WC146 JanFeb 2026 - Magazine - Page 10
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Mad as a Hatter
Drinking water contamination and its e昀昀ects on brain chemistry
BY AARON ATCHESON AND SOPHIE DENNIS ABRO
ETALS CONTAMINATION of drinking water
is a significant concern in a number of communities, and its propensity to alter brain chemistry
can affect everything from stress levels to decision-making capacity. So, why do different jurisdictions have different views on what level is dangerous?
The exact way lead causes its toxic effects varies depending on the biological system or process being affected.
When lead enters the body through drinking water, it is
absorbed through the blood stream, affecting many cellular
processes and the central nervous system. In the nervous
system, lead has the ability to partially mimic the function
of Ca2+, enabling lead to bind to these calcium sites and
interfere with synaptic transmissions. Once inside the cell,
lead binds to and alters the important functions of enzymes,
proteins, and DNA. Research has revealed that lead increases the production of reactive oxygen species, which may
lead to oxidative stress. This stress damages cellular membranes, proteins, and nucleic acid, exacerbating damage
and the impairment of neural function. Research has also
shown that severe lead exposure can reduce levels of metallothionein-3 (MT-3), a protein in the brain which protects
cells from metal toxicity. These reduced levels of MT-3
leaves neurons more susceptible to the toxic effects.
Inorganic mercury compounds are water soluble, making
it the form of mercury most present in drinking water. Inorganic mercury alters membrane permeability and macromolecular structure by binding to sulfhydryl groups which
are found on the cell membrane, in the cytoplasm, and are
a part of cysteine—an amino acid. Exposure to mercury can
induce oxidative stress as well as mitochondrial dysfunction
which may result in altered calcium homeostasis and an
increase in lipid peroxidation. Both lead and mercury can
trigger programmed cell death, known as apoptosis, with
M
Aaron Atcheson is a partner with Miller
Thomson LLP in London, Ont., and is the
leader of the firm’s Projects Group.
Sophie Dennis Abro is a student at
Wilfrid Laurier University studying
Psychology and Neuroscience.
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WATER C AN ADA • JANUARY/ FEBRUARY 2026
inorganic mercury causing a decreased number of neurons
and astrocytes in the motor cortex.
By disrupting neuronal signalling, both lead and mercury
can impair cognitive processes, manifesting as developmental
delays, behavioural complications and long term cognitive
decline. Governments have recognized these issues and responsible legislatures around the world have enacted safe
limits on metals in drinking water. But what is behind the
variance in views on what is safe? California, long regarded
a leader in environmental protection, allows double the
amount of mercury permissible in Canadian jurisdictions (2
ppb vs. 1 ppb under the Guidelines for Canadian Drinking
Water Quality). And in respect of lead, while California has
the same stated guideline level for lead as the Health Canada
stan dards (5 ppb), and the U.S. EPA has a stated acceptable
level of zero lead content in drinking water, the U.S. EPA
“action level” for lead is much higher, at 15 ppb. Ontario,
often regarded as one of the leaders on environmental issues
in Canada, has also lagged behind the 2019 update in national standards, by leaving its limit at 10 ppb. Why are leading
jurisdictions lagging behind on mercury and lead?
The answer is likely a combination of history, public
consciousness and constrained resources. While Ontario has
been considering reducing its limit to 5 ppb since at least
2021, surveys indicate that the recommended reduction
in lead levels would result in an almost 50 per cent jump
in the number of municipalities in which drinking water
quality would fail to meet guideline levels. Similarly, in the
U.S., the higher “action level” for lead appears to reflect the
reality that most municipalities do not have sufficient financing to undertake system-wide lead service replacement.
In the case of California and mercury, its history of gold
mining resulted in higher mercury numbers in some water
bodies; the elevated cost of reducing mercury levels and the
existence of higher concentrations in drinking water sources
is a reality, and may have led California to a more relaxed
position on mercury in drinking water.
While it is hard to argue against a “less is best” policy,
requirements need to be achievable and the costs to comply
are significant. But this does not change the fact that metals
contamination has material public health and individual
effects on brain chemistry, mental capacity and behaviour.
The public should continue to push their political representatives to follow current science in these areas and to
continually consider elevated treatment of drinking water to
minimize potential negative public health effects.
WAT E R C A N A D A . N E T
