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Bull Environ Contam Toxicol (2007) 78:400–404 DOI 10.1007/s00128-007-9094-x Heavy Metals in Wet Method Coffee Processing Wastewater in Soconusco, Chiapas, Mexico Y. Siu Æ G. Mejia Æ J. Mejia-Saavedra Æ J. Pohlan Æ M. Sokolov Received: 30 June 2006 / Accepted: 15 March 2007 / Published online: 20 June 2007 Ó Springer Science+Business Media, LLC 2007 Abstract One of the driving forces of the economy in southeast Mexico is agriculture. In Soconusco, Chiapas, coffee is one of the main agricultura
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  Heavy Metals in Wet Method Coffee Processing Wastewaterin Soconusco, Chiapas, Mexico Y. Siu Æ G. Mejia Æ J. Mejia-Saavedra Æ J. Pohlan Æ M. Sokolov Received: 30 June 2006/Accepted: 15 March 2007/Published online: 20 June 2007 Ó Springer Science+Business Media, LLC 2007 Abstract One of the driving forces of the economy insoutheast Mexico is agriculture. In Soconusco, Chiapas,coffee is one of the main agricultural products and is tradedon the international market. Coffee grown in this region isprocessed using the wet method in order to be commer-cialized as green coffee. In the beneficio (coffee processingplant) water is an essential resource which is required ingreat quantities (Matuk et al.,1997; Sokolov,2002) as it is used to separate good coffee berries from defective ones, asa method of transporting the coffee berries to the pro-cessing machinery, in the elimination of the berry husk from the coffee grains (pulping) and finally in the post-fermentation washing process. This process gives rise toone of the smoothest, high-quality coffees available (Zul-uaga,1989; Herrera,2002). Currently, many producers in Soconusco are opting for ecological coffee production,which has, among its many criteria, human health andenvironmental protection (Pohlan,2005). Furthermore,increasing concern during the past few years regarding theproduction of food that is free from contaminants such asheavy metals, and recent environmental policies in relationto aquatic ecosystem protection, have given rise to ques-tions concerning the quality of water used in coffeeprocessing, as well as pollutants produced by this agroin-dustry. Water used in the coffee processing plants srci-nates from the main regional rivers whose hydrologicalbasins stretch from the Sierra Madre mountain range downto the coastal plain. As well as providing water, these riversalso receive the wastewater produced during coffee pro-cessing (Sokolov,2002).There are no previous studies pertaining to heavy-metalpollution in these rivers, however, the presence of theseelements in river water could be related to the compara-tively recent geology of the region (Mu¨llerried,1957).Heavy metals could also be a result of the coffee agroin-dustry as the metals considered in this study; lead (Pb),copper (Cu), iron (Fe), zinc (Zn), manganese (Mn) andarsenic (As), are regarded as part of the residual com-pounds produced by agroindustrial activities (Adriano,1986; Metcalf and Eddy,1996). These metals are classified as priority and Pb, Cd and As are regarded by the WorldHealth Organization as possible causes of cancer in hu-mans. The aim of this study is to determine the concen-tration of Pb, Cu, Cd, Mn, Zn, Fe, Ni, As, the pH,conductivity, turbidity, dissolved oxygen, chlorides, hard-ness, phosphorous, nitrates and total nitrogen in the waterthat is used and discharged in wet method coffee pro-cessing. Materials and Methods This study was carried out in three wet method processingplants located in the Santa Fe´, Eduviges and Chinice´coffee  fincas (plantations) in the Soconusco region of Chiapas,Mexico. The Santa Fe processing plant is supplied by waterfrom the Comaltitla´n River, whilst the Eduviges and Chi-nice´plantations use water from the Huehueta´n River.Two samples were taken at each processing plant duringthe 2005 coffee-harvesting season. Three sampling sites Y. Siu Á G. Mejia Á J. Pohlan Á M. Sokolov ( & )El Colegio de la Frontera Sur, Carretera Antiguo AeropuertoKm.2.5, CP. 30700 Tapachula, Chiapas, Me´xicoe-mail: msokolov@tap-ecosur.edu.mxJ. Mejia-SaavedraFacultad de Medicina, Universidad Auto´noma de San LuisPotosı´, Av. Venustiano Carranza No. 2405, San Luis Potosı´,Me´xico  123 Bull Environ Contam Toxicol (2007) 78:400–404DOI 10.1007/s00128-007-9094-x  were selected at each plant: where water enters the pro-cessing plant (inflow), at the pulping process stage, andfinally at the point of