Fish from a polluted lake (Lake Chivero, Zimbabwe): a food safety issue of concern
Francis Manjengwa*, Tamuka Nhiwatiwa*, Elijah Nyakudya**, Petronella Banda***
*Faculty of Science, Biosciences Department, University of Zimbabwe, PO Box MP167, Mt. Pleasant, Harare, Zimbabwe
**Faculty of Agriculture, Soil Sciences & Agricultural Engineering Department, University of Zimbabwe, PO Box MP167, Mt. Pleasant, Harare, Zimbabwe
***Faculty of Agriculture, Animal Sciences Department, University of Zimbabwe, PO Box MP167, Mt. Pleasant, Harare, Zimbabwe
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.
Francis Manjengwa, Tamuka Nhiwatiwa, Elijah Nyakudya, Petronella Banda. Fish from a polluted lake (Lake Chivero, Zimbabwe): a food safety issue of concern. Food Qual Safet, 2019, 3(3): 157-168.
