Influence of anthropogenic activities on sediment characteristics and heavy metal concentrations in Lake Baringo, Kenya

Abstract

Lake Baringo waters and sediments are being impacted negatively by metal contaminants sourced from the lake’s watershed posing a human and environmental health concern. The main objective was to determine the concentration of heavy metals cadmium (Cd), copper (Cu), mercury (Hg) and lead (Pb) in water and sediments, and to characterize sediments in terms of grain size and total organic carbon and relate them to the heavy metal levels encountered at the sampled sites. 5 sites were selected and samples collected over a period of six months. Water samples were collected in polypropylene bottles and acidified with ultra-pure HNO3 to pH < 2 and stored at 4oC prior to analyses. Sediments were collected using a grab sampler and analyzed for total extractable metals using the multi-acid digestion method. Particle size classification was done by standard method of analysis by sieving and organic carbon (OC) was estimated using the Loss on Ignition (L.O.I) method. Data obtained was tested for normality and homogeneity of variance. Heavy metal concentrations were compared using analysis of variance (ANOVA) to test for differences among sites (α = 0.05). Pearson correlation was used to establish inter metallic relationships. Mean values of the physico-chemical parameters studied for all sites (pooled data) were as follows: E.C. 374.19±0.5μScm-1, pH 7.62±0.03, temperature 28.4±0.15°C, T.D.S. 373.6±0.5 and salinity 0.12±0.05%. There were significant differences between the sites for all parameters measured (p<0.05) except for percent salinity (p=0.739). The range mean concentrations of heavy metals in water were as follows Cu (0.4–0.7), Cd (0.6–0.8) and Hg (0.003-0.005) ppb. The range of mean sediment concentrations (in mg/kg) were as follows: Cu (6.95-17.0), Cd (1.04–1.21), and Hg (0.18–0.27). Sites with higher percentages of silt and clay recorded a higher concentration of Cd and Cu same as to the percentage of TOC. Mean concentrations of heavy metals in water and sediments columns showed that a greater percentage of Cu (90.2 %) was retained in sediments while Cd and Hg released a greater percentage to the water column compared to what was in the sediment (36.8 % and 29.8%). Over 95% of the concentrations of Cd and Hg in water and sediments were significantly lower than those recommended by the WHO and USEPA as drinking water guideline values. The findings can be useful in policymaking with regard to environmental management and conservation of regional lakes facing similar challenges. Information on metal concentrations in the lake’s freshwater can also be used in protecting human health. Further research on metal partitioning in water and sediments is recommended.