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Journal of Environmental Management xx (2008) 1e8www.elsevier.com/locate/jenvman

Survey of trace metals in drinking water supplied to ruralpopulations in the eastern Llanos of Venezuela

Abrahan Mora*, Cesar Mac-Quhae, Malvis Calzadilla, Luzmila Sanchez

Laboratorio de Fisicoquımica, Estacion de Investigaciones Hidrobiologicas de Guayana, Fundacion La Salle de Ciencias Naturales,San Felix 8051, Estado Bolıvar, Venezuela

Received 12 March 2007; received in revised form 20 August 2007; accepted 13 January 2008

Abstract

To ascertain the water quality for human consumption, chemical parameters such as pH, conductivity and total dissolved calcium, magne-sium, iron, aluminum, zinc, copper and manganese were measured during four sampling periods (November 2002; March, May and July 2003)in drinking water wells which supply several forest camps and rural populations located in the eastern Llanos of Venezuela. Copper levels indrinking water in November 2002 were found to be significantly higher (P< 0.05) than the other assessed periods. Temporal variations of theother parameters considered were not statistically significant. Calcium and magnesium concentrations were found to be extremely low (meanconcentration� S.D. of 0.27� 0.25 mg/l for Ca and 0.219� 0.118 for Mg) during the four sampling periods, probably because of the carbonatebearing scarcity in the soils lithic component. The rest of the metals complied with the Venezuelan and International guidelines of quality criteriafor drinking water.� 2008 Elsevier Ltd. All rights reserved.

Keywords: Drinking water; Water quality; Metals; Eastern Llanos; Mesa formation

1. Introduction

The eastern Llanos of Venezuela is constituted by a regionof low relief covered by the Mesa formation. This zone islocated at the south of the Anzoategui and Monagas states,and is formed by consolidated and partly unconsolidated sed-iments from the actively uplifting mountain belts to the northand west of the Orinoco basin (Gonzalez de Juana et al.,1980). The Mesa formation, constituted during Pleistocene(Carbon and Schubert, 1994), has a maximum relief lessthan 200 m and consists of horizontally bedded alluvial sedi-ments, represented by light gray, coarse grained quartz sand,with cross-bedding marked by ochre, red and pink alteration,and gravels cemented with ferruginous material (Gonzalezde Juana et al., 1980). The typical topography consists of

* Corresponding author. Tel.: þ58 286 931 12 81; fax: þ58 286 931 10 45.

E-mail addresses: abrahan.mora@fundacionlasalle.org.ve (A. Mora),

cesarmac@hotmail.com (C. Mac-Quhae), malvismc@cantv.net (M.

Calzadilla), luzsanchez@cantv.net (L. Sanchez).

0301-4797/$ - see front matter � 2008 Elsevier Ltd. All rights reserved.

doi:10.1016/j.jenvman.2008.01.005

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mesas north of the left margin of the Orinoco River. To thenorth of the mesas there is topography of low hills coveredby blocks of ferruginous crusts. The sediments on the alluvialplains of the eastern Llanos were stored for a sufficiently longtime that chemical weathering could decompose unstablesedimentary grains. This weathering caused an increase inchemical maturity as the alluvial sediments were reworked,producing a marked decrease in the fraction of less stable min-eral and lithic components with increasing distance from themountain front (Stallard et al., 1991). Thus, the substratum’snature makes rivers and groundwater sources that have catch-ments entirely within the eastern Llanos of Venezuela can bechemically poor, and the possible chemical scarcity of somebio-essential elements (as calcium and magnesium) in drink-ing water wells is of extreme importance in risk assessmentto human health for populations in this geological location.

The scarcity of some base cations as calcium and magnesiumin drinking water has been associated with cardiovasculardiseases (Nerbrand et al., 2003; Kousa et al., 2006; Yang et al.,2006). In Spain, an increased death rate from cardiovascular

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and cerebrovascular diseases was reported in areas supplied withsoft drinking water (Ferrandiz et al., 2004). Also, soft drinkingwater could provoke some physiological disorders in humanssuch as calcifications disorders (Driessens and Verbeeck, 1988)and magnesium deficiency can cause neuronal damage whichcould manifest as depression (Eby and Eby, 2006).

