The Influence of pH and Salinity on Heavy Metal Contaminants Released into Stormwater from Pipe and Tank Materials

The objective of this study was to investigate the effects of pH, salinity, and time of contact on leaching of metals from different pipe, gutter, and storage tank materials. The release of heavy metals from eight pipe and gutter materials was examined during static leaching tests. During the first phase, the materials were submerged into containers with buffered (pH 5 and 8) roof runoff and stormwater. During the second phase, the samples were submerged into natural bay and river waters. Water samples from each leaching container were periodically collected and analyzed over a three month period for a wide range of metallic contaminants, pH, conductivity, and toxicity (using Microtox screening methods), plus periodic samples were collected to describe the basic chemical characteristics of the water. Lead releases were detected only in the galvanized steel material samples. Copper concentrations in containers with the copper materials increased with decreased pH. The greatest copper concentrations were detected under bay water conditions (high salinity). Galvanized materials were the greatest source of zinc. During the first day of exposure, high zinc releases from galvanized steel materials were observed at lower pH conditions. During short periods of exposures, lower zinc concentrations were leached from the galvanized steel materials in river water samples compared to the bay water samples; however, during long period exposures, zinc releases in the bay water samples were exceeded by those in the river water samples. Phase and Pourbaix diagrams are used to determine the predominant forms of species and to compare maximum observed concentrations in the sampled waters with theoretical equilibrium and saturation concentrations.