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.

Worth a Closer Look: Raman Spectra of Lead-Pipe Scale

“…To understand what controls the concentrations of dissolved and particulate lead in drinking water requires knowledge of what phase is precipitating on the walls of the LSLs. The precipitating phase is not always that which has been calculated to be in equilibrium with the composition, pH, and Eh of the water [3,4,11]. RS can help determine if this apparent discrepancy between theory and observation is due to the development of an unpredicted phase or simply the ability of an earlier-precipitated phase to adjust its composition via chemical substitution, i.e., to exhibit solid solution.…”

“…Given the high Ca/Pb ratios in typical water systems, a Ca-apatite phase is not unexpected, and a lead phosphate was subsequently detected elsewhere in this pipe. Kinetic factors, including those controlling mineral nucleation, can affect the order in which the solids precipitate [3]. Such low-solubility, non-lead phases might be important as temporary stabilizers of underlying lead-bearing scales in times of compositional fluctuation in the water supply.…”

“…The fact that type (b) material directly overlies type (a) suggests that the spectra have captured plattnerite in the process of maturation from recent precipitate (b) into a more ordered, more stable crystalline solid (a) as it grows outward from the pipe wall over time. There is repeated recognition in the literature [3,11,63] of a large component of retrieved scale material that is called amorphous, which typically means undefinable by XRD. Both the chemical composition (in many cases rich in Al, Si, and P, in addition to Pb, which may be minor) and the degree/lack of crystallinity of such material are important to its physical and chemical stability and, therefore, important to define.…”

“…There is a wide range in the degree of atomic ordering between fully crystalline and X-ray amorphous forms of a solid phase, and specification within that range is attainable by Raman spectroscopy (well exemplified in carbonaceous material: e.g., [64,65]; see Figure S7). When chemically identical solids exist in both atomically more ordered and less ordered/amorphous forms, the amorphous one is always more soluble than the well-crystalline one [3,66]. Recognition of differences in crystallinity among mineral scales of identical composition, therefore, is important to the assessment of expected lead concentrations in the water.…”

“…The selection of treatment methods to reduce lead-pipe corrosion relies on the well-supported assumption that plumbosolvency is a major key in mitigating lead release. The model is that the solubility of individual leadbearing minerals that form scales on the inner pipe walls will control lead concentration in the enclosed pipe water [2,3]. The corollary to this reasoning is that changes in the properties of the water will cause different minerals to form and/or destabilize pre-existing mineral scales.…”