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Chemical fractionation of boron and heavy metals in soils irrigated with wastewater in central Mexico Carlos A Lucho Constantino a Francisco Prieto Garc ab Luz Mar a Del Razoc Refugio Rodr guez Va zquez a He ctor M Poggi Varaldoa aCINVESTAV IPN Depto de Biotecnolog a y Bioingenier a Apdo Postal 14 40 Me xico 07000 D F Mexico bUAEH Centro de Investigaciones Qu micas Carr Pachuca Tulancingo km 4 5 Cd Universitaria CP 42067 Pachuca Edo de Hgo Mexico cCINVESTAV IPN Seccio n Externa de Toxicolog a Me xico D F Mexico Received 18 May 2004 received in revised form 10 December 2004 accepted 15 December 2004 Abstract The aim of the present work was to evaluate the accumulation of selected trace elements boron cadmium chromium mercury lead and arsenic inagricultural soils ofthe Zone 1 ofthe Irrigation District 03 DR03 inthe State ofHidalgo Mexico The soils of Zone 1 have on average been irrigated with raw wastewater for about 20 years range 6 41 years A clear positive correlation between the organic carbon contents in soils and the irrigation time was found The total concentrations of the elements analysed were 0 51 1 89 mg Cd kg 1 11 59 27 42 mg Cr kg 1 3 99 47 08 mg Pb kg 1and 9 2 123 8 mg B kg 1 Samplesoftopsoils 0 30 cm wereextractedusingamodifi edTessier methodaccordingtoasixfractionscheme easilysoluble F0 exchangeable F1 bound to carbonates F2 associated with oxides of iron and manganese F3 bound to organic matter and sulphides F4 and the residual fraction F5 In general the elements were distributed in the fractions F0 F4 and F5 The concentrations of total arsenic and mercury were below the detection limits 0 03 and 0 01 mg kg 1 respectively except for 0 77 mg Hg kg 1in one soil The concentrations of total Cr and Pb did not exceed the maximum permissible levels set by the regulations of the European Union whereas total Cd was on the verge A linear increase between the total metal concentrations and the irrigation time was found In this study several crops harvested from soils showed Cd and Pb contents higher than those recommended by the Dutch and German guidelines It can be concluded that the soils may pose a potential risk to the trophic chain and effective restrictions for the cultivation of crops that are sensitive to or known to accumulate heavy metals i e nopal onions garlic lettuce potatoes beets and turnips should be considered 2005 Elsevier B V All rights reserved Keywords Agriculture Fractionation Irrigation Plants Soil Trace elements Wastewater 1 Introduction Water demand for agricultural industrial com mercial and domestic uses is steadily increasing The Agriculture Ecosystems and Environment 108 2005 57 71 Corresponding author Tel 52 55 5747 3800 x4324 fax 52 55 5747 7002 E mail address hectorpoggi2001 H M Poggi Varaldo 0167 8809 see front matter 2005 Elsevier B V All rights reserved doi 10 1016 j agee 2004 12 013 increase in demand is due to the increase of world population characterized by an accelerated growth of the urban population with almost half of the total population living in cities by the early 2000s EPA 1992 The growing urbanization increases domestic water usewhile supplying wastewater that can be used for non potable purposes such as agricultural irriga tion Thewastewater is becoming a preferred marginal water source since its supply is reliable and uniform and is increasing due to population growth and increased awareness of environmental quality In principle the costs associated to this water source are low compared with those of other water sources Bahri 1999 In developed countries the predominant trend in agricultural wastewater reuse is to irrigate treated wastewater Haruvy 1997 Bahri 1999 Smith et al 1996 Nicholson et al 2003 In contrast most developing countries such as Mexico Peru Chile and Argentina rely on raw wastewater for agricultural irrigation Siebe and Cifuentes 1995 Peasey et al 2000 Mexico City and its metropolitan region discharge 60 m3s 1of raw wastewater that has been used to irrigate agricultural land at the Mezquital Valley in Mexico for nearly 100 years The Valle del Mezquital is one of the largest if not the largest in theworld that is using raw wastewater from a Megalopolis Torta jada and Castela n 2003 British Geological Survey and Comisio n Nacional del Agua 1995 INEGI 1999 The wastewater of Mexico City and its metropolitan area is transported to the Mezquital Valley by three main canals Tajo de Nochistongo Gran Canal and Emisor