Effects of ortho- and polyphosphates on lead speciation in drinking water

Abstract

Polyphosphates may increase lead solubilityviacomplexation, but the risk is not well characterized. Size-exclusion chromatography with multi-element detection could help determine the prevalence of lead-polyphosphate complexes in drinking water.

Seasonal lead release to drinking water and the effect of aluminum

“…41 We assumed that lead solubility was controlled by hydroxypyromorphite, a mineral that has been identified in lead pipe corrosion scale recovered from the distribution system described here. 42 While polyphosphate-dosed at the treatment plant at approximately 0.04 mg P L -1 -is known to form soluble complexes with lead, we did not identify lead-polyphosphate complexation at the point of use via SEC-ICP-MS. 20,42 For this reason, we opted not to include polyphosphate in the solubility model. (Lead-polyphosphate complexes were evident by the same method in another distribution system, at a higher polyphosphate dose of approximately 0.2 mg P L -1 .…”

“…(Lead-polyphosphate complexes were evident by the same method in another distribution system, at a higher polyphosphate dose of approximately 0.2 mg P L -1 . 42 ) Since there were not enough paired distribution system data to include aluminum in the model, we fit a separate model to account for aluminum's effect. We calculated hydroxypyromorphite solubility on a grid of orthophosphate and aluminum concentrations at pH 7.5 and 5 mg L -1 of dissolved inorganic carbon, assuming that both hydroxypyromorphite and variscite (AlPO4 • 2H2O) reached equilibrium with the solution.…”

Halifax Water's Lead Service Line Replacement Program Gets the Lead Out

“…In 2015, Halifax Water switched its corrosion control product from the zinc ortho/polyphosphate blend to a zinc orthophosphate to better control lead release. In 2018, the CWRS reported evidence of a lead‐polyphosphate complex in the drinking water of a nearby municipality (Trueman et al 2018). At the time, the municipality added a blended ortho‐polyphosphate corrosion inhibitor to treated water, and the CWRS’ finding was consistent with warnings from the research community that polyphosphate may increase lead solubility (Edwards & McNeill 2002).…”

“…When full-scale changes are proposed to a corrosion control product or dose (such as the doubling of dose in 2016), Halifax Water recruits volunteers to participate in studies to monitor lead concentrations at the tap before and after changes to systemwide corrosion control. Sampling the same homes regularly allows for controlled determination of how corrosion control can affect lead exposure (Trueman et al 2018). ($2,500, $4,000) ($4,000, $5,500) ($5,500, $7,000) ($7,000, $8,500) ($8,500, $10,000) >$10,000 After reviewing the practices of leading utilities in North America, weighing the benefits and disadvantages of regulatory-versus incentive-driven approaches, and gaining approval from its board of commissioners, Halifax Water developed a business case.…”

Influence of phosphate dosing on biofilms development on lead in chlorinated drinking water bioreactors

“…Since the 1990s most of the UK's public water supplies are being dosed with orthophosphate acid or a sodium orthophosphate to minimise plumbosolvency [5][6][7] , using concentrations ranging from 0.5 to 2 mg/L of phosphate (PO 4 3− ) 6 . The different PO 4 3− species are able to interact with the soluble lead ions (Pb 2+ ), to form a layer of lead phosphate compounds which covers the inner side of the pipe [8][9][10] . Cities like Brussels or The Hague have chosen the costly option of substituting lead pipes in their distribution networks 4 , yet using PO 4 3− is a successful and cost-effective alternative to spending~£10 billion to remove all lead pipes in the UK 7 .…”