Experimental Study of Lead Contamination in Drinking Water Supply Systems with Lead-soldered Joints

Lead (Pb) is a toxic heavy metal that may be present in household drinking water supply systems fitted with lead containing components such as pipe connections and fittings. Worldwide there have been incidents of excess lead found in drinking water supply systems, raising public health concern. Unlike many other countries where lead contamination has been investigated, lead pipes are not used in drinking water supply system of Hong Kong. It is suspected that the water is contaminated by the lead-containing soldered joints and brass components. The mechanism of lead releasing and transport is not clear, yet it is hypothesized that the electro-chemical coupling between lead solders and copper pipes results in galvanic corrosion which leads to the rapid release of lead in both dissolved and particulate forms. This study investigates the mechanisms leading to excess lead concentration in drinking water and their subsequent transport to the consumer’s tap through systematic experiments.

Leaching experiments in stagnant water were carried out in copper pipes connected to a brass valve/lead-solder joint at the middle. Small solder discs attached to copper pipes and PVC were also used to determine the contribution of galvanic corrosion to lead releasing. The pipes were filled with tap water and stagnated for 0.5-18 hours before water samples are collected for lead concentration measurement using the Inductively Coupled Plasma Mass Spectrometry (ICP-MS) method in an accredited laboratory. In addition, flow-through experiments were conducted to measure the lead concentration profile at the consumer tap of a water supply chain after different stagnation periods. The pipe rigs are made of lead-soldered pipes dismantled from public housing buildings in Hong Kong. A specifically designed sampling protocol is adopted to capture the time variation of lead concentration for locating the lead sources in the pipe line by Galilean transformation.

The stagnation test results show that the mass of lead released from a brass valve or a lead-soldered joint increases non-linearly with time and can be predicted using the Fickian diffusion law. The mass of lead released from solder materials attached to copper pipes are one to two orders higher than that attached to PVC pipes, suggesting galvanic corrosion is the dominant mechanism of lead release. The results show that the lead concentration peaks can be traced back to locations of brass components or lead-soldered joints. The average lead level in pipe rigs with leaded solders is several times higher than rigs with only brass fixtures, consistent with the measurements in single-component stagnation tests.