Urban Highway Runoff in Nigeria 1: Heavy Metals in Sheet Flow from the Main Expressway in Lagos Metropolis

Whole-unfiltered-water samples were collected from the runoff of a major highway in Lagos metropolis at four different points along the road and at the receiving stream through which the runoff eventually discharges into the lagoon. The study was conducted to characterize the types and levels of pollutants on a typical Nigerian road and was carried out during three different rainy days between the months of February and May, 2004. The collected samples were analysed for the presence of heavy metals; Cd, Cr, Cu, Pb and Zn. Pollution-indicating indices such as dissolved oxygen, BOD5, total solids, conductivity, chlorides, hardness, alkalinity and acidity were also determined. The results of the analyses showed that Zn was most prominent in the sampled runoffs with mean concentrations of 68.7c3.0, 119.7c58.3 and 33.1c24.0 ppb in the three sampled events. Cd -at a concentration of 0.6 ppb was only detected in one of the samples. The concentrations of these metals were shown to vary with the time of sampling during the precipitation. Levels were generally higher in first flush samples.