Abstract
BACKGROUND: As water flows through habitats associated with estuaries, such as mud flats, salt marshes, sea grass and mangrove forests, pollutants such as heavy metals are filtered. The fine sediment dominant in intertidal and subtidal estuarine systems is an important sink for these contaminants. Periwinkle, which inhabit estuarine ecosystems, are known to bioaccumulate large quantities of contaminants. OBJECTIVES: In view of the widespread consumption of periwinkle in the Niger Delta, Nigeria, this study was designed to assess the concentration and potential human health hazards of heavy metals due to the consumption of this rich, inexpensive and readily available source of protein in Calabar, Nigeria. METHODS: Lead (Pb), cadmium (Cd), chromium (Cr) and nickel (Ni) content of edible tissues of periwinkles obtained from major markets in Calabar were determined using Shimadzu atomic absorption spectrophotometer (Model AA-6800, Japan) after wet digestion. RESULTS: The ranges of concentration (mg/kg dry weight) were Pb (0.011-0.056), Cd (0.008-0.032), Cr (0.014-0.157) and Ni (0.053-0.261) for Watt Market and Pb (0.009-0.052), Cd (0.011-0.032), Cr (0.012-0.052) and Ni (0.012-0.322) for Mariam Market. Concentrations of all the metals were below Food and Agricultural Organization (FAO), FAO/World Health Organization (WHO) and Commission of European Communities maximum permissible limits. The estimated daily intake (EDI) of Pb and Cd were slightly higher compared to the recommended daily intake for the metals. The EDI of all metals under study were lower than the upper tolerable daily intake. The target hazard quotients (THQ) computed to estimate the human health risk posed by each metal were above the safe limits of unity, except for Cr. The hazard index (HI) for a typical adult of 60.7 kg body weight was found to be 9.7 for Watt Market and the relative contributions to the aggregated risk were 24.66%, 54.51%, 0.0001% and 20.70% for Pb, Cd, Cr and Ni, respectively. The HI for Marian Market was 10.7 and the relative contributions to the aggregated risk were 22.31%, 57.55%, 0.06% and 20.09% for Pb, Cd, Cr and Ni, respectively. CONCLUSIONS: Consumption of periwinkles purchased from major markets in Calabar poses toxicological risk with respect to Pb, Cd and Ni poisoning. COMPETING INTERESTS: The authors declare no competing financial interests.