Science of the Total Environment 409 (2011) 3527–3536

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Biomonitoring of Cd, Cr, Hg and Pb in the Baluarte River basin associated to a miningarea (NW Mexico)

J. Ruelas-Inzunza a,⁎, C. Green-Ruiz b, M. Zavala-Nevárez b, M. Soto-Jiménez b

a Technological Institute of Mazatlán, P.O. Box 757, Mazatlán, Sinaloa, Mexicob Universidad Nacional Autónoma de México/Instituto de Ciencias del Mar y Limnología, P.O. Box 811, Mazatlán, Sinaloa, Mexico

⁎ Corresponding author. Tel.: +52 669 983 8400; faxE-mail address: ruelas@ola.icmyl.unam.mx (J. Ruelas

0048-9697/$ – see front matter © 2011 Elsevier B.V. Aldoi:10.1016/j.scitotenv.2011.05.035

a b s t r a c t

a r t i c l e i n f o

Article history:Received 16 December 2010Received in revised form 10 May 2011Accepted 18 May 2011

Keywords:FishCrustaceansMexicoBaluarte RiverMetalsMining area

With the purpose of knowing seasonal variations of Cd, Cr, Hg and Pb in a river basin with past and presentmining activities, elemental concentrations were measured in six fish species and four crustacean species inBaluarte River, from some of the mining sites to the mouth of the river in the Pacific Ocean between May 2005and March 2006. In fish, highest levels of Cd (0.06 μg g−1 dry weight) and Cr (0.01 μg g−1) were detectedduring the dry season in Gobiesox fluviatilis and Agonostomus monticola, respectively; the highest levels ofHg (0.56 μg g−1) were detected during the dry season in Guavina guavina andMugil curema. In relation to Pb,the highest level (1.65 μg g−1) was detected in A. monticola during the dry season. In crustaceans, highestlevels of Cd (0.05 μg g−1) occurred in Macrobrachium occidentale during both seasons; highest concentrationof Cr (0.09 μg g−1) was also detected inM. occidentale during the dry season. With respect to Hg, highest level(0.20 μg g−1) was detected during the rainy season in Macrobrachium americanum; for Pb, the highestconcentration (2.4 μg g−1) corresponded to Macrobrachium digueti collected in the dry season. Consideringaverage concentrations of trace metals in surficial sediments from all sites, Cd (pb0.025), Cr (pb0.10) andHg (pb0.15) were significantly higher during the rainy season. Biota sediment accumulation factors aboveunity were detectedmostly in the case of Hg in fish during both seasons. On the basis of themetal levels in fishand crustacean and the provisional tolerable weekly intake of studied elements, people can eat up to 13.99,0.79 and 2.34 kg of fish in relation to Cd, Hg and Pb, respectively; regarding crustaceans, maximum amountswere 11.33, 2.49 and 2.68 kg of prawns relative to levels of Cd, Hg and Pb, respectively.

+52 669 984 7209.-Inzunza).

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1. Introduction

Main anthropogenic sources of metals comprise municipal andindustrial wastewaters, agrochemical compounds, disposal ofdredged materials, combustion of fossil fuels, manufacture of textiles,and smelting and mining activities. Mining wastes are of greatconcern because of their potential to pollute the surroundings of themines; in this context, Thornton (1996) considers that soil pollutionwith potentially toxic metals and metalloids represents an environ-mental hazard from abandoned mines in countries with historicmining industries. Moreover, mine wastes can affect more thesurroundings of the mines than mining operations themselves(Fernández-Caliani et al., 2009), due to the allocation of pollutantsby mine drainage and atmospheric transportation (Chopin andAlloway, 2007; López et al., 2008). Mining exploitation in the regionis mostly based in sulfides lead ores (e.g. galena) (Soto-Jiménez et al.,2006). Thus, metals non-extracted during ore processing are presentin tailings such as metallic sulfides. Most of the tailings are deposited

in creeks and form big accumulations in areas close to mines. Aciddrainage and metal leaching from tailings occur when water movesover metal sulfide and eventually forms sulfuric acid (Dudka andAdriano, 1997). Fractions of sulfide metals are also eventuallyincorporated to oxides and in a lesser extent to carbonates increasingtheir solubilities (Olvera-Balderas, 2011). Dissolved fractions of Cdand Pb (II), Cr (III) and Hg (0) are then lixiviated to groundwater andsurficial water (from creeks to rivers and eventually to coastalwaters). Some metals are also transported to river watershed byfluvial and eolian forces.

