Environ Geochem Health (2008) 30:345–353

DOI 10.1007/s10653-008-9167-8

ORIGINAL PAPER

Arsenic and Xuoride in the groundwater of Mexico

M. A. Armienta · N. Segovia

Received: 1 May 2006 / Accepted: 1 February 2007 / Published online: 12 March 2008© Springer Science+Business Media B.V. 2008

Abstract Concentrations of arsenic and Xuorideabove Mexican drinking water standards have beendetected in aquifers of various areas of Mexico. Thiscontamination has been found to be mainly caused bynatural sources. However, the speciWc processesreleasing these toxic elements into groundwater havebeen determined in a few zones only. Many studies,focused on arsenic-related health eVects, have beenperformed at Comarca Lagunera in northern México.High concentrations of Xuoride in water were alsofound in this area. The origin of the arsenic there isstill controversial. Groundwater in active miningareas has been polluted by both natural and anthropo-genic sources. Arsenic-rich minerals contaminatethe fractured limestone aquifer at Zimapán, CentralMéxico. Tailings and deposits smelter-rich fumespolluted the shallow granular aquifer. Arsenic contami-nation has also been reported in the San Antonio–ElTriunfo mining zone, southern Baja California, andSanta María de la Paz, in San Luis Potosí state. Evenin the absence of mining activities, hydrogeochemistryand statistical techniques showed that arsenopyriteoxidation may also contaminate water, as in the caseof the Independencia aquifer in the Mexican Altiplano.High concentrations of arsenic have also been detectedin geothermal areas like Los Azufres, Los Humeros,

and Acoculco. Prevalence of dental Xuorosis wasrevealed by epidemiological studies in Aguascalientesand San Luis Potosí states. Presence of Xuoride inwater results from dissolution of acid-volcanic rocks.In Mexico, groundwater supplies most drinkingwater. Current knowledge and the geology of Mexicoindicate the need to include arsenic and Xuoridedeterminations in groundwater on a routine basis,and to develop interdisciplinary studies to assessthe contaminant’s sources in all enriched areas.

Keywords Arsenic · Chronic arsenicism · Fluoride · Fluorosis · Groundwater · Mexico

Introduction

Groundwater has in México, as in other arid andsemi-arid countries, a signiWcant role on Mexicanwelfare and economic development. Potable watersupply for about 75% of the total population relies ongroundwater abstraction. On the other hand, poten-tially toxic elements may reach hazardous concentra-tions in groundwater as a result of geochemicalprocesses. These elements are ubiquitous in certaingeologic environments and may, with time, be releasedto groundwater. Exploitation of aquifers naturallyenriched in toxic elements may increase their concen-tration, and produce adverse health eVects on theexposed population. Rational use and protection ofaquifers is thus a primary goal of Mexican society.

M. A. Armienta (&) · N. SegoviaInstituto de Geofísica, Universidad Nacional Autonoma de Mexico, UNAM, Mexico, D.F 04510, Mexicoe-mail: victoria@geoWsica.unam.mx

123

346 Environ Geochem Health (2008) 30:345–353

The complex geology of Mexico with igneous,sedimentary, and metamorphic rocks and an activetectonic setting predisposes the environment to “natu-ral” groundwater contamination. However, two ele-ments, arsenic and Xuoride, have been clearly identiWedas causing adverse eVects on health through ingestionof contaminated groundwater. Moreover, these twoelements are recognized worldwide as the most seriousinorganic contaminants in drinking water (Smedleyand Kinniburgh 2002; Ng et al. 2003). Abundance ofarsenic and Xuoride in the subsoil has led to Mexicobecoming one of the world’s premier producers ofarsenic and Xuorite. In 2003, Mexico occupied thefourth place in arsenic production, following China,Chile, and Peru (COREMI 2004). Fluorite is one ofthe main non-metallic minerals exploited in Mexico,mostly in Coahuila, Durango, and San Luis Potosístates. In 2003 Mexico occupied the world’s secondplace in Xuorite production.

In 1958, high levels of arsenic in drinking waterwere identiWed for the Wrst time as the cause ofadverse eVects on health at “Comarca Lagunera”,North Mexico (Cebrián et al. 1994). Arsenic levelsabove the Mexican drinking water standards havesince been detected at other locations also. On theother hand, the high Xuoride content of groundwaterhas caused teeth and bone diseases in some areas, forexample San Luis Potosí and Aguascalientes states,Central México. The aim of this paper is to give anoverview of the reported occurrences, sources andhealth eVects of arsenic and Xuoride in the groundwa-ter of Mexico.

Arsenic and Xuoride in sedimentary basins and inactive volcanic regions

Comarca Lagunera (Durango and Coahuila states),located in the central part of North Mexico is one ofthe most important agricultural and livestock areas ofthe country. Due to its dry weather, groundwaterexploitation was a signiWcant component of its eco-nomic growth during the 20th Century. In 1958,Cebrián et al. (1994) reported for the Wrst time occur-rence of chronic arsenic poisoning in this area. HealtheVects resulting mainly from ingestion of pollutedgroundwater included peripheral vascular disease,keratosis, skin cancer, skin pigmentation changes,gastrointestinal disturbances and alterations in the