wastewater discharge into the river(outflow). Two samples were taken at each site, one inorder to analyze heavy metals, collected in 250 ml VWRTrace Clean polyethylene bottles and the other to deter-mine chemical parameters, collected in one liter Nalgenbottles. The samples were conserved at 4 ° C before beingtransported to the laboratory. The samples that were to beused for heavy metal analysis were conserved in nitric acidat pH 2.In situ pH (pH meter, HI98127 Hanna USA), conduc-tivity, turbidity (Electrode Water Checker U10 HoribaUSA) and dissolved oxygen (oxygen meter HQ10 HACHLDU, USA) were all determined using selective electrodes.In the laboratory, chloride concentration was determinedusing the argentometric method, water hardness by ethy-lenediaminetetracetic acid (EDTA) titrimetric, total phos-phorous using the tin chloride method, nitrates byspectrophotometer and total nitrogen using the Kjeldalmethod (APHA,1995).In order to determine heavy metal measurements, thepulping process and discharge water samples were filteredas they presented high organic matter content. The samplestaken at the entrance to the processing plant were analyzedwithout any previous treatment. The analysis of Pb, Cu, Cdand Mn was carried out using a 3110 atomic absorptionspectrometer with a HGA-600 graphite furnace and an AS-60 Perkin Elmer autosampler. Zn, Fe and Ni were deter-mined in a SpectrAA 220 vanian flame atomic absorptionspectrometer. Arsenic was measured in a Perkin ElmerPrecisely A Analyst 200 atomic absorption spectrometercoupled with a FIAS 100 flow injection analysis systemand a AS 90 Perkin Elmer autosampler. Calibration curveswith 1000 mg/L SIGMA standards were elaborated foreach metal analyzed and 0.2% HNO3 was used as a dilu-tant. Intensitron Perkin Elmer and Varian hollow cathodelamps were used. The general specifications of the equip-ment used for the detection of each element are given inTable1. Results and Discussion The physical and chemical characteristics of the water thatentered the coffee processing system were notably modi-fied in the pulping stage (Table2), pH and dissolvedoxygen levels were markedly reduced and the water wasacidified by the chemical composition of the coffee berrypulp (Zuluaga,1989).The mean pH value for the evaluatedcoffee processing plants was five. Sokolov (2002) andMejia (2006) report values ranging from 4.5 to 5.5 inpulping process water. The high organic matter contentsaturates the water, reducing the dissolved oxygen con-centration. The chemical components of the coffee berrypulp were dissolved; thus, values of conductivity, turbidity,salinity, chlorides, hardness, nitrates, phosphorous andnitrogen all increased.Water contaminated by coffee components is dischargeddirectly into the rivers; Matuk et al. (1997) and Sokolov(2002) mention that these wastewaters cause serious des-equilibrium in aquatic ecosystems. In this study, all thewastewater physicochemical parameters were below themaximum permitted limits established by the officialMexican environmental regulations (1996) regarding waterdischarged into rivers. In general, wastewaters srcinatingfrom coffee processing plants present high organic matterconcentrations (Zuluaga,1989). It is worth pointing outthat due to hurricane Stan in 2005, coffee producers suf-fered huge losses and were harvesting mainly defective,damaged coffee berries. Mejia (2006) states that waste-waters generated from the processing of defective berriespresent lower concentrations of nitrogen, phosphorous andtotal suspended solids (40, 30 and 110 mg/L, respectively).With the exception of Zn and Ni, all the identified heavymetals (Pb, Cd, As, Cu, Mn and Fe) were detected in thewater entering the coffee processing plant, as all theseelements are found naturally in the river water that suppliesthese plants. The concentrations detected were below themaximum permitted limits for water for general use andhuman consumption established by the Official MexicanEnvironmental Regulations (1994). All the identified heavy Table 1 Condition of equipment used for heavy metaldetectionThe results were analyzed usinganalysis of variation (ANOVAwith a p \ 0.05 significancelevel by means of the JMPstatistic programElement Method Wave length/slit (nm) Lamp current (mA) Detection limitPb Graphite furnace 228.8 / 0.7 6 0.113 l g/LCu Graphite furnace 324.8 / 0.7 6–15 0.014 l g/LCd Graphite furnace 283.3 / 0.7 10–12 0.25 l g/LMn Graphite furnace 279.5 / 0.2 20–25 0.025 l g/LZn Flame 213.9 / 1 5 0.1 mg/LNi