Elements termed as essential are part of biota and performimportant metabolic activities; nevertheless, at elevated concentra-tions they might be harmful. Another type of trace metals are knownas non-essential since they are not involved in metabolic activities. Inthis context, it is important to know whether metal levels inorganisms from mining areas are detrimental to them and to finalconsumers of these aquatic resources. In order to assess the degree oftrace metal contamination in a given area, it is necessary to makeanalyses of a suite of environmental samples, i.e. water, sediments orbiota. The approach of water and sediments analyses does not supplyinformation on the bioavailability (Phillips, 1977; Bryan et al., 1985);this problem can be resolved by using organisms, which reflect the

3528 J. Ruelas-Inzunza et al. / Science of the Total Environment 409 (2011) 3527–3536

bioavailability of contaminants. The term biomonitor denotes thoseaquatic species which accumulate trace metals in their tissues andmay be analyzed to monitor the bioavailability of such contaminantsin aquatic ecosystems (Rainbow and Phillips, 1994). Organisms usedas biomonitors should fulfill several requirements (Bryan et al., 1980):abundant, long lived, easy to identify and sample all over the year,tolerating high levels of metals and permitting laboratory studies ofmetal kinetics.

The studied area belongs to the Plomosas–Rosario mining district(NW Mexico). This district is located in the western branch of thenorth-northwest belt of polymetallic deposits (Clark et al., 1982) thatincludes some of the oldest epithermal deposits in Mexico (Camprubíet al., 2003). Metallic ores associated with sedimentary rocks includestratiform and strata-bound Cu deposits (Staude and Barton, 2001).Considering the historical exploitation of metals like Pb and Au(DIFOCUR, 1991) in the region, and on the basis of the renewedinterest for mineral extraction for the next 50 years, it is necessary tomonitor the occurrence of certain elements in the area in order tohave a view on the degree of metal bioavailability to representativebiota and man. The current study is the first effort to monitor tracemetal pollution in this mining region by using biomonitors; for this

Fig. 1. Locationof sampling sites in thedrainagebasinofBaluarte River inNWMexico(T—TamaSombrero; N — Nieblas).

purpose, Cd, Cr, Hg and Pb were measured in six fish species and fourcrustacean species during the rainy and dry seasons in selected sitesalong Baluarte River, from some of the mining sites to the mouth ofthe river on the Pacific coast.

2. Materials and methods

2.1. Study area

Thebasinof BaluarteRiver (betweenparallels 21° 24′00″ and23° 52′48″N;meridians 106° 06′ 00″ and 103° 44′ 24″W)accounts for a surfaceof 5323 km2 (CNDM, 1988). The river starts at the Sierra MadreOccidental in the state of Durango, crosses Sinaloa state, and ends in theshores of the Pacific Ocean (Fig. 1). Gold and silver ores were exploitedin the area (in the towns of Pánuco and Copala) since the XVI century;nowadays, minerals containing silver, lead and other metals are stillextracted (CRM, 1991). Mining activity has regained interest and newpermissions for exploration and exploitation have been granted inwidesurfaces for at least 50 years (INEGI, 2005). Theweather in this region isdry with summer rains in Rosario (35 m above sea level) and subhumid

rindo; I— Iguanero; Ch—Chupaderos; J— Las Juntas; SM— SantaMaría;B—Batanga; S—El

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with summer rains in Pánuco (330 m above sea level), with a meanannual temperature of 25 °C (García, 1973).

2.2. Field work

Sampling was carried out between May 2005 and March 2006;collections during May and June 2005, and March 2006 correspondedto the dry season while samplings performed during September,October and November 2005 belonged to the rainy season. Fish andprawns were collected from eight selected sites along the BaluarteRiver (Fig. 1), from the mining areas to the mouth of the river. Fishwere collected by using a cast net, prawns were collected by hand.Biometric information of collected biota is provided in Table 1. Aftertaxonomic identification of organisms, muscle tissue of prawns andfish were separated for the analyses. Due to the small size of somespecimens, pooled samples of three to six individuals were made. Inaddition, bedstream sediments were collected with a plastic spatulafrom 7 sites. After this, samples were placed in acid washed (Moodyand Lindstrom, 1977) plastic bags, transported to the laboratory atlow temperature (4 °C) and kept frozen until analysis.

