AWWA WQTC71524

The dissolution of lead corrosion products that are present as scales on lead pipes in distribution systems can be a source of lead to drinking water. Corrosion products that develop in pipe scales include lead(II) oxides, carbonates, and phosphates as well as lead(IV) oxides when high concentrations of free chlorine are present. Changes in treatment processes that influence the distribution system water chemistry have the potential to enhance or inhibit the dissolution of lead-containing corrosion products. The dissolution rates of three lead-containing solids that have been observed in distribution systems have been systematically measured as a function of important water chemistry parameters. The lead corrosion products studied are lead(II) carbonate hydrocerussite, lead(II) phosphate hydroxylpyromorphite, and lead(IV) oxide plattnerite. Dissolution rates were varied as a function of pH, dissolved inorganic carbon, orthophosphate concentration, and the presence or absence of monochloramine. The dissolution rates of all three corrosion products were strongly influenced by pH. The presence of phosphate dramatically decreased the dissolution rate of all three phases; for hydrocerussite, the addition of phosphate induced the gradual transformation of a lead(II) carbonate solid into a lead(II) phosphate solid. The influence of dissolved inorganic carbon was more complex. Includes 5 references, figure.