Heavy Metal Concentrations in Urban Stormwater Runoff and Receiving Stream.

Abstract

Stormwater and receiving stream water samples were collected along Abeokuta- Ibadan road at four different locations and analysed for heavy metals: copper, zinc, lead, cadmium, chromium  and other pollution indicating indices like DO, BOD5, COD, total dissolved solid, EC, pH, chloride, hardness, and alkalinity. The result of the analyses showed the mean concentration of heavy metals were:  0.66 mg/L (Pb), 0.83 mg/L (Zn), 1.93 mg/L (Cu), 0.51 mg/L (Cd) and 0.44 mg/L (Cr). Copper is the most prominent metal both in the stormwater and the receiving streams in the study area compared to others.  Average physico-chemical properties of stormwater such as pH w as 9.15±0.49, temperature, 26.27±0.51, EC, 276.00±48.86 uScm-1, hardness, 93.25±48.0 and alkalinity, 2.78±1.04 for the stream. Dissolved Oxygen (DO) in the stormwater ranges from 2.88 to 3.97 mg/L. Mean TDS, COD and BOD5 were 128.7 mg/L, 156.25 mg/L, and 47.06 mg/L respectively. None of these values exceeded the limit considered as potential hazard according to international standards. However, in the nearest future the pollution level may likely increase drastically exceed the recognised standards due to increasing urban activities, hence, there is the need to safeguard the health of the urban ecosystem by reducing stormwater pollution from sources and the development of sustainable urban stormwater management using best management practices (BMPs).

Keywords: Highways; Pollution; Urbanisation; Stormwater; Stormwater Management.