Everyone has seen in the news the water issues plaguing the city of Flint Michigan and the basis behind the contamination issues comes down to chemistry.
The issues arose when the city decided to switch their water supply from the Detroit River to the Flint River water in 2014. The new water was treated with the same chlorine disinfectant as the previous source, but lacked orthophosphate corrosion inhibitors that had been added to the Detroit River water previously used. Within months of switching problems began to occur.
Lead concentrations were found in the water to be ~50 times more than the EPA's standards. Olson et. al were concerned that the pipes were the possible culprits to be blames for the contamination. Using inductively an inductively coupled plasma mass spectrometer (ICPMS) they were able to observe the metal content in various samples of lead service line pipes. In most pipes build ups of various substances are expected throughout the pipes lifetime. In pipes from Flint Michigan, the build up was found to be composed of 12.4% lead, which was significantly lower than that of lead pipes from other areas which didn't use the Flint River water, which had values around 54%.
How does chemistry play into this issue?
The answer is the removed mineral preservation layer. Mineral preservation layers protect the pipes from corrosion by adding phosphate (PO44-) ions to the water before it is distributed. This encourages the formation of a lead (II) phosphate (Pb3(PO4)2) crust inside the pipes, which prevents the lead in the pipes from undergoing a characteristic redox reaction, which oxidizes the lead from its neutral solid state and leaches itself into the water.
With phosphate not being added the mineral layer present in the pipes began to degrade and expose the metal lead in the pipes.
The study also found that the low pH (7-8 compared to 10 from other water systems) of the water exiting the facility was contributing to corrosion by increasing the solubility of the lead (II) carbonate (PbCO3), which may also act as a protection layer in the pipes. When PbCO3 dissolves it allows for the formation of carbon dioxide and releases free lead ions into the water, disrupting the equilibrium depicted below.
These chemical factors above caused the lead contamination issues above, but through recognizing the problem and switching back to Detroit’s water supply the city was able to begin to reverse their water chemistry. The problems however do highlight the issues surrounding the continued use of lead pipes and the importance of replacing and upgrading aging civil infrastructure.
Sources:
https://www.pbs.org/newshour/science/study-confirms-lead-got-flints-water
https://www.michiganradio.org/post/flint-water-crisis-began-5-years-ago-city-better
Environ. Sci. Technol. Lett. 2017, 4, 9, 356–361
I think I might have preferred something that mentions pollution in the title like, "Chemistry of the Water Pollution Crisis in Flint Michigan." The first figure is effective. It draws the reader in. The second figure is informative but a little hard to read in our format. You explain the problem and the chemistry clearly and concisely. You might have noted that this issue has been discussed in more general interest media such as the PBS Newshour (https://www.pbs.org/newshour/science/study-confirms-lead-got-flints-water).
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