Friday, February 19, 2016

The Chemistry Behind the Flint Water Crisis explained

Also in this week's C&EN, a phenomenal article by Michael Torrice about the problems of lead in Flint, MI. I had been looking for a detailed explanation of the chemistry issues, and here we are: 
...Most important, the treated Flint River water lacked one chemical that the treated Detroit water had: phosphate. “They essentially lost something that was protecting them against high lead concentrations,” Giammar says. Cities such as Detroit add orthophosphate to their water as part of their corrosion control plans because the compound encourages the formation of lead phosphates, which are largely insoluble and can add to the pipes’ passivation layer. 
Flint didn’t use orthophosphate despite a recommendation to do so from Veolia, an environmental services company that studied the quality of the treated Flint River water after the switch­over. In a March 2015 report, Veolia suggested that the city spend $50,000 annually to add the corrosion inhibitor.* By press time, C&EN was unable to get a comment from Flint city officials about why a corrosion inhibitor wasn’t added to the river water. 
The entire Flint water crisis could have been avoided if the city had just added orthophosphate, Edwards says. He bases his opinion, in part, on experiments his group ran on the treated Flint River water. The researchers joined copper pipes with lead solder and then placed the pieces in either treated Flint River water or treated Detroit water. After five weeks in the Flint water, the joined pipes leached 16 times as much lead as those in the Detroit water, demonstrating just how corrosive the treated Flint water was. But when the scientists added a phosphate corrosion inhibitor to the Flint water, the factor went down to four. 
Still, orthophosphate isn’t the only corrosion solution. Some water utilities treat water so it has a high pH and high alkalinity, Giammar says. Such conditions decrease the solubility of lead carbonates, which also contribute to the pipe’s protective mineral layer.
The treated Flint River water had a relatively low pH that decreased over time. 
According to monthly operating reports from the Flint treatment plant, the city’s water had a pH of about 8 in December 2014, but then it slowly dropped to 7.3 by August 2015. Environmental engineers say that if water pH drifts too low in the absence of orthophosphate, the water can start to leach high levels of lead from pipes.
In the comments (keep scrolling), a very interesting statement from a former operator at the Flint water plant:
I was an operator at the Flint water plant in 2014-15. To answer your question about a target pH, it was 8.5-9.0. I would add that Flint utilized lime softening so the pH was raised to a target range of 11.0-11.6 and subsequently reduced through the addition of carbon dioxide.  
As far as the decision to not implement optimized corrosion control, that was a decision by committee including the city, their engineering firm and the Michigan DEQ. It was the DEQ that misinterpreted the Lead and Copper Rule requirement for communities with over 50,000 residents to implement corrosion control immediately after a source water change. Instead, the DEQ allowed Flint to conduct the two consecutive six month monitoring periods first....
As a parent that is incredibly paranoid about lead, this is pretty awful. It seems to me that whatever systems are in place to attempt to avoid these sorts of issues is not robust enough.

(We don't usually think about infrastructure like water treatment very much, but it probably is an area that we, as a country, should think a little more about (and probably pay a little more financial and scientific attention to.))

*UPDATE: Michael Torrice writes in the comments that this sentence has been corrected by C&EN. Veolia recommended the addition of polyphosphate, which would not have prevented the corrosion issue. 


  1. Whatever city officials are responsible for this oversight should go to f-ing prison.

  2. The sentences about the water quality report from Veolia were incorrect. A reader pointed out that the report advised Flint to add polyphosphate to the water, not orthophosphate. The company was looking for a solution to the discolored water problems Flint was experiencing and polyphosphate would help control the iron corrosion responsible for that issue. Unlike orthophosphate, polyphosphate wouldn't control lead corrosion, and some think it actually might make it worse. So it's probably a good thing that Flint didn't take Veolia's advice.

    We just put up a correction notice online this morning. But wanted to point it out here since you quoted a section containing the Veolia bit.

    1. I do not buy it. If it can precipitate out iron phosphate it will precipitate out lead phosphate. In an aqueous solution, the difference between polyphosphate and orthophosphate might be significant (I have no idea) but the path way for corrosion resistance is the same, aqueous phosphate ions. Lead ions would react faster than iron ions with the aqueous phosphate based on the solubility of the formed complexes. Assuming I still remember my general chemistry.

  3. I asked my sources from the story about the poly v. orthophosphate chemistry before we issued the correction. They told me that the differences with respect to lead are well-known in corrosion control circles. One source cited a manual from the American Water Works Association:

    From page 41 of the AWWA Manual 58 Internal Corrosion Control in Water Distribution Systems--"polyphosphate can be effective for the control of particulate iron and manganese in finished water but is generally not recommended for lead and copper corrosion control".

    Page 43--"polyphosphate can be effective for the control of red water by mobilizing friable iron and helping to stabilize the corrosion scale core...the complexation properties of polyphosphates can be effective for the control of iron (red water), manganese (black water), and carbonate scaling but may also significantly increase the solubility of lead in home plumbing systems...Dodrill and Edwards (1995) reported that the 90th percentile lead release when dosing polyphosphate at 1 mg P/L was more than double that when dosing orthophosphate in utilities with alkalinities less than 30 mg/L and a pH < 7.4."

    1. Huh. I cannot wrap my head around why this would be the case. However, this is well outside of my wheelhouse. Thanks for the information.

    2. I am not an expert too, and who knows how many different factors (pH, complexation preference of lead vs. iron with phosphates etc.)are at play here. My guess is polyphosphates are not good ligands for Pb(II) and other minerals (ligands) in water bind stronger to Pb(II). So, you mobilize and make Pb(II) more soluble reaching to people's homes? Of course, I may be completely wrong.

  4. So the question is, how does one passivate lead piping in a water supply system. The problem is hardly unique to Flint, and IIRC the article mentions that lead and iron piping are going to be found in most older water distribution systems, where, presumably and hopefully, soluble lead in the water is not an issue. My town issues a water quality report every year. Our main water source is a very shallow aquifer under the local river, and radon and its other unstable friends from the granite in the area is perhaps the biggest chronic concern. As an old eastern seaboard town its a pretty sure bet there's lead and iron piping used. How do other areas handle the passivation issue?