Analysis of environmental chemical residues in products of emerging aquaculture industry in Uganda as case study for Sub-Saharan Africa

Abstract

A study was conducted to analyse market-regulated heavy metals (lead, mercury and cadmium), organochlorine pesticides and total polychlorinated biphenyls (PCBs) in samples of 38 farmed fish comprising Nile tilapia (Oreochromis niloticus) (20 samples) and African catfish (Clarias gariepinus) (18 samples) from ten selected fish farms in Uganda. The goal of this case study was to understand the safety of aquaculture products from Sub-Saharan Africa. Lead was detected in all the 38 samples (maximum = 1.08 mg kg⁻¹ (dry weight)), mercury in 31 out of 38 samples (maximum = 0.35 mg kg⁻¹ (dry weight)), and cadmium in two samples (maximum = 0.03 mg kg⁻¹ (dry weight)). Total levels of PCBs were below the limit of detection of 0.02 mg kg⁻¹ (wet weight) in all the samples. Traces of 4,4′-dichloro-diphenyldichloroethylene (DDE) were detected in ten out of 38 samples (maximum = 0.01 mg kg⁻¹ (wet weight)) making it the most prevalent organochlorine pesticide. Other pesticides detected were: 4,4′-dichloro-diphenyl-trichloroethane (DDT) and endosulfan sulphate, which were found in one fish sample (both 0.002 mg kg⁻¹ (wet weight)). There was no statistically significant difference between the levels of lead and mercury in catfish and tilapia (t-test at p = 0.05). More catfish samples (eight) contained DDE as compared with tilapia (two). Cadmium, DDT and endosufan sulphate were only detected in catfish implying that catfish is more prone to contamination than tilapia. The levels of contaminants were below the US Food and Drug Administration (USFDA) action levels and European Union maximum residue limits (MRLs), indicating that such fish have the potential for export to these markets.

Keywords:

• environmental chemical contaminants
• heavy metals
• organochlorine pesticides
• polychlorinated biphenyls
• aquaculture products
• African catfish
• Nile tilapia
• Uganda
• Sub-Saharan Africa

Acknowledgements

This study was conducted as part of the PhD research of A. Bagumire through a study grant from the Ford Foundation International Fellowship Programme, which funded the work. The authors acknowledge the technical contributions of Kirk Stuart, Michael Church, and Justin Zyskowski in the toxicology laboratory at the Diagnostic Centre for Population and Animal Health, Michigan State University.