Research Articles 1 Trace Metals © ecomed publishers, D-86899 Landsberg, Germany and Ft. Worth/TX, USA • Tokyo, Japan • Mumbai, India • Seoul, Korea ESPR – Environ Sci & Pollut Res 8 (2001) Research Articles Trace Metal Levels in Freshwater Fish, Sediment and Water* Zsuzsanna Sandor 1 , Istvan Csengeri 1 , Maria B. Oncsik 1 , Maria N. Alexis 2 and Elena Zubcova 3 1 Research Institute for Fisheries, Aquaculture and Irrigation, 5541 Szarvas, POB 47, Hungary 2 National Center of Marine Research, Institute of Marine Biological Resources, Aghios Kosmas, Hellinico, GR-16604 Athens, Greece 3 Institute of Zoology of the Moldavian Academy of Sciences, Kishinau, Moldova Corresponding author: Zsuzsanna Sandor; e-mail: sandorzs@haki.hu Many aquatic animals are able to excrete the excess propor- tion of their metal intake under contaminated conditions and thus maintain trace metal concentrations in the body at normal levels. Freshwater fishes can regulate the levels of essential elements: copper, chromium, molybdenum, and zinc over a range of ambient concentrations, and some regula- tion of nonessential metals such as cadmium and mercury may also occur (Leland 1985). Organisms that cannot ex- crete or otherwise regulate contaminants can readily bio- magnify these materials with age (Bryan 1979). In natural waters, only a very small percentage of the dis- solved heavy metals, such as copper, lead, cadmium or zinc, are present as free (aqua) metal ion; most of the metal is adsorbed to colloidal particles or combined in complexes (Flo- rence et al. 1992). Knowledge of trace element speciation in waters is essential to understand aquatic toxicity. Ingested food may also be a significant source of metals assimilated by aquatic organisms. For many bioaccumulative compounds, the prin- cipal route of movement into and through aquatic food webs appears to be dietary ingestion rather than bioconcentration from water, because these compounds generally exhibit low water solubility and tend to concentrate in the lipid fractions of biological tissues (Suedel et al. 1994). The analysis of the water, sediment and aquatic living be- ings, such as fish, planktonic and benthic organisms could indicate the level and the tendency of the pollution. This is important not only for protection of the environment, but for the quality of the cultured fish in the water. Little has been done concerning quality standards of aqua- culturally produced fish, which is an area of primary impor- tance for the European Community. Differences are expected to exist among fish collected from different areas, depend- ing on the feeding, the water quality and geographical prop- erties of the area. Trace metal levels in fish depend also on age, body size of the fish, feeding habits, season and tem- perature of the water, and other factors that influence the metabolic rate of fish (Phillips 1990). The first part of the present study aimed at establishing the baseline levels of trace elements in fish meat samples of vari- ous species of fish from different water bodies and originat- ing from different fish culture technologies. In the second part of the study, water, sediment, fish carcass and fish feed have been examined in fishponds differing in stocking den- sities and the intensity of feeding. The retention of the trace metals in the fish has been studied by measuring the levels in each of the possible sources of the heavy metals. DOI: http://dx.doi.or g/10.1065/espr2001.08.075 Abstract. The trace metal concentrations in water, sediment and aquatic organisms, such as fish, could indicate the level and ten- dency of the pollution. This is important not only for the protec- tion of the environment, but for evaluation of the quality of fish meat either captured from natural waters or cultured in fishponds. The total trace metal concentrations in samples of fish from dif- ferent regions of Hungary and from different species have been determined by using an X-ray fluorescence technique (EDXRF). Water, sediment and fish samples from fishpond systems with different feeding and stocking has also been analyzed. In the case of zinc contents, differences have been traced between the cultured and wild common carp. In the case of common carp reared under different feeding conditions, differences were also observed in the zinc concentration. The retention of the trace met- als in the fish has been studied by measuring the levels in sedi- ment, water and feed. The different retention can be explained by the different availability of zinc in the applied feeds, which can be related to the presence of different metal species in the feeds. Keywords: EDXRF; finfish; fishpond; freshwater fish; meat; sedi- ment; trace metals; water; X-ray fluorescence technique (EDXRF) Introduction Bioaccumulation of certain heavy metals along the food chain is a well-recognized process. Essentiality and toxicity of trace metals in organisms depend on the concentration of the metal; below a certain level they could be considered as es- sential for biochemical processes, but in the case of a high accumulation in organisms, intoxication may occur. The mechanisms of accumulation and storage of trace metals in aquatic animals are diverse, varying with chemical form of the metal, mode of uptake and animal species. A great deal of information and numerous measurements are involved in determining biomagnification, including information regard- ing an organism's position in a complex food web, preda- tor-prey relationships, feeding habits, age and sex of the sampled organisms, tissue chemistry data, lipid composi- tion, and gut content analyses. In many cases, studies at- tempting to assess biomagnification have been plagued by poor experimental design, resulting in a high degree of vari- ability (Suedel et al. 1994). * This paper was presented at the 7th FECS Conference on Chemistry and the Environment 'Metal Speciation in the Aquatic Environment', held at Oporto, Portugal, August 27-30, 2000.