Analysis of soil for trace elements along two highways of Kenya
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For a long time, the toxicity of metals was considered as an occupational hazard. Industrialization, urbanization, increased vehicular traffic and use of fertilizers and pesticides in agriculture have resulted in increased contamination of environment by heavy metals. The toxicity of metals in the environment is becoming a matter of concern for the general population. It has been observed that the toxic metals, attributed to vehicular emissions, such as Lead, arc deposited at relatively short distances from the road. Hay (1984) has reported that about 2OOO tons of lead is deposited on the earth annually due to the use of tetra-ethyl lead and tetra-methyl lead in fuel. Studies on the toxicity and essentiality of toxic trace elements have been carried out by several researchers (Nelson, 1991; Reichlnayr-Lais & Krichgebner, 1991; Mukhtar et al., 1991; Duane et al., 1996; Hong & Ha, 1996; Oluwole et al., 1994; Ostachowicz...et al., 1995; Murti Krishna & Viswanathan, 1991; (heavy metal task force, 1991). At the same time, all mineral elements are essential to the environment, human beings and animals but their excess 'may lead to serious health hazards. Kinyua et al. (1991, 1993) have reported the concentrations of mercury, lead, cadmium, copper, manganese and iron in water and fish samples from Nairobi-Athi river, and Naivasha area in Kenya, respectively. The study of the levels of mercury in water, fish, sediments and blood samples from different regions of Kenya have been done by Kamau et al. (1991). The adjacent lands along most major highways of Kenya are left as open spaces, or used for small scale farming and grazing of cattle and livestock. Some grass and plants are expected to have high levels of lead and other toxic metals. So far, no study has been carried out to determine the concentrations of toxic metals in soil samples along Thika and Mombasa highways of Kenya. This work will be important and essential to study the impact of pollution on the health and environment.