coproporphyrin/uroporphyrin excretion ratio (Cebriánet al. 1994; Hernández-Zavala et al. 1998). Variousstudies have been developed in this area to assessspeciWc aspects of the eVects of arsenic on the exposedpopulation. Alteration of bilirubin excretion was stud-ied in individuals living in three villages exposed todiVerent As levels in water (0.014, 0.1 and 0.3 mg/l).Increased serum alanine aminotransferase activityand predominantly conjugated hyperbilirubinemiawere related to total arsenic concentration in urine.Average urine arsenic concentrations increased withwater As content. Results of this study suggested thepresence of cholestasis in As-exposed individuals(Hernández-Zavala et al. 1998). A group of 30 indi-viduals exposed to 0.408 mg/l As in drinking watershowed cytogenetic damage. Total arsenic in urinewas 20 times higher in the exposed population than incontrols in the same area. A signiWcant increase wasobserved in the frequency of chromatid and isochro-matid deletions in lymphocytes, and of micronuclei inoral and urinary epithelial cells, of exposed individu-als relative to controls (Gonsebatt et al. 1997).

Del Razo et al. (2002), estimated the levels ofarsenic ingestion through cooked food prepared withcontaminated water (0.410 § 0.035 mg/l) in a villageof Comarca Lagunera. Results showed averageintakes of 16.6 and 12.3 �g/kg body weight/day forsummer and winter, respectively, in the populationexposed to high As drinking water. In contrast, aver-age As intakes of 0.94 and 0.76 �g/kg body weight/day for summer and winter, respectively, were calcu-lated in a population consuming water with a lowerAs concentration (0.012 § 0.004 mg/l) in the samearea.

Arsenic is unevenly distributed in the wells of thisregion. In 1990, a concentration range from 0.008to 0.624 mg/l was found in 128 sampled wells. Fiftypercent of the samples had concentrations higher than0.05 mg/l (the Mexican drinking water standard inthose years). A rural population of 400,000 inhabit-ants was considered to be exposed to high As levels.As(V) was the predominant arsenic oxidation state in93% of the wells (Del Razo et al. 1990). A survey of58 wells in the year 2000, reported arsenic concentra-tions up to 0.718 mg/l (Molina 2004). Several studieshave been performed to identify the source of arsenicin the water. However, the origin of arsenic atComarca Lagunera is still controversial. A hydrothermalsystem with high contents of lithium, boron, arsenic,

123

Environ Geochem Health (2008) 30:345–353 347

and Xuoride was proposed as the arsenic source byGonzalez-Hita et al. (1991). Ortega-Guerrero (2004),on the basis of chemical and isotopic composition ofgroundwater and regional groundwater Xow modeling,postulated evaporation as the primary mechanismof arsenic enrichment in the most southeastern part ofthis area.

Molina (2004) proposed several geochemical pro-cesses in diVerent zones of the aquifer as possiblesources of arsenic contamination. In the granularaquifer, desorption of arsenic retained on clays maymobilize arsenic from the aquifer matrix to thegroundwater. Dissolution of iron and manganeseoxides and desorption would also increase the arsenicwater content. Oxidation of sulWdes may also releasearsenic in the limestone aquifer.

Groundwater contamination may produce high lev-els of arsenic in pasture and contribute to increasedarsenic levels in cattle and their products. This arsenictransfer is specially relevant since Comarca Lagunerais one of the main milk producers of México. Rosaset al. (1999) conducted research in dairy farms of thisarea to determine arsenic distribution in the agricul-tural environment. Arsenic contents in farm wellsranged from 0.007 to 0.740 mg/l; concentrations insoil reached 30 �g/g, with only 12% of extractablearsenic. Up to 3.16 �g/g arsenic, mostly accumulatedin the roots, were measured in alfalfa. Concentrationsin milk ranged from <0.9 to 27.4 ng/g. Ten percent of50 samples analyzed were higher than the concentra-tion level (10 ng/g) suggested as a permitted arseniclevel in milk by the International Dairy Federation(IDF 1986). Application of a pharmacokinetic approachshowed the value of the milk biotransfer factor wasup to 6 £ 10¡4. Analyses of the results suggested thatarsenic presence in milk was due mainly to consumptionof contaminated water by cattle.

Fluoride is also enriched in groundwater atComarca Lagunera. Concentrations from less than 0.5to 3.7 mg/l Xuoride were reported in 1993. Levelswere higher in wells located in As-polluted areas (DelRazo et al. 1993).

Arsenic-enriched groundwater was also detectednorthwestern México, in Sonora state. Results fromanalyses performed in 173 samples from wells duringtwo sampling periods showed As concentrations werefrom 0.002 to 0.305 mg/l. Some of the most pollutedwells were located in the most populated cities of the

state: Hermosillo (610,000 inhabitants), Caborca,(69,000 inhabitants), and Etchojoa (56,000 inhabit-ants). Groundwater Xuoride concentrations were alsohigh, and positively correlated with arsenic at Hermo-sillo city. The speciWc origin of these elements hasnot yet been identiWed. Nevertheless, based on thegeographic distribution of the contaminants, and thelack of obvious external contamination, the authorshypothesized a geogenic source (Wyatt et al. 1998a).

