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The chemistry behind the Flint Water Crisis: Corrosion of pipes, erosion of trust
By George Lane
When Flint, Michigan changed its water supply in 2014, it initiated a cascade of chemical reactions inside decades-old water pipes that caused Lead to leach into its drinking water, triggering a major public health crisis. When Flint used its own river as a water supply, drinking water contained a staggering 13,200 parts per billion (ppb) Lead, almost 900 times higher than the 15 ppb regulatory limit set by the Environmental Protection Agency (EPA). Some water samples exceeded the EPA criteria for Lead concentration in hazardous waste, 5,000 ppb.
Although Lead pipes have been used for water distribution for over two thousand years beginning with the Romans, the use of Lead pipes carrying water in the United States on a major scale began in the late 1800s, particularly in larger urban cities. By 1900, more than 70% of cities with populations greater than 30,000 used Lead-lined pipes for drinking water.
The use of Lead pipes to carry drinking water was recognized as a cause of Lead poisoning by the late 1800s in the United States. In 1890 the Massachusetts State Board of Health advised the state’s cities and towns to avoid using Lead pipes to transport drinking water. By the 1920s, many cities and towns were prohibiting or restricting their use. To combat this trend, the Lead industry carried out an effective campaign to promote the use of Lead pipes, affecting public health and delaying the replacement of Lead water pipes.
Normally water managers add chemicals to water, such as orthophosphates, to prevent corrosion. Orthophosphates bond with Lead in pipes, creating a protective coating between Lead and water. When that shield is intact, corrosive chemicals like Dissolved Oxygen (DO) can’t interact with the Lead; however, orthophosphates have to be added continually or the barrier breaks down. If the barrier does break down, DO combines with Lead atoms, oxidizing them. Oxygen takes electrons from Lead, grabs its Hydrogen protons, turning into water, and allows Lead to leach into drinking water. Once oxidized, Lead dissolves into the water instead of sticking to the pipe.
Flint’s water treatment plant did not add orthophosphates, allowing the pipes to corrode, and Lead quickly contaminated the drinking water. Additionally, Flint River water had high levels of chlorides, which accelerate corrosion. There were two other sources of chloride: Ferric chloride used in Chlorine disinfection of water and road salt applied during tough Michigan winters. Switching from Detroit’s Lake Huron to Flint River water created a perfect storm for Lead leaching into Flint drinking water.
A complex brew of acids, salts, Chlorine and many other chemicals were involved in oxidizing Flint’s metal pipes and releasing Lead. High levels of Lead in Flint drinking water weren’t reported to the public for 18 months; however, the corrosion happened quickly, especially in the warmer summer months. Without effective treatment to control corrosion, Flint’s water leached high levels of Lead from the city’s pipes into city drinking water. Following the switch, E. coli bacteria was also found in the water.
To combat E. coli, extra Chlorine was added as a disinfectant to remove it. Ferric chloride was also added as a coagulant to remove organic matter from the water, initiating a domino effect of chemical causes and effects. Flint’s water quality problems were also caused by corrosion in both the Lead and Iron pipes that distribute water. When city residents began using the Flint River as its water source, the water’s ability to corrode those pipes wasn’t adequately controlled. This led to high Lead levels, rust-colored tap water, and the growth of pathogenic microbes.
When Flint changed its water supply, the city didn’t adequately control corrosion. Flint isn’t the only city susceptible to these problems. The pipes in its old distribution system had seen the same water for decades, similar to many other cities. Switching water supplies changed the chemistry of the water flowing through those pipes.
When a switch like this happens, the chemistry in the water system moves toward a new equilibrium. In Flint the change was catastrophic. Flint was getting its water from the Detroit Water & Sewerage Department, which would draw water from Lake Huron and then treat it before sending it to Flint.
To lower the city’s water costs, in 2013 Flint officials decided to take water from another source which was building its own pipeline from the lake. Shortly after that, Detroit told Flint it would terminate their original long-term water agreement within a year and offered to negotiate a new, short-term agreement. Flint declined the offer. While waiting for the new pipeline to be finished, Flint began taking water from the Flint River and treating it at the city plant.
Problems with the city’s tap water started the summer after the switch in 2014. First, residents noticed foul-tasting, reddish water coming out of their taps. In August, the city issued alerts about E-coli contamination and told people to boil the water before using it. A General Motors plant in Flint stopped using the water because it was corroding steel parts.
In early 2015 Lead reached Flint’s University of Michigan campus. Researchers sampled water from 252 Flint homes and reported the results (www.flintwaterstudy.org). Hurley Children’s Hospital in Flint released data showing that since the water change, the number of Flint children with elevated levels of lead in their blood had increased from 2.4% to 4.9%.
Lead is neurotoxic, causing behavioral problems and decreased intelligence. The Blood Brain Barrier limits the passage of ions, but because it has not formed in children, they can absorb from 40% to 50% of water-soluble Lead compared with 3% to 10% for adults.