Estimation of Heavy Trace Metals in Various Local Fish Species and Relevant Marine/Fresh Waters

Abstract

Sixteen marine, fifteen creek and thirty four freshwater commercial fish species, together with relevant waters, were analyzed for ten essential/non-essential heavy trace metals by flame/flameless atomic absorption technique. The metals included Ni, Cu, Mn, Hg, Fe, Cr, Cd, Pb, As and An. Muscle, liver and kidney of various fish species were subjected to trace metal analysis to study the multi-organ distribution pattern of some of the metals. Study on the nutritional status of local fish was conducted on certain marine and freshwater species in terms of their Ca, Na, K and Mg content. The estimations were based on wet oxidation procedure, using nitric acid at ambient temperature to digest the fish samples without involving any preconcentration step. Replicate results quoted as ug/g, wet weight basis, at +S confidence level, were compared statisticall6y with those obtained by conventional wet oxidation and dry ashing methods in terms of standard deviation and coefficient of variation, Recovery studies were also carried out using standard fish samples in order to validate the quantification of data. The results obtained were mutually comparable. Interlaboratory comparison using recovery evaluation based on WHO fish standards was also conducted. The mutual agreement was within 1-2% on the average. The study on trace metal content of edible muscle of marine fish revealed that Ni, Cr and Pb concentration in Scomberomorus commerson were higher than those found in other species, so being true about Cd and As content of Nandus nandus. In general, the metal levels in all the species were found to be within the permissible levels laid down for human consumption the only exception was that of Pb (1.895 ug/g) in Scomberomorus commersson that crossed the upper allowed level. Compared with muscle, the corresponding levels of the metals in liver and kidney were higher and varied considerably. The study showed that Ni, Cr, Cd, Pb, and As accumulated more in kidney than in liver. The tissue sequence in case of distribution of Cu, Mn, Hg, Fe and Zn, however, was liver keidney muscle. The metals levels in Pampus argenteus, Formio niger, Thunnus tonggel and Sardinella longiceps were higher as compared with other fish. In order to look into a probable local pollution effect, the levels of trace metals in various marine and creek fish, harvested from the coastal waters of the Arabian Sea, along the Karachi shore, were analyzed as to their trace metal content. The trace metal distribution in the fish was found to be highly species-specific, with mean concentrations of the metals fulfilling the recommended daily allowance (RDA) laid down for safe consumption. Only mercury was found to exceed the safe limit (1 ug/g) in three species: Sillago plateado (1.203 ug/g), Scomberoides commersonnianus Lacedpede (1.025 ug/g) and Cynoglossus bilineatus (1.211 ug/g). The fresh water fish, obtained from local market, streams and hatchery ponds in the provinces of Punjab, NWFP and Sind, were analyzed along with relevant waters to establish possible correlations between the heavy metal concentrations in fish muscle and in relevant waters. The estimated concentrations in fish (ug/g, wet weight) in the muscle showed a big scatter: 0.010-38.000 for Ni, ).002-7.200 for cu, ).002-11.157 for Mn, 0.020-37.735 for Hg, 0.725-180.550 for Fe, 0.010-13.200 for Cr, 0.004-1.500 for Cd, 0.785-50.650 for Zn, 0.010-45.316 for Pb and 0.005-7.500 for As. The study showed a positive correlation between the concentration of zinc and arsenic in the fish muscle and in relevant waters, while the distribution of metals was found to suffer largely from individual variability, irrespective of area of catch. The study on the linear regression analysis of the data was conducted using the MSTAT statistical package on a WANG Personal Computer. The macronutrient study was confined to twelve marine and seventeen freshwater fish species for the estimation of Ca, Na, K and Mg in the edible muscle only. In marine fish the observed Ca concentrations ranged from 95-210 ug/g (wet weight basis), with an average of 131.5 ug/g for all the species. The K content ranged from 1648-3015 ug/g, while the levels of magnesium ranged from 150-330 ug/g. Similarly, Na levels were averaged at the extremum values of 350 and 1210 ug/g. Of the freshwater species, Ompok bimacultus, Puntius ticto, Mystus seenghala, Rita rita, wallago attu, Catla catla, Heteropneustes fossilis and Tilapia nilotice were found to be deficient in Ca content. This ranged from 60-591 ug/g. In case of K only two fish species Heteropneustes fossilis and Cirrhinus mrigala qualified for nutritional quality, while the remaining fish were only close to standard EDI levels. The observed range for K was from 692-3045 ug/g. The levels of Mg ranged from 162 to 524 ug/g and those of Na from 140 to 1215 ug/g, wet weight. On the whole, the local marine and freshwater fish were found to be a potential source of macronutrients and, except for a few identified cases, does not pose any physiological problem to the consumers.