Excretion of arsenic in urine by children exposedto As-containing water was determined in Hermosillocity by Wyatt et al. (1998b). Arsenic levels of watersupplied to the population had been reduced by dilu-tion with non-polluted water when the study was per-formed. Drinking water concentrations in threestudied areas ranged from 0.007 to 0.038 mg/l.Arsenic dose values calculated from water intake(0.253 to 2.995 �g/kg/day) exceeded the recom-mended EPA (Environmental Protection Agency)reference dose (EPA 1988). A positive correlation wasfound between As in water and As in urine. Arsenic in24-h urine excreted by children 7 to 11 years oldranged from 5.78 �g As/g creatinine (in the controlzone) to 114.29 �g As/g creatinine in the zone withthe highest water As content. Concentrations of Asand Xuoride in groundwater samples from drinkingwater sources of the studied population had a positivecorrelation (r = 0.93), indicating a common sourcewithin the aquifer. The arsenic and Xuoride content ofurine samples from children also correlated (r = 0.47,P = 0.01) (Wyatt et al. 1998b), reXecting their levelsin water.

Two wells of Meoqui City, Chihuahua, located1,945 km north of Mexico City, near the USA border,showed elevated concentrations of Xuoride (5.9 and4.8 mg/l) and arsenic (0.134 and 0.075 mg/l). Piñón-Miramontes et al. (2003) evaluated a treatment methodto remove Xuoride and arsenic from water of thesewells. The combined use of cake alum (aluminium sul-fate octadecahydrate) and small amounts of a poly-meric anionic Xocculant (PAF) reduced arsenic andXuoride concentrations by up to 99% and 77%, respec-tively. EYciency of Xuoride and arsenic removaldepended on the amount of cake alum. On the otherhand, Xuoride removal also varied with pH, beingoptimal at pH 7.1 (adjusted with a 8% NaOH solution).A concentration of 450 mg/l cake alum and 1 mg ofPAF added to 1 l water (containing 5.9 mg/l F¡ and

123

348 Environ Geochem Health (2008) 30:345–353

0.134 mg/l As), reduced F¡ to 1.4 mg/l and As to<0.001 mg/l.

In the Guadiana valley, Durango state, northernMexico, 74 wells used as potable water source forDurango City (491,000 inhabitants) were sampledevery three months during a year (Alarcón-Herreraet al. 2001a). About half of the wells exceeded0.05 mg/l As (59% of wells located in the city and48% in the rural area). The highest concentration was0.167 mg/l in the volcanic zone of the valley. LowestAs contents were found in the recharge zone of theaquifer. Arsenic presence was related to aquifergeology. However, the geochemical processes releas-ing arsenic to the groundwater were not identiWed.Fluoride concentrations above drinking water stan-dards (1.5–5.67 mg/l) have also been measured in thegroundwater of this valley (Alarcón-Herrera et al.2001b; Ortiz et al. 1998). Approximately 94% of 51wells sampled in the city of Durango had Xuoridecontents from 1.5 to 5.4 mg/l. About 95% of the pop-ulation was estimated to be exposed to Xuoride levelshigher than 2.0 mg/l (Ortiz et al. 1998). The propor-tion of wells exceeding the Mexican drinking waterstandard (1.5 mg/l) was lower in the rural area. How-ever, the highest contamination was found in ruralwells—up to 16.0 mg/l of Xuoride. The exposed pop-ulation showed dental Xuorosis and increased bonefractures. Prevalence and severity of dental Xuorosisin children increased according to the Xuoride con-centration of their home water supplies (Alarcón-Herrera et al. 2001b).

Based on geochemical, and statistical interpreta-tions of chemical, isotopic, hydrogeological, petro-logical and mineralogical data, Mahlknecht et al.(2004) explained As and F enrichment in the Indepen-dence aquifer, Central Mexico. A complex aquifersystem formed mainly by marine sediments, volcanicrocks, and lacustrine deposits has been identiWed inthis area. Lacustrine deposits, composed of sands int-erstratiWed by gravels and clay are the most exploitedunit. Concentrations as high as 16 mg/l of Xuoride and0.12 mg/l of As were measured in wells. IncreasedpH, temperature, Na+, F¡, and SiO2 occur in the samegeographical zone. Groundwater Xuoride was ascribedto dissolution of F-rich rhyolite rocks or ash. On theother hand, oxidation of arsenic-bearing sulWdes maybe releasing As into groundwater.

Concentrations from less than 0.005 to 0.050 mg/l Aswere measured in the Rioverde basin, central Mexico

(Planer-Friedrich et al. 2001). Increased groundwaterconcentrations were found with lacustrine sedimentsand decreased concentrations with Xuvial quaternarysediments. Arsenic increase is probably due to thesorption capacity of sediments and slightly reducingconditions. A correlation of 0.675 (P < 0.001) wascalculated between arsenic and Xuoride. Although anegative correlation was found between As and Ba,thermodynamic modeling with PHREEQC indicatedthat BaHAsO4.H2O might be a limiting phase forarsenic, but at higher concentrations than those foundin the study.

Groundwater contamination by Xuoride has beenreported in San Luis Potosí and Aguascalientes states,central Mexico. Prevalence of dental Xuorosis wasstudied in 445 children living in Aguascalientes stateand 201 children living in San Luis Potosí (Hernán-dez-Montoya et al. 2003; Grimaldo et al. 1995). Mostwater-supply wells in Aguascalientes state showedconcentrations higher than 1.5 mg/l. Almost 100% ofchildren exposed to tap water containing more than5.0 mg/l in Aguascalientes were found to suVer fromdental Xuorosis. Sixty one percent of tap water sam-ples contained from 0.7 to 1.2 mg/l of Xuoride in fourareas of San Luis Potosí City (670,532 inhabitants inthe year 2000) (Grimaldo et al. 1995; INEGI 2000).Bottled water was also found to contain 0.33–6.97 mg/l Xuoride. Severity and prevalence of dentalXuorosis increased with water Xuoride content. Eachmg/l increase in Xuoride water produced an incrementof 0.54 mg/l (P < 0.0001) of Xuoride in urine. Preva-lence of dental Xuorosis was higher in San Luis Potosíthan in cities in the United States consuming tapwater with similar Xuoride concentrations. Resultsshowed that ambient temperature, direct consumptionof boiled water, and consumption of food preparedwith boiled water, explain the prevalence of dentalXuorosis in the area (Grimaldo et al. 1995).

