Polycyclic aromatic hydrocarbons and trace metal contamination of coastal sediment and biota from Togo

Abstract

The state of contamination of tropical environments, particularly in Africa, remains a relatively under explored subject. Here, we determined polycyclic aromatic hydrocarbon (PAH) and trace metal concentrations in coastal sediment and biota samples (fish and mussels) from Togo (West Africa). In the sediments, the ∑21 PAH concentrations ranged from <4 ng g(-1) to 257 ng g(-1), averaging 92 ng g(-1). Concentration ratios of low molecular weight PAHs (2-3 rings) versus high molecular weight PAHs (≥4 rings) were always lower than 1 (ranging from 0.08 to 0.46) indicating that high molecular weight PAHs were dominant in all sediment samples, and that PAHs originated mainly from anthropogenic combustion activities. The sediments were also analyzed for major elements and a total of 15 trace metals, which were found in elevated concentrations. The calculated enrichment factor (EF) values relative to the Earth's crust show that the contamination is extremely severe for Cd (EF = 191), severe for Cr (EF = 18) and U (EF = 17.8), moderately severe for Zr (EF = 8.8), for Ni (EF = 6.8), Sr (EF = 5.9) and Ba (EF = 5.4), and moderate for V (EF = 3.6) and Zn (EF = 3.4). Sediments sampled in areas affected by the dumping of phosphorite mine tailings showed particularly high concentrations of trace metals. Overall, concentrations of both PAHs and trace metals in sediment tend to increase from the coastline to the open sea (2 km offshore). This is attributable to the increasingly finer texture of coastal sediment found offshore, which has a terrigenous origin and appears loaded with various contaminants through adsorption processes. Such high loads of trace metals were also found in the biota (fish and mussels). The ratio of measured trace metal concentrations in biota to threshold limits set by the World Health Organization herein defined as relative health factor (RHF) was high. Average RHF values in fish were highest for Se (470), As (250), Ag (97), Ni (78), Mn (63), Fe (53), Pb (36), Cd (10), and Cr (7) while lowest for Cu (0.08) and Zn (0.03). Cd and Al did not bioaccumulate in the analyzed fish species. In mussels, the RHF values were highest for Fe (9,108), As (295), Pb (276), Se (273), Mn (186), Ni (71), Ag (70), Cd (14), and Cu (4).

Annotated checklist and fisheries interactions of cetaceans in Togo, with evidence of Antarctic minke whale in the Gulf of Guinea

“…A significant environmental threat to Togo's coastal habitat, hence to inshore occurring cetacean species, consists in phosphorites mining in the basin near Hahotoé and Kpogamé (Gnandi & Tobschall 1999;Gnandi et al 2011). Transported to Kpémé beach, ore is enriched through rinsing with sea water.…”

A review of the human activities impacting cetaceans in the eastern tropical Atlantic

“…polychlorinated biphenyls, PCBs), which are lipophilic and resilient to degradation (Islam & Tanaka , Gnandi et al. ). A wide range of pesticides and insecticides are used in the ETA, including internationally banned agrochemicals such as dichlorodiphenyltrichloroethanes, aldrin and lindane (Scheren et al.…”

“…Given their long life spans, position at the top of the food chain and transfer of contaminant loads to their offspring via milk, cetaceans are vulnerable to bioaccumulation of persistent organic pollutants such as pesticides and chlorinated compounds (e.g. polychlorinated biphenyls, PCBs), which are lipophilic and resilient to degradation (Islam & Tanaka 2004, Gnandi et al 2011. A wide range of pesticides and insecticides are used in the ETA, including internationally banned agrochemicals such as dichlorodiphenyltrichloroethanes, aldrin and lindane (Scheren et al 2002).…”

Searching Relationships between Tissue Elemental Concentrations and Geographical Distribution of Bigeye Tuna(Thunnus Obesus) from the South Atlantic Ocean

“…Enhanced levels of Cu were also reported in the African coast and linked to sources existing both in the continent and in the shelves (Loeff et al, 1997). Despite limited information is published on trace element concentration in other fish species from this remote area (Gnandi et al, 2013;Bandowe et al, 2014), increased concentration of Cd, Co and Cu in water may influence the levels found in tuna's prey. Being the increase of concentrations found in the liver suggests that food is the accumulation pathway.…”