This article was downloaded by: [New York University] On: 11 January 2015, At: 09:35 Publisher: Taylor & Francis Informa Ltd Registered in England and Wales Registered Number: 1072954 Registered office: Mortimer House, 37-41 Mortimer Street, London W1T 3JH, UK Toxicological & Environmental Chemistry Publication details, including instructions for authors and subscription information: http://www.tandfonline.com/loi/gtec20 Cd, Pb, and Cu in water and sediments and their bioaccumulation in freshwater fish of some lakes in Hanoi, Vietnam a b Ha Thu Le & Huong Thi Thuy Ngo a Faculty of Biology, Hanoi University of Science, Vietnam National University, Hanoi, Vietnam b Department of Geochemistry and Environment, Vietnam Institute of Geosciences and Mineral Resources, Hanoi, Vietnam Published online: 30 Jan 2014 To cite this article: Ha Thu Le & Huong Thi Thuy Ngo (2013) Cd, Pb, and Cu in water and sediments and their bioaccumulation in freshwater fish of some lakes in Hanoi, Vietnam, Toxicological & Environmental Chemistry, 95:8, 1328-1337, DOI: 10.1080/02772248.2013.877462 To link to this article: http://dx.doi.org/10.1080/02772248.2013.877462 PLEASE SCROLL DOWN FOR ARTICLE Taylor & Francis makes every effort to ensure the accuracy of all the information (the “Content”) contained in the publications on our platform However, Taylor & Francis, our agents, and our licensors make no representations or warranties whatsoever as to the accuracy, completeness, or suitability for any purpose of the Content Any opinions and views expressed in this publication are the opinions and views of the authors, and are not the views of or endorsed by Taylor & Francis The accuracy of the Content should not be relied upon and should be independently verified with primary sources of information Taylor and Francis shall not be liable for any losses, actions, claims, proceedings, demands, costs, expenses, damages, and other liabilities whatsoever or howsoever caused arising directly or indirectly in connection with, in relation to or arising out of the use of the Content This article may be used for research, teaching, and private study purposes Any substantial or systematic reproduction, redistribution, reselling, loan, sub-licensing, systematic supply, or distribution in any form to anyone is expressly forbidden Terms & Downloaded by [New York University] at 09:35 11 January 2015 Conditions of access and use can be found at http://www.tandfonline.com/page/termsand-conditions Toxicological & Environmental Chemistry, 2014 Vol 95, No 8, 1328–1337, http://dx.doi.org/10.1080/02772248.2013.877462 Cd, Pb, and Cu in water and sediments and their bioaccumulation in freshwater fish of some lakes in Hanoi, Vietnam Ha Thu Lea and Huong Thi Thuy Ngob* a Faculty of Biology, Hanoi University of Science, Vietnam National University, Hanoi, Vietnam; Department of Geochemistry and Environment, Vietnam Institute of Geosciences and Mineral Resources, Hanoi, Vietnam Downloaded by [New York University] at 09:35 11 January 2015 b (Received 15 June 2013; accepted 17 December 2013) The seasonal variations of Cd, Pb, and Cu in the water, sediments, and freshwater fish (Hypophthalmichthys molitrix, Cirrhinus molitorella, and Oreochromis mossambicus) of four lakes in Hanoi, Vietnam, were investigated Samples for analysis were taken four times from April 2010 to March 2011 The levels in water were lower than the Vietnamese standards, except for Pb, but they were all much higher than the Canadian standards for protection of aquatic life; in the sediments, they were higher than world average levels Bioaccumulation of the three metals in fish was site-dependent and species-dependent, but correlations of their levels in fish to those in water and sediments were weak Levels of Pb in fish exceeded those of the UK and the WHO standards, and the recommended values of Vietnam for human consumption Overall, the results show that the lakes are polluted with these metals, and consumption of high quantities of fish from them may be problematic The outcome of this research helps to establish