The aquifer system of San Luis Potosí valley isformed by a shallow unconWned aquifer that overliesa clay lens and a deep fractured volcanic aquifer.Three Xow systems were identiWed in the aquifer: alocal Xow controlled by the clay layer, an intermedi-ate system in which water inWltrates beyond theboundary of the clay layer, and a regional systemoriginating outside the surface catchment. Groundwa-ter chemistry in the regional Xow path is dominatedby natural water-rock reactions (Carrillo-Riveraet al. 1996). Fluoride concentrations correlated with

123

Environ Geochem Health (2008) 30:345–353 349

temperature in this valley. Leaching of rhyolitic rockswas postulated as the Xuoride source in the deepaquifer (Carrillo and Armienta 1989; Cardona et al.1993). Increased pumping from the upper part of thedeep aquifer has induced an upward regional Xow,rising temperatures and increasing water-rockreactions, especially those related with Xuoride. Thedeep waters containing high Xuoride concentrationscontaminated the shallower waters (Carrillo-Riveraet al. 1996). Saturation indices suggested that Xuoritesolubility controls Xuoride concentrations in regionalwaters. The appropriate mixture of cold and thermalXows may be used to decrease Xuoride concentrationsin abstracted groundwater (Carrillo-Rivera et al.2002).

Arsenic in mining zones

Arsenic minerals occur in association with ores inseveral mining areas of México. Notable occurrencesof arsenic-bearing minerals like arsenopyrite, scoro-dite, mimetite, adamite, tennantite, and nickelinehave been reported in various locations. Extractionand processing of ores in these zones may be a sourceof arsenic pollution. Besides, high arsenic levelsmay also be naturally present in these environ-ments. Few studies have been developed in México toidentify each source and its environmental arseniccontribution.

A multidisciplinary approach was developed in themining area of Zimapán, located in central Mexico, tocharacterize the arsenic contamination problem, anddevelop feasible solutions. Mining is the most impor-tant economic activity in Zimapán. Silver extractionhas been performed since the 16th Century. Extrac-tion and processing of silver, zinc, and lead ores iscurrently going on. Wastes from the selective Xotationprocess have accumulated near the town for more than50 years and are now within its limits. Various arsenicminerals occur in the Zimapán area. Arsenopyrite(FeAsS) is widely distributed in the mineralized areas,but scorodite, lolingite, tennantite, adamite, mimetite,geochronite, and hidalgoite (PbAl3(AsO4)(SO4)(OH)6)have also been recognized (Simons and Mapes-Vázquez 1956; García and Querol 1988; Villaseñoret al. 1996).

Water is a scarce resource in the area. Potablewater relies totally on groundwater. Arsenic was Wrst

identiWed in the water by the National Commissionof Water while looking for cholera bacteria in1992. A series of studies was subsequently started bythe National Autonomous University of México(UNAM). Concentrations up to 1.1 mg/l were deter-mined in deep wells used for potable water supply.About 34% of samples from shallow and deep wellshad As contents over 0.05 mg/l. As(V) is the predom-inant form of arsenic. Presence of arsenic is due tomultiple sources, both natural and anthropogenic.Hydrogeological, geological, and chemical studiesallowed their identiWcation.

The Zimapán aquifer system is formed mainly byfractured limestone overlain by fanglomerate andalluvial deposits. Geochemical and hydrogeologicalevidence showed that oxidation of arsenopyrite anddissolution of scorodite naturally present in the aquiferrelease arsenic and contaminate the limestone aquifer(Armienta et al. 1997a, 2001; Rodríguez et al. 2004).Exploitation of deep wells promotes this process byallowing oxygen interaction with minerals. SulWdeminerals oxidize during the dry season and the rise inthe water table mobilizes arsenic during the rainyseason (Rodríguez et al. 2004). Tailings constituteanother pollution source, with As concentrations up to8.25%. Complex chemical processes occur within tail-ings, releasing and retaining arsenic (Méndez andArmienta 2003; Romero et al. 2006). Although mostarsenic occurs in a low-available form, it has reachedthe shallow aquifer that is exploited mainly for non-drinking water uses (Armienta et al. 1997a). Arsenic-rich fumes from smelters operating until the mid 20thCentury were another source of arsenic in shallowgroundwater. Fumes settled on the soil and increasedits As content (Ongley et al. 2003), and by the actionof rain and irrigation the As was transported to theshallow aquifers.

Zimapán town is a low-income community ofnearly 15,000 inhabitants. Arsenic-related healtheVects caused by consumption of polluted water havebeen shown by various studies. Armienta et al.(1997b) determined hair arsenic concentrations andconducted a poll to identify possible health problemslinked with arsenic exposure. Of 120 sampled inhabit-ants, 97 showed some degree of eVect on the skin.SigniWcant diVerences in hair contents were obtainedamong people with some degree of skin disease andindividuals with no visible health eVect. Skin diseasessuch as light and dark skin spots and thickening of the

123

350 Environ Geochem Health (2008) 30:345–353

outer layer of palms and soles were related with thecontinuous consumption of water containing morethan 0.3 mg/l of arsenic. Sister chromatid exchanges(SCE) in the broad bean Vicia faba were used toexamine contaminated water at Zimapán. SigniWcantincreases of SCE were observed compared with con-trols; a concentration–response relationship was alsodetermined (Gómez-Arroyo et al. 1997).

