Abstract
Trace metal species in the water column of a canal system forming a wetland filled with wastewater were analyzed to determine their correlation with metal accumulation in the gills of locally fished Oreochromis niloticus. The metal concentrations in the suspended particles and water dissolved were analyzed. The metal species were calculated using Windermere Humic Aqueous Model version VII showing that the high organic matter and major cation contents were important parameters. Also, the free ion metal concentration was expected to correlate with the organic matter aromaticity; however, organic compounds other than humic susbtances seem to be complexing the metals in the system. Additionally, no clear correlation could be found between metal accumulation in gills and any of the dissolved metal species. Nonetheless, certain trends could be seen between the calculated metal species and metal accumulation in the tilapia from the suspended particles.
Highlights
The toxicity, bioavailability and mobility of heavy metals depend on their speciation rather than on their total concentrations in water [1,2]; trace metal speciation has become an important piece of information in the geochemical and ecotoxicological impacts of metals
The studied canals varied from the widest and longest in the Agricultural site (AI); the medium sized Urban canal (UI), which ends in a lagoon surrounded by houses with clandestine domestic waters; the wide Recreational canal (RI), almost a minor lagoon with a small island used for occasional theatrical representations; and the Wastewater canal (WW) near an important dock with a high volume outlet from the wastewater treatment plant, which imparts the canal with the highest flow of all the canals and has almost no sediment
Our study did not show a clear relationship between organic matter and metal content in suspended particles, most of the metal content in the water column was associated to suspended particles (>90%)
Summary
The toxicity, bioavailability and mobility of heavy metals depend on their speciation rather than on their total concentrations in water [1,2]; trace metal speciation has become an important piece of information in the geochemical and ecotoxicological impacts of metals. The most toxic metallic chemical species are free ions and small metal complexes in solution [5,6] and these bioavailable forms are proposed as the major forms incorporated by aquatic organisms. These metals can be incorporated via the diet (by the incidental intake of particulate matter), i.e., in benthic and benthopelagic organisms. In this context, digestive processes and chemical conditions prevailing in the organism’s digestive tract (pH, digestion time, redox state) determine whether non-bioavailable metals in the external environment are absorbed and assimilated into the gastrointestinal epithelium [7]
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