Central and used to irrigate the 83 000 ha of the Irrigation Districts DR03 and 100 DR 100 Siebe and Cifuentes 1995 Jime nez and Landa 1998 The DR03 has a surface area ca 45 000 ha District 03 and inhabits 500 000 persons with 27 500 farmers Its annual agricultural production in 1998 consisted of 3 104 434 ton alfalfa 526 650 ton of corn 97 153 ton of forage oat 24 030 ton of bean 15 410 ton of marrow 14 688 ton of green chili 17 941 ton of tomatoes green plus red varieties among others INEGI 1999 Crops grown in this area are mainly marketed to Mexico City and Pachuca capital city of Hidalgo State generating nearly US 100 000 000 In Mezquital Valley the wastewater is used as a sourceofirrigationwateraswellasasourceoforganic matter soil conditioner and humus replenisher and plant nutrients such as nitrogen phosphorus and potassium allowing the farmers to minimize the costs of mineral fertilizers Since the precipitation at the DR03 is relatively low 450 mm year 1 in contrast theevaporationratecanreachvaluesupto 2100 mm year 1 British Geological Survey and Comisio n Nacional del Agua 1995 the irrigation with wastewater has become an indispensable practice for sustaining the agricultural production since 1896 Herna ndez Silva et al 1994 British Geological Survey and Comisio n Nacional del Agua 1995 At the DR03 fl ooding is the main irrigation technique used and the applied amounts range between 80 and 140 cm year 1 British Geological Survey and Comi sio n Nacional del Agua 1995 although it has been reported up to 200 cm year 1for alfalfa Medicago sativa Siebe and Cifuentes 1995 Most of the irrigated water is raw wastewater consisting of a mixture of municipal sewage water and a substantial share of industrial effl uents This is of concern because the wastewater contains several potentially toxic trace of organic and inorganic substances such as heavy metals boron salts etc that may negatively affectthelong termproductivityofthesoil theanimal and human health Bahri 1999 In the last 10 15 years there has been a moderate interest on the Mezquital Valley as a case study The studies have focused on the revision of the micro biological guidelines for helminth ova and bacterial indicators total coliforms and fecal coliforms of C A Lucho Constantino et al Agriculture Ecosystems and Environment 108 2005 57 7158 CECcation exchange capacity dwdry weight DR 103 Irrigation District 103 DR 100 Irrigation District 100 ECelectrolytic conductivity fwfresh weight NURnitrogen uptake rate OCorganic carbon OMOM P signifi cance probability P F for the analysis of variance of the regression R correlation coeffi cient TKNtotal Kjeldahl nitrogen wastewater reused in the agriculture irrigation Peasey et al 2000 as well as on the monitoring of trace elements heavy metals boron accumulation on soils Ram rez Fuente et al 2002 Flores et al 1997 Mendoza et al 1996 Siebe 1995 Siebe and Cifuentes 1995 Flores Delgadillo et al 1992 Cajuste et al 1991 and groundwater pollution Gallegos et al 1999 With the exception of Flores et al 1997 the other cited studies although very valuable did not include trace elements of interest in the trophic chain such as arsenic and mercury did not assess the fractionation of potentially toxic elements in the different fractions Lucho Constantino et al 2002 ofthetopsoilanddidnotreportthe geographical position of the soils sites investigated The sequential extraction method of Tessier et al 1979 is one of the most widely accepted and used for the distribution analysis of trace elements in soils sediments and wastes Manan et al 1987 Kim and Fergusson 1991 Ure et al 1993 Accomasso et al 1993 Hon Wah et al 1997 Pe rez et al 2001 Navas and Lindhorfer 2002 Liu et al 2003 Tessier et al 1979 partitionedtracemetalstakingintofi vefractions likelytobe affected byvarious environmental conditions as follows i fraction 1 that is easily exchangeable it has been demonstrated that trace metals can be adsorbed onto the soil matrix and may desorb and become available as a result for example of changes in water ionic composition ii Fraction 2 boundtocarbonatesandsusceptibletopHchanges iii fraction3bound to ironandmanganese oxidesas these oxides are excellent scavengers for trace metals and may result thermodynamically unstable under anoxic conditions i e lowoxidation reductionpotential iv fraction4boundtoseveralformsofsoilorganicmatters detritus organic coatings on mineral particles living organisms etc whichcomplexandpeptizewithhumic and fulvic acidsas