The most polluted wells tapping the limestonedeep aquifer also have the highest yield of the valley,and until early 2004 were the main potable watersource. Currently, a new well drilled in other valleysupplies non-polluted water to Zimapán. Neverthe-less, its low production does not fulWll the townrequirements, and groundwater from a contaminatedwell is still mixed with non-polluted water. Arsenicconcentration of 0.15 mg/l was measured by UNAMin the potable water supply in February 2005.

A mining area dominated by epithermal veins withthe important presence of arsenopyrite is located inSouthern Baja California (Carrillo-Chávez et al.2000). Silver and gold ores have been mined since thelate 1700s. A shallow unconWned aquifer in highlyfractured igneous rocks and patches of alluvial mate-rial constitutes the local aquifer. Groundwater near themineralized zone showed high concentrations of totaldissolved solids, sulfate, bicarbonate, and arsenic. Thehighest As values (0.41 mg/l) were found in this area,near mine waste piles, and decreased with distancealong the groundwater Xow. Geochemical modelingindicated that dilution, precipitation of calcite, andarsenic sorption on to iron hydroxide surfaces are themost likely processes occurring along the Xow-path(Carrillo-Chávez et al. 2000).

Mining has been carried out at Santa María De laPaz (approximately 500 km NNW of Mexico City) inthe state of San Luis Potosí, for more than 200 years.Ore deposits consist of a Pb–Zn–Ag ore body and aCu–Au (Zn) ore body. Mineralogy of the Pb–Zn–Agore body is constituted by galena, arsenopyrite, pyrite,sphalerite, and Cu-Sb sulfosalts (Megaw 1999; Razoet al. 2004). Wastes produced from ore processinghave accumulated in Wve tailing impoundmentsaround the town of Villa de la Paz (5,120 inhabitants).Water samples from mine channels and storage pondsin the mining district ranged from 0.059 to more than0.400 mg/l of arsenic. Mine water is directly used forirrigation. One sample contained more than 5.900 mg/l. Oxidation of sulWde minerals contained in mine

wastes, arsenopyrite oxidation in the aquifer, and natu-ral release of As by dissolution of sulWdes present inthe aquifer under high alkalinity and anaerobic condi-tions may be causing the groundwater arsenic increase(Razo et al. 2004). Irrigation with mine water has alsocontaminated agricultural soils with arsenic and toxicmetals (Castro-Larragoitia et al. 1997). Childrenexposed to arsenic and lead in surface soil at Villa de laPaz, showed DNA damage in blood cells (Yáñez et al.2003).

Arsenic and Xuoride in geothermal areas near active volcanic zones

Los Azufres in Michoacán state West Mexico, in theMexican Volcanic Belt, is one of the main geothermalWelds of the country. It has been exploited since 1982.A study carried out from November 1994 to May 1996showed contamination of shallow aquifers and surfacewaters. Arsenic and Xuoride reached maximum valuesof 24 and 17 mg/l, respectively, in geothermal wells,and of 8 and 16.3 mg/l, respectively, in surface waters.The concentration increase in surface waters was pro-duced by inadequate exploitation of deep brines,mainly from leakage of evaporation ponds. Leaking ofpipelines, occasional overXowing of reinjection wellsand pond rims, and out-Xowing of brines during reha-bilitation or drilling operations have also contributed towater pollution. River pollution decreased down-stream of contamination sources. However, concentra-tions above background levels were found as far as10 km outside the geothermal Weld (Birkle and Merkel2000). Arsenic enrichment of water from geothermalexploitation wells (up to 73.6 mg/l) was also measuredat Los Humeros geothermal Weld in Puebla state, Cen-tral Mexico (González-Partida et al. 2001). The geo-thermal area of Acoculco, Puebla, is a volcanic calderawith rhyolitic domes, scoria, and andesitic Xows. Higharsenic contents of calcic-sulfate type spring waterslocated inside the caldera were reported in this zonealso (Quinto et al. 1995).

Groundwater arsenic and Xuoride in areas from undetermined sources

In Acámbaro, Guanajuato state, Central México,Gutierrez-Pizano et al. (1996) reported arsenic

123

Environ Geochem Health (2008) 30:345–353 351

concentrations up to 16 times the Mexican drinkingwater standard in 1996 (0.05 mg/l) in well water. Theauthors also refer the existence of cutaneous diseaseslinked with arsenic consumption in that area.

The Salamanca aquifer system (central Mexico)has been aVected by As, Pb, and benzene from diVer-ent pollution sources (Rodríguez et al. 2005). Salam-anca City is an important industrial center. An oilreWnery, pesticides manufacturing industries, and athermoelectric plant are located in the city. An activefault associated with an intense groundwater abstrac-tion regime, crosses the urban area and the reWnerylands. Three units compose the local aquifer system—a shallow non-exploited granular with a predomi-nance of clay and clay-sand layers, an intermediateexploited region including granular material, and adeep formation formed mainly of fractured volcanicrocks exploited only by the thermoelectric powerplant. Groundwater is the only drinking water sup-ply of the population. Most urban wells containedover 0.025 mg/l (the Mexican drinking water stan-dard in 2005) of arsenic. A maximum concentrationof 0.28 mg/l was measured in a well near a fault area(Rodríguez et al. 2005). The presence of As in ground-water could be associated with a hydrocarbon spillwhich occurred in 1992, with leakages from industrialwastes, or with As-bearing rocks (Rodríguez et al.2001, 2005).

