Fish from a polluted lake (Lake Chivero, Zimbabwe): A food safety issue of concern

Abstract

Objectives: A study to determine food safety hazard status of fish products from Lake Chivero was conducted in selected high density suburbs of Harare. Lake water and fish were tested for E. coli O157:H7, total bacterial, fungal counts, mercury (Hg) and aflatoxin B1 (AFB1) to determine contamination levels and assessing human health hazard exposure. Materials and Methods: Membrane filtration method was used to determine E. coli O157:H7 viable counts using CHROM agar. Plate count and Potato dextrose agar were used for determination of total viable bacterial and fungal counts. Concentrations of Hg and AFB1 in fish and water were determined by Atomic Absorption Spectrophotometer and High Performance Liquid Chromatography-Mass Spectrometry. A questionnaire survey was conducted on 136 adult fish consumers to determine the fish consumption patterns to assess hazard exposure against international standards. Results: Significant levels of microbial contamination above international standards in both fish and water were recorded. Mean E. coli O157:H7 counts were 106 ± 10 (cfu/cm2) in fish and 52 ± 14 (cfu/100ml) in water. Mean Log10 TBC were 8.98 ± 0.26 (cfu/cm2) in fish and 9.05 ± 0.05 (cfu/ml) in water. Mean Log10 TFC were 4.83 ± 0.02 (cfu/cm2) in fish and 4.56 ± 0.03 (cfu/ml) in water. Hg and AFB1 were 0.018 (μg/kg) and 0.025 (μg/kg) in fish and 0.008 (μg/kg) and 0.005 (μg/kg) in water, both with a hazard quotient (HQ) <1 using CODEX STAN 193-1995 of 2015. Conclusion: Fish and water are contaminated with E. coli O157:H7, contain bacterial and fungal loads above international food safety guidance levels. Fish were caught already contaminated with pathogens together with toxigenic Hg and carcinogenic AFB1 although their concentration levels are within international food safety toxicological levels. Levels of Hg and AFB1 in water were almost double that of fish, implying bio-accumulation occurred in fish. Thus, fish consumers are exposed to food safety hazards and are at risk of contracting foodborne illnesses from consuming contaminated fish.