Friday, November 30, 2007

Leave Your Shoes At The Door

Question: My sister always insists that we take our shoes off at the door. She says that it is cleaner and safer. I think that it is an old wives tale. Is there any data to support her claim?

Response: In the olden days (as my kids call them), taking your shoes off at the door was the norm. This custom is still the standard practice in Korea, Japan, and many other countries. Even in countries where shoes are generally worn indoors, related practices are followed, as door mats are often placed at entryways for people to wipe their feet before entry.

These "shoe off" and "door mat" practices came about to reduce the amount of dirt that gets tracked into your home. Shoes clearly can be a source of substantial dirt, as is evident from the footprints left when you walk in shoes on a clean, wet floor. Not only can shoes bring dirt into your home, but they can also bring pesticides, lead, and other chemicals that can be present in dirt. The U.S. Environmental Protection Agency (EPA), for example, showed that people bring lawn pesticides into their homes on their shoes. These pesticide-laden shoes were a major source of pesticide exposures, especially for young children who spend a lot of time on the floor and who put dirty fingers, dust, and toys in their mouths. Somewhat surprising was that the study showed that indoor shoe-wearing was a larger source of children’s pesticide exposures than eating non-organic fruits and vegetables. Taking your shoes off and wiping your feet on a door mat or other carpeting before entering were found to be important pollutant reduction measures.

Even if you do not use pesticides on your lawn or have lead in your soil, you can still have pesticides, lead and other chemicals on your shoes from your travels to other lawns and other places. These pesticides and chemicals can stay on your shoes for quite some time. So, it clearly makes sense to listen to your sister (at least in this one case) and take your shoes off before you enter your home. For added insurance, you can put a door mat just inside your door to store the shoes or to have people wipe their feet before coming inside. Your home will not only be cleaner, but may also look better, especially if you chose a nice looking door mat.

Wednesday, November 28, 2007

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?

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.

Monday, November 12, 2007

Does an Organic Diet Matter?

Question: I only buy organic foods for my family, even though it is more expensive. I’ve always assumed that this reduces my family’s exposure to pesticides, but recently read in the news that this isn’t true. Does it?

Response: Yes, with qualifications.

Organic foods are essentially free of pesticides, while nearly every type of conventional fruit and vegetable has at least one type of pesticide applied to it sometime from when the seeds are put into the ground to when they are sold. Logically then, eating organic foods rather than conventional foods will reduce your family’s exposure to pesticides.

The qualifications relate to the amount and importance of that reduced exposure.

The amount of the reduction in pesticide exposures will, of course, depend on what your family eats. The best scientific studies of pesticide exposures from foods suggest that an organic diet will basically eliminate one microgram of pesticides that would otherwise be eaten on a conventional diet in a typical day. [Putting this microgram into perspective is difficult, but for what it’s worth, a person eating 1,800 calories a day will typically eat 70 grams (or 70,000,000 micrograms) of fat, while a wasp sting delivers about 2 micrograms of venom. Of course, these comparisons say nothing about their dangers, as the toxicity of the pesticides differs tremendously from that of the fat and venom.]

The impact of switching to an organic diet is illustrated by a Seattle, Washington study, in which 23 children ate non-organic foods on the first three days and last seven days of the study. On the days in between, the children ate organic fruits and vegetables in addition to conventional meat and dairy products. During the first and third stages of the study, every one of the children had measurable amounts of pesticide metabolites (which are the less toxic break-down products of pesticides) in their urine. During the second organic fruit and vegetable stage, the amount of metabolites for two common pesticides chlorpyrifos and malathion was about ten times lower than the conventional diet periods.

Whether these lower levels translate into less health risks is not known, since pesticide metabolite levels during both the organic and non-organic diet periods were lower than US EPA limits. Also, these lower levels do not consider pesticide exposures that occur through the air, soil, indoor dust and water. Although its contribution varies by pesticide and by person, for the average person, food is only a minor contributor to exposures many common pesticides, including chlorpyrifos (used mostly on cotton, corn, almonds, and orange and apple fruit trees) and permethrin (used mostly on cotton, wheat, corn, alfalfa, and poultry). For example, in one scientific study, food accounted for only a few percent of total exposure to chlorpyrifos, while breathing indoor air contributed more than 80%. As a result, it is quite possible that a diet of organic foods will have only a modest effect on total exposure to pesticides.

That said, a growing number of scientific studies have shown that exposures to even small amounts of pesticides are harmful, especially to young children – which I think provides a pretty persuasive reason for you to keep buying organic food. A steady organic food diet is a good and relatively easy way (costs notwithstanding) to lower your risks from pesticides.