Final remarks

Arsenic and Xuoride concentrations above drinkingwater standards have been detected in various Mexicanaquifers. Both elements coexist at hazardous levels insome areas. Arsenic enrichment has been caused bygeogenic processes in most of the studied sites. Water–rock interaction with volcanic rocks and As-rich oreshad released arsenic in fractured aquifers. Desorptionfrom clays and Fe and Mn oxides, and evaporation,may account for arsenic in granular aquifers. Fluoridecontamination is related mainly to dissolution of acidvolcanic rocks. On the other hand, the aquifers’ com-plexity has made it diYcult to identify the speciWcsource of these elements in all known polluted areas.Interdisciplinary studies including geology, hydrogeol-ogy, and geochemistry should be done to constrainarsenic and Xuoride sources in the majority of contami-nated aquifers. Most research in México has been

focused on biomarkers and health eVects caused byintake of contaminated drinking water. Epidemiologi-cal studies have shown the link between adverse healthconsequences and ingestion of water containing highlevels of arsenic and Xuoride. Results of these investi-gations prompted the authorities to supply water fromother non-polluted sources in some of the pollutedareas. However, these studies were conducted in somezones only. There is a need to conduct similar studiesin all polluted areas. Six-hundred and Wfty-three aqui-fers exist in the Mexican territory (CNA 2004). Aglobal evaluation of the concentration of these andother, minor, toxic elements should be conducted in allMexican territory. IdentiWcation of the oxidation stateof arsenic would also be advisable, because of thehigher toxicity of As(III) than As(V).

The geological characteristics of the Mexican terri-tory indicate that As and F may be above drinkingwater standards in many areas of the country. Theexposed population may be larger than that alreadyidentiWed. Therefore, arsenic and Xuoride must bedetermined in all groundwater sources in Mexico on aregular basis. Much research is needed to ascertainthe actual levels, causes, and mobilization of theseelements in aquifers. These studies will give optionsfor delivering good-quality water based on abstrac-tion regimes or treatment procedures. Meanwhile,however, an eVort must be made to supply gooddrinking quality water to the inhabitants.

References

Alarcón-Herrera, M. T., Flores-Montenegro, I., Romero-Navar, P.,Martín-Domínguez, I. R., & Trejo-Vázquez, R. (2001a).Contenido de arsénico en el agua potable del valle del Guadi-ana, México. Ingeniería Hidráulica en México, XVI, 63–70.

Alarcón-Herrera, M. T., Martín-Domínguez, I. R., Trejo-Vázquez, R., & Rodríguez-Dosal, S. (2001b). Well waterXuoride, dental Xuorosis, bone fractures in the GuadianaValley of Mexico. Fluoride, 34, 139–149.

Armienta, M. A., Rodriguez, R., Aguayo, A., Ceniceros, N.,Villaseñor, G., & Cruz, O. (1997a). Arsenic contaminationof groundwater at Zimapán, México. Hydrogeology Jour-nal, 5, 39–46.

Armienta, M. A., Rodriguez, R., & Cruz, O. (1997b). Arseniccontent in hair of people exposed to natural arsenic pol-luted groundwater at Zimapán, México. Bulletin of Envi-ronmental Contamination and Toxicology, 59, 583–589.

Armienta, M. A., Villaseñor, G., Rodríguez, R., Ongley, L. K.,& Mango, H. (2001). The role of arsenic-bearing rocks ingroundwater pollution at Zimapán Valley, México. Envi-ronmental Geology, 40, 571–581.

123

352 Environ Geochem Health (2008) 30:345–353

Birkle, P., & Merkel, B. (2000). Environmental impact by spillof geothermal Xuids at the geothermal Weld of Los Azufres,Michoacán, Mexico. Water, Air, and Soil Pollution, 124,371–410.

Cardona, B. A., Carrillo R. J. J., & Armienta, H. M. A. (1993).Elemento traza: contaminación y valores de fondo en aguassubterráneas de San Luis Potosí, SLP, México. GeofísicaInternacional, 32, 277–286.

Carrillo, J. J., & Armienta, M. A. (1989). Diferenciación de lacontaminación inorgánica en las aguas subterráneas delValle de la ciudad de San Luis Potosí, S.L.P., México.Geofísica Internacional, 28, 763–783.

Carrillo-Chávez, A., Drever, J. I., & Martínez, M. (2000).Arsenic content and groundwater geochemistry of the SanAntonio-El Triunfo, Carrizal and Los Planes aquifers insouthernmost Baja California, Mexico. EnvironmentalGeology, 39, 1295–1303.

Carrillo-Rivera, J. J., Cardona, A., & Moss, D. (1996). Impor-tance of the vertical component of groundwater Xow: A hy-drogeochemical approach in the valley of San Luis Potosí,Mexico. Journal of Hydrology, 23, 23–44.

Carrillo-Rivera, J. J., Cardona, A., & Edmunds, W. M. (2002).Use of abstraction regime and knowledge of hydrogeolog-ical conditions to control high-Xuoride concentration in ab-stracted groundwater: San Luis Potosí Basin, Mexico.Journal of Hydrology, 261, 24–47.

