Abstract
The present study investigated the concentration and species of heavy metals As, Hg, Cr, Pb and Zn in water and As, Hg, Cr, Pb and Zn in sediments collected along the coastal marine areas of Tanzania so as to determine their behaviour and remobilization potential in the environment and the degree of their availability to edible aquatic biota for monitoring purposes. Sequential extraction revealed the presence of a significant proportion of heavy metals Cr, Pb and Zn bound to available fractions of sediments. Arsenic had the highest concentration in non available residual fractions. PCA analysis found that As-Hg, Cr-Pb were strongly correlated and that the two may be derived from the same source most likely from storm water drainage of waste water discharges, while Zn may have come from the different source like watershed erosion. Further, PCA clearly confirms the same. Generally, Zn among all heavy metals analysed was the most available to aquatic biota due to its higher average concentrations in the acid soluble fraction, followed by chromium. However, high percentages of metal species studied in Tanzania coastal marine areas were found in non available fractions which indicated that the edible aquatic biota was safe for human consumptions.
Highlights
Different physico-chemical forms of an element can co-exist and may or may not be in thermodynamic equilibrium with one another [1]
The present study investigated the concentration and species of heavy metals As, Hg, Cr, Pb and Zn in water and As, Hg, Cr, Pb and Zn in sediments collected along the coastal marine areas of Tanzania so as to determine their behaviour and remobilization potential in the environment and the degree of their availability to edible aquatic biota for monitoring purposes
Sequential extraction revealed the presence of a significant proportion of heavy metals Cr, Pb and Zn bound to available fractions of sediments
Summary
Different physico-chemical forms (species) of an element can co-exist and may or may not be in thermodynamic equilibrium with one another [1]. Knowledge of the chemical forms of elements is essential for estimating their biological availability, physico-chemical reactivity and elemental transport in the environment. Inorganic arsenic in seawater is biotransformed into organoarsenic compounds by marine biota and more than 20 organoarsenic compounds have been identified [2]. The oxidation state of an element plays an important role on bioavailability and toxicity. Among the two chromium oxidation states, Cr (III) is considered one of the essential elements for living organisms, whereas Cr (VI) is toxic to biota and has been reported as carcinogenic. As (III) is much more toxic than As (V) [3]
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