Friday, 10 February 2017

Investigating the cause of the water crisis in Flint Michigan.

In April 2014 the city of Flint, Michigan changed the source of its water from the Detroit River to the Flint River, the first stage of a project eventually intended to source water from Lake Huron via a new pipeline. However almost immediately people began to complain of a reduction in water quality, reporting that the water was cloudy in colour and gave off a foul odour. Cases of lead poisoning began to be reported in the city in February 2015, with tests showing dangerously high levels of lead in the blood of 15% of children in parts of the city. Shortly thereafter state officials found water in the city also contained dangerously high levels of trihalomethanes.

In a paper published in the journal Environmental Science & Technology on 1 February 2017, Kelsey Pieper, Min Tang, and Marc Edwards of the Department of Civil and Environmental Engineering at Virginia Tech present the results into the cause of the Flint water crisis.

Until 25 April 2014 Flint obtianed treated water from the Detroit Water and Sewer Department, however from that date water supplies were changed to a treatment plant on the Flint River, as part of a long-term plan to switch supplier to the Karegnondi Water Authority in 2016. This Flint River water was known to be more corrosive than the Detroit water, but no corrosion control measures were put in place, and, to make matters worse ferric chloride (FeCl₃) was added to the water as a coagulant to control total trihalomethanes, which further raised the corrosivity of the water.

Corrosive chemicals in water can dissolve lead and other metals (such as copper and iron) from pipes releasing them into the water supply as contaminants. The addition of corrosion inhibitors such as orthophosphate (PO₄³⁻) removes this dissolved metal from the water, forming insoluble scaling on the inside of metal pipes. However if such corrosion control is stopped, then the corrosive chemicals not just resume corroding the metal pipes, but also any scaling on the interior of the pipes, leading to higher levels of metal contamination in the water.

 Formation and destabilisation of protective scales: (a) corrosion inhibitors (e.g., PO₄³⁻) control the release of metals from plumbing through the formation of protective scales and (b) without corrosion inhibitors previously formed protective scales can become unstable and deteriorate resulting in high lead and iron in water. Pb = lead; Fe = iron; Zn = zinc; and Cd = cadmium. Pieper et al. (2017).

The U.S. Environmental Protection Agency's Lead and Copper Rule, water from a selection of households should regularly be tested for the presence of these metals. However the majority of tested homes in Flint did not receive their water via any route that involved lead service pipes, and therefore did not show significant signs of raised lead, which led officials within the town to conclude that the water supply was safe, though a subsequent report by the Flint Water Advisory Task Force set up by Governor Rick Snyder concluded that a large number of test results were excluded from the study 'conveniently and without adequate investigation'.

One resident that did find signs of problems with their water supply (referred to as 'Resident Zero' since the property was 'Ground Zero' for the lead pollution incident in Flint), reported problems with discoloured and foul tasting water in January 2015, collecting a series of water samples which showed raised lead levels when tested, with subsequent tests on water collected from the property in February, March and April showing that lead levels had continued to rise. During the same period a child in the home was shown to have a sharp rise in blood lead levels. However this was treated as an anomalous result by city officials, who cut the water supply to the property in the belief that this was a localised problem.

Association between water discolouration and lead concentrations for water samples collected in January 2015. A photo of the original sample bottles is overlaid with a bar chart of lead in water concentrations. Pieper et al. (2017).

Inspection of the home later in the month by officials from the Environmental Protection Agency could find no source of lead contamination within the home, at which point Resident Zero contacted the scientists at Virginia Tech for help.

The Virginia Tech team were able to arrange for the water supply to the property to be reconnected in order to run a series of tests on 28 April 2015. They collected a series of samples at low (1.3 L/min), moderate (4.2 L/min), and high flow rates (7.5 L/min) from a cold water tap within the property.

All of the samples had lead levels considerably above the Environmental Protection Agency's action level of 15 μg/L, with the lowest measurement at 217 μg/L, and several exceeded the 5000 μg/L limit above which the agency classifies contaminated water as hazardous waste, with the highest sample reaching 13 200 μg/L lead. All of the samples also contained iron in excess of the Environmental Protection Agency's safe limit of 0.3 mg/L, with the lowest sample having an iron content of 0.7 mg/L and the highest 6.5 mg/L. There was a strong correlation between lead and iron levels in the waters, which the Virginia Tech team interpreted as indicative of the breakdown of lead-bearing iron rust layers within supply pipes.

Next the scientists obtained samples of the piping supplying the property, finding that they were galvanised (zinc-coated) iron pipes with a significant level of scaling, and that this scaling contained significant levels of zinc, iron, lead, cadmium and tin, all of which were being released into the water as a result of the raised corrosivity of the supply.
Pieper et al. conclude that the water contamination experienced by Flint, Michigan came about largely as a result of the cessation of of corrosion control measures following the change in water supplier in 2014, and that this would probably have gone undetected without the scientific and investigative work of Resident Zero. The levels of lead found at the property were so high as to present an immediate danger to health, with a single 250 mL glass of water with a lead concentration of 217 μg/L (the lowest recorded concentration in any sample from the property) able to raise a child's blood level significantly and such a glass with a concentration of 2500 μg/L or above able to raise the blood lead level in a child with no previous exposure to lead above the Centers for Disease Control and Prevention’s level of concern immediately (lead is a cumulative toxin that builds up in the body rather than something to which an immunity can be developed).

Based upon this conclusion they note that, even if Resident Zero was receiving the most contaminated water in the city of Flint, something that they have no reason to suspect, then there would be good reason to have serious concerns about the quality of the water supply being received by other residents of the city (as it was, a state of emergency was declared in Flint after a spike in blood lead levels was recorded in children across the city in September 2015).

See also...

http://sciencythoughts.blogspot.co.uk/2016/12/tracing-origin-of-hexavalent-chromium.htmlhttp://sciencythoughts.blogspot.co.uk/2016/12/chemical-spill-leaves-corpus-christi.html
http://sciencythoughts.blogspot.co.uk/2016/10/selenium-arsenic-and-molybdenum-in.htmlhttp://sciencythoughts.blogspot.co.uk/2016/07/saskatchewan-city-forced-to-cut-water.html
http://sciencythoughts.blogspot.co.uk/2015/12/widespread-lead-poisonng-prompts-city.htmlhttp://sciencythoughts.blogspot.co.uk/2015/08/cryptosporidium-discovery-at-water.html
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