How dangerous is the chemical 1,4 dioxane
if it gets into water? It may seem an obscure question but
if you live somewhere where there's dioxane contamination it's an important one
1,4 dioxane, let's call it dioxane for short
is a colorless, flammable liquid that's used as an industrial stabilizer and solvent
it dissolves readily in water and doesn't easy biodegrade
which is potentially a problem if it gets into the environment
and to make matters worse it's considered a probable human carcinogen
by the US Environmental Protection Agency.
All of this is not good news if stuff somehow gets into your water supply
but just how worried should you be if your supply's affected?
According to toxicology studies, dioxane
--not to be confused with the similarly named but chemically different "dioxin"--
can damage the liver and kidneys if consumed in large quantities.
However, an adults would need to be drinking couple
microliters of the stuff everyday, or around half
thousandth of a teaspoon, for serious harm to occur.
This is for non-cancer health risks though.
When it comes to cancer things look somewhat different.
Based on animal studies the US EPA estimates that
if an adult spends their life drinking water contaminated with just
three and a half micrograms of dioxane for every liter of water
that's less than 1 millionth of a teaspoon
they have a one in 100,000 chance of developing liver cancer.
But what does this mean in reality? The city of Ann Arbor provides a useful case
study here for
making practical sense of a somewhat academic
risk assessment. From the 1960's to the 1980's
tens of thousands of gallons of dioxane were released into the environment
to the west to the city. Aquifers underneath the city were contaminated
and some dioxane ended up in private wells.
Clean-up operations are still ongoing and there is a groundwater use prohibition
zone where contamination levels are excessive. There's also a fear that the
contamination
could reach the city's major water source--a local river--in the future
and over the past few decades some people
will have been exposed to the chemical. The Michigan cleanup limit for dioxane
is 85 parts-per-billion or just under 20
millionth of a teaspoon per liter of water.
This is the theoretical level of contamination people could be exposed to
before
action is taken. So, useful question is what's the cancer risk at this level?
Following the US EPA analysis, if you were to drink
water contaminated with dioxane at 85 parts-per-billion your whole life
your chances of developing liver cancer would be around
one in four thousand. This sounds high,
but it's based on some assumptions that may not be
realistic. Such as assuming that affected adults will be drinking
two liter of contaminated water every day of their life
seventy years. So what if we consider a more realistic scenario.
Imagine for instance that you've lived in Ann Arbor for twenty years and
only drink one liter a day of tap water. Your highest dioxin related cancer risk in
this case is closer to
one in 30,000. Still high but much lower than the one in four thousand.
Or imagine you're a teenager who drank 10 liters a week of contaminated water
ten years before leaving for college.
According to current research your cancer risk would be closer to
one in 35,000.
These calculations
do need to be treated with some care. That's still
uncertainty over how 1,4-dioxane causes cancer in animals
and the human risk estimates here do err on the side
caution. But the do show how a detailed
scientific assessment can be used to put a number on
real world risks. However, just being able to put a number on the probability of
something bad happening
does raise some more challenging questions, including
what you do with that number once you have it and who decides how much risk is OK
especially if someone else created the risk in the first place.
These though questions for another risk bites
and another day. For more information on 1,4-dioxane
check out the links below this always please
do join the conversation in the comments.