On the other hand, it is well known that high trace metalconcentrations in food and drink can provoke serious healthhazards in humans. For example, elevated copper and manga-nese levels in drinking water may have a neurotoxic potentialand can produce mental diseases such as Alzheimer’s andManganism (Dieter et al., 2005). High manganese levels indrinking water have also been shown to affect intellectualfunctions in 10-year-old children in Araihazar, Bangladesh(Wasserman et al., 2006). Elevated zinc intakes can causedemyelinating diseases in humans (Zatta et al., 2003). Also,aluminum in drinking water has been associated with thedevelopment of dementia-type syndromes and postulated asone of the etiological agents of Alzheimer’s disease (Flaten,1987; Martyn et al., 1989; Heininger, 2000; Kawahara,2005). Similarly, although iron is a bio-essential metal, itsexcess accumulation is harmful. The mutagenicity of iron,nephrotoxicity and induction of renal cell and heptacellularcarcinoma have been well documented in the literature (Boyceand Holdsworth, 1986; Wong, 1988; Fargion et al., 1991).

The present, continuous drinking water quality monitoringestablished by the Environmental and Natural ResourcesDepartment of Venezuela (MARN) is limited to the biggestVenezuelan cities. In countryside regions or areas a longway from the populated centers, principally in the eastern Lla-nos, water quality information is scarce. Thus, the objective ofthe present paper was to evaluate some chemical parameterssuch as pH and conductivity and the concentration of total dis-solved calcium, magnesium, iron, aluminum, zinc, copper and

Fig. 1. Map showing the sampling area and the

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manganese in eight drinking water wells located in the easternLlanos of Venezuela during the four sampling periods, asa way to ascertain the water quality for human consumption.

2. Materials and methods

2.1. Sampling area

The Venezuelan eastern Llanos are at the south of Anzoate-gui and Monagas States, in the northeastern region ofVenezuela. In these alluvial plains, the soils are sandy, stronglyacidic, with a low cation exchange capacity and excessiveinternal drainage (Torres and Franco, 1994). The climate isthat of a dry tropical forest. Rainfall in the area varies between900 mm and 1300 mm per year, and the mean annual tempera-ture is of 26.5 �C. The climate is constituted by a rainy seasonand a dry season. The rainy season starts in May and lasts untilNovembereDecember. June, July and August are the monthswith maximum precipitation values. In this zone, 400,000 haof pine (Pinus caribaea var. hondurensis) plantations havebeen established by PROFORCA, which is a governmentcompany responsible for supplying raw material for woodproduction purposes. Likewise, PROFORCA is responsiblefor the water supply in Uverito, Chaguaramas and Coloraditopopulations, which are located surrounding pine plantations.The population density of this zone is relatively low and thearea is essentially rural. Uverito, Chaguaramas and Coloraditohave a population of approximately 8000 habitants and theprincipal economic activities of these people are based on theforest industry. Also, PROFORCA has established severalforest camps to provide adequate housing for its workers.

All the water supplied to populations and forest camps aretaken from groundwater sources by pumping systems andstored in tanks for distribution. Fig. 1 shows the map

drinking water wells assessed in this study.

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indicating the location of the water wells assessed in thisstudy. Wells A, B and C supply water to the Chaguaramas pop-ulation (w4500 habitants). Well E supplies water to the entireUverito population (w2500 habitants). Wells G and H supplywater to Coloradito rural village (w1000 habitants) and wellsD and F supply water to PROFORCA forest camps located inChaguaramas and Uverito, respectively. Table 1 shows thelocation and the geographic coordinates of the drinking waterwells assessed in this study.