well bioaccumulate in certain living organisms Under oxidizing conditions in natural waters the organic matter can be degraded and this in turn may lead to a release of trace metals v the fraction 5 residual comprises primary and secondary minerals within the crystal structure that is unlikely to be released in the mid and long term under the conditions normally found in nature The aim of the present work was to evaluate the accumulation of selected trace elements boron arsenic cadmium chromium mercury and lead in agricultural soils of a portion Zone 1 of the irrigation district 03 of the Mezquital Valley in the State of Hidalgo Mexico We divided the valley into three zones in this article we report results of the Zone 1 which is a region that has been irrigated with raw wastewaters for about 20 years average range 6 41 years It was chosen as the fi rst part of a more comprehensive study covering the full district whose results are intended to be used by the environmental authorities of the State of Hidalgo and Mexico City Samples of topsoils 0 30 cm depths were extracted using a modifi ed Tessier method giving a six fraction scheme 2 Materials and methods 2 1 Study site The Zone 1 of the DR03 is located in central Mexico in the Mezquital Valley at latitude 208000N and longitude 998100W and it has a surface area of 8913 ha which represents 18 6 of the arable soils Fig 1 The Zone 1 is a region of DR03 characterized by relatively short irrigation times range between 6 and 41 years with an average of 20 years and no crop restrictions i e all crops can be planted including fresh produce regardless of raw or cooked consump tion In the Mezquital Valley the climate is arid with an average temperature of 16 7 8C and a mean annual precipitation of 450 mm mainly during the summer British Geological Survey and Comisio n Nacional del Agua 1995 The soils of Zone 1 are predominantly Phaeozems according to the FAO classifi cation INEGI 1984 Amorphous silicates are very abundant being the andesite the most abundant although anorthite quarzite cristobalite and silicon oxides are also present as minor components Prieto Garc a and Lucho Constantino 2002 Topsoils were sampled using a random stratifi ed method Pulido 1994 Composite samples for each site consisted of 13 cores of soil from the Ap horizon 30 cm depth from 3adjacent plots total of39 cores The cores were mixed into one composite sample for each soil and analyzed by triplicate Soils were classifi ed according to their physical texture and the irrigation time Table 1 C A Lucho Constantino et al Agriculture Ecosystems and Environment 108 2005 57 7159 2 2 Characteristics of the irrigation wastewater Mexico City generates 1637 million m3of waste water per year and only 9 receives some type of treatment Tortajada and Castela n 2003 British Geological Survey and Comisio n Nacional del Agua 1995 reported that the concentration of heavy metals and boron in wastewaters from Emisor Central canal and Salado River contributing to 70 and 22 of the total irrigated wastewater in DR03 respectively were 0 036 0 053 mg Cr VI L 1 0 86 1 76 mg B L 1 and 0 037 0 300 mg Pb L 1 These concentrations seem to be below the maximum allowable limits set as monthly averages issued in the current Mexican regulations for use in agricultural irrigation NOM 001 SEMARNAT 1996 Diario Ofi cial de la Federa cio n 1996 We analyzed several samples of waste water used for irrigating soils in Zone 1 data not shown and the parameter values fell within the ranges reported in the international literature cited above 2 3 Chemical analyses The soil samples were air dried and sieved mesh 10 ASTM 2 mm before analysis Soil texture cation exchange capacity CEC with barium acetate nitrate NO3 and nitrite NO2 sulphate and chloride were analyzed according to the methods of C A Lucho Constantino et al Agriculture Ecosystems and Environment 108 2005 57 7160 Fig 1 Map of the Irrigation District DR03 Mezquital Valley State of Hidalgo Mexico Primo and Carrasco 1973 The total Kjeldahl nitrogen TKN was determined by the method outlined in Bremen and Mulvaney 1982 The inorganic carbon was determined by adding 20 mL of 1 M HCl solution to 1 g air dried soil and total carbon content was determined by digesting the sample with a strong acid oxidizing solution accord ing to the method described by Amato 1983 The organic carbon was found by difference The pH and electrolytic conductivity EC were determined in a water soil extract 1 1 using a Beckman pH meter