Chemistry
Popular Science
Lead in Water: Why? Where? and What Can We Do?
19.2.16
By now we’ve all heard about the tragic water situation in Flint. To very briefly summarize, after a switch in water sources in Flint, Michigan, there was an increase in leaching of lead from old pipes in flint into the water, resulting in a massive exposure to dangerous levels of lead across the area. Unfortunately, for many of this a situation like this could hit closer to home than we realize, with many older homes containing lead in the pipe infrastructure that, depending on the situation, could/is leaching lead.
What’s the Problem with Lead?
Most of us (hopefully) know that lead is not good for us. According to the WHO, lead poisoning at its worst attacks the central nervous system and can, in extreme cases, be fatal. Even relatively low levels of lead exposure can cause adverse effects, particularly in young children, including complications in brain development that can lead to permanent intellectual and behavioural disadvantages. Even doses that were previously thought to be benign are now recognized as being biologically toxic by most regulatory bodies, leading to the ultimate cease in use of lead in various products such as paint, gasoline, and water pipes and fixtures. The unfortunate truth, however, is that the once pervasive use of lead has made it extremely difficult to eradicate existing lead-containing structures. The latest case of lead-related disasters that has caught media attention is the lead found commonly in pipe-fittings and solder connections for municipal water systems. While this inclusion of lead in and of itself is not necessarily problematic, (the leaching of these lead compounds into most water running through the pipes is low under ‘normal’ conditions) chemical and/or physical properties of local water supply can lead to increased lead leaching from old pipe fittings, leading to unsafe lead in drinking water as evidenced by the situation in Flint, Michigan and other cities across North America.
Why Did We Even Use Lead In The First Place?
Despite being biologically toxic, lead is/was actually pretty useful. Leaded-paint was widely used until the 1970s owing to its unique ability to decrease drying time, resist corrosion, and generally preserve appearance. Believe it or not, the use of lead in pipes is so historic that the term ‘plumbing’ was actually derived from the Latin word for lead - ‘plumbum’ (I personally can’t believe I never picked up on this). Lead was likely the material of choice for so long due to its easy-to-manipulate malleability combined with its long-lasting durability, making it a great long-term choice for large-scale water distribution systems. As was alluded to earlier, the use of lead in pipes is not necessarily detrimental, although certain water chemistries, namely presence of certain dissolved salt species and acidity/alkalinity, can increase leaching of lead from pipes, resulting in unsafe concentrations in tap water for some homes.
How Much Lead is Safe?
As with almost anything in chemistry, concentration matters. Despite the high toxicity of lead, we are all likely exposed to very low concentrations of lead, with no negative biological impact. In fact, test almost any municipal water sample and you’ll find that although the lead concentration is not identically zero, there is often little cause for concern. The most significant (and troublesome) source of exposure to lead through water is through the aforementioned water distribution infrastructure. According to Health Canada, the maximum concentration of lead deemed acceptable in drinking water is 0.01 mg/L, a concentration thought to be high enough to induce negative effects particularly in young children.
Unfortunately, there are places, even within Canada, where lead levels in drinking water from taps is higher than the national acceptable maximum due largely to the use of old lead in pipes and water fixtures installed pre-1950s.
So What Can We Do?
While the most attractive solution for everyone is to simply remove all lead-containing infrastructure from water service lines, this is a complicated feat. Many cities have put plans in place to replace lead pipes on city owned land; however, when it comes to private property, this responsibility falls into the hands of the homeowner; a task that is far too expensive for many. In light of this, municipalities have resorted to chemical addition tactics for reducing lead leaching from the existing pipes. These so-called ‘corrosion control plans’ vary by region and can range from phosphoric acid addition to the water supply thus producing a protective orthophosphate coating on pipe interiors, to pH increases by addition of NaOH known to decrease leaching ability. The choice of appropriate course of action (ideally) depends on inherent water properties in the region, as lead solubility is affected significantly by water softness and acidity.
Quite unfortunately, though not unexpectedly, this chemical addition has received backlash in some areas due primarily to lack of public knowledge about the chemical means of decreasing lead exposure. Public retaliation of this kind threatens to delay implementation of such measures, exposing thousands of people to dangerously toxic lead levels on a daily basis. Although I am certainly not one to believe in blindly trusting government officials, the fact is that years of science have gone into decreasing lead leaching, and what’s more, any addition of tiny quantities of (very safe) chemicals to your local water supply will most certainly be less harmful than the very real threat of lead poisoning. We can only hope that what we are currently witnessing in Flint will, if nothing else, help us to reconsider any reservations about current and upcoming chemical measures put in place designed to protect us, and motivate those that can to replace lead pipes.
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