Trends in Heavy Metals\' Levels in the Rivers of the Nairobi Region and Measures to Reduce them

Abstract

The Nairobi, Ngong and Mathare are among the major rivers traversing the city of Nairobi, Kenya\'s capital city. The Ngong and Mathare rivers are both tributaries of the Nairobi River. The Nairobi river flows through the city centre; the Ngong River flows through the industrial belt to the south of the city centre while the Mathare River flows mainly through the slum areas to the north of the city centre. The main aim of this study was to determine the levels of faecal coliform and heavy metals (lead, chromium, mercury and cadmium) along these rivers; and identify the health risks associated with the river water use for domestic purposes. The study was carried out over a period of five months. Faecal coliforms were minimal upstream of the slum and street children habitats with values as low as zero FC/100 ml at SP1. Downstream of these points the faecal coliform were as high as 2,400,000 FC/100 ml. However, this paper concentrates mainly on the presentation of results of heavy metals analyses. Heavy metal levels were notably high along the Ngong River just after it traversed the industrial belt. Sample means were computed for all the selected parameters for both the “dry” and “wet” seasons to enable comparison of the seasonal variation of pollution levels along the three rivers. Lead pollution was fairly high along the three rivers with a maximum mean value of 0.58ppm being recorded along the Ngong River. Domestic and industrial wastes were identified as major sources of pollution. However, urban run-off and leachate from the numerous refuse pits along the rivers contribute a lot to the pollution load in these rivers. Approaches to reduce this pollution have been suggested.