Lead pollution in urban roadside environments of Dar es Salaam city

Abstract

Lead is among the most toxic elements in nature. It is non-biodegradable and its toxicity does not change with time. Use of leaded gasoline in motor vehicles is known as the major source of lead pollution in cities in the world. Dar es Salaam, the main city of Tanzania, has thousands of cars traveling along its roads. The lead contaminating urban roadside environments of Dar es Salaam was determined. Soil and vegetation samples were collected at various distances from the road edges of the New Bagamoyo, Sam Nujoma and Mandela roads in Dar es Salaam and analyzed for lead using Atomic Absorption Spectrophotometric methods. The results show that the soils and grasses along these major highways of Dar es Salaam were contaminated with lead. The highest lead contents (152.5 ppm in soil and 35.7 ppm in couch grass) were found in soils and vegetation within 1 to 5 meters from the road edge. The background lead levels measured at 150 meters from the road side were less than 1.2 ppm in both soil and vegetation. The lead levels along these roads exhibited strong correlation with the average traffic density (r = 0.912 for soil and r = 0.88 for grass). The levels of lead decreased exponentially with increasing distance away from the road. This suggests the major source of lead contamination of these areas was emissions from automobile traffic on these highways. The high levels of lead at 0 – 10 m from the roadside edge also suggest that soil and vegetation close to the roadside were a potential health hazard to both humans and animals.