsenic, at: http://wri.wisc.edu/Arsenic.pdf (March,2004)U.S. EPA, Arsenic in Drinking Water, at http://www.epa.gov/safewater/arsenic.html (February1, 2005)U.S. EPA, 2001, Fact Sheet: Drinking WaterStandard for Arsenic, at: http://www.epa.gov/safewater/ars/ars_rule_factsheet.htmlUSGS, Arsenic in Groundwater, at: http://water.usgs.gov/nawqa/trace/arsenic/USGS, Data map: 31,350 ground-water arsenic sam-ples collected in 1973-2001, at: http://water.usgs.gov/nawqa/trace/pubs/geo_v46n11/fig1.html USGS Fact Sheet 063-00, May 2000, Arsenic inGround-Water Resources of the United States, at:http://water.usgs.gov/nawqa/trace/pubs/fs-063-00/Vermont Department of Health, Arsenic, at:http://www.vermont.gov/Wilkes University Center for EnvironmentalQuality, Arsenic in Drinking Water and Groundwater:Residential Water Supply and Homeowner DrinkingWater Testing Evaluation Program, at: http://www.water-research.net/arsenic.htmWorld Health Organization, May 2001, Arsenic indrinking water, at: http://www.who.int/mediacentre/factsheets/fs210/en/

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This publication was funded by the Rio Grande Basin Initiative administered by the Texas Water Resources Institute ofTexas Cooperative Extension, with funds provided through a grant from the Cooperative State Research, Education, andExtension Service, U.S. Department of Agriculture, under Agreement No. 2005-45049-03209.

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AcknowledgmentsGuidance and assistance was provided by the TexasGroundwater Protection Committee and the TexasCommission on Environmental Quality. The effortwas partially funded by the U. S. EnvironmentalProtection Agency.

Educational programs conducted by Texas Cooperative Extension serve people of all ages regardless of socioeconomic level, race, color, sex. reli-