Arai, T.

Chino, N.

Ismail, A.

Rahman, F.

UKM Journal Article Repository

HEAVY METALS OF A TROPICAL ANGUILLD EEL IN MALAYSIA 43Malays. Appl. Biol. (2012) 41(1): 43–46* To whom correspondence should be addressed.RESEARCH NOTEHEAVY METAL CONCENTRATIONS IN A TROPICAL EELAnguilla bicolor bicolor IN PENINSULAR MALAYSIA, MALAYSIAARAI, T.1*, RAHMAN F.1, CHINO, N.2 and ISMAIL, A.11Department of Biology, Faculty of Science, Universiti Putra Malaysia,43400 UPM Serdang, Selangor, Malaysia2International Coastal Research Center, Atmosphere and Ocean Research Institute,The University of Tokyo, 2-106-1 Akahama, Otsuchi, Iwate 028-1102, Japan*Email: arai@science.upm.edu.my; Tel: 603-89466633; Fax: 603-86567454Heavy metals are omnipresent in hydrosystems as aconsequence of the daily anthropogenic activitiesand the persistence of some compounds used in thepast. The detection and evaluation of the influenceof hazardous chemicals is of growing concernbecause of the potential threat to wildlife and humanhealth by inducing a wide range of adverse effects.Biological indicators such as bivalves (oysters,mussels), crustaceans or fish are commonly used toevaluate the chemical state of aquatic environments.A number of studies supported the use of freshwatereels Anguilla spp. as reliable bioindicators ofenvironmental changes and contaminantconcentrations in the eel tissue are suitableindicators reflecting the environmental exposure topollutants (Le et al., 2009, 2010a, b). The EIFAC/ICES Working Group on Eels (WG Eel, 2006) andthe Scientific, Technical, and Economic Committeefor Fisheries (STECF, 2006) have recommended thatthe Water Framework Directive should use theanguillid eel as a sentinel species for monitoring thechemical status of surface waters with respect tohazardous substances.Freshwater eels are widely consumed in manycountries including Malaysia. The major markets forthe eel export are Asian countries such as China,Japan and Taiwan and a small number of Europeancountries including Italy, Germany and TheNetherlands. The market value of the anguillid eelsdepends on the species and varies between differentcountries. Currently prices range from USD 3-15/kgwhich rank the eel among the most precious speciesof food fish.In Peninsular Malaysia, there is a speciesAnguilla bicolor bicolor (Arai et al., 2011, 2012).Recently this species was considered to be a majortarget species for the eel trading market. However,little attention has been given to the naturalpopulations and resource management of eels inMalaysia. In Malaysia, a lot of information has beenreported in the literature using mussels asbiomonitor of heavy metals (e.g. Yap et al., 2003,2006, 2009) but not for eels. Therefore, theobjective of this study was to gain basic informationof heavy metals such as cadmium (Cd), copper (Cu),iron (Fe), lead (Pb), nickel (Ni) and Zinc (Zn) in atropical eel A. bicolor bicolor collected in thePeninsular Malaysia. This is the first study to assessthe heavy metal levels in freshwater eels inMalaysia.A total of 30 specimens were collected by localfishermen mainly in Kurau River in Bukit Merah (7specimens) and Pinang River in Penang Island (23specimens) of the northwestern peninsular (4°59’-5°23 N, 100°12-100°40’E) during November 2008and August 2010. The eels were collected byangling and bamboo trap at night. The total length(TL) and body weight (BW) were measured. Thesamples were brought to the laboratory on the sameday and kept in a freezer (-20°C) until metalanalysis. For metal analysis, muscle tissues weredissected out, put in clean polyethylene bags, andstored at -20°C. The muscles were dried in an ovenat 60°C for 72 hours until a constant dry weight (dw)by using an air-circulating oven. About 1.0 g of thetissue parts were weighed and digested in 10 mL ofconcentrated nitric acid (AnalaR grade, BDH 69%).They were put into a digestion block first at 40°Cfor 