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

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.

Physicochemical Quality of the Water and Heavy Metal Contamination of the Sediment, Water, and Flesh of Some Fish in the Lower Reaches of the Mono River (Benin, West Africa)

“…The heavy metals originating from pollution sources in the upper and middle reaches would be drained downstream (the lower reaches), where they would be added to local pollution to produce high concentrations of heavy metals (Blanc et al, 2005;Damy, 2011;Moruf and Akinjogunla, 2019). The phenomenon of water releases from the Nangbéto Dam, responsible for high erosion in the basin (Amoussou et al, 2012), would facilitate this accumulation of metals in the lower course (Kondo et al, 2021). High-water velocity in a river encourages bank erosion, releasing particles (including organic matter, metals, etc.)…”

“…However, there is a lack of data on water and sediment quality in other parts of the basin and on the quality of fishery products throughout the basin. As the lower reaches is the final receptacle for pollution from the upper and middle reaches (Kondo et al, 2021), and fish is the main source of protein for riverside populations, there is an urgent need to assess the quality of the biotope of the lower reaches and the quality of the flesh of the fish species most consumed by riverside residents. This study aims to assess the physicochemical quality of the water and the concentrations of heavy metals in the sediment, water, and flesh of the most abundant fish species and those most appreciated by residents in the lower reaches of the Mono basin.…”

“…These sources of pollution end up in the water through run-off, altering the quality of the biotope (sediment and water), the life of the biocenosis (plankton, invertebrates and vertebrates) and, consequently, the nutritional quality of fishery products (fish, prawns, crabs, gastropods, bivalves, etc.) (Ennouri et al, 2013;Erasmus et al, 2018;Kondo et al, 2021). The accumulation of pollutants in organisms and their transfer along the food chain are more rapid in continental waters (rivers, lakes, lagoons, etc.…”