background data for future monitoring Keywords: metals; Cd; Pb; Cu; Hanoi lakes; sediments; water pollution; freshwater fish Introduction Pollution of aquatic ecosystems by metals is relevant for public health because of the potential bioaccumulation of some of them in aquatic organisms including fish used for human consumption Bioaccumulation of certain metals by aquatic animals may entail toxic effects, even at levels as low as in the natural environment (Ngo, Gerstmann, and Frank 2011a, 2011b, 2011c) The metals investigated here, i.e., Cd, Cu, and Pb, may be incorporated into suspended particles which ultimately sink into the sediments When physicochemical conditions such as pH, salinity, or redox potential are favorable, they may be remobilized back to the water column (Calmano, Hong, and F€orstner 1993) to become available for organisms living in or near the benthic zone, e.g., mollusks, common carp, or mud carp (Cross, Duke, and Willes 1970), to interfere with synthesis and activity of enzymes involved in fundamental biochemical and physiological processes (Donkin, Ohlson, and Teaf 2000; Nordberg et al 2007; Schmitt, Brumbaugh, and May 2007; Vinodhini and Narayanan 2008; Ngo, Gerstmann, and Frank 2011b) As fish are at the top of aquatic food chains, they are good indicators of metal pollution (Rashed 2001) Hanoi is known as “Lake City” throughout its history because of its large number of lakes Due to rapid economic development, the population of Hanoi has expanded to approximately five million people; many industries have been established in and around *Email: ngothithuyhuong@gmail.com Ó 2014 Taylor & Francis Toxicological & Environmental Chemistry 1329 Downloaded by [New York University] at 09:35 11 January 2015 the city during the last decades In consequence, the discharge of untreated effluents has risen steadily, rendering the lakes ecologically unstable and changing their ecosystems This has led to massive losses of naturally inhabiting fish in Truc Bach, Thanh Nhan, and Thien Quang Lakes, almost every year between 2006 and 2013 Most studies on trace metals in Hanoi lakes have been performed on the West Lake, the largest natural one in Hanoi (Pham, Pulkownik, and Buckney 2007; Kikuchi, Hai, and Tanaka 2010) The aim of this study is to investigate the spatial and temporal variations of Cd, Pb, and Cu in the water and sediments of Truc Bach, Thien Quang, Thanh Nhan, and Yen So Lakes, and to monitor their bioaccumulation in the freshwater fish species, silver carp (Hypophthalmichthys molitrix), mud carp (Cirrhinus molitorella), and tilapia (Oreochromis mossambicus) The data are compared with safety limits established by the World Health Organization (WHO 1989), the UK permissible limits (CEFAS 2000), and the Vietnamese safety standard (VMOH 2007) in order to raise awareness on food safety issues Materials and methods Study sites and species Water and sediment samples were taken and fish were caught from the four lakes four times between April 2010 and March 2011 A map of the lakes and sampling sites is presented in Figure Truc Bach Lake has a surface area of about 24 ha, with a median depth of 5.8 m in the dry season and 6.2 m in the rainy season Thien Quang Lake has a surface area of 5.5 ha, with a depth of about 3–6 m Thanh Nhan Lake has approximately 8.4 surface area, with a depth of 2.5–4 m Yen So Lake is the first of five regulatory lakes of the same name belonging to the drainage system of Hanoi because most of the city’s wastewater runs through them; samples were taken from the first one which has a surface area of 29.8 The three fish species investigated in this study were the following: (1) silver carp (H molitrix, Valenciennes 1844), a cyprinid freshwater fish native to North and Northeast Asia, a herbivorous filter feeder without stomach and feeding continuously on phytoplankton; (2) mud carp (C molitorella, Valenciennes 1844), a ray-finned fish mainly found in southern China and Vietnam, dwelling on the bottom of slow-flowing rivers and lakes, omnivorous, consuming mainly organic detritus, filamentous