Flame 232 / 0.2 5 0.7 mg/LFe Flame 248.3 / 0.2 25–40 0.03 mg/LAs Hydride Generation 193.7 / 0.7 10 0.1 l g/LBull Environ Contam Toxicol (2007) 78:400–404 401  123  metals, except for Pb, increased during the coffee pulpingprocess (Table3). Pb is regarded as one of the most toxicheavy metals (ATSDR,2005), characterized by a lack of mobility and a tendency to be absorbed by organic matter(Moore and Ramamoorthy,1984). Therefore, the reductionin Pb concentration in the pulping process and dischargewater is probably due to some Pb remaining in the coffeepulp.Cadmium was the least concentrated metal found in theprocessing waters of the three coffee processing plants;however, in the pulping process and discharge water theconcentrations increase when compared with the waterentering the processing plant. The same pattern is displayedwith As (Fig.1). Furthermore, notable differences are ob-served between the three coffee processing plants. Theconcentration of As in the water entering each plant wasdifferent due to variations in natural occurring elements ineach river. The increase in Cd and As detected in thepulping-stage water in the studied processing plants isprobably due to the type of machinery which is used duringthe process; Cd and As are typical residual elements pro-duced in agroindustrial activities as Cd forms part of themachinery enamel and red paint, while As is used as anadditive in metal alloys such as the lead and copper onesused for making machinery (Metcalf and Eddy,1996;Valde´s,1999). Friction between the coffee berries and themachinery, and the acidity of the pulping water, could haveprovoked a modification of the machinery enamel andpaint. In the pulping water from the Santa Fe plantationprocessing plant there was a higher concentration of As(9.1 l g/L). This could be due to the pulping water in thisplant having the most acidic pH values (4.3), which couldresult in greater machinery corrosion. The concentrationsof Cd and As in the discharge water in the three processingplants were less than those measured in the pulping-processwater but higher than in the water entering the processingsystem. Fortunately these concentrations were below themaximum permitted limits established for discharge wa-ters, since these elements are considered by the WorldHealth Organization as toxic contaminants and have car-cinogenic effects in humans (Herna´ndez et al.,1999).The presence of Zn in wet method processing was ob-served only in the pulping water from the Eduviges coffeeprocessing plant and in the discharge water from all three Table 2 Physicochemicalcharacteristics of water in wetmethod coffee processing plantsat the Santa Fe, Eduviges andChinice coffee plantationsNA = not applicable, *water forgeneral use and humanconsumption, **waterdischarged in riversPhysicochemicalparametersWater enteringprocessingplant (inflow)Pulping-stagewaterDischargewastewater(outflow)Maximum permitted limits*NOM-127-SSA 1–1994**NOM-001-ECOL-1996pH (units) 6.7–7.1 4.3–5.4 5.3–5.7 6.5–8.5 5–10Conductivity ( l S/cm) 50–263 400–1,600 429–578 NA NATurbidity (NTU) 8- 117 584–927 309–685 5 NADissolved oxygen (mg/L) 7.4–7.7 2.2–4.3 3.0 NA NASalinity ( & ) 0.0 0.01–0.07 0.01–0.02 NA NAChlorides (mg/L) 3.0–4.2 3.5–5.2 3.0–4.2 250 NAHardness (mg/L) 20–152 59–206 59–206 500 NANitrates (mg/L) 0.4–3.8 3.3–4.4 3.8–5.9 10 NAPhosphorous (mg/L) 0.4–1.3 11–70 5–25 NA 30Nitrogen (mg/L) 0.6–3.0 37–64 25–64 NA 60 Table 3 Mean heavy metalconcentrations ( l g/L) detectedin water from wet methodcoffee processing plants of Soconusco, Chiapas, MexicoND = not detected, NA = notapplicable, *water for generaluse and human consumption**water discharged into rivers; a,b,c statistical differences(  p \ 0.05)Heavymetals( l g/L)Water enteringprocessingplant (inflow)Pulping-stagewaterDischargewastewater(outflow)Maximum permitted limits*NOM-127-SSA1–1994**NOM-001-ECOL-1996Pb 2.5 a 0.8 b 0.8 b 10 400As 2.9 a 6.4 b 4.5 a 50 200Cd 0.25 a 0.35 a 0.39 a 5 200Zn ND 6.7 a 13.7 a 5,000 20,000Cu 10 a 113 b 36 c 2,000 6,000Mn 63 a 200 b 420 c 150 NAFe 212 a 1,013 b 1,872 b 300 NANi ND ND 23 NA 4,000402 Bull Environ Contam Toxicol (2007) 78:400–404  123  plants. This could indicate that the Zn srcinated in fertil-izers or chemical formulas used for pest control such as Znsulphate applied to coffee plants before the harvest (Mar-tinez, 2004). In addition, a soil analysis of the Santa Fe´plantation reveals that there is an excess of Zn in the soil.Copper concentrations differ greatly between samplingsites