1 hour and then the temperature was increasedto 140°C for at least 3 hours (Ismail & Ramli, 1997).Later, the digested samples were diluted to 40mLwith double distilled water (DDW). The sampleswere then filtered through Whatman No. 1 filter-papers and the filtrates were stored in 4°C untilmetal determination. After filtration, the preparedsamples were determined for Cd, Cu, Fe, Ni, Pb and44 HEAVY METALS OF A TROPICAL ANGUILLD EEL IN MALAYSIAZn by using an air-acetylene flame atomicabsorption spectrophotometer (AAS) Perkin-ElmerModel AAnalyst 880. The data are presented inμg/g dry weight basis. Multiple-level calibrationstandards were analysed to generate calibrationcurves against which sample concentrations werecalculated. Standard solutions were prepared from1000 mg/l stock solution of each metal (MERCKTitrisol). All apparatus were acid-washed (5% ofnitric acid) by dipped for 24 h then rinsed withdistilled water before used. All solutions used wereprepared using double de-ionized water (USFMaxima, 18.2 MÙ cm-1). Procedural blanks wereanalyzed once for every ten samples to check forsample accuracy. A quality control sample wasroutinely run through during the period of metalanalysis. The limits of detection (μg/g) achieved inthis study were calculated as Cd: 0.003, Cu: 0.001,Fe: 0.001, Ni: 0.005, Pb: 0.006 and Zn: 0.002.Differences between data were analyzed using theMann-Whitney U-test (Sokal & Rohlf, 1995).Significance of the correlation coefficient andregression slope were tested by Fisher’s Z-transformation and an analysis of covariance(ANCOVA) (Sokal & Rohlf, 1995).The TL and BW of Anguilla bicolor bicoloreels ranged from 293 to 686 mm and from 38.9 to645 g, respectively. In the relationship betweeneach metal level and both TL and BW, norelationship was observed between those levels andboth TL and BW (ANCOVA, p > 0.05) in this eelspecies. The levels of Cd, Cu, Fe, Ni, Pb and Zn inmuscles of the freshwater eel are given in Table 1.There were no significant difference betweensamples from Bukit Merah and Penang in Cd, Cu,Ni, Pb and Zn (Mann-Whitney U-test, p>0.05) but asignificant difference was found in Fe between thosesites (Mann-Whitney U-test, p<0.005). The rangesof concentrations of metals (μg/g dry weight) wereCd: 0.08-0.44, Cu: 0.84-2.07, Fe: 11.0-36.6, Ni:1.88-4.09, Pb: 2.39-13.2 and Zn: 39.2-113. The meanconcentrations of heavy metals in the muscle ofAnguilla bicolor bicolor are followed an increasingsequence of Cd < Cu < Ni < Pb < Fe < Zn.Fish has been considered good indicators forheavy metal contamination in aquatic systemsbecause they occupy different trophic levels withdifferent sizes and ages (Burger et al., 2002).Meanwhile, fish are widely consumed in many partsof the world by humans, and polluted fish mayendanger human health. The freshwater eel genusAnguilla has been also a major target species forhuman consumption especially in East Asia. Theannual eel consumption in Japan is 120,000 to130,000 tonnes with per capita consumption ofabout 5 eels a year (Kato & Kobayashi, 2003).Eighteen percent of the eel consumed in Japan isproduced in the country while the remainder isimported from China, Taiwan, and Malaysia (Kato& Kobayashi, 2003). In the present study, levels ofheavy metals such as Cd, Cu, Ni and Zn in themuscles of Anguilla bicolor bicolor were found tobe below the acceptable limits of heavy metalpollution in fishes and shell fish (FAO/WHO, 1984),although some Pb levels were higher than the worldstandard (10 μg/g). This shows that the levels of Cd,Cu, Ni and Zn in the eel habitats are still tolerable,while there is a need for constant monitoring of thelevel of Pb. The Pb level in A. bicolor bicolor foundin the present study was 2-200 times higher than theother anguillid eel species such as A. anguilla fromFrance, A. japonica from Japan and A. marmoratafrom Vietnam (Table 2). The Pb level in musclesfound in tilapia