model F41 equipped with a combined electrode glass Ag AgCl and a conductivity meter model HI8633 Hanna Instruments Co respectively The calibration and measuring procedures of the manufacturers were followed The metals in the soils were sequentially extrac ted following a slight modifi cation of the method described by Tessier et al 1979 here named modifi ed Tessier method The modifi cation consisted of initially extracting with double distilled water 2 g ofsoilshakenfor4 hindistilledwaterof EC 0 02 mS cm 1 followed by centrifugation dur ing 10 min at 3000 rpm This step F0 represents the fraction that is water soluble and most easily available to plants and easily leacheable into the groundwater It has been proposed and used by others Kabata Pendias 1993 Siebe 1995 Kabata Pendias and Pendias 2001 p 47 Following this the usual extractions according to the conventional Tessier s method were conducted using 1N MgCl2at pH 7 for exchange cations F1 CH3COOH CH3COONa at pH 5 for metals bound to carbonates F2 0 04 M NH2OH HCl in 25 CH3COOH for metals bound to Fe and Mn oxides F3 8 8 M H2O2in 0 02 M HNO3 during 5 h at 85 8C followed by addition of a solution of 3 2 M CH3COONH4in 25 HNO3for metals bound to organic matter and sulphides F4 and extraction with 10 mL concentrated HNO3and a buffer solution of CH3COOH CH3COONa at pH 5 for metals in the residue F5 As a check total metals were determinedinanextractfromaciddigestionwith HNO3 HClO4 Morabito 1995 Cropsgrownonsoilsatselectedsites withinZone1 were collected and washed in 3 HCl immediately after sampling and then dried at 65 8C The plant samples were ground in a stainless steel grinder Ten milliliters of concentrated nitric acid was added in to C A Lucho Constantino et al Agriculture Ecosystems and Environment 108 2005 57 7161 Table 1 Physical and chemical characteristics of soils irrigated with wastewater in zone1 of Irrigation District 03 DR03 Mezquital Valley State of Hidalgo Mexico dw dry weight Soils sitePositionIrrigation time years EC dS m 1 a CEC cmol kg 1 b pHH2OSO42 g kg 1soil Cl g kg 1soil Organic carbon g kg 1soil Total nitrogen g kg 1soil NO3 g kg 1soil NO2 g kg 1soil NH4 g kg 1soil USDA textural classifi cationc S1 Julia n Villagra n 2082405000N 9980602100W 61 11 0 10 d15 60 2 39 9 09 0 25 0 10 0 02 0 12 0 01 3 14 0 20 1 44 0 10 0 16 0 01 5E 031 27 0 02 Clay S2 Ixmiquilpan2082902100N 9981501300W 71 75 0 06 68 07 4 27 8 71 0 19 0 67 0 15 0 22 0 02 3 58 0 35 1 45 0 11 0 17 0 01 7E 031 26 0 02 Clay loam S3 Ixmiquilpan2082802400N 9981205700W 1014 10 1 07 57 46 6 95 8 10 0 03 2 46 0 33 3 13 0 01 3 44 0 23 9 66 0 80 8 74 0 04 15E 030 90 0 01 Clay S4 San Salvador2081704000N 9885804600W 321 49 0 13 52 41 6 75 8 95 0 01 0 01 0 001 0 22 0 03 12 97 0 95 2 01 0 15 0 50 0 03 nde1 50 0 01 Clay S5 Actopan2081403100N 9885502900W 381 56 0 22 51 19 2 50 8 79 0 01 0 03 0 008 0 20 0 02 13 72 1 14 0 78 0 12 0 47 0 02 nd0 30 0 01 Clay loam S6 Lagunilla2082101500N 9980105700W 411 06 0 05 31 85 6 26 8 50 0 01 0 11 0 01 0 01 0 002 14 91 1 15 1 62 0 03 0 20 0 01 nd1 42 0 01 Clay loam a Electrolytic conductivity in water soil extract 1 1 b Cation exchange capacity c USDA United States Department of Agriculture d Numbers in parentheses are standard deviations e Not detected 2 g of representative plant sample in a Tefl on vessel and digested for 10 min in a microwave oven Mars X The extracts from soils and plant digestates were analyzed for As and Hg using a Varian SpectrAA 800 atomic absorption spectrophotometer equipped with Zeeman device fl ame with hydride generation for As and cold vapor for Hg Boron cadmium chromium and lead were determined in a Perkin Elmer 3000 XL inductive coupled plasma equipment 3000XL fol lowing the method 6010 USEPA 1986 Double distilledwaterwasusedandthereagentsusedforAAS were ultrapure and further purifi ed by chelation extraction Welz 1985 The detection limits for total metals in soils and plants were calculated according to Skoog and Leary 1992 and determined to be in mg kg 1 0 06 for Cd 0 01 for Hg 0 03 for As 0 003 for B 0 15 for Cr and 0 17 for Pb Quality control for total metals included the analysis of a standard reference soil from the National Institute of Standards and Technology SRM 2709 concurrently with soil samples Recoveries ranged from 96 5 to 104 and the coeffi cient of variation ranged between 3 and 10 in triplicate analysis 2 4 Statistical analysis Descriptive statistical analysis was done for all variables Regression analysis was performed to assess