Castro-Larragoitia, J., Krama, U., & Puchelt, H. (1997).200 years of mining activity at La Paz/San Luis Potosí/Mexico-Consequences for environment and geochemicalexploration. Journal of Geochemical Exploration, 58,81–91.

Cebrián, M. E., Albores, A., García-Vergas, G., & Del Razo, L.M. (1994). Chronic arsenic poisoning in humans: The caseof Mexico. In: J. O. Nriagu (Ed.), Arsenic in the environ-ment Part II (pp. 93–107). New York: Wiley.

COREMI. (2004). Anuario Estadístico de la Minería Mexicana2003. Pachuca: Consejo de Recursos Minerales, 252 pp.

CNA, Comisión Nacional del Agua. (2004). Statistics on waterin Mexico 2004. México, D.F.: Comisión Nacional delAgua, 141 pp.

Del Razo, L. M., Arellano, M. A., & Cebrián, M. E. (1990). Theoxidation states of arsenic in well-water from a chronic ar-senicism area of northern Mexico. Environmental Pollu-tion, 64, 143–153.

Del Razo, L. M., Corona, J. C., García-Vargas, G., Albores, A.,& Cebrián, M. E. (1993). Fluoride levels in well-waterfrom a chronic arsenicism area of northern Mexico. Envi-ronmental Pollution, 80, 91–94.

Del Razo L. M., Garcia-Vargas G. G., García-Salcedo J.,Sanmiguel M. F., Rivera M., Hernandez M. C., & CebrianM. E. (2002). Arsenic levels in cooked food and assessmentof adult dietary intake of arsenic in the Region Lagunera,Mexico. Food and Chemical Toxicology, 40, 1423–1431.

EPA, Environmental Protection Agency. (1988). Risk Assess-ment Forum, Special Report on Ingested InorganicArsenic: Skin Cancer Nutritional Essentiality. EPA/625/3-87/013.

García, S., & Querol, S. F. (1988). Descripción de algunosyacimientos del distrito de Zimapán, Hidalgo. In: G. P.Salas (Ed.), Geología económica de México (pp. 383–400).México, D.F.: Fondo de Cultura Económica.

Gómez-Arroyo, S., Armienta, M. A., Cortés-Eslava, J., &Villalobos-Pietrini, R. (1997). Sister chromatid exchangesin Vicia faba induced by arsenic-contaminated drinkingwater from Zimapan, Hidalgo, Mexico. Mutation Research,394, 1–7.

Gonsebatt, M. E., Vega, L., Salazar, A. M., Montero, R., Guz-mán P., Blas, J., Del Razo, L. M., García-Vargas, G., Alb-ores, A., Cebrián, M. E., Kelsh, M., & Ostrosky-Wegman,P. (1997). Cytogenetic eVects in human exposure to ar-senic. Mutation Research, 386, 219–228.

González-Hita, L., Sánchez, L., & Mata, I. (1991). Estudio hid-rogeoquímico e isotópico del acuífero granular de laComarca Lagunera. Morelos: Instituto Mexicano de Tec-nología del Agua.

González-Partida, E., Hinojosa, T. E., & Verma, M. P. (2001).Interacción agua geotérmica-manantiales en el campo geo-térmico de Los Humeros, Puebla, México. Ingeniería Hid-ráulica en México, XVI, 185–194.

Grimaldo, M., Borja-Aburto, V. H., Ramírez, A. L., Ponce, M., Ro-sas, M., & Díaz-Barriga, F. (1995). Endemic Xuorosis in SanLuis Potosí, Mexico. Environmental Research, 68, 25–30.

Gutiérrez-Pizano, A., Rodríguez, R. E., Romero, G. J., & Veláz-quez, G. A. (1996). Eliminación del arsénico en agua pota-ble de pozos. Actas INAGEQ, 2, 319–322.

Hernández-Montoya, V., Bueno-López, J. I., Sánchez-Ruelas,A. M., García-Servín, J., Trejo-Vázquez, R., Bonilla-Pe-triciolet, A., & Márquez-Algara, C. (2003). Fluorosis y car-ies dental en niños de 9 a 11 años del estado deAguascalientes, México. Revista Internacional de Con-taminacion Ambiental, 19, 197–204.

Hernández-Zavala, A., Del Razo, L. M., Aguilar, C., García-Var-gas, G. G., Borja, V. H., & Cebrián, M. E. (1998). Alterationin bilirubin excretion in individuals chronically exposed toarsenic in Mexico. Toxicology Letters, 99, 79–84.

IDF, Internacional Dairy Federation. (1986). Levels of traceelements in milk and milk products. Questionnaire 2386/E.Brussels.

INEGI, Instituto Nacional de Estadística, Geografía e Informá-tica. (2000). XII Censo General de Población y Vivienda.Retrieved February 15, 2006, from: http://www.inegi.gob.mx.

Mahlknecht, J., Steinich, B., & Navarro de León, I. (2004).Groundwater chemistry and mass transfers in the Indepen-dence aquifer, central Mexico, by using multivariate statis-tics and mass-balance models. Environmental Geology, 45,781–795.

Megaw, P. (1999). The high temperature Ag-Pb-Zn-(Cu) Car-bonate-replacement deposits of Central Mexico. In: J. L.Jambor (Ed.), VMS and carbonate-Hosted polymetallicdeposits of Central Mexico (pp. 25–40). Vancouver: Brit-ish Columbia and Yukon Chamber of Miner.

