Accumulation of trace elements in sediment and biota in the Wouri Estuary, Douala, Cameroon.

Abstract

The Wouri Estuary on Cameroon’s Atlantic Coast is located adjacent to the Douala metropolitan area. Three rivers (Wouri, Dibamba, and Mungo) discharge into the Wouri Estuary. Seventy percent of the industries (soap, brewery, food processing, salt, cement, petroleum and pharmaceutical) in Cameroon are found in the City of Douala. These industries discharge their waste into the estuary. Urban and agricultural runoff are also discharged into the estuary. The urban population of the City of Douala consume shrimp and fish from the estuary daily. This thesis investigated the concentrations of trace element (As, Cd, Cr, Cu, Hg, Ni, Pb and Zn) in sediment and biota (bonga, catfish and shrimp) in the Wouri Estuary and assessed the human health risk associated with the consumption of fish and shrimp sourced from the estuary by households in the Douala’s Akwa and Makepe Missoke neighbourhoods.

A questionnaire based survey was used to collect data on the consumption rates of fish and shrimp in the Douala’s Akwa and Makepe Missoke neighbourhoods. The results of the survey showed that more than 60% of households in both neighbourhoods consumed fish and shrimp sourced from the Wouri Estuary. Average consumption rates ranged from 39-387g for dried shrimp and fish, and 455-2083.3g for fresh shrimp and fish.

None of the sediment samples collected from the Wouri Estuary had trace element concentrations that exceeded the ANZECC Interim Sediment Quality Guideline High. However, concentrations of Cr, Cu and Ni exceeded the ANZECC Interim Sediment Quality Guideline Low at some sites. The trace elements most enriched in sediment from the Wouri Estuary were Cd, Cu and Pb.

The concentrations of As, Cd, Cr, Cu, Pb and Zn were generally higher in liver than in gills and muscle of bonga and catfish. None of the trace element concentrations in biota exceeded guidelines for human health. Although trace element concentrations were low, the risk assessment conducted for the Douala’s Akwa and Makepe Missoke neighbourhoods indicated that As and Pb from dried fish bought from the market are of concern for fish consumers.