The pervasive threat of lead (Pb) in drinking water: Unmasking and pursuing scientific factors that govern lead release

Abstract

The Flint water crisis raised questions about the factors resulting in unacceptable soluble lead concentrations in the city's drinking water. Although water treatment strategies, failure to follow regulations, and unethical behavior were all factors, knowledge deficits at the intersection of several scientific fields also contributed to the crisis. Pursuit of opportunities to address unresolved scientific questions can help avert future lead poisoning disasters. Such advances will enable scientifically based, data-driven risk assessments that inform decisions involving drinking water systems. In this way, managers and decision makers can anticipate, monitor, and prevent future lead in water crises.

Keywords: corrosion; drinking water; lead; public health; thermodynamics.

Fig. 1.

Thermodynamic diagrams exhibiting the types of calculations that describe the Pb–drinking water system. (A) Chemical stability diagram highlighting the relative stabilities of various Pb-based compounds as a function of pH and total soluble Pb concentration. The EPA action limit of 15 μg/L Pb²⁺ is included for reference (horizontal dashed line). Diagrams were constructed for a representative drinking water chemistry where the concentrations of carbonate and chloride are 1 mM each, and an inhibitor concentration of [PO₄³⁻] = 0.1 mM utilizing thermodynamic data in Lange’s Handbook of Chemistry (37) except for the hydroxylated carbonate and phosphate compounds (dashed lines), which were taken from the American Water Works Association (8). (B) The effect of water hardness in limiting available phosphate (aqueous) in drinking water. (C) The effect of decreasing particle size on destabilizing the solid phase assuming a surface energy of 3 J/m² for Pb₃(PO₄)₂ particles in water.

Fig. 2.

Schematic illustration of the kinetic processes controlling lead service line scale formation and Pb release at (A) short times and (B) long times. The total soluble Pb concentration increases with time toward the equilibrium concentration for that particular compound, which may be (C) above the LCR or (D) below the LCR, depending on the compound. The effect of flow is important too, as it influences the mass transport of Pb away from (E) the pipe wall to the pipe centerline and also (F) downstream to the endpoint device.