Levels of Physico-Chemical Parameters and Polycyclic Aromatic Hydrocarbons in Water from Ngong and Nairobi Rivers, Nairobi County-Kenya
Kiage, Mobegi E.
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Polycyclic aromatic hydrocarbons (PAHs) are hazardous organic chemicals consisting of two or more aromatic rings. United States Environmental Protection Agency (US EPA) has identified 16 priority PAHs are carcinogenic and mutagenic. The World Health Organization (WHO) recommends that their levels not to exceed 50 ng/L in water. Nairobi city is the economic and industrial hub for Kenya with increasing industrialization and urbanization. This increase has led to water and air pollution as a result of poor waste management, posing a health hazard to humans and the environment. European Union (EU) and US EPA have recommended that PAHs to be measured in a variety of matrices including water and effluent releases. Data on PAHs in rivers Nairobi and Ngong is limited. The aim of the study was to determine physico-chemical parameters (pH, dissolved oxygen, turbidity, flow rate, conductivity) and levels of sixteen (16) US EPA priority PAHs in water in the Ngong and Nairobi rivers. Physico-chemical parameters were measured using LabQuest vernier multi-parameter meter. PAHs from water samples were extracted, cleaned prior to identification and quantified (internal standard method) by GC-MS. All the Physico-chemical parameters measured were found to be within the recommended levels set by WHO except for turbidity, dissolved oxygen and conductivity. The total concentrations of 16 PAHs in Ngong River water ranged from 2.69 ng/L to 14.22 ng/L with an overall mean of 11.53 ng/L and in Nairobi River the range was between 5.19 ng/L and 9.14 ng/L with an overall mean of 10.08 ng/L. Significant differences (p<0.05) in water from Ngong and Nairobi rivers were noted in the levels of dibenz(a,h)anthracene, benzo(b)Flouranthene and flourene. Generally, the results show that water from the two rivers was contaminated with PAHs although the levels were below the recommended WHO limit of 50 ng/L. However, it is feared that continuous use of their water by man may result to risk exposure to PAHs.