Tolerance of fish to contaminated habitats: underlying mechanisms probed with isotopic tracers
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Date
2006
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International Atomic Energy Agency
Abstract
Future scenarios indicate agricultural and industrial expansions in major river basins and enhanced world populations focusing in coastal watersheds [1], particularly in SE Asia. Such scenarios are consistent with increasing concentrations of various contaminants, including metals and radionuclides. It is important to assess the likely impacts on fisheries, their response and possible adaptability to enhanced contaminant levels and the implications for resulting transfer factors and contaminant levels in fisheries, that can be the major sources of subsistence and livelihood for coastal communities. The likely future responses of fisheries to projected increases in contaminant loadings over broad geographical scales can be probed through the employment of currently highly contaminated aquatic environments. Such a system with these attributes, that we have investigated periodically since the early 1970s, is the Finniss River in tropical northern Australia, that has continued to receive acid mine drainage from the Rum Jungle U/Cu mine since the 1950s. Prior to mine-site remediation in the early 1980’s measured loadings of Cu, Zn, Mn and sulfate caused severe impact to fish diversity and abundanc e, including fish kills observed in the main Finniss River and its East Branch. Following mine-site remediation and measured reductions in contaminant loadings, there has been recovery of fish communities in the main Finniss River and considerable recolonisation of the still highly contaminated region of the East Branch, that was virtually devoid of fish populations prior to remediation [2]. Following mine site remediation reductions in annual-cycle contaminant loads of sulfate, Cu, Zn, and Mn by factors of 3-7 were accompanied by an unexpected degree recovery in fish community structure in the contaminated region of the Finniss River, to the extent that they were not statistically (P > 0.05) distinguishable from unexposed environments [2]. However, these fish communities continue to be exposed to considerable annual tonnages of these contaminants, as well as the naturally-occurring radionuclides associated with uranium mine wastes. Hence their capacity to accumulate contaminants under these conditions of long-term exposure and their adaptive response can be critically investigated, and is of concern to local stakeholders, both Aboriginal and European, who consume some of these fish species [ 3]. A more unexpected field observation was made in 1993 when five small fish species were found living in the East Branch of the Finniss River, where individual species penetrated the pollution gradient to varying degrees, but with one species (Melanotaenia nigrans) occurring at extremely high concentrations of Cu [4]. A laboratory-based study investigated the mechanisms of copper tolerance in M. nigrans from the polluted East Branch, compared to unexposed or reference populations. The bioconcentration of cyclotron-generated 64/67Cu in fish was used to investigate the mechanism of copper tolerance in exposed fish. In this shortterm experiment Cu concentrations in all tissue sections were significantly (P<0.05) less (up to 50%) in exposed fish compared with the respective tissue sections of reference fish, when exposed to both low and elevated Cu water concentrations. The mechanism of copper tolerance was concluded to be reduced copper uptake in the gills, rather than increased binding or elimination. Initial and subsequent allozyme electrophoresis showed that heterozygosity was reduced in exposed fish compared with that of reference fish. Collectively, these results suggest that genetic selection may have occurred in the exposed fish population. This was the first study on the mechanisms of copper tolerance in a wild fish population that has been exposed to elevated copper concentrations [5]. A pilot study of Cu, U, Zn, Co, Ni, Pb, Mn, Ra and Po-210 in several edible species of fish that now occur in abundance in the region of the main Finniss exposed to mine effluents has shown the following. Each contaminant water concentration was enhanced in the contaminated zone at the time of sampling. Compared to unexposed control sites, flesh samples from two species [Bony bream (Nematalosa erebi) and Eel- tailed catfish (Neosilurus ater)] were not significantly (P>0.05) enhanced in mean concentrations of any of these contaminants, with some being actually reduced (P<0.05) in the most contaminated region. This pattern of reduced accumulation in the exposed populations under field conditions is comparable to that obtained experimentally for Cu uptake in M. nigrans.
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Keywords
Watersheds, Agriculture, Industry, Ecosystems, Asia, Contamination, Rivers
Citation
Jeffree, R. A., Markich, S. J., Twining, J. R., Gale, S., (2006). Tolerance of fish to contaminated habitats: underlying mechanisms probed with isotopic tracers. In Proccedings of an international conference held held in Monaco, 25–29 October 2004 organized by the International Atomic Energy Agency and co-sponsored by the Abdus Salam International Centre for Theoretical Physics, International Hydrological Programme of UNESCO, Intergovernmental Oceanographic Commission of UNESCO and the Commission Internationale pour l’Exploration Scientifique de la Mer Méditerranée, "Isotopes in Environmental Studies Aquatic Forum 2004". (pp. 316-317). Retrieved from https://www-pub.iaea.org/MTCD/Publications/PDF/CSP_26_web.pdf