Pulling Copper Along

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Science  19 Oct 2007:
Vol. 318, Issue 5849, pp. 361
DOI: 10.1126/science.318.5849.361b

Copper is a common choice for constructing pipes that carry drinking water because of its relatively strong resistance to corrosion, but over time oxidative chemistry can introduce metal ions into the streams emerging from the faucet. A complex series of factors contributes to the ion concentration, ranging from the water's pH to the precipitation equilibria of various hydroxide, oxide, and carbonate salts, as well as biochemical processes that accompany the formation of bacterial biofilms on the pipes' inner surfaces. In general though, a simplifying assumption has been that the aqueous copper ion concentration is limited by diffusion during stagnant periods between flow, when water rests in the pipe. Calle et al. have now found that the influence of flow dynamics cannot in general be neglected. Through a series of measurements on a pipe system connecting a well to a household in Chile, they uncovered concentration patterns suggesting that a significant quantity of ions is dislodged from surface biofilms by virtue of interfacial forces arising during flow. Thus, the interplay of hydrodynamics with sorption equilibria in these systems merits further study. — JSY

Environ. Sci. Technol. 41 10.1021/es071079b (2007).

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