algae, pieces of aquatic weeds, and insects; (3) and tilapia (O mossambicus, Peters 1852), native to southern Africa, but occurring now in many freshwater and brackish water habitats of tropical and subtropical countries, an opportunistic omnivore, feeding mainly on algae and phytoplankton, but taking also aquatic plants, zooplankton, small invertebrates, and fish larvae All three are important as part of the diet of lakeshore residents and their customers Labware and sampling procedure All glassware and plastic equipments used for containing samples and analytical purposes were soaked for 24 h in 1:1 conc HNO3 and rinsed thoroughly with bidistilled water before use Water samples were collected in April 2010, July 2010, November 2010, and in the beginning of March 2011 After being taken into a 0.5-L acid-washed polyethylene bottle, the water sample was immediately acidified with mL of conc HNO3 per liter of water, transported on ice to the laboratory, and stored in a refrigerator till analysis was done within week Sediment samples (0–15 cm in depth) were collected at the same time Downloaded by [New York University] at 09:35 11 January 2015 1330 H.T Le and H.T.T Ngo Figure A map showing the location of the investigated Lakes in Hanoi (above), and the locations of sampling sites in Truc Bach (ST1–ST3), Thien Quang (SQ1–SQ3), Thanh Nhan (SN1– SN3), and Yen So Lakes (SY1–SY2) (below) using a Petersen grab (Cole-Parmer, Hanoi, Vietnam) At each sampling station, three grabs from three points located approximately 25 m apart in a triangle and 30 m from the shore, were taken and pooled (about kg), stored in a food-grade polyethylene bag, and transferred to the laboratory At the same time and sampling stations, silver carp, mud carp, and tilapia, about 300–500 g each, were caught by fishermen They were transported alive to the laboratory in labeled 10-L transparent polyethylene bags Sample preparation and metal analysis An aliquot of 50 mL of each water sample was taken into a 100-mL Erlenmeyer flask, mL of suprapur HNO3 (60% v/v) were added, and the mixture was heated on a hot plate Downloaded by [New York University] at 09:35 11 January 2015 Toxicological & Environmental Chemistry 1331 to 95  C for h Upon cooling to room temperature, the sample was adjusted to 50 mL with bidistilled water in a volumetric flask; finally, the sample was filtered through a syringe filter of 0.45 mm pore size (Whatman, Singapore) Upon arrival at the laboratory, the fish were immediately excised and muscle tissues were prepared for metal analysis by wet digestion (Perkin-Elmer Corporation 1996a) Briefly, the samples, 0.1–0.2 g wet weight each, were cut into small pieces and digested in mL aqua regia in 20-mL borosilicate glass tubes for h at 60  C, followed by h at 120  C The samples were cooled to room temperature and 500 mL of conc H2O2 were added, followed by heating to 120  C in a hot block until clear solutions were obtained, taking about h The digestates were diluted to 20 mL each with bidistilled water and filtered through 0.45-mm cellulose syringe filters Sediment samples were dried in an oven at 70  C for days, ground with mortar and pestle, sieved through a 50-mm sieve, and wet-digested according to Perkin-Elmer Corporation (1996b), with the following modifications An aliquot of 0.5 g ground sediment was digested in 10 mL aqua regia as described above, and mL of conc H2O2 was added The digestion was complete when the digestates were clear, taking about h The digestates were diluted to 20 mL each with bidistilled water The concentrations of Cd, Pb, and Cu were determined by inductively coupled plasma Ò mass spectrometry (ICP-MS, ELAN 9000; Perkin-Elmer SCIEX, Waltham, MA, USA); detection limits for Cd, Pb, and Cu were 2.8 ng LÀ1, 7.7 ng LÀ1, and 45 ng LÀ1, respectively The analytical method was validated with certified standard reference materials from oyster and fish liver (Graham B Jackson Pty Ltd, Dandenong, Victoria, Australia) Recoveries were within the certification range, i.e., 93% Ỉ 12 for Cd, 90% Ỉ for Pb, and 92% Ỉ for Cu Procedural