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

James Omondi Outa,Franz Jirsa,Annemariè Avenant-Oldewage,Chrispin O Kowenje

doi:10.1007/s00244-020-00715-0

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.

Highlights

Aquatic ecosystems consist of several compartments, each of which has certain physicochemical properties that determine the fate of trace elements therein
Due to the high mobility of L. niloticus, we treated all fish for this study as one sample, whereas values for O. niloticus were calculated per site
With the exception of Cu and Ag, which were highest in O. niloticus liver, the invertebrates had the highest concentrations of the trace elements measured in this study

Summary

Introduction

Aquatic ecosystems consist of several compartments, each of which has certain physicochemical properties that determine the fate of trace elements therein. Apart from Mwamburi (2013), who reported on Pb accumulation in the crustacean Caridina nilotica and on Fe, Mn, Cu, and Pb in the bivalve Sphaerium sp., there are no other reported studies on trace element contents of invertebrates, which form an integral part of the aquatic food chain. In the view of these findings, we performed a comprehensive study on the accumulation of trace elements in the lake’s fauna with a link to potential health risks posed to humans who consume food products from the lake. 35% of the lake’s total fish production is landed in Kenya for internal and external markets, of which Nile perch L. niloticus accounts for 84.7% of total fish exports to Europe, Asia, United States, and Central America (FAO 2015)

Methods

Results

Conclusion