First flush effect of metals and anions in stormwater runoff from roads in mid-Sweden

The first flush effect of metals and anions was studied in stormwater runoff from one highway and one local urban road. The runoff events followed upon a dry period of three days. The results indicate that 50-60% of the total mass of Zn, Cu, Pb, Ni, CO, Cd and As was transported with the first 30% of runoff. At the highway site the first flush concentrations of Cu exceeded the target values for small watercourses by a factor of 3. At the local urban road site the runoff concentrations were considerably higher, but might be affected by the road materials, the rain intensity and by vehicles stopping at the traffic lights. It is concluded that the first flush effect from single rain events can cause high concentrations of, for example, Cu and Pb, which may be toxic to the biota.