Trace metals in water and fish (Unga species, Pungu maclareni, catfish Clarias maclareni) from Lake Barombi Mbo, Cameroon

Abstract

Lake Barombi Mbo is an isolated oligotrophic lake situated in the volcanic range of West Cameroon and home to several endangered endemic cichlids. A fieldwork was carried out at the lake where water and fish samples were collected as part of an investigation. The aim of this study was to investigate (i) whether studied trace metals were present at levels exceeding ambient water criteria, (ii) link uptake of trace metals in gills and liver of fish to water chemistry, (iii) accumulation of mercury in muscles and biomagnification along the food chain. ICP-MS and ICP-OES analysis for concentration of trace metals in water samples from the lake showed that, the total concentrations of investigated trace metals were below U.S. Environmental Protection Agency (EPA) criteria limits, Canadian Council of Ministers of the Environment (CCME), South Africa Water Quality Guidelines and World Health Organization (WHO) guidelines for protecting aquatic life. Linking uptake and water chemistry, bioconcentration factor (BCF) analyses showed accumulation of trace metals in both gills and liver of fish. With minor differences in accumulation sequence, all fish species accumulated Al, Mn, and Sr in highest concentration in their gills with Cu, Cd, Co, Cr, Pb, and U highest in liver. The highest mean concentration of metal accumulated was observed for Cu (1153 µg/g dw) in liver of U. species. P. maclareni accumulated Al, Cr, Co, Sr, and Pb in highest concentrations. While U. species had Mn and Cu in highest concentration, Cd was present in highest concentration in C. maclareni. The high accumulation of Al, Mn and Sr on gills of the three fish species, indicates that they are bioavailable and probably high levels in Lake Barombi Mbo. Total mercury concentrations (mg/kg ww) were low with mean values of 0.0093 in U. species, 0.0274 in P. maclareni and 0.0266 in C. maclareni compared to 0.2 mg/kg WHO recommended guideline for Total Dietary Intake (TDI) to protect vulnerable groups (pregnant women and children) from mercury toxicity. Stable isotope analysis of carbon δ 13 C used as index for carbon source and flow, and nitrogen δ 15 N as index for trophic position within the aquatic food chain were determined. Hg concentrations in muscle of fish coupled mean δ 13 C (‰) and nitrogen δ 15 N (‰), showed that U. species had the lowest Hg concentrations, δ 13 C (- 32.9 ‰) and δ 15 N (6.6 ‰), and so occupied the lowest position of the food chain. C. maclareni and P. maclareni both had the highest Hg levels, but C. maclareni had the highest δ 15 N (9.9 ‰) and occupied the highest trophic level. Log THg vs. δ 15 N among all species sampled showed a significant positive relationship indicative of mercury biomagnification along the food web of Lake Barombi Mbo. Results of trace metal levels in water and fish tissues suggest that trace metals do not pose a serious threat to the aquatic biota of Lake Barombi Mbo.