Mercury Levels in Sediment, Shellfish and Fish of a Water Body in the Niger Delta

Abstract

The concentrations of mercury in sediment and the muscle tissues of shellfish and fish of Bonny River and creeks around Okrika were determined in order to identify possible sources and indicator species that can be used to monitor pollution of the ecosystem, as well as assess possible health risk. Sediment samples were taken from ten (10) locations including the refinery effluent discharge channel, while shellfish and fish were randomly taken within the studied area. All samples were prepared and analysed by the cold vapour technique. The mean level of detectable values (ppm) in the sediment was 0.273±0.016. Those of shellfish were: P. aurita (0.016±0.012) and G. rhizophorea (0.018±0.026), while for fish we have: P. koelreuteri (0.014±0.019), M. cephalus (0.011±0.010), S. marderensis (0.008±0.011) and T. guineensis (0.026±0.032). The sediment results reveal largely anthropogenic enrichments mainly from refinery effluent. The pattern of accumulation by both fish types was both physiologically and ecologically characterized an indication that it is only the dissolved forms of metals that are effectively available to fish for bioaccumulation. The remarkable bioaccumulation factor (130.00) was associated with T. guineensis, which appeared to be the most efficient accumulator, and therefore a good bioindicator to monitor mercury pollution of the system. Mercury levels in all sample types were however generally low and do not portend serious danger with respect to human health. Nevertheless, the continued discharge of industrial effluents without regular monitoring may have imminent detrimental effect on the flora and fauna, since the metal is detectable in all the samples at sub-lethal concentrations.

KEYWORDS: concentrations, shellfish, fish, mercury, indicator species, Bonny River