2.2. Sampling and analysis

The samplings were conducted for each well for fourperiods representing the seasonal variation that occurred ineastern Llanos: November 2002 (ending wet season) andMarch (dry season), May (starting wet season) and July2003 (wet season). The water samples were taken from pump-ing stations, before water could be stored in tanks. The waterwas to be run to waste for 5 min before collection of thesample in polyethylene bottles, which were pre-washed withconcentrated nitric acid (1:1) and deionized water severaltimes prior to use. The sample water bottles were filled com-pletely, capped tightly, put in ice and transported to the labo-ratory in San Felix town, approximately 3 h from the samplinglocation.

Immediately upon return to the laboratory, the pH andconductivity measurements were made on unfiltered samplesusing standard electrochemical techniques (APHA, 1995).The water samples were filtered through 0.45 mm membranefilters to obtain samples for dissolved metal estimation andacidified to 1% v/v with ultra pure nitric acid to minimizetrace elements precipitation/adsorption on storage. The sam-ples thus preserved were stored at 4 �C in sampling kits forcalcium, magnesium and trace elements analysis. Precipitationdata from the eastern Llanos measured in Uverito station wereobtained through PROFORCA.

2.3. Analysis of metals

Stock standard solutions of calcium (Ca), magnesium (Mg),iron (Fe), aluminum (Al), zinc (Zn), copper (Cu) and manga-nese (Mn) were obtained from Accustandard Inc. in concentra-tions of 1000 mg/l. The concentrations of Fe, Al, Zn, Cu andMn were determined by graphite furnace atomic absorptionspectrometry (GFAAS, GBC Avanta Model GF 3000). To

Table 1

Locations and geographic coordinates for the drinking water wells assessed in

this study

Well Location Latitude Longitude

A Chaguaramas I sector A 8�3903200N 62�4603600W

B Chaguaramas I sector B 8�3902000N 62�4700600W

C Chaguaramas II 8�4003200N 62�4603300W

D Chaguaramas Camp 8�3903700N 62�4703900W

E Uverito 8�4002300N 62�3704900W

F Uverito Camp 8�4000400N 62�3804200W

G Coloradito I 8�4501500N 63�2901200W

H Coloradito II 8�4402400N 63�3001800W

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avoid the contamination of graphite tubes during analysis,samples with high Fe levels (>100 mg/l) and high Zn levels(>30 mg/l) were measured initially by flame atomic absorptionspectrometry. Concentration of Ca and Mg were determinedby nitrous oxideeacetylene flame atomic absorption spec-trometry (FAAS, GBC Avanta Model 908G). Standards andsample aliquots for Ca and Mg determinations also contained2000 mg/l of potassium, which served to prevent analyteionization.

Samples were allowed to warm up to room temperatureprior to analysis. Instrument operational conditions were ad-justed to yield optimal determinations. A five-point calibrationcurve was established for each element by linear regressionanalysis of absorbance versus standard concentration. Fivedeterminations were made on all samples. The precision ofthe analytical procedure, expressed as the relative standarddeviation (RSD), ranged from 1 to 10%.

2.4. Statistical analysis

One-way ANOVA and Fisher’s least significant differencetest for multiple comparison (Fisher LSD Test) were used tocompare data among seasonal periods (Stat Graphics Plus5.1 statistical program). Also, non-parametric sign test wascarried out to evaluate whether the concentration differencesin chemical species between each well were significant ornot during this study (Statistica 5.0 statistical program).Differences were considered significant for any P value lessthan 0.05.

3. Results and discussion

Data for the pH, conductivity and total dissolved calcium,magnesium, aluminum, iron, copper, zinc and manganese con-tent in the drinking water wells assessed are shown in Table 2.This table contains the minimum and maximum values foundas well as the mean concentrations and the standard deviationsfor the parameters considered. Similarly, Table 2 comparesthese values against the detection limits reported for thelaboratory analysis and the values proposed in internationalguidelines of quality criteria for drinking water establishedby the World Health Organization (WHO, 1993) and Venezue-lan Official Gazette (VOG, 1998). All the values were aboveor equal to the detection limits reported for the laboratoryanalysis. Precipitation values, drinking water metals, conduc-tivity and pH were also evaluated in accordance with theseasonal variations, as depicted in Fig. 2. The precipitationvalues in July are higher than the other periods, whereasMarch is the month with minimum precipitation values.