2.3. Analytical procedure

Muscle and sediment samples were freeze-dried for 72 h (−49 °Cand 133×10−3 mbar) then ground in an agate mortar. Powdered andhomogenized muscle samples (0.25 g) were predigested overnightusing Teflon vials with caps (Savillex) and digested by using 5 ml ofquartz distilled concentrated nitric acid at 120 °C for 3 h (MESL, 1997);digestion of bulk sediment samples (0.2 g) was made by using a mix ofhigh purity concentrated acids (HNO3, HCl and HF) and capped Teflon(Savillex) vials (Loring and Rantala, 1993). Digested muscle andsediment samples were stored in polyethylene containers for furtheranalysis. Duplicated samples were analyzed. Analyses of Cd, Cr and Pbwere made by graphite-furnace atomic absorption spectrophotometry(GFAAS); Hg determinations were performed by cold-vapor atomicabsorption spectrophotometry. Measurements were made in a VarianSpectrAA220 equipment. Blanks were run with every batch of samples.Precision and accuracy of the analytical methods were assessed byreplicate (6 subsamples from a single organism and sediment sample)and using certified referencematerials consisting of fishmuscle (MA-B-3/TM) and sediment (SD-N-1/2) (IAEA, 1987). A satisfactory agreementbetween analytical results and certified values was obtained (recoveryfrom 89 to 106%; relative standard deviation from 6 to 13%). Limits ofdetection (in μg g−1) for Cd, Cr, Hg and Pbwere 0.002, 0.004, 0.014 and0.042, respectively.

In order to define statistical differences of metal concentrationsbetween the dry and rainy seasons, a Student's t test was performedby using GraphPad Prism 4.0 (Graph Pad Software, San Diego, CA). The

Table 1Collection sites and biometric information of fish and crustaceans from the drainage basin

Species Common name Feeding habit

FishMugil curema White mullet DEAgonostomus monticola Mountain mullet OGuavina guavina Guavina DEOreochromis sp. Red tilapia OGobiesox fluviatilis Mountain clingfish OOreochromis urolepis Wami tilapia O

PrawnsMacrobrachium digueti River prawn OMacrobrachium americanum River prawn OMacrobrachium occidentale Freshwater shrimp OAtya sp. Black lace pincers prawn O

D— dry; RA— rainy; T— Tamarindo; I— Iguanero; Ch— Chupaderos; J— Las Juntas; SM— Sant

ability of fish and prawns to accumulate metals from the associatedsediments was calculated by the biota–sediment accumulation factor(BSAF) according to Szefer et al. (1999):

BSAF=[Metal] in muscle of organism/[Metal] in associatedsediment.

Tolerable weekly intake of metals was estimated according to theFood Agriculture Organization/World Health Organization (FAO/WHO, 1972).

3. Results and discussion

From Table 1, it can be seen that collected biota did not occur in allsampling sites and seasons; such condition is normal in biomonitoringstudies in tropical latitudes where high biodiversity exists in compar-ison to temperate regions. Since diet is known as the main pathway ofentrance of trace metals in aquatic biota, some trophic characteristics(Harrison and Howes, 1991; Chace and Hobbs, 1969) were provided inTable 1. In general, fish and crustacean were collected in more sitesduring the dry season than during the rainy season, partly becauseremote areaswere not accessiblewhen heavy rainswere frequent. Totalmetal concentrations in bedstream sediments during the dry and rainyseason are presented in Table 2. Significant seasonal differences wereobserved for Cd (pb0.025) and Cr (pb0.10), with the highestconcentrations during the rainy season due to the increase in washing,leaching and transport (erosion) of mining tails during rainfall. For Hg alower significant difference (pb0.15) was also found; however, thisresulted from the high concentrations at El Sombrero (1.09 μg g−1) andChupaderos (1.02 μg g−1), where Ag ores have been treated by Hgamalgamation over the last four centuries (Ramírez-Meza, 1992) andmining tails enriched with this metal have been deposited elsewhere.The other four sampling sites had similar Hg concentrations during therainy (0.19 to 0.39 μg g−1) and dry (0.17 to 0.36 μg g−1) seasons.Because of the distribution of the sampling sites and the existence ofseveral active and inactive Ag and Pb mines along the tributaries ofBaluarte River, it was not observed a downstream gradient in metalconcentrations. During the dry season, the highest concentrations of Cd,Cr, Hg and Pbwere found in bedstream sediments from SantaMaria, LasJuntas, Iguanero and Tamarindo, respectively; while in the rainy season,the highest levels (Cd and Hg) occurred at El Sombrero and Tamarindo(Cr and Pb). Dissolved andparticulatemetals can be available to riverinebiota. In the river waters, the reduced form of Cr is oxidized to Cr (VI)increasing its solubility and toxicity. Predominance of sandy sedimentswith a low content of organic matter, oxidant and slightly alkaline pHconditions in the sediments of the river (besides a low availability oflabile dissolved organic carbon and sulfates in the water column),suggested that Hg methylation in the Baluarte River is not occurring(Fitzgerald and Lamborg, 2005). Thus, Hg in the studied part of Baluarte