blanks consisting of aqua regia were below detection limits The results were reported in mg LÀ1 for water, mg kgÀ1 for sediment dry weight, and mg kgÀ1 for fish wet weight The working standards of the metals for ICPMS were prepared from stock solutions of their nitrate salts in HNO3 (0.5 mol LÀ1) by dilution with appropriate volumes of 2% HNO3 All reagents used were of analytical grade (Merck, Darmstadt, Germany) Data analysis The data were presented as means Ỉ SD (standard deviation) Two-way analysis of variance was used to determine whether differences in metal concentrations among lakes and sampling times, and among lakes and species were significant When significant difference was found, the Student–Newman–Keuls test was applied (GraphPad Software, San Diego, CA) Results and discussion In water, Cu had the highest concentration, followed by Pb and Cd (Table 1) Cu levels varied between sampling times (Yen So Lake) and lakes (p < 0.05), i.e., Thien Quang Lake (40 Ỉ mg LÀ1) showing the lowest concentration at all times (p < 0.05) A possible explanation for this might be that this lake receives only runoff and domestic wastewater from households and nearby restaurants, while the others receive wastewater from a variety of sources including a paper mill, tanneries, breweries, and hospitals In Yen So Lake, Cu was higher in winter (November and March) than in the rainy season (July) and spring (April) (p < 0.01) There is almost no rain during winter; hence metals are more concentrated in urban wastewater directed to the lake Highest levels of Cd were observed Thien Quang 0.20 (0.01) a 0.17 (0.05) a 0.18 (0.06) a 0.22 (0.08) a 0.17 (0.08) a 29.0 (1.2) a 32.4 (4.2) a 31.6 (3.3) a 31.1 (3.2) a 31.0 (3.0)a 40.2 (7.1) a 38.6 (6.5) a 37.4 (6.9) a 42.0 (6.6) a 39.6 (6.1)a Truc Bach 0.12 (0.05) a 0.16 (0.04) a 0.15 (0.05) a 0.15 (0.06) a 0.14 (0.06) a 24.3 (3.4) a 27.0 (3.4) a 40.2 (7.7a 36.3 (6.7) a 32.0 (8.1) a 50.5 (3.1) b 61.8 (8.2) b 63.5 (7.9) b 53.4 (8.6) b 57.3 (8.4) b April 2010 July 2010 November 2010 March 2011 April 2010 July 2010 November 2010 March 2011 April 2010 July 2010 November 2010 March 2011 Dates 58.1 (8.3) b 52.9 (6.2) b 60.7 (6.6) b 55.0 (8.2) b 48.3 (9.3) b 26.6 (4.23) a 27.7 (4.8) a 29.0 (4.1) a 28.9 (4.3) a 32.1 (4.2) a 0.15 (0.06) a 0.14 (0.04) a 0.13 (0.06) a 0.13 (0.04) a 0.16 (0.04) a Thanh Nhan 44.5 (9.3) bà 71.9 (8.5)bÃà 76.8 (8.3)b à 60.3 (14.3) b 48.1 (3.9) b 23.5 (4.0) a 41.3 (7.9) a 34.2 (10.1) a 31.3 (9.4)a 26.1 (5.8) a 0.57 (0.19) b 0.85 (0.17) b 0.68 (0.19) b 0.62 (0.20) b 0.69 (0.20) b Yen So Canadian guideline 1.0, 2.0, 4.0, and7.0 mg LÀ1 at 0–60, 60–120, 120–180, and >180 mg LÀ1 CaCO3 2.0, 3.0, and4.0 mg LÀ1 at 0–120, 120–180, and >180 mg LÀ1 CaCO3 0.017 mg LÀ1 i Note: Asterisks denote statistically significant differences from first sampling (April 2010) values (ÃÃp < 0.01) Different superscript letters (a, b) indicate that values of each metal (at different sampling times, and average value) in different lakes are significantly different (p < 0.05; ANOVA followed by Student–Newman–Keuls test) iCanadian Water Quality Guidelines for the Protection of Aquatic Life (CCME 2007) Bold values indicate the average in order to easily differentiate with other numbers, and to compare with the Canadian criteria (which were also bold) Average Cu Average Pb Average Cd Metals Locations Table Concentrations of Cd, Pb, and Cu in the water of four Hanoi lakes (mg LÀ1) over year Mean values (standard deviations in parentheses) for three to five samples Downloaded by [New York University] at 09:35 11 January 2015 1332 H.T Le and H.T.T Ngo Downloaded by [New York University] at 09:35 11 January 2015 Toxicological & Environmental Chemistry 1333 in Yen So Lake at all seasons (p < 0.01) The lake receives water from heavily polluted rivers, i.e., Kim Nguu, Set, Lu, and especially To Lich River burdened with wastewater from rubber, tobacco, and battery factories Metal levels in sediments were also high; they did not differ between seasons (p > 0.05) but between lakes (p < 0.05; Table 2) Cd was the lowest; Pb and Cu