fish Oreochromis niloticus collectedin Bangi area, Selangor of Peninsular Malaysia was0.10-0.18 μg/g dry wt, respectively (Taweel et al.,2011), and the level was much less than those foundin A. bicolor bicolor. Anguillid eel has commonecological niche and the eel lives with tilapia fishsympatrically in freshwater ecosystem, althoughtheir lives such as migration, habitat and feeding aredifferent. Thus, the difference found in Pb level inthe eel muscles could be due to regional differencein Pb level. Further study should be carried out thesystematical monitoring to reveal the reason of highPb accumulation in A. bicolor bicolor. The othermetal levels such as Cd, Cu, Ni and Zn found in A.bicolor bicolor were in the range of the other eelspecies collected various sites (Table 2). However,it should be noted that heavy metals are toxic orpoisonous even at low concentrations. It suggeststhat heavy metal pollution of water bodies shouldbe reduced to the barest minimum. This is tominimize fish food contamination that will in turnreduce clinical poisoning in human who consumethe freshwater eel as well as other fish species.There was no relationship between eachbiological character such as TL and BW and eachmetal level in Anguilla bicolor bicolor. Such failureto detect bioaccumulation of metal with growth wasTable 1. Heavy metal concentrations (µg/g dry weight) in muscle of the freshwater eel Anguilla bicolor bicolor collected in Peninsular MalaysiaNumber                       Cd                        Cu                        Fe                       Ni                        Pb                       ZnLocation ofsamples mean±SD range mean±SD range mean±SD range mean±SD range mean±SD range mean±SD rangeBukit Merah 7 0.19±0.12 0.08-0.40 1.12±0.24 0.88-1.40 16.4±3.85 11.3-23.6 2.54±0.68 1.88-3.68 9.33±3.10 4.35-13.2 65.9±10.6 53.0-87.3Penang 23 0.26±0.09 0.08-0.44 1.22±0.34 0.84-2.07 23.8±5.66 11.0-36.6 3.04±0.52 2.11-4.09 7.18±2.75 2.39-12.2 75.3±18.9 39.2-113HEAVY METALS OF A TROPICAL ANGUILLD EEL IN MALAYSIA 45Table 2. Heavy metal concentrations (µg/g dry weight) in muscle of the freshwater eels Anguilla spp.Country           Species Cd Cu Fe Ni Pb Zn SourceFrance Anguilla anguilla NA 0.70-1.33 NA NA 0.05-0.56 38.3-90.6 Neto et al., 2011Japan Anguilla japonica 0.32-1.32 32.5-175 NA NA 0.25-1.10 122-416 Le et al., 2010aMalaysia Anguilla bicolor bicolor 0.08-0.44 0.84-2.07 11.0-36.6 1.88-4.09 2.39-13.2 39.2-113 This studyVietnam Anguilla marmorata 0.02-0.13 1.21-2.19 NA NA 0.11-0.18 42.3-82.1 Le et al., 2009NA: data not availablefound in the Japanese eel A. japonica (Le et al.,2010a). The sizes of aquatic animals including fishhave been shown to play an important role in metalcontents of tissues. However, this evidence wasconsistent generally for mercury in different groupsof aquatic animals (Canli & Atli, 2003). Heavymetals like copper, zinc and iron are essential forfish metabolism while some others such as mercury,cadmium and lead have no known role in biologicalsystems. For the normal metabolism of fish, theessential metals must be taken up from water, foodor sediment. However, similar to the route ofessential metals, non-essential ones are also takenup by fish and accumulate in their tissues. Studiesfrom the field and laboratory experiments showedthat accumulation of heavy metals in a tissue ismainly dependent upon water concentrations ofmetals and exposure period, although some otherenvironmental factors such as salinity, pH, hardnessand temperature play significant roles in metalaccumulation (Canli & Atli, 2003). Thus, suchvarious factors would suggest less correlationbetween growth and metal accumulation in thefreshwater eel. 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Heavy metal concentrations in a tropical eel Anguilla bicolor bicolor in Peninsular Malaysia, Malaysia

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