Bioaccumulation of Trace Metals in Biota (Algae and Chironomids) from Kenyan Saline Lakes (Bogoria and Nakuru): Evaluation and Verification of Two Compartment Toxicokinetic Models.

Abstract

This study was carried out to assess the suitability of various aquatic biota particularly those associated with some Kenyan Saline lakes, as biomonitors of trace metals. The study also aimed at evaluating the use of two-compartment and logistic regression models as predictive tools in assessment of environmental quality in the specific ecosystems. Experimental organisms namely, algae (Arthrospira fusiformis) and chironomids (Lepotochironomous deribae) among others, were obtained particularly from, Lakes Bogoria and Nakuru. Environmental sediment samples were also collected from the lakes, for a survey of the pertinent elemental background levels. Using the obtained organisms, exposure and depuration experiments were set up at The Nakuru Municipal/L. Nakuru National Park laboratory and at The School of Biological Sciences in the University of Nairobi, Kenya. Experimental samples were stored in a freezer at -20~'C and were later dried at 80~'C, before transportation to the Aquatic Ecology Laboratory in The University of Oldenburg, Germany, for chemical and data analysis. In the chemical analysis, aliquots of 10 mg samples were digested in 2 ml safe-lock Eppendorf reaction tubes for 3 hours at 80~'C with 100 ~kl HNO3 (65% suprapure). Cadmium, Cu and Pb elements were analysed using a Varian SpectrAA 880 Zeeman instrument and a GTA 110 graphite tube atomiser. Zinc was analysed using an air-acetylene flame (Varian SpectrAA-30, deuterium background correction) and a manual micro-injection method (100 μl sample volume). All metal concentrations in biological tissues are reported in ~kg g-1 dry weight (dw). For validation of the method, Certified Reference Materials (CRMs) namely BCR-CRM No.279 Sea Lettuce (Ulva lactuca) and Standard reference Material 1572 Citrus leaves, from the Commission of The European Communities (Community Bureau of Reference), and TORT-2 Lobster hepatopancreas and CRM 278R Mussel tissue (Mytilus Edulis) from the National Research Council of Canada were analysed using the same methods. Results obtained were in agreement with the certified values at 95% confidence level. Statistical analysis and modelling were done using SYSTAT version 10 and EXCEL programmes.