Risk assessment of the possible contamination of trace metals in fish samples from Lake Kariba, Zambia

M.Sc. (Chemistry)

Department of Chemistry

Exposure to inorganic endocrine disrupting chemicals (EDCs) has been linked to cause carcinogenic and mutagenic effects on human health and aquatic species. Trace metals in food are widely acknowledged as a public health concern yet largely ignored in many African nations where legislation is not yet fully implemented. Thus, the study aimed to extract and determine the toxic levels of inorganic EDCs of interest at certain doses and possible health risk associated with metal ions in fish sold in the open markets from Siavonga, Lake Kariba (Zambia). Sampling was done for two consecutive years, 2021 and 2022. Two fish species, which constitute Lake Kariba, were sampled; the bream (Oreochromis mortimeri) and Kapenta (Limnothrissa miodon): Firstly, twenty-eight fresh Kariba bream (Oreochromis mortimeri), five sun-dried Kariba bream (Oreochromis mortimeri) and five batches of sun-dried Kapenta (Limnothrissa miodon) were sampled from Lake Kariba open market. Secondly, six fresh Kariba bream (Oreochromis mortimeri), five sun-dried Kariba bream (Oreochromis mortimeri) and five batches of sun-dried Kapenta (Limnothrissa miodon), were purchased in an open market in Siavonga. Fish muscle tissues were excised to analyze trace metal ions before being digested using a microwave digestion system and analyzed using ICP-OES and MS. Eleven trace elements: Aluminum (Al), Arsenic (As), Cadmium (Cd), Chromium (Cr), Copper (Cu), Iron (Fe), Lead (Pb), Manganese (Mn), Mercury (Hg), Selenium (Se) and Zinc (Zn) were analyzed in fish muscle tissues (epaxial and hypaxial myomers). The results showed that the mean metal concentration for the first sampling was not significantly higher ( > 0.05) than the mean concentration for the second fish sampling, except for sun-dried Kapenta. The first sampling collected in November (2021) revealed that the fish collected on a Zambian open market contained higher levels of Cr, Mn and Fe ranging from 6.50±3.30 to 101.40±22.69 mg kg-1 in sun-dried bream. At the same time, sun-dried Kapenta contained high levels of Cr, Mn, Fe, As and Al ranging from 0.49±0.05 to 160.72±132.60 mg kg-1. In contrast, fresh bream contained high levels of Cr, As and Mn ranging from 13.99±7.96 and 22.30±12.20 mg kg-1. Compared to the second sampling around August (2022) they revealed high levels of Cr, Mn, As, Se and Fe ranging from 0.15±0.07 to 110.6±63.82 mg kg-1 in Sun-dried bream. In contrast, sun-dried Kapenta contained high levels of Cr, Mn, As, Se, Fe and Zn levels ranging from 0.78±0.03 to 187.8±58.59 mg kg-1. In comparison, fresh bream contained high Cr, Mn, As, Se and Fe ranging from 0.26±0.16 to 163.00±68.41 mg kg-1. The obtained results showed that the concentrations of metals exceeded the recommended maximum permissible limits proposed by the Joint Food and Agricultural Organization and World Health Organization (FAO/WHO) Expert Committee on food for fish consumption. However, fish were safe from adverse health effects due to Hg not being detected in fish sampled. The pollution index was assessed to determine the extent of pollution. The estimated daily intake (EDI) for all metals were higher than the provisional tolerable daily intakes (PTDI) recommended by FDA for both adults and children. Target hazard quotients (THQ) and hazard indices (HI) was higher than 1, indicating health risks from a non-carcinogenic lifetime of fish consumption. The lifetime average daily dose (LADD) was used to estimate the incremental lifetime cancer risk (ILCR). All metals were lower than 1×10 4 except for fresh bream 2021 for both children and adults, indicating a carcinogenic risk of 1 in 10,000 from consumption of Kapenta and Kariba bream from Lake Kariba in a lifetime. This raises concern over an adverse health effect on the consumption of fish consisting of excess trace metals. Long-term exposure to trace metals through fish consumption poses potential non-carcinogenic and carcinogenic health risks to the residents and suggests possible adverse health effects.

National Research Foundation (NRF) and Mining Qualification Authority (MQA)