CONTAMINATION OF SOILS, MAIZE, WHEAT AND MILK WITH LEAD FROM MOTOR-VEHICLE EMISSIONS IN UASIN-GISHU DISTRICT, KENYA

Levels of lead were determined for soil, maize, wheat and milk collect ed from sites close to heavily used roads, and compared to levels in c ontrol samples taken away from the roads. In soil samples, lead levels decrease exponentially from values of about 3 ppm at the edge of the road to values typically around 1 ppm, 80 metres away from the road. A t the control site lead levels in soil have a value of 0.6 ppm. Maize cultivated close to the road had lead values of between 0.13 and 0.25 ppm, while maize grown at the control site had 0.06 ppm lead. Wheat cu ltivated close to the road had lead values ranging from 0.04 to 0.23 p pm, compared to a value of 0.05 ppm at the control site. Milk from cow s that graze close to the roads had lead value ranging from 0.1 ppm to 0.5 ppm, as compared to a value of 0.1 ppm in milk from cows that gra ze away from the roads. All the results indicate significant differenc es in lead content for samples from near the roads compared to samples in the control site at the 95% confidence level. By extrapolating the exponential decay curves obtained in this study, the minimum distance away from the road which farming activities can take place is deduced to be about 200 metres, in order for effects of vehicular emissions t o be minimised.