Contribution to the Assessment of Heavy Metal Contamination in Fish and Shrimp from the Continental and Marine Areas of Cameroon

Heavy metals occur naturally in the environment. However, human activities such as industry, agriculture, and mining are responsible for a significant increase in their concentrations in ecosystems, including waterways and marine environments. This study aims to assess heavy metal contamination in fish and shrimp from Cameroon’s continental and marine areas. Fish were sampled in situ in the Wouri, Nkam, and Dibamba rivers. The shrimp were collected from local fishermen at the landing sites in Youpwé and Kribi. Water samples for laboratory analysis of trace metals were collected upstream in the rivers using 1,000 mL polyethylene bottles and then analyzed in the laboratory using standard methods. The trace metal content was measured using mass spectrometry. The results for water show that the highest average concentrations of zinc (5.325 mg/L) are observed at Youpwé, while the Nkam station has the highest average mercury concentration (7 mg/L). The sediments of Kribi have high concentrations of lead (10.39 mg/kg), those of Dibamba have high concentrations of cadmium (119.7 mg/kg) and nickel (0.6182 mg/kg), those in Youpwé have high concentrations of zinc (7.7 mg/kg), and those in Wouri have high concentrations of mercury (166.2 mg/kg). The most abundant traces of heavy metals in the two fish species (Oreochromis niloticus and Chrysichthys nigrodigitatus) were lead and cadmium, particularly at the Wouri and Dibamba sites, with values exceeding the permitted limits (0.01 μg/g). However, in the Kribi area, there is contamination (CF > 1) of the shrimp species Penaeus notialis by lead and high contamination (CF > 6) of all shrimp species by mercury. The fish species Oreochromis niloticus bioaccumulates zinc in the Dibamba River, and the shrimp species Penaeus notialis bioaccumulates lead in Kribi (BCF > 1). The study found that the concentrations of trace metals in the water exceed the WHO guidelines for the ecological status of surface water. The water at urban stations (Wouri and Dibamba) shows very high levels of cadmium, lead, and mercury contamination, which could be due to the presence of various industries. Sediments at all stations are extremely polluted with mercury, while only sediments at the Wouri and Dibamba stations are extremely polluted with cadmium.