The Ca and Mg concentrations in the assessed drinkingwater wells show the extreme scarcity of these bio-essentialbase cations in the groundwater sources from the eastern Lla-nos of Venezuela. Ca and Mg high levels in waters have beenassociated with the carbonate bedrock weathering. The watersin contact with carbonate bedrock are enriched in base cationsand they are of relatively high alkalinity (w4000 mEq/l) andpH (w8). The scarcity of carbonate bearing in the Mesa

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Table 2

Minimum, maximum and mean values of pH, conductivity and metal concentrations present in the eight drinking water wells located in the eastern Llanos of

Venezuela during the four assessed periods, and comparison against the detection limits (D.L.) reported for the laboratory analysis and the levels allowed by World

Health Organization (WHO, 1993) and Venezuelan Official Gazette (VOG, 1998)

Parameter Mean� S.D. Minimum Maximum WHO VOG D.L.

pH 5.63� 0.61 4.70 6.49 6.5e8.5

Conductivity (mS/cm) 29.9� 18.2 15.1 85.9

Ca (mg/l) 0.27� 0.25 0.01 0.70 0.01a

Mg (mg/l) 0.219� 0.118 0.005 0.384 0.003a

Al (mg/l) 14.8� 18.1 1.0 73.0 200 200 0.2b

Fe (mg/l) 201� 430 6 1 840 2 000 1 000 0.3b; 50a

Cu (mg/l) 4.4� 4.1 0.3 19.4 2 000 20,000 0.3b

Zn (mg/l) 55.0� 71.5 7.0 237 3 000 5 000 0.02b; 10a

Mn (mg/l) 34.2� 55.8 2.3 179 500 500 0.2b

a Reporting limits for flame atomic absorption spectrometry.b Reporting limits for graphite furnace atomic absorption spectrometry.

pH

55,25,45,65,866,26,4

58,1

0,1

232,4253,7

0

50

100

150

200

250

300

Precip

itatio

n (m

m)

Nov Mar May Jul

010203040506070

Co

nd

uctivity (µ

S/cm

)

0

Ca

0,1

0,2

0,3

0,4

0,5

0,6

Co

ncen

tratio

n (m

g/L

)

Fe

0200400600800100012001400

Co

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tratio

n (µ

g/L

)C

on

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)

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)C

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Zn

020406080100120140160

Mn

0

20

40

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Nov Mar May Jul

Cu

0246810121416

Al

0

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20

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60

Mg

0

0,1

0,2

0,3

0,4

0,5

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Co

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n (m

g/L

)

Fig. 2. Precipitation values from the eastern Llanos over each sampling period and seasonal variations of pH, conductivity and total dissolved metals in the drinking

water supplied to eastern Llanos populations, Venezuela. Lines on the bars denote �S.D.

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formation lithic component (Torres and Franco, 1994; Gonza-lez de Juana et al., 1980), which is formed mainly by coarsegrained quartz sands and ferruginous materials, makes ground-water sources that have catchments entirely within this geolog-ical zone, have a relative low pH, low conductivity andextremely low Ca and Mg concentrations (see Table 2).