and the three processing plants (Fig.2).In the pulping-process water in the Santa Fe and Eduviges processingplants, copper concentrations increased to 140 and 160 l g/ L respectively and although in the Chinice´plant theseconcentrations were not reached, higher values weremeasured than in the entrance water. This is probably dueto the wearing of the machinery that is made mainly fromcopper; Klein et al. (1974) report high copper concentra-tions in wastewater from non-metallic industrial systemssuch as those in the food industry. Although the copperconcentrations in the discharge water decrease they are stillgreater than in the entrance water. In the Chinice´coffeeprocessing plant, higher concentrations of copper (50 l g/ L) are discharged than in the other two processing plants;however, these values are below the maximum permittedlimits for wastewater discharge into rivers (Official Mexi-can Environmental Regulations,1996).The concentrations of Mn and Fe in the three coffeeprocessing plants showed notable differences but all fol-lowed the same pattern; the discharge-waters contained agreater concentration of Mn and Fe than the water enteringthe plant and the water in the pulping process. (Figure3).In Santa Fe the water entering the plant displayed a higherconcentration of manganese (90 l g/L) than in the otherplants due to the nature of the Comaltitla´n River whichsupplies the water for coffee processing. Iron was the metaldetected in the greatest concentrations, moreover, in theChinice´coffee plantation it exceeded the maximum per-mitted limits (300 l g/L) for general use and human con-sumption established by the Mexican EnvironmentalRegulations (1994). Whilst iron is not harmful to humanhealth, this element, which is found in soluble form, iseasily oxidized, damaging water pipes, pumps and othermachinery. In the pulping process manganese and ironconcentrations increased in all the coffee processing plants,probably because these metals are natural minerals foundin coffee. Zuluaga (1989) reports iron concentrations incoffee pulp, however, the extremely high amounts of ironin the pulping water (1,500 l g/L) are the result of corro-sion and wearing of the machinery, which is made of ironand copper.In the case of the Santa Fe´coffee processing plant thedischarge wastewater presented the highest Mn and Feconcentrations, reaching values of 290 and 2,295 l g/L,respectively. This could be due to the high levels of Mn(14,600 l g/L) and Fe (132,533 l g/L) found in the soil(Martı´nez, 2004). Although the official Mexican environ-mental regulations do not stipulate maximum permittedlimits for these elements in discharge systems, and thereare no records of harmful effects on human health, theseelements can oxidize easily, causing problems such asstaining of clothes, blocking of pipes, pumps and othermachinery related to water supply systems in communitiesdownstream that are supplied by the river water. Further-more, the elevated concentrations of Mn can acceleratebiological growth in water distribution systems, contrib-uting to problems of the taste and smell of the water(RIPDA,2003). 012345678910    é   F  a   t  n  a   S  s  e  g   i  v  u   d   E   é  c   i  n   i   h   C   é   F  a   t  n  a   S  s  e  g   i  v  u   d   E   é  c   i  n   i   h   C   é   F  a   t  n  a   S  s  e  g   i  v  u   d   E   é  c   i  n   i   h   C EntranceCdAsPulping Discharge Fig. 1 Concentrations of cadmium and arsenic ( l g/L) detected in thewater of wet method coffee processing plants at Soconusco, Chiapas,Mexico 050100150200    é   F   a   t  n  a   S  s  e  g   i  v  u   d   E   é  c   i  n   i   h   C   é   F   a   t  n  a   S  s  e  g   i  v  u   d   E   é  c   i  n   i   h   C   é   F   a   t  n  a   S  s  e  g   i  v  u   d   E   é  c   i  n   i   h   C EntranceZnCuPulping Discharge Fig. 2 Concentrations of zinc and copper ( l g/L) detected in thewater of wet method coffee processing plants at Soconusco, Chiapas,Mexico 05001000150020002500    S  a  n   t  a   F   é   S  a  n   t  a   F   é   C   h   i  n   i  c   é   C   h   i  n   i  c   é   E   d  u  v   i  g  e  s   E   d  u  v   i  g  e  s   S  a  n   t  a   F   é   C   h   i  n   i  c   é   E   d  u  v   i  g  e  s Entrance MnFe Pulping Discharge Fig. 3 Concentrations of manganese and iron ( l g/L) detected in thewater of wet method coffee processing plants at Soconusco, Chiapas,MexicoBull Environ Contam Toxicol (2007) 78:400–404 403  123
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