were in about the same range Of the four lakes, levels of the three metals were highest in sediments of Truc Bach Lake and lowest in Yen So and Thanh Nhan Lakes Truc Bach Lake is the oldest, with high population density and many industrial activities around it, so metals have accumulated in its sediments over longer time Presently, the metal levels in sediments of Thien Quang, Thanh Nhan and Yen So Lakes were similar to those of West Lake sediments (Kikuchi, Hai, and Tanaka 2010), the largest natural lake in Hanoi, next to Truc Bach Lake; but the sediment levels in the Truc Bach Lake were higher than those reported for West Lake sediment in 2007 (Pham, Pulkownik, and Buckney 2007) and in 2010 (Kikuchi, Hai, and Tanaka 2010) Truc Bach Lake received wastewater from several industries but not the West Lake Overall, metal pollution in water and sediments is lower than reported for lakes in Africa, e.g., Lake Victoria, Kenya (water: Cd 10–20 mg LÀ1 and Pb 150–440 mg LÀ1; sediment: Cd 0.4–2.8 mg kgÀ1 and Pb 17–77 mg kgÀ1 dry weight [d.w.]) (Tole and Shitsama 2003), Lake Manzala, Egypt (water: Cd 20 mg LÀ1, Cu 55 mg LÀ1) (Bahnasawy, Khidr, and Dheina 2011) In western countries, lakes showed generally lower metal levels in water and sediments, e.g., Cd and Pb in the water of Altenw€orth Lake, Austria, ranged from 0.05 to 0.06 mg LÀ1 and from 0.13 to 0.21 mg LÀ1, in sediments from 0.06 to 0.8 mg kgÀ1 and from 2.6 to 119 mg kgÀ1 d.w (Colley 1989) Generally, Pb levels in water of the four Table Concentrations of metals in sediments of four Hanoi lakes (mg kgÀ1 dry weight) at different sampling times Mean values (standard deviations in parentheses) for three to five samples Locations Metals Cd Dates Average Thanh Nhan Yen So 1.54 (0.50) c 1.31 (0.35) c 0.50 (0.14) a 0.33 (0.10) a 1.16 (0.16) b 0.71 (0.24) b 0.61 (0.24) a 0.46 (0.09) a November 2010 March 2011 1.62 (0.41) c 1.38 (0.37) c 1.46 (0.37) c 0.48 (0.11) a 0.46 (0.14) a 0.44 (0.12) a 0.91 (0.32) b 0.82 (0.32) b 0.90 (0.28) b 0.67 (0.10) a 0.72 (0.16) a 0.62 (0.17)a World average 0.17 April 2010 July 2010 November 2010 March 2011 142.5 (44.1) b 154.5 (25.2) b 205.4 (18.0) b 172.2 (32.3) b 168.6 (36.5) b 50.1 (9.0) a 44.5 (10.7) a 54.6 (10.5) a 51.4 (11.1) a 50.1 (9.2) a 64.7 (19.1) a 52.2 (16.1) a 61.5 (14.3) a 47.7 (10.7) a 56.5 (14.3) a 36.9 (8.19) a 35.1 (6.6) a 39.3 (5.1) a 41.5 (5.2) a 38.2 (6.0)a 19 April 2010 July 2010 November 2010 March 2011 120.2 (10.5) c 113.8 (6.2) c 116.9 (19.0) c 104.6 (16.1) c 113.9 (13.3) c 48.7 (3.5) a 44.5 (6.7) a 41.6 (7.9) a 46.8 (7.8) a 45.4 (6.1) a 84.1 (22.4) b 74.9 (23.5) b 72.1 (18.4) b 82.6 (20.7) b 78.4 (19.0) b 53.2 (12.1) a 42.6 (12.7) a 43.8 (5.8) a 57.8 (12.9) a 49.3 (11.4)a 33 Average Cu Thien Quang April 2010 July 2010 Average Pb Truc Bach ii Note: Different superscript letters (a–c) indicate that values of each metal (at different sampling times, and average value) in different lakes, are significantly different (p < 0.05; ANOVA followed by Student–Newman–Keuls test) iiWorld Average for Sediment (Bowen 1979) Bold values differentiate the average values with others Downloaded by [New York University] at 09:35 11 January 2015 1334 H.T Le and H.T.T Ngo Hanoi lakes exceeded the Vietnamese standard for conservation of aquatic animals and plants (Pb 20 mg LÀ1) but not Cd and Cu (Cd mg LÀ1, Cu 200 mg LÀ1) Nevertheless, all three metals were much higher than the Canadian Water Quality Guidelines for the Protection of Aquatic Life (CCME 2007), i.e., up to 50 times for Cd, up to 15 times for Pb, and up to 50 times for Cu (Table 1) The sediment levels in all the four Hanoi lakes were higher than world average (Bowen 1979), i.e., up to eight times for Cd, up to nine times for Pb, and up to four times for Cu (Table 2) The metal concentrations in fish from the four lakes are summarized in Figure 2, the differences for the three species likely being due to their different feeding habits, ages, and sizes (Linde et al 1998; Canli and Atli 2003) Cu had the highest concentrations (1.2–5.5 mg kgÀ1 wet weight [w.w.]), while Cd had the lowest (0.009–0.036 mg kgÀ1 w w.; Figure 2) Seasonal variations were only found for tilapia (Figure 2); specifically, in Yen So Lake, Cd level in November was higher than in other seasons, in Thanh Nhan Lake, Pb level in July was higher compared to that of other sampling times (p < 0.05; Figure 2), although no such seasonal changes were observed in water and sediments (p > 0.05, Tables and 2) Other factors such as solute metal speciation, influence of other cations, pH, and redox potential may contribute to their bioavailability and bioaccumulation (Luoma 1983) For silver carp and mud carp, the Cd levels tend to be higher in July (Thanh Nhan Lake) and in November (Yen So Lake) in comparison to other seasons Figure Concentrations (mg kgÀ1 w.w.) of (a) Cd; (b) Pb; and (c) Cu in fish (wet weight basis) of the four lakes at different sampling times Note: Asterisks denote statistically significant differences among sampling times in comparison to the lowest value (Ãp < 0.05) Different superscript letters (a, b) indicate that values of the same species from different lakes within the sampling time interval are significantly different (p < 0.05; ANOVA followed by Student–Newman–Keuls test) Downloaded by [New York University] at 09:35 11 January 2015 Toxicological & Environmental Chemistry 1335 When comparing metal levels among species from the same lake, mud carp from Yen So Lake had higher levels of Cd and Pb than the other two species, while in Thien Quang Lake it showed lower Pb concentrations (p < 0.05); no differences were found for Cu in all lakes (p > 0.05; data not shown) However, the mean metal concentrations in fish from all lakes (Table 3) were not significantly different between species (p > 0.05) In most cases, metal levels in the same species differed between lakes (p < 0.05; Figure 2) Cd was found to be the lowest in all three fish species from Truc Bach Lake (p < 0.05; Figure 2(a)), the highest in mud carp from Yen So Lake, where Cd levels in the water were also the highest (Figure 2(a); Table 1) Pb concentrations in fish were about 30– 70 times higher than Cd, especially in mud carp from Yen So Lake (ca mg kgÀ1 w.w.), while silver carp exhibited low Pb levels all year round (p < 0.05; Figure 2(b)) The high Pb levels found in the mud carp from Yen So Lake, although Pb concentrations in sediments in this lake were lower than in other lakes, might be explained that Pb uptake rates were increasing in the presence of high Cd level in this lake (Komjarova and Blust 2009) Mud carp from Thien Quang Lake had lower levels of Pb and Cu than those from other lakes (p < 0.05; Figure 2(b), (c)) Overall, metal concentrations in the same species vary among lakes, depending on its levels in water and sediments Other environmental and physicochemical factors are known to be relevant (Pagenkopf 1983) Some correlations of metal levels in water and sediments to those in fish were found (data not shown) such as between Cd in water and in silver carp (rs ¼ 0.63) and tilapia (rs ¼ 0.71) of Truc Bach Lake, or Pb in water and its levels in silver carp (rs ¼ 0.80) and tilapia (rs ¼ 0.60) from Thanh Nhan and Thien Quang Lakes For Cu, a positive correlation was found between water and silver carp from Yen So Lake (rs ¼ 0.71; p < 0.05); the two species tilapia and silver carp often filter large volumes of water to collect food, and therefore, may absorb the metals mainly from water and contaminated phytoplankton Correlations were also found for mud carp and metals in sediments (Pb: Truc Bach, rs ¼ 0.77, and Yen So Lake, rs ¼ 0.72; Cu: Truc Bach Lake, rs ¼ 0.56) Mean levels of the metals in fish (Table 3) differ from previously published data (Pham, Pulkownik, and Buckney 2007; Puttaiah and Kiran 2008; Puttaiah and Kiran Table Cd, Pb, and Cu in fish muscle of the present study and their maximum acceptable limits (mg kgÀ1 w.w.) Mean values of fish from all lakes and standard deviations are in parentheses Concentration (present study) Metal iii Silver carp Mud carp Tilapia Cd 0.007–0.052 (0.020 Ỉ 0.007) 0.008–0.043 (0.021 Ỉ 0.006) 0.005–0.042 (0.017 Ỉ 0.005)