This extreme scarcity of Ca and Mg can produce severaldiseases in populations which use this water for drinkingand cooking purposes. Epidemiologic studies in Sweden(Nerbrand et al., 2003), Finland (Kousa et al., 2006) andTaiwan (Yang et al., 2006), where the minimum values foundfor Ca and Mg levels were much higher than the values foundin our study (average of 12.5 mg/l for Ca and 3.3 mg/l for Mgin Sweden; 4.39 mg/l for Ca and 1.00 mg/l for Mg in Finland;minimum value of 25.1 mg/l for Ca in Taiwan), have showna protective effect of Ca and/or Mg from drinking water onthe risk of death from cardiovascular diseases. Statistical stud-ies carried out in Taiwan (Yang, 1998) and Spain (Ferrandizet al., 2004) have demonstrated the protective effect of Caand/or Mg in drinking water against cerebrovascular mortal-ity. Furthermore, Ca intake from drinking water can havea protective effect on the risk of rectal cancer (Yang andChiu, 1998), whereas Mg deficiency in drinking water canproduce calcification disorders (Driessens and Verbeeck,1988) and neuropathologies including traumatic brain injury,headache, suicidal ideation, anxiety, irritability, insomnia,short-term memory loss and general depression (Eby andEby, 2006).

Since the major proportion of Ca and Mg intake for humansis via food, and to a lesser extent via drinking water, water-borne Ca and Mg can make an important contribution to hu-man total intake. The recommended dietary amounts for Mgis 6 mg/kg/day (Durlach, 1989), whereas the calcium intakeaverage in United Sates and European countries is higherthan 800 mg/day. Assuming a mean water ingestion of 2 Lper person per day, the estimated daily intakes of Ca andMg from drinking water in population living in eastern Llanosof Venezuela were 0.6 and 0.4 mg, respectively, which consti-tute only a contribution of 0.075% for Ca and 0.11% for Mg tothe intake recommended levels.

Temporal variations of the conductivity, pH and Ca and Mgconcentrations in the assessed drinking water wells were notstatistically significant. However, Ca and Mg concentrationswere higher in Chaguaramas Camp, Chaguaramas I sector Aand Chaguaramas I sector B (mean 0.56� 0.15 mg/l for Caand 0.353� 0.063 mg/l for Mg) than the other wells (mean0.09� 0.03 mg/l for Ca and 0.139� 0.049 mg/l for Mg)during the four sampling periods.

Iron concentrations showed the major temporal and spatialvariability than the other parameters under considerations.Drinking water Fe for the dry season (472� 749 mg/l) wasfound to be higher than the other periods, but the differencewas not statistically significant (Fig. 2). The high Fe concen-trations found in Chaguaramas I sector A (1500 mg/l) andChaguaramas I sector B (1840 mg/l) in comparison with theother wells (73� 94 mg/l) during the dry season could indicatea major quantity of ferruginous crusts present in the soils

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around these two wells, which are very closer. In this sense,the high residence time of groundwater in the subsoil duringdry season (low flow) can produce Fe accumulation in waterdue to the mobilization and release of Fe from Fe-rich-soilsources under low pH and/or redox conditions (under anoxicand/or redox conditions, Fe oxides in the subsoil are reducedto soluble Fe2þ). This phenomenon could be responsible forthe high dissolution of Fe during dry season in these two wells.Consequently, during the starting wet season, the Fe concen-tration in these wells is considerably decreased (240 and6 mg/l in Chaguaramas I sector A and Chaguaramas I sectorB), mainly because of the excessive internal drainage of thesoils, which cause the flushing of the Fe-rich water when therains begin to fall (see Fig. 2). This fact has also been docu-mented in groundwater from the upland areas in Scotland(Abesser et al., 2006).

The high Fe levels in reservoir waters assigned for humanconsumption can represent a risk for human health since Feexcess accumulation is correlated with the oxygen-free radicalformation, which may be carcinogenic (Stevens, 1990). Themaximum Fe concentrations found in this study were lowerthan the value proposed by WHO guidelines (WHO, 1993).VOG established 1000 mg/l as the maximum value acceptedfor drinking water (VOG, 1998). However, this value is basedin the organoleptic properties of water rather than the impacton human health, because beyond this level the taste andappearance of drinking water could usually be affected(WHO, 1993).

