Levels of selected toxic and essential elements in fish and oysters from Western Indian Ocean, Coast of Tanzania

Abstract

Concentrations of toxic and essential elements in selected finfish and shellfish collected from Dar es Salaam and Tanga, Indian Ocean coast of Tanzania are presented. The elemental concentrations were determined using Energy Dispersive X-ray Fluorescence (EDXRF) spectrometer coupled with X-lab ProTM software. The mean concentrations of metals observed in finfish and shellfish collected from Tanga ranged from 3.40–5.75, 1.8–37.17, 3.5–7.1, 0.6–1.3, 0.53–0.73 and 16.80–96.70 mg kg–1 for As, Cu, Mn, Ni, Pb and Zn, respectively. For Dar es Salaam, the mean concentrations of metals ranged from 3.34–9.46, 2.90–30.53, 3.4–6.9, 0.7–1.0, 0.57–0.80 and 14.2–100.90 mg kg–1 for As, Cu, Mn, Ni, Pb and Zn, respectively. Thumbprint emperor showed the highest levels of Cu and Ni; octopus showed the highest values of As and Pb, while sardines showed the highest level of Mn. Oysters, used as pollution indicators in this study showed the highest elemental concentrations and exceeded their mean levels in finfish from Dar es Salaam by factors of 1.30, 7.15, 6.27, 2.72, 1.29 and 35.57 for As, Cu, Mn, Ni, Pb and Zn, respectively. In samples from Tanga, the metal concentrations in oysters were several times higher (3.76, 17.68, 1.12, 3.89, 1.88 and 66.92 for As, Cu, Mn, Ni, Pb and Zn) than in finfish, respectively. Based on metal concentrations in oysters, it can be concluded that coastal waters are contaminated with heavy metals. However, with an exception of arsenic and copper, the elemental levels in finfish are within the maximum permissible levels recommended by various international standards and guidelines.

Keywords: Finfish, toxic elements, essential elements, pollution, EDXRF