Trace Elements in Crustaceans, Mollusks and Fish in the Kenyan Part of Lake Victoria: Bioaccumulation, Bioindication and Health Risk Analysis

Abstract

This is the first comprehensive report on the accumulation of Cr, Ni, As, and Ag in the fish species Nile tilapia Oreochromis niloticus and Nile perch Lates niloticus from Lake Victoria, complemented with recent data on Cu, Zn, Cd, and Pb. This also is the first report on Cr, Ni, As, and Ag levels in invertebrates: the shrimp Caridina nilotica, gastropod Pila ovata, and bivalve Mutela bourguignati. The study was conducted at five sites in the Kenyan part of Lake Victoria: four sites in Winam Gulf influenced by various anthropogenic pressures, including a site near Kisumu City, and one in the main lake, with lesser direct anthropogenic influence. Apart from Cu and Ag, which were highest in O. niloticus liver, the invertebrates had higher levels of trace elements than fish. Contamination of the gulf with trace elements was best mirrored by the invertebrates, whose mobility is limited; they accumulated Cr, Cd, Ag, and Pb corresponding to the levels in the surface sediment. The accumulation of trace elements in fish species and their bioindicative potential corresponded to their habitats and feeding behaviour. The tissue contents of most trace elements were higher in the inshore-dwelling, omnivorous O. niloticus compared to the pelagic, piscivorous L. niloticus. Cu (465 ± 689 mg/kg dw) and Ag (3.45 ± 1.49 mg/kg dw) in the liver of O. niloticus were up to 10 and 119 times higher than in L. niloticus, respectively. Oreochromis niloticus therefore has bioindicative potential for Cu and Ag contamination. Both the invertebrates and fish showed positive correlations between Cu and Ag concentrations, indicating similar source and/or uptake route. The target hazard quotients (THQ) show that there is no human health risk associated with the consumption of these fish. However, the levels of Zn, Cd, and Pb in P. ovata surpassed maximum food safety limits and are hence potentially unsafe for human consumption.

Descriptive Analysis of Heavy Metals Content of Beef From Eastern Uganda and Their Safety for Public Consumption

“…On a broader scale, this falls squarely into the ecological cycle of pollution in Uganda which has been shown to involve everything from waste management ( 11 , 15 , 16 ), sources of natural water ( 12 – 14 ), effect on aquatic wildlife ( 10 ), state of drinking water ( 5 , 6 ) to production of alcoholic beverages ( 8 , 9 ) as well as food sold to the general public in the streets of Uganda ( 7 ). Similar findings of heavy metals have been reported in Kenya fishes and beef ( 2 , 47 ).…”

“…Contamination of food by heavy metals such as lead (Pb), iron (Fe), chromium (Cr), cadmium (Cd), copper (Cu), cobalt (Co), Nickel (Ni) and zinc (Zn) in developing countries is a major public health problem ( 1 , 2 ). This has been demonstrated in Uganda, for example, in beef ( 3 , 4 ), in drinking water ( 5 , 6 ), street food ( 7 ), alcoholic beverages ( 8 , 9 ), fish ( 10 ), food crops grown at dumpsites ( 11 ), and in food consumed around Lake Victoria and Lake George ( 12 – 14 ).…”

Preliminary study on the distribution of metals and persistent organic pollutants (POPs), including perfluoroalkylated acids (PFAS), in the aquatic environment near Morogoro, Tanzania, and the potential health risks for humans

“…On the other hand, the concentrations of Fe, Mn and Al were within the same range or much higher than those reported in the Msimbazi River (78 -620 mg/kg Fe, 9.9 -110 mg/kg Mn and 40 -200 mg/kg Al in the Msimbazi River; Ak'habuhaya and Lodenius, 1988). Compared to the Kenyan part of Lake Victoria, the Cu, Zn and Ni concentrations in invertebrates collected in the present study were within the lower part of the range detected at Lake Victoria (6.45 -148 mg/kg Cu, 49.7 -1361 mg/kg Zn and 0.325 -36.1 mg/kg Ni), and only the Cr concentrations were higher in invertebrates from the Morogoro Rivers (<LOQ -20.1 mg/kg in the Morogoro Rivers, compared to 0.271 -5.05 mg/kg in Lake Victoria) (Outa et al, 2020).…”

Integrated characterisation of Daubaylia burnupiae n. sp. (Nematoda: Daubayliidae) from a freshwater gastropod in South Africa, with comments on the biology of Daubaylia spp.

“…Consequently, the sensitivity of aquatic biota to changes in environmental conditions makes them important tools for biomonitoring. For instance, free-living aquatic invertebrates and vertebrates, are often used as accumulation and effect indicators ( Chovanec et al, 2003 ; Outa et al, 2020a ). However, biomonitoring using parasites tends to receive less attention ( Gilbert and Avenant-Oldewage, 2017 ).…”

“…However, since fish are mobile and intermixing of individuals from polluted and unpolluted habitats in an ecosystem is likely to occur, interpretation of pollution effect on parasitism in fish from field studies should be done cautiously ( Morley and Lewis, 2004 ). Gastropods on the other hand are less mobile, and likely to offer better results in point source pollution in field surveys ( Outa et al, 2020a ). Unfortunately, the response of parasites of molluscs to environmental changes is often overlooked, with only a few studies focused on digenean trematodes ( Morley et al, 2003 ; Sures et al, 2017 ; Outa et al, 2020b ).…”