As shown in Fig. 2, the highest total dissolved Al concen-trations (22.5� 27.7) were found in May (starting wet season),but the difference with the other periods was not statisticallysignificant. Al and Fe in rivers and groundwater sourceshave been found to be positively correlated because thesetwo elements are commonly associated with clays (Nealet al., 2000). However, in the present study, Al and Fe didnot correlate to each other. This circumstance may be theresults of the fine fraction scarcity in the substratum lithiccomponent of this geological zone. Also, the major Fe concen-trations in comparison with Al levels can be associated withclays insufficiency and Fe-rich-soils.

Although several ecological epidemiological studies haveassociated Al in drinking water with the incidence of metaldiseases as Parkinson’s and Alzheimer’s (Flaten, 1987; Martynet al., 1989), World Health Organization explains that epide-miological and physiological evidence at present may not sup-port a causal role for Al in these diseases (WHO, 1993).However, the value proposed by WHO guidelines for Al indrinking water is 200 mg/l. In our study, the highest Al concen-tration was 73 mg/l in Chaguaramas II during the starting wetseason and the lowest Al content was 1 mg/l in Uverito duringwet season. These results were lower than WHO and VOGguidelines values, and much lower than Al concentrationsfound in drinking water (w533 mg/l) from other Venezuelanlocations as Maracaibo City (Tahan et al., 1994).

The Zn concentrations in drinking water can be muchhigh as a result of the leaching of Zn from piping and fit-tings (WHO, 1996). The mean Zn concentration in our study

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(55.0� 71.5 mg/l) was lower than WHO and VOG guidelinesvalues. Temporal variations of Zn levels were not statisti-cally significant (Fig. 2). The highest Zn concentrationswere found in Chaguaramas II (202� 28 mg/l), whichshowed relatively high concentrations (>150 mg/l) duringthe four sampling periods. The wells located in Uverito,Uverito Camp and Chaguaramas I sector A and sector Bshowed the lowest Zn concentrations, with values lowerthan 30 mg/l (mean 16� 8 mg/l). These concentrations prob-ably reflect background values, since Zn levels in surfaceand ground waters normally do not exceed 10 and 50 mg/l(WHO, 1993).

High Cu levels in drinking water have been associated withdifferent pathologies in humans. In London, there were severalreports on specified liver complaints in infant patients whowere found to live in areas served by public drinking watersupplies that contained high Cu concentrations (Fewtrellet al., 1996). Acute gastrointestinal effects, which include nau-sea, vomiting and diarrhea, may be observed in some individ-uals at Cu concentrations in drinking water above 3 mg/l(WHO, 1993). Also, elevated Cu and Mn levels in drinkingwater may have a neurotoxic potential and can produce mentaldiseases as Alzheimer’s and Manganism (Dieter et al., 2005).Even though Cu and Mn concentrations in the drinking waterwells assessed in our study were lower than the values recom-mended by WHO and VOG guidelines (WHO, 1993; VOG,1998), the Cu levels were extremely low. This Cu scarcity indrinking water could cause deficiency, since Cu is considereda bio-essential metal. The most encountered clinical manifes-tations of Cu deficiency are anemia, neutropenia and boneabnormalities (Danks, 1988). Studies realized by Badilla-Ohlbaum and Lagos (1999) expose the toxicity/deficiency

Table 3

Results of non-parametric sign test (n¼ 36) showing the differences in the concentra

the four sampling periods)

Wells A B C

E A> E B> E C> E

% 85.71 80.56 69.44

P value 0.000 0.000 0.030

No. of ties 1 0 0

Z value 4.06 3.50 2.17

F A> F B> F C> F

% 71.43 72.22 69.44

P value 0.018 0.012 0.030

No. of ties 1 0 0

Z value 2.37 2.50 2.17

G A>G N.S. N.S.

% 77.78

P value 0.002

No. of ties 0

Z value 3.17

H A>H B>H C>H

% 75.00 69.44 68.57

P value 0.005 0.030 0.043

No. of ties 0 0 1

Z value 2.83 2.17 2.03

% Indicates the percentage of variables values (pH, conductivity, Ca, Mg, Fe, Al,

ferences between wells.

