Effect of PHOSPHATE inhibitors on lead release from pipes

Hexametaphosphate tends to increase release of both particulate and soluble lead to drinking water. In this study, for every milligram per litre of residual hexametaphosphate, soluble lead increased by ∼ 1.6 mg/L after 72‐h stagnation in pure lead pipes compared with the same condition dosed with orthophosphate. Utilities need to consider these adverse effects whenever polyphosphate is used to prevent scaling or iron precipitation; in fact, polyphosphates cannot be recommended for lead corrosion control. Although soluble lead release in these experiments was in reasonable agreement with predictions of solubility models, particulate lead release was dominant. In some cases, a peak in lead release was observed as water was held stagnant in pipes. Analysis of these data indicated that particulate lead can reattach to the pipe surface under some circumstances.