Méndez, M., & Armienta, M. A. (2003). Arsenic phase distribu-tion in Zimapán mine tailings, Mexico. Geofísica Internac-ional, 42, 131–140.

Molina, M. A. (2004). Estudio hidrogeoquímico en la ComarcaLagunera, México. M.Sc. Thesis, Posgrado en Ciencias dela Tierra, National Autonomous University of Mexico,UNAM, México D.F.

Ng, J. C., Wang, J., & Shraim, A. (2003). A global health prob-lem caused by arsenic from natural sources. Chemosphere,52, 1353–1359.

123

Environ Geochem Health (2008) 30:345–353 353

Ongley, L. K., Armienta, A., & Mango, H. (2003). Concentra-tions of heavy metals in soil, Zimapan, México. Journal dePhysique IV, 107, 983–986.

Ortega-Guerrero, M. A. (2004). Origin of high concentrations ofarsenic in groundwater at the “La Laguna Region”, northernMexico, and implications on aquifer management. In Work-shops: Program with Abstracts, 32nd IGC Florence, p. 1486.

Ortiz, D., Castro, L., Turrubiartes, F., Milan, J., & Diaz-Barriga,F. (1998). Assessment of the exposure to Xuoride fromdrinking water in Durango, Mexico, using a geographicinformation system. Fluoride, 31, 183–187.

Piñón-Miramontes, M., Bautista-Margulis, R. G., & Pérez-Her-nández, A. (2003). Removal of arsenic and Xuoride fromdrinking water with cake alum and a polymeric anionicXocculent. Fluoride, 36, 122–128.

Planer-Friedrich, B., Armienta, M. A., & Merkel, B. J. (2001).Origin of arsenic in the groundwater of the Rioverde basin,Mexico. Environmental Geology, 40, 1290–1298.

Quinto, A., Santoyo, E., Torres, V., González, E., & Castillo, D.(1995). Estudio geoquímico-ambiental de los eXuentesnaturales producidos en la zona geotérmica de Acoculco,Puebla. Ingeniería Hidráulica en México X, 21–27.

Razo, I., Carrizales, L., Castro, J., Díaz-Barriga, F., & Monroy,M. (2004). Arsenic and heavy metal pollution of soil, waterand sediments in a semi-arid climate mining area inMexico. Water, Air, and Soil Pollution, 152, 129–152.

Rodríguez, R., Armienta, A., Berlín, J., & Mejía, J. A. (2001).Arsenic and lead pollution of the Salamanca aquifer, Mex-ico: Origin, mobilization and restoration alternatives. In: S.F. Thornton & S. E. Oswald (Eds.), Groundwater quality:Natural and enhanced restoration of groundwaterpollution (pp. 561–565). Proceedings of the GroundwaterQuality 2001, SheYeld U.K., IAHS Publ 275, Walling-ford, Oxfordshire.

Rodríguez, R., Ramos, J. A., & Armienta, M. A. (2004).Groundwater arsenic variations: The role of local geologyand rainfall. Applied Geochemistry, 19, 245–250.

Rodríguez, R., Armienta, M. A., & Mejía Gómez, J. A. (2005).Arsenic contamination of the Salamanca aquifer system in

Mexico: A risk analysis. In: J. Bunduschuh, P. Bhattach-arya, & D. Chandrasekharam (Eds.), Natural arsenic ingroundwater: Occurrence, remediation and management(pp. 77–83). London: Taylor & Francis Group.

Romero, F. M., Armienta, M. A., Villaseñor, G., & González, J.L. (2006). Mineralogical constraints on the mobility ofarsenic in tailings from Zimapán, Hidalgo, Mexico. Inter-national Journal of Environment and Pollution, 26, 23–40.

Rosas, I., Belmont, R., Armienta, A., & Baez, A. (1999).Arsenic concentrations in water, soil, milk and forage inComarca Lagunera, Mexico. Water, Air, and Soil Pollution,112, 133–149.

Simons, S. F., & Mapes-Vazquez, V. E. (1956). Geology andore deposits of the Zimapán Mining District, State ofHidalgo, Mexico. US Geological Survey ProfessionalPaper 284.

Smedley, P. L., & Kinniburgh, D. G. (2002). A review of thesource, behaviour and distribution of arsenic in naturalwaters. Applied Geochemistry, 17, 517–568.

Villaseñor, C. M. G., Petersen, E. U., Avendaño-Cano, S., Go-mez-Caballero, J. A., Sousa, J., & Reyes-Salas, A. M.(1996). Minerales del grupo de la tetrahedrita en las minasde Lomo de Toro y Las Animas, Zimapán, Hidalgo. ActasINAGEQ, 2, 129–134.

Wyatt, C. J., Fimbres, C., Romo, L., Méndez, R. O., & Grijalva,M. (1998a). Incidence of heavy metal contamination inwater supplies in Northern Mexico. Environmental ResearchA, 76, 114–119.

Wyatt, C. J., Lopez, Q. V., Olivas, A. R. T., & Méndez, R. O.(1998b). Excretion of arsenic (As) in urine of children, 7–11 years, exposed to elevated levels of As in the City watersupply in Hermosillo, Sonora, México. Environmental Re-search A, 78, 19–24.

Yáñez, L., García-Nieto, E., Roas, E., Carrizales, L., Mejía, J.,Calderón, J., Razo, I., & Díaz-Barriga, F. (2003). DNAdamage in blood cells from children exposed to arsenic andlead in a mining area. Environmental Research, 93, 231–240.

123