The Persistence of Pesticides

One of my Facebook friends recently asked me if pesticide residues were a problem in finished compost. She had heard that pesticide residues weren’t an issue in Canada because all legal pesticides here were biodegradable. As I found out while researching the chapter on pesticides in my new book, that is a very big and very loaded question. The three main categories of pesticides (the umbrella term for the chemicals) are: insecticides (pesticides that kill insects); herbicides (pesticides that kill weeds); and fungicides (pesