Researchers aim to prevent a Flint-like crisis from happening in Canada
An interview with Prof. Robert Andrews, Sarah Jane Payne (Post-Doc) and Aki Kogo (MASc Candidate).
In 2014, the city of Flint, Michigan, switched its water source from Lake Michigan to the Flint River. Inadequate treatment and reporting caused lead (Pb) contaminated drinking water to be delivered to Flint residents, resulting in a state of emergency being declared.
Researchers at the University of Toronto’s Drinking Water Research Group (DWRG) have been actively studying the behaviour of lead (Pb) in water distribution systems since 2012, with a particular focus on southern Ontario drinking water sources.
“The problems in Flint emerged because the alternate water source had a slightly different water chemistry that disturbed the protective lead (Pb)-scale on the existing lead (Pb) pipes,” said Prof. Robert Andrews, a principal investigator with the DWRG. “Short of replacing all the lead (Pb) service connections in the system immediately, it will take time for the damaged scale on the interior of the pipes to build up with time and repair itself.”
Sarah Jane Payne, U of T Post-Doctoral Fellow, explains that scale (the buildup of materials lining the inside of water pipes), much like rust, can be relatively stable. However, it can cause significant issues when disturbed, as it was with the water change in Flint.
“Municipalities add different chemicals, called corrosion inhibitors, to the local water, which react with dissolved lead (Pb) in the water and re-deposit it on the surface of the pipe to form the scale,” Payne describes. “Each water source (lake or river) has a different chemistry, such as alkalinity, pH and inorganic carbon, which affects how the corrosion inhibitors react.”
“The crisis in Flint highlighted what many people take for granted,” said Andrews. “Researchers are aware of real-life issues and through careful experimentation are always looking for unintended consequences. Asking ourselves if we make one change, how is this going to affect something else?”
The science of inhibitors
As far back as the fourth century B.C.E, the ancient Greeks preferred terracotta pipes over lead (Pb). They knew, even then, that lead (Pb) negatively impacted health. Today, we know lead (Pb) is a powerful neurotoxin with serious implications for neurological development in children. Despite this, lead (Pb) has persevered as a material for pipes due to its durability and ease of use. Lead (Pb) service lines, connecting the water main to the home, were widely employed in North America until the early 1950s, when regulations ended the use of lead materials for new lines.
Municipalities today use a variety of methods including the application of corrosion inhibitors, like orthophosphate and zinc-orthophosphate, to reduce the amount of lead (Pb) consumed by the general population. These chemicals react with lead (Pb) to form a compound that precipitates out of solution to form a stable, crystal-like lining on the inner surface of the pipe. The lead (Pb)-scale is very thin – only a few microns thick.
The problem can be made even more complex when considering physical disturbances, changes or fluctuations in water chemistry, and seasonal changes in temperature, which can loosen existing scales and disrupt the chemical balance between the water and the pipes.
Utilities try to form the strongest scales possible given varying water chemistry. Local water quality conditions dictate what needs to be changed or added to reduce corrosion.
“When phosphate-based corrosion inhibitors are used, lead (Pb)-phosphate scales become more and more stable over time,” said Andrews. “Understanding that chemistry and timeline is actually quite complex.”
“Reducing corrosion isn’t just about adding corrosion inhibitors. It can also be about changing the attributes of the water itself, such as adjusting the pH,” said Payne. “It is being aware of these details, looking at them holistically that determines what combination of attributes and additives might lead (Pb) to the least amount of lead (Pb) in drinking water.
Study: Comparing inhibitors
Researchers with the DWRG wanted to compare corrosion control options for Lake Ontario water using the two most common corrosion inhibitors: zinc-orthophosphate and orthophosphate. However, as phosphates are a finite resource, sodium silicate was also selected as a non-phosphate-based inhibitor to research.
“Phosphates are expensive and the price is volatile, so we wanted to include an alternative. That’s why we looked at sodium silicate,” said Payne. “Sodium silicates’ corrosion inhibitor properties have been known since the 1920s, but the funny thing is that no one really knows exactly how they work. So we compared it to the performance of phosphate-based inhibitors to try to understand more about this corrosion inhibitor.”
To fully understand how Lake Ontario water will interact in local water distribution systems, lead (Pb) pipes that had been in use for 65 years were sourced. To simulate a scenario where a homeowner has not replaced their portion of the water service line, a partial lead (Pb) service line replacement was set up in the DWRG laboratory.
“All of our test pipes came out of a community in Ontario. When you think about these pipes, many have been underground since the 1940s. They’ve had decades of different chemical combinations pass through them,” explained Payne. “What their particular scale is formed of and what conditions keep them stable is not well understood. We use real lead (Pb) pipes that have been pulled out of the ground that we know have a history. We can do more realistic experiments with those because using a new lead (Pb) pipe would be a totally different story.”
“Both phosphate-based inhibitors performed very well, though zinc-orthophosphate did seem to perform a little better,” said Aki Kogo, MASc Candidate. “Initially, the sodium silicate did not do very well but later in the experiment we started to see some better results with it.”
Now that testing has wrapped up at the DWRG lab, this setup of lead (Pb) testing equipment will be moved to a municipality’s water treatment facility for future studies.
“It’s through a lot of hard work by smart people that this research gets done,” Payne said. “Just to get the water every week, Aki and Jim Wang [DWRG Research Chemist] transported 500 litres of ‘untreated’ water back to the tanks in our lab. There is so much physical work, time and intellectual dedication that goes into research like this.”
The impact of research
“People in the water industry are very passionate about public health and that’s always at the forefront of any water treatment research,” explains Andrews.
“What we do every day affects millions of people. Our research is done quietly, but it’s really quite important. There are strong researchers in Canada, who are truly focused on the health of Canadians and those around the world.”
Public health plays a significant role in directing the research on drinking water quality.
“There’s the epidemiology and toxicology side that drives the health-based inquiry,” said Payne. “The engineering side looks into accomplishing what is required to meet the standards set by health-based researchers. It is a back and forth iterative process that helps regulators set standards that municipalities must meet.”
“In Canada, we have a lot of utilities that are forward thinking,” explains Andrews. “It is extremely rare for a municipality to change its water source. Because of the safeguards in sampling and reporting that we have in Canada, along with the conscientiousness and vigilance of water treatment personnel, it is very unlikely that a Flint-like emergency situation will happen in Canada.”
About the Drinking Water Research Group
The Drinking Water Research Group (DWRG), formed in 1998, is a consortium of researchers from the University of Toronto. The group operates as a team working to improve drinking water quality through sound research and engineering. With over 25 ongoing projects, the DWRG typically undertakes collaborative projects examining treatment, distribution, compliance and innovation to meet future water needs. Unique resources, including a large number of municipal and industrial partners, allow for various issues to be examined.