Abstract

Heavy metals are potentially toxic to organisms causing lethal and sub lethal effects. Above threshold levels, these metals have been shown to adversely affect both aquatic and terrestrial organisms. Human health may also be impacted negatively through consumption of metal-contaminated foods and water. Lake Naivasha, Kenya, like many freshwater bodies in developing countries is a source of fish and water for human consumption in Naivasha town and its environs. Ironically, the lake receives untreated floricultural, agricultural and industrial effluents from its catchment area. In the recent past, there have been unconfirmed reports that fish from this lake are contaminated with heavy metals mainly Cu, Hg, Cd and Pb to levels that are harmful to humans. It is against this background that this study was conducted to determine the sources of the aforementioned heavy metals in the lake, their concentrations in water and sediments and in common carp (Cyprinus carpio) that constitutes a major portion of the Lake Naivasha fishery. Water, sediment and fish samples were collected from purposefully selected sites in six sampling occasions during both the dry and wet seasons. Analyses for heavy metals in fish, sediment and water samples were done using an Atomic Absorption Spectrophotometer (AAS). The study findings indicate that the heavy metal concentrations in the water and sediments collected from impacted sites were significantly higher (p<0.05) compared to those from unexpected sites. In spite of this, the metal concentrations in water were significantly lower than those recommended by the WHO and USEPA as drinking water guideline values. Metal concentrations in C. carpio were also significantly lower (p<0.05) than the World Health Organization (WHO) recommended levels for fish intended for human consumption. Based on these findings, it is safe to conclude that drinking water and fish collected from Lake Naivasha do not pose immediate health risks to human health. Despite this observation, we recommend continuous monitoring of heavy metal concentrations in water and sediment in the lake given their potential for bioaccumulation and biomagnifications and likely adverse effects on aquatic organisms and humans.

Keywords:

Cyprinus carpio, floriculture, heavy metals, Lake Naivasha, sediment quality, water quality,

References

Competing interests

The authors have no competing interests.

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The authors have no competing interests.