Don’’t Eat Yellow Snow…or Black…or Brown…or Pink…

Question:My kids always want to eat snow. If I can help it, I don’t let them, but I can’t watch them all the time. It’s driving me crazy. What do you think?

Response:
If the snow is yellow, black, brown, pink or otherwise dirty, it should not be eaten, as the colors each point out the presence of a different kind of pollution – yellow pollution from animals, black and brown pollution from dirt, cars, and people, and pink from bacterial contamination. The snow can collect these pollutants once it falls to the ground by being stepped on, splashed on, or otherwise having pollution fall on it. More surprisingly, perhaps, snow can also become contaminated by pollution as it falls to the ground.

It turns out that snow is a fairly efficient pollution collector when it is in the air. Snow is formed by water vapor that moves in clouds in cold air. As the water vapor moves in the cold air, it can stick to a tiny piece of dust and then have other water molecules attach to it, forming a crystal. Once formed, the crystal can continue to grow and can stay in the air for hours before it falls to the ground. It is during this time that the snow crystal can collect or “scavenge” pollutants that are present in the air. As a result of this scavenging, snow can contain all kinds of airborne pollution, even if it is white and freshly fallen. They types of pollution that the snow can contain vary by location, but could include metals, acidic pollutants, and persistent organic pollutants (POPs). The amount of pollution in white, fresh snow is generally very low in rural areas and is higher in cities and other areas with a lot of traffic, since traffic is known to be a major air pollution source.

Even so, should you be worried? For white, freshly fallen snow, probably not, given that scientific studies show low amounts of pollution in fresh snow and given that kids generally don’t eat much snow. But for colored snow and for snow that has been sitting on the ground for a while, it is definitely best for your kids to look and not eat. A good way to show them why may be to melt some snow in a container and see what you find. Almost always, you will find dirt, sticks and other debris that were previously hidden.

What distance is a "safe" distance from a highway?

Question:
I have read, with great interest some of your statements and a presentation of yours on indoor air pollution resulting from close proximity to highways. My wife and I are considering a relocation, in order to decrease my commute time. However, almost every property we look at is within 1.5 miles of a major highway, which is often congested with trucks, etc. I have read over 10 studies documenting increased risk for childhood leukemia and asthma. What is considered a"safe distance" from a major highway? These studies don't state the exact distance at which they measured. Also, I have read of the ability of plants such as bamboo and areca palm in removing 80% of benzene in the air. Have you read those claims and do they seem to be valid?

Response:
You are right that many recent studies have shown that pollution from traffic, especially diesel-powered traffic (such as trucks) is bad for health. Traffic pollution has been linked to increased death and hospital admissions for heart and lung disease, increased asthma attacks, and early indicators of cardiac disease. Consistent with these findings, several studies have also shown that living near a major highway or road presents greater health risks. While there have been some differences among studies, there seems to be a general consensus that the critical distance from a busy road or highway is within 100 meters (or about 300 feet). After this distance, you generally no longer see a dramatic increase in traffic-related pollution above urban background. In a city, however, it is difficult to get away from all traffic-related pollution as it can travel relatively long distances.

It is not clear what pollutant or pollutants emitted from motor vehicles are responsible for the observed health problems. It is possible that plants (such as bamboo) under certain conditions can be used to remove certain gaseous pollutants from motor vehicles, such as benzene, carbon monoxide and nitrogen dioxide. I haven't heard of any plants that remove particles from motor vehicles. l think that most of the studies examining pollutant removal by plants have been conducted in closed environments. The effectiveness of using plants to clean your air in your yard will probably be much lower, as outdoor air moves pretty freely.