of Baluarte River, Sinaloa (NW Mexico).

Length(cm)

Weight(g)

Site code Time of collection

32.2±1.6 375.2±63.2 T, J D19.0±3.4 91.4±42.2 Ch, T, J, SM, B D, RA21.4±3.0 141.8±58.0 Ch, S D21.5±2.7 178.6±155.4 T, I D, RA17.8±1.3 81.0±26.4 Ch D24.2±22.2 182.2±166.9 Ch, T, J, SM D, RA

3.5±5.0 4.6±6.2 Ch, J, SM, B D, RA18.0±2.8 81.5±67.3 Ch, T, B, S D, RA13.2±9.6 42.1±69.3 T, J, SM, B, N D, RA9.2±6.3 53.1±36.2 Ch, T D

aMaría; B— Batanga; S— El Sombrero; N—Nieblas; DE— detritivorous; O— omnivorous.

Table 2Total metal concentration (μg g−1) in sediments from Baluarte River, Sinaloa (NW Mexico).

Site Cd1 Cr2 Hg3 Pb

Dry Rainy Dry Rainy Dry Rainy Dry Rainy

El Sombrero 0.30 0.64 63.00 97.80 0.20 1.09 25.78 30.07Chupaderos 0.13 0.20 61.70 59.61 0.26 1.02 18.16 29.17Santa María 0.34 0.26 52.60 51.91 0.17 0.19 20.49 25.77La Batanga 0.09 0.33 83.94 49.50 0.29 0.23 22.07 16.14Las Juntas 0.08 0.37 90.16 87.98 0.36 0.39 31.47 20.95El Tamarindo 0.20 0.48 32.86 106.93 0.25 0.29 38.46 37.13El Iguanero 0.18 – 9.60 – 0.47 – 35.01 –

Mean 0.19 0.38 56.27 75.62 0.28 0.53 27.35 26.54Standard deviation 0.10 0.16 28.07 25.00 0.10 0.41 7.76 7.37

Significant differences: 1pb0.025; 2pb0.10; 3pb0.15.

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River ismostly as the elemental species. Cadmium and Pb are non redoxsensitive elements, thus they are kept as divalent metals.

Variations of Cd and Cr (μg g−1 dry weight) in fish collected alongthe Baluarte River basin during the dry and rainy seasons are presentedin Fig. 2; for both elements, highest levels were recorded during the dryseason. Highest level of Cd (0.06 μg g−1) was detected in Gobiesoxfluviatilis from Chupaderos (Ch) site. In relation to Cr, the highestconcentration (0.01 μg g−1) occurred inAgonostomusmonticola from LaBatanga (B) site. Average concentrations of Cd and Cr in all the fishspecimens collected every season were compared, no significantdifferences (pN0.05) were found between the dry and rainy seasonsfor thesemetals. Comparisons of Cd andCr concentrations amongfish ofthe same species collected during the two sampling seasons resulted insignificant differences of Cd levels; Guavina guavina from El Sombrerostation (S) had significantly (pb0.05) higher levels of Cd during therainy season. Concentrations of Hg and Pb in fish collected during thetwo sampling seasons are shown in Fig. 3; for both metals the highestconcentrations occurred during the dry season. Highest concentrationsof Hg (0.56 μg g−1)weremeasured inG. guavina from Chupaderos (Ch)and inMugil curema from Tamarindo (T) site. Regarding Pb, the highestlevel (1.65 μg g−1) was detected in A. monticola from Tamarindo (T)site. Considering all fish, Pb was significantly (pb0.05) higher inspecimens collected during the dry season.