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paradigm of Cu in drinking water. Moreover, low levels ofCu in drinking water have been under scrutiny from the per-spective of the potential deficiency of an essential element(IPCS, 1999).

Cu and Mn seasonal variations are depicted in Fig. 2.Drinking water Cu levels (8.4� 5.9 mg/l) in November(ending wet season) were found to be significantly higher(P< 0.05) than the other assessed periods, whereas Mnconcentrations did not show significant temporal differences.

The differences in the concentration of dissolved chemicalspecies between each well during the four sampling periodsare shown in Table 3. The sign test computes the concentrationdifferences of dissolved species between the paired values fortwo wells throughout the study (four sampling periods) andclassifies the differences as either ‘‘higher than’’, ‘‘lessthan’’ or tied. The differences between wells A, B, C and Dwere not statistically significant and were not included inTable 3. The concentrations of dissolved species in wells A,B and C (which supply water to the Chaguaramas population)are statistically higher than the concentrations of dissolvedspecies in wells E, F and H (which supply water to the Colo-radito and Uverito populations) throughout the study. This canindicate that wells E, F and H are closer from the rechargezones than wells A, B and C. Well E, located in Uverito forestcamp, showed the least concentrations of chemical species incomparison with the other assessed wells (with the exceptionof well F).

4. Conclusions

An important issue concerning the trace metals content indrinking water is the pH. The low pH values found in the

tion of dissolved species between each well throughout the study (this includes

D E F G H

D> E e N.S G> E H> E

77.14 68.57 71.43

0.002 0.043 0.018

1 1 1

3.04 2.03 2.37

N.S. N.S. e N.S. N.S.

N.S. G> E N.S. e N.S.

68.57

0.043

1

2.03

N.S. H> E N.S. N.S e

71.43

0.018

1

2.37

Zn, Mn and Cu) ‘‘higher than’’ between two wells. N.S., non-significant dif-

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drinking water assessed in our study can produce corrosion inpipes, valves, pumps and fittings, which are structural parts ofthe supply system. This process can cause partial solubilizationof the materials constituting the distribution system and can in-crease the Fe, Cu, Zn and other trace metal concentrations indrinking and cooking water. However, the Al, Zn, Cu andMn levels in drinking water supplied to Uverito, Chaguaramasand Coloradito populations were lower than the values pro-posed by WHO and VOG guidelines during the four samplingperiods. Fe concentrations during the four assessed periodswere lower than the WHO guideline value, but Fe levels foundin two wells during dry season were higher than the VOGguideline value, which is based on taste considerations ratherthan the possible impact on human health. In general, it wasthought that Fe, Al, Zn, Cu and Mn levels in the assesseddrinking water wells did not appear to be a matter of healthconcern for the Venezuelan eastern Llanos populations.

Because of the link between Ca and Mg deficiency andmortality from ischemic heart disease and other aforemen-tioned diseases, the scarcity of Ca and Mg in drinking waterwells located in the eastern Llanos of Venezuela is of extremeimportance to the health of populations in this zone. Althoughthe major proportions of Ca and Mg intake are via food, thereason why Ca and Mg in water can play a critical role is theirhigher bio-availability. These elements in water appear ashydrated ions, which are more easily absorbed than the sameelements in food. Moreover, the loss of Mg from food ishigher when the food is cooked in magnesium-poor water(Haring and Delft, 1981).

Finally, we recommended Ca and Mg supplementation asa possible way of reducing the risk of heart and other diseases.Methods of supplementary Ca and Mg can include addition ofthem to water tanks and water supplies, fortification of foods,public education to change dietary habits and oral supplemen-tation with biologically available Ca2þ and Mg2þ.

Acknowledgments

This project was partially supported by ProductosForestales de Oriente, C.A. (PROFORCA). The authors wouldlike to thank Francisco Visaez and Jorge Medina for theircollaboration in this work. Also, contributions of Lafit Moraare acknowledged.

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