ABSTRACT

This study investigated hazard indices and human health risks associated with consumption of bivalve mollusc from the Niger delta. The research was conducted in two phases; The first was the analysis of consumption pattern and perception of  bivalve molluscs in the studied locations through the use of structured questionnaire while in the second phase, four species of  bivalve mollusc; Bloody cockle (Anadara senilis), Donax clam (Donax rugosus), Knife clam (Tagelus adansonaii) and Mangrove oyster (Crassosstra gasar) collected from four different  locations in the Niger delta were assessed for microbiological hazards, toxic element contents, concentrations and compositional pattern of polycyclic aromatic hydrocarbons (PAHs), levels of polychlorinated biphenyls (PCB) congeners in bivalves as well as the estimated  human health risk associated with the consumption of bivalve with these chemical contaminants. Standard methods of analyses were employed in the determination of microbiological hazards and levels of toxic elements, PAHs and PCBs concentrations in bivalves were determined through the use of gas chromatography while the United State Environmental Protection Agency (US EPA) method was used to estimate the human health risk of chemical contaminants in bivalves consumed in the Niger delta. Results of consumption pattern and perception indicated that bivalve consumption were driven by attributes such as easy availability, low-price and pleasant flavor. A chi-square test indicated a positive significant relationship (p<0.05) between demographic variables of the respondents and the level of perception toward bivalve consumption. Microbiological hazards isolated from bivalve samples included; Vibrio cholerae, Vibrio parahaemolyticus, Salmonella spp, Shigella spp, Listeria monocytogenes and Escherichia coli in levels above the stipulated FDA standard for shellfish which rendered the product unsafe for human consumption.  Lead concentration was within the 1.5mg/kg acceptable limits while cadmium, arsenic and mercury were higher than FAO limits of 0.5, 0, 0.5 mg/kg respectively. The individual tissue burden of PAHs indicated bloody cockle (53.75μg/kg), knife clam (50.00μg/kg), mangrove oyster (40.34μg/kg) and Donax clam (36.94μg/kg) while the compositional pattern of PAHs indicated the dominant of  low molecular weight PAHs in Andoni location while other study locations were dominated with high molecular weight PAHs. The diagnostic ratio showed that the PAH burden originated from petrogenic source at Andoni while that of other locations were from pyrogenic or combustion processes. The result of analysis for PCBs indicated the presence of lower chlorinated PCB congeners in all the study location. The total concentrations of PCB congener were highest at Bonny (1.75ng/g) while Andoni had the least (0.36ng/g). The PCB burden in bivalve tissue indicated that mangrove oyster accumulated the highest concentration (1.38ng/g) followed by bloody cockle (1.11ng/g) while Donax clam (0.60ng/g) had the least. The estimated human health risk indicated a non-carcinogenic values and hazard indices higher than threshold value of one for cadmium, total arsenic and methylmercury while risk values for carcinogens were higher than the US EPA stipulated one in one million chances for developing cancer. This implies that toxic elements apart from lead, carcinogenic PAHs and PCBs in bivalves from these locations can induce potential deleterious health effects to the consumers.