By Dr. Mercola
If you grew up in a snowy region, you almost certainly have memories of sticking out your tongue to catch snowflakes and, probably, also eating it by the mittenfull. It's practically a childhood rite of passage.
Back then, you probably didn't give a thought to what was actually in that snow, so long as it wasn't brown or yellow. But even snow that's bright white may not be as pure as it appears.
In fact, new research suggests snow is quite effective at absorbing pollutants from the air, which then become embedded in the snow itself.
Snow May Be Full of Toxins
Canadian researchers collected snow from a park in Montreal and measured levels of toxic particles typically found in automobile exhaust. The researchers explained in the journal Environmental Science: Processes & Impacts:1
"Exposure to vehicle exhaust can drive up to 70% of excess lifetime cancer incidences due to air pollution in urban environments.
Little is known about how exhaust-derived particles and organic pollutants, implicated in adverse health effects, are affected by freezing ambient temperatures and the presence of snow."
The analysis revealed that snow appears to act as a sponge, soaking up multiple toxins from the air. Among them:
- Benzene: a known human carcinogen that's also been linked to birth defects
- Toluene: chronic exposure to toluene is linked to anemia, lowered blood cell count, liver or kidney damage, and may affect a developing fetus
- Ethylbenzene: another known carcinogen
- Xylenes: volatile organic compounds (VOCs) that affect the central nervous system, with symptoms such as headache, dizziness, nausea and vomiting
The snow was tested one hour after exposure to exhaust fumes, and levels of the contaminants rose significantly during that period. The researchers suggested that as the snow melts, it might then release the toxins back into the air, possibly leading to a rapid increase in air pollution.
Study author Parisa Ariya, Ph.D., a professor at McGill University, told The Huffington Post:2
"Snow flakes are ice particles with various types of surfaces, including several active sites, that can absorb various gaseous or particulate pollutants …
As a mother who is an atmospheric physical chemist, I definitely do not suggest my young kids to eat snow in urban areas in general."
The 'Cleanest' Snow Comes Later in the Storm
If you simply must eat snow, wait until it's been snowing for a while (a few hours, ideally) and then collect it. According to John Pomeroy, Ph.D., a researcher at the University of Saskatchewan who spoke to NPR, "snow acts like a kind of atmospheric 'scrubbing brush.'"3
As snow continues to fall, air pollution levels will fall. This means snow collected later should theoretically be cleaner than the snow at the beginning of the storm.
Even still, contaminants in snow are unlikely to reach toxic levels, according to University of Arkansas chemistry professor Jeff S. Gaffney, Ph.D., and there's probably little risk from taking a small bite here and there.4
That being said, if you live in an urban environment near heavy traffic, or anywhere with high levels of air pollution, the snow will likely reflect that. Further, it's not only urban areas that may have dirty snow.
Agricultural practices also have a large impact on snow's purity, according to researchers at the Joint Institute for the Study of the Atmosphere and Ocean at University of Washington. Research scientist Sarah Doherty, Ph.D. told Futurity:5
"Our work suggests that land use and farming practices might matter as much as diesel emissions in many parts of the Great Plains."
Another Snow Hazard: Road Salt
With snow and ice comes hazardous travel, and so, every winter, the U.S. spends more than $2 billion to remove snow and ice from roadways, a cost that includes over 15 million tons of salt.6
Damage from salt corrosion is estimated to cost the U.S. up to $19 billion per year, in part because it's highly corrosive to bridges and other steel roadway components.7
Then, when the snow and ice melt, the salt (sodium chloride) dissolves into sodium and chloride ions, which make their way into the environment, often into waterways.
Chloride concentrations equivalent to one teaspoon of salt in five gallons of water (230 mg/L) can harm aquatic life and affect the taste of drinking water.
The U.S. Environmental Protection Agency (EPA) recommends levels be kept below this amount, but a study by the U.S. Geological Survey (USGS) found that 40 percent of urban and suburban steams tested in the northern US had levels at or above this threshold.8
Elevated chloride levels may inhibit plant growth, impair reproduction and reduce the diversity of organisms in streams, according to USGS.
Further, when animals drink melted snow that has high concentrations of road salt in it, it may lead to symptoms of salt toxicity, including weakness, confusion and dehydration.
Trees and other plants near roadways may also be damaged by salt, even if they're more than 600 feet away.9 Even the health of the soil is impacted by road salt. USGS researchers called for "deicer management options that minimize the use of road salt while still maintain safe conditions."
When best-management practices, such as pre-salting roads and wetting the salt before use, are used, the University of Waterloo found that chloride levels in groundwater could be reduced by half.10
You can also help on an individual level by minimizing the salt you apply on your driveway and walkways. Shoveling early after a storm will help minimize the need for salt, and if you do need to use it, try a mixture of pre-wetted sand and salt (1:1) to minimize the release of chlorides.
You Don't Have to Eat Snow to Be Affected by Air Pollution
Outdoor air pollution is a serious environmental health risk linked to both chronic and acute health conditions, including stroke, heart disease, lung cancer, asthma, chronic obstructive pulmonary disease and respiratory infections.
While you can easily avoid the air pollutants in snow by simply not eating it, they're not so easily avoided when it comes to the air you breathe.
According to the World Health Organization (WHO), ambient (outdoor) air pollution in both cities and rural areas caused an estimated 3.7 million premature deaths worldwide in 2012, the majority of which were due to heart disease and strokes.11 As WHO noted:12
"Most sources of outdoor air pollution are well beyond the control of individuals and demand action by cities, as well as national and international policymakers in sector like transport, energy waste management, buildings and agriculture."
Particulate matter is air pollution made up of extremely small particles or liquid droplets. Typically it's composed of any number of toxicants, including organic chemicals, metals, soil or dust. The smaller the diameter of the particle, the greater its risk of health damage becomes, as these can easily pass into your lungs, causing well-known damage to your heart and lungs.
"Fine" particulate matter is generally defined as particles that are 2.5 micrometers or less. These particles may come from smoke (such as forest fires) as well as gases emitted from power plants, industries and, of course, automobiles.
For comparison, the U.S. Environmental Protection Agency (EPA) considers any particles that are 10 micrometers or less as a potential health concern.13 If you happen to live in a heavily polluted area, the best option is to move, but I realize that isn't always a practical option.
If you can't move, pay attention to the Air Quality Index (AQI), released by the EPA to calculate five major air pollutants:
- Ground-level ozone
- Particulate matter
- Carbon monoxide
- Sulfur dioxide
- Nitrogen dioxide
If the AQI in your area is high, it may be best to stay indoors as much as possible. At the very least, avoid exercising outdoors when air pollutants are high (such as during rush-hour traffic).
Your Heart May Be Most at Risk From Snow
Unless snow is on your daily menu, it's unlikely to pose much of a threat, consumption-wise. A more tangible risk is likely that posed to your heart while attempting to shovel. This occurs not only because of the physical exertion but also because of the cold temperatures.
Winter is the most common season for heart attacks. Research shows there are up to 53 percent more heart attacks in winter than in summer, and twice as many heart attacks a day in January compared to July.14
A study from the U.K. even found that each 1.8 degree Fahrenheit drop in temperature on any given day was linked to about 200 additional heart attacks.15 Why does cold weather increase your risk of a heart attack? For starters, cold temperatures can cause a rise in your blood pressure along with increasing levels of proteins that raise your risk of blood clots.
When the weather is cold, your heart must also work harder to maintain body heat and your arteries tighten, which restricts blood flow and reduces the oxygen supply to your heart. When combined, all of these factors could trigger a heart attack, especially in the elderly or those with existing heart disease.
There is also the issue of hypothermia, which occurs when your body temperature falls below normal. Heart failure is the leading cause of death in hypothermia cases, which is why it's very important to dress appropriately for the weather if you plan to be outdoors in the cold. Further, don't overdo it when you're shoveling snow; take frequent breaks and, if necessary, get help to clear your snow.