In relation to crustaceans, concentrations of Cd and Cr in prawnscollected during the two sampling seasons are shown in Fig. 4. Highestlevels of Cd (0.05 μg g−1) occurred inMacrobrachium occidentale fromTamarindo (T) site during both seasons. In the case of Cr, highestconcentration (0.09 μg g−1) was also detected in M. occidentale fromTamarindo (T) site during the dry season. Considering all prawnspecies, no significant (pN0.05) differences were found for bothelements between the dry and rainy seasons. Comparison of metallevels between specimens of M. occidentale collected during the dryand rainy season revealed that Cr levels were significantly (pb0.05)higher during the rainy season. Variations of Hg and Pb in shrimpcollected along the Baluarte River basin during the dry and rainyseasons are presented in Fig. 5. In the case of Hg, highest level(0.20 μg g−1) was detected during the rainy season in Macrobrachiumamericanum from Tamarindo (T) site. For Pb, the highest concentration(2.49 μg g−1) corresponded to Macrobrachium digueti collected fromBatanga (B) site in the dry season. Average concentrations of Hg and Pbin all the specimens collected in both seasons were compared, nosignificant differences (pN0.05) were found for these metals.

The basin of Baluarte River has been subjected to mining activity formany years and currently some areas have been reopened to mineralextraction; in this sense, it has been documented that wastes fromabandoned mines in countries with historic mining industries couldaffect their surroundings (Fernández-Caliani et al., 2009). In general,highest levels would be expected to be found near to sources (i.e., themines itself), especially downstream, but some degree of pollutant

allocation can be done by atmospheric transportation (Chopin andAlloway, 2007; López et al., 2008); in the study area point sources arenot the most common situation, instead, there are several mine sitesdownstream, so the normal pattern is not observed. Additionally, mostof the studied prawn and fish species did not occur in the same sitesduring both seasons in order to make intraspecific comparisons; in thisrespect, it is worth mentioning that even closely-related species mayshowdistinctmetal accumulation strategies resulting inwide variationsof elemental levels in their tissues (Rainbow et al., 1990). Nevertheless,highest levels of analyzed metals in fish were recorded during the dryseason of the northern and central parts of Baluarte basin. In relation tocrustaceans, highest levels of Cr and Pb were also detected during thedry season but in the central areas of Baluarte basin; for Hg, levels weremore elevated during the rainy season but also in the central part of thestudied basin. On the basis of the behavior of trace elementconcentration in all fish and prawns of the river basin during everyseason, and considering the corresponding levels in surficial sediments,there is no concordance between the higher levels of Cd, Cr and Hg inbiota and in sediments. Only in the case of Pb, higher levels in fish andsediment occurred during the dry season. Apparently, organisms do notreflect metal variation in associated sediments within a short time.

Values of BSAF in fish and crustaceans from Baluarte River basinduring the dry and rainy seasons are presented in Tables 3 and 4.Considering the mean values of BSAF of analyzed metals in all fishspecies, sequences were HgNCdNPbNCr during the dry and rainyseasons; in the case of prawns, the sequence was HgNCdNCrNPb andHgNCdNPbNCr during the dry and rainy seasons, respectively.Regarding individual BSAF figures, highest values were as follows; infish, the highest value of Cd (0.43) and Cr (0.6×10−3) were detectedduring the dry season in G. fluviatilis from Chupaderos site (Ch) andOreochromis urolepis from Las Juntas (J) respectively.With respect to Hg(3.0) and Pb (0.10), highest values corresponded to G. guavina from ElSombrero (S) and A. monticola from La Batanga (B) collected during therainy season. In crustaceans, highest BSAF values of Cd (0.33) and Cr(0.9) were recorded during the dry season in M. americanum from siteCh andM. occidentale fromSantaMaría (SM), respectively. Highest BSAFvalues of Hg (1.4) and Pb (0.15) corresponded to M. americanum fromsite S and M. digueti from site B during the rainy season.

It has been established that sediments can act as sinks for a widevariety of contaminants; on the other hand, they can supply metals toorganisms living in the close vicinity (Villares et al., 2001). In thiscontext, and considering that some of the studied biota is of benthichabits, the BSAF reflects the efficiency of organisms to concentrate agiven metal (Soto-Jiménez et al., 2001). In the present study, BSAFvalues above unity were observed only in the case of Hg in fish, thisfact reveals the capacity of fish for accumulating Hg. Such capacity forthe net accumulation of metals in aquatic biota results from thesimultaneous processes of uptake as well as regulation and detoxi-fication; in this sense, Phillips and Rainbow (1989) have proposed

Fig. 2. Variations of Cd and Cr concentrations (in μg g−1 dry weight) in muscle tissue of fish from the drainage basin of Baluarte River during the dry and rainy seasons (1. Guavinaguavina, 2. Agonostomus monticola, 3. Oreochromis urolepis, 4. Gobiesox fluviatilis, 5. Mugil curema, 6. Oreochromis sp.).

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Fig. 3. Variations of Hg and Pb concentrations (in μg g−1 dry weight) in muscle tissue of fish from the drainage basin of Baluarte River during the dry and rainy seasons (1. Guavinaguavina, 2. Agonostomus monticola, 3. Oreochromis urolepis, 4. Gobiesox fluviatilis, 5. Mugil curema, 6. Oreochromis sp.).

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Fig. 4. Variations of Cd and Cr concentrations (in μg g−1 dry weight) in muscle tissue of crustaceans from the drainage basin of Baluarte River during the dry and rainy seasons(1. Macrobrachium digueti, 2. Atya sp., 3. Macrobrachium americanum, 4. Macrobrachium occidentale).

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Fig. 5. Variations of Hg and Pb concentrations (in μg g−1 dry weight) in muscle tissue of crustaceans from the drainage basin of Baluarte River during the dry and rainy seasons(1. Macrobrachium digueti, 2. Atya sp., 3. Macrobrachium americanum, 4. Macrobrachium occidentale).

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Table 3Biota-sediment accumulation factor (BSAF) in fish and crustaceans during the dryseason.

Species Site Cd Cr×10−4 Hg Pb

FishGuavina guavina S 0.05 0.7 1.6 0.04Agonostomus monticola Ch 0.16 0.9 1.5 0.05Oreochromis urolepis Ch 0.23 0.4 1.4 0.05Guavina guavina Ch 0.32 0.7 2.1 0.05Goviesox fluviatilis Ch 0.43 0.7 1.0 0.06Agonostomus monticola SM 0.03 0.1 0.8 0.03Agonostomus monticola B 0.01 0.1 1.2 0.07Mugil curema J 0.03 0.8 0.7 0.04Oreochromis urolepis J 0.03 0.6 0.5 0.05Agonostomus monticola J 0.03 0.4 1.3 0.04Agonostomus monticola T 0.07 0.2 1.3 0.04Oreochromis urolpeis T 0.05 0.2 0.1 0.02Oreochromis sp I 0.12 0.1 0.9 0.04

PrawnsMacrobrachium digueti Ch 0.01 0.4 0.2 0.12Atya sp. Ch 0.21 0.2 0.6 0.08Macrobrachium americanum Ch 0.33 0.2 0.6 0.08Macrobrachium occidentale SM 0.02 0.9 0.4 0.06Macrobrachium digueti SM 0.05 0.1 0.8 0.03Macrobrachium americanum B 0.04 0.8 0.6 0.03Macrobrachium occidentale B 0.03 0.2 0.4 0.04Macrobrachium digueti B 0.03 0.9 0.2 0.11Macrobrachium digueti J 0.03 0.1 0.2 0.03Macrobrachium occidentale J 0.06 0.1 0.3 0.04Macrobrachium occidentale T 0.25 0.4 0.3 0.02Atya sp. T 0.16 0.1 0.4 0.04

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that organisms used as biomonitors vary fromweak net accumulatorsto very strong net accumulators. Fish species studied here can beconsidered as moderate bioaccumulators of Hg but very weakbioaccumulators of Cd, Cr and Pb. In the case of crustaceans, all theconsidered species were poor accumulators of the analyzed elements.Taking into account another classification based on BSAF values(Dallinger, 1993), fish and prawns studied here can be considered asdeconcentrators (BSAFb1) of Cd, Cr and Pb. In the case of Hg, analyzedbiota behaved as microconcentrators (2NBSAFN1); only in one case a

Table 4Biota-sediment accumulation factor (BSAF) in fish and crustaceans during the rainyseason.

Species Site Cd Cr×10−4 Hg Pb

FishGuavina guavina S 0.04 0.04 3.0 0.05Agonostomus monticola Ch 0.16 0.07 0.5 0.08Oreochromis urolepis Ch 0.14 0.03 0.7 0.07Guavina guavina Ch 0.25 0.01 0.8 0.07Gobiesox fluviatilis Ch 0.33 0.01 0.4 0.08Oreochromis urolepis SM 0.12 0.01 1.8 0.04Agonostomus monticola SM 0.03 0.06 1.9 0.04Agonostomus monticola B 0.02 0.02 1.5 0.10Mugil curema J 0.05 0.08 0.6 0.06Oreochromis urolepis J 0.07 0.06 0.4 0.07Agonostomus monticola J 0.06 0.04 1.2 0.06Oreochromis sp. T 0.03 0.04 0.8 0.03

PrawnsMacrobrachium americanum S 0.04 0.06 1.4 0.04Atya sp. Ch 0.16 0.03 0.2 0.07Macrobrachium occidentale SM 0.17 0.03 0.4 0.04Macrobrachium digueti SM 0.07 0.01 0.2 0.04Macrobrachium americanum B 0.11 0.01 0.8 0.04Macrobrachium occidentale B 0.08 0.01 0.5 0.06Macrobrachium digueti B 0.09 0.02 0.2 0.15Macrobrachium digueti J 0.07 0.01 0.2 0.04Macrobrachium occidentale J 0.12 0.07 0.3 0.06Macrobrachium occidentale T 0.10 0.08 0.2 0.04Macrobrachium americanum T 0.05 0.01 0.7 0.02

fish species (G. guavina) could be considered as a macroconcentrator(BSAFN2) of Hg.

The Joint Food and Agriculture Organization/World HealthOrganization (FAO/WHO) Expert Committee on Food Additives hassuggested a provisional tolerable intake of Cd of 400–500 μg; Hg,300 μg; Pb, 3 mg per week for man (FAO/WHO, 1972). In the case ofCr, no evidence of adverse effects associated with supplementaryintake of Cr has been established (SCF, 1993). Considering the highestaverage concentrations in all fish (Cd 0.0286 and Hg 0.3758 μg g−1

during the rainy season; and Pb 1.278 μg g−1 during the dry season)and prawn (Cd 0.0353 and Pb 1.121 μg g−1during the dry season; Hg0.1205 μg g−1 during both seasons) specimens, the maximumamounts of fishery products from the studied area that human canconsume perweek with no harmwere estimated. People can eat up to14.0, 0.8 and 2.3 kg of fish in relation to the concentrations of Cd, Hgand Pb, respectively; regarding crustaceans, maximum amounts were11.3, 2.5 and 2.7 kg of prawns relative to the respective levels of Cd,Hg and Pb.

4. Conclusion

Considering average concentrations of analyzed metals in all fishcollected every season, Pb was significantly (pb0.05) higher in fishcollected during the dry season. In the case of a fish species collectedduring both seasons, Cd concentration was significantly (pb0.05)higher in G. guavina from El Sombrero station during the rainy season.Regarding crustaceans, comparison of average metal concentrationsfor all prawns showed no significant (pN0.05) differences betweenthe dry and rainy seasons. Levels of Cr in M. occidentale weresignificantly (pb0.05) higher during the rainy season. The highestlevels of studied elements in fish were recorded during the dry seasonof the northern and central parts of Baluarte basin. In crustaceans,highest levels Cr and Pb were detected during the dry season whereasthe highest Hg levels were detected during the rainy season in thecentral part of the studied basin. Considering surficial sedimentscollected every season, average values of Cd, Cr and Hg weresignificantly higher during the rainy season. Estimated BSAF valueswere above unity only in the case of Hg in fish during both seasons;this fact reveals the capacity of fish for accumulating Hg. Consideringaverage concentrations of Cd, Hg and Pb, people can eat up to 14.0, 0.8and 2.3 kg of fish and 11.3, 2.5 and 2.7 kg of prawns per weekrespectively, without exceeding the provisional tolerable intake.

Acknowledgements

Special thanks are due to S. Rendón-Rodríguez for sampling andtaxonomic identification of crustaceans, F. Amezcua-Martínez for fishidentification, H. Bojórquez-Leyva for laboratory work, C. Ramírez-Jáuregui for bibliographic support, G. Ramírez-Reséndiz for theelaboration of maps, V. Montes-Montes for her help with cartography.Financial support was provided through a project from theMinistry ofPublic Education (Mexico) (DGEST 911.05-P).

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