Heavy Metal Contamination Levels in Clams (Galatea paradoxa, Born 1778) and Surface Sediments from Mono River Estuary, Togo, and its Health Implications

Kamarou Faré Kondo ,Komlan Mawuli Afiademanyo ,Hodabalo Dhéoulaba Solitoke ,Kamilou Ouro-Sama ,Kissao Gnandi

doi:10.7176/jbah/11-4-06

Abstract

Heavy metal pollution in aquatic ecosystems is one of the most important threats of human health and food chain. Thus, in this study, the level of Cd, Fe, Hg, Mn, Pb and Zn accumulation in surface sediments and in Galatea paradoxa , were investigated to estimate their potential health risks via consumption to residents alongside the Mono river, Togo-Benin border. Samples were collected at two fishing areas and analyzed using flame atomic absorption spectrophotometry Moreover, the likely health risks developed as a result of human contamination by heavy metal through clam consumption was also assessed using target hazard quotient (THQ) and hazard index (HI). The mean maximal metal concentrations (μg/g dw) were as follows: Fe (25624) > Mn (1176.0) > Zn (23.29) > Pb (4.67) > Hg (0.038) in silty sediments and Fe (15692) > Mn (654.78) > Zn (12.53) > Pb (2.42) > Hg (0.034) in sandy sediments. Cd content were all below the detectable limit. When compared against some consensus-based sediment quality guidelines (TEL, ERL, AFNOR), it was observed that all the concentrations, excluding Fe levels in the samples, were lower than reference values. Similarly, computed PLI was less than 1 indicating that the lower tidal parts of the Mono were unpolluted. The accumulation pattern of studied trace metals in the clams followed a slightly different trend from that found in the sediments (Fe>Zn>Mn>Hg>Pb>Cd). Fe (1353 ± 162 μg/g dw) and Zn (51,8 ± 8.9 μg/g dw) content in whole tissues of G. paradoxa were well above the maximum concentration allowable by food safety criteria. In contrast, Cd (0.097 mg/kg dw), Hg (0.24 mg/kg dw) and Pb (0.18 mg/kg dw) content were very low. Computed THQ values were all below 1, with highest results found in the small size clams regardless of the heavy metals. The HI values indicate that none of the analyzed heavy metals may pose serious risk to consumers through the clams studied. The highest risk was posed by small clams, followed in decreasing order by medium and large clams. We therefore suggest that the clams taken from main fishing locations at Mono river are safe to eat. Keywords: Heavy metals, Sediment pollution, Galatea paradoxa , Human health, Mono River DOI: 10.7176/JBAH/11-4-06 Publication date: February 28 th 2021

Highlights

Pollution of coastal waters has increased dramatically in recent years and has led to an increase in environmental problems in many developing countries (Kumar et al 2013)
The Fe content was very high with a maximum value of 25624 ± 2843 μg/g recorded during the rainy season and a minimum value of 15692± 1260 μg/g measured during the dry season
To Fe, the Mn concentration were very high with a maximum value that amounted to 1176 ± 111 μg/g measured in the rainy season in the mud sediment

Summary

Introduction

Pollution of coastal waters has increased dramatically in recent years and has led to an increase in environmental problems in many developing countries (Kumar et al 2013). In Togo, since the second half of the 1900s, rivers, estuaries and coastal lagoons have received high inputs of pollutants due to the escalation of the activities of palm oil plantations, the misuse of pesticides in cotton cultivation, the cross-border traffic in adulterated fuel and above all, the discharge of untreated waste from the treatment of phosphates at the Kpémé plant (Gnandi & Tobschall, 2001; Gnandi, 2003; Rezaie-Boroon, 2011; Tanouayi et al 2015) Metals such as Zn, Cu, Mn, Co and Fe are known to be essential elements, which play important roles in biological metabolism at very low concentrations (Saeed et al 2008), all trace metals whether essential or not, are potentially toxic at a threshold bioavailability. Factors known to affect the uptake of trace metals and their accumulation in bivalves include metal bioavailability, characteristics of the physical environment, season of sampling, size and physiological state of the organism (Boening, 1999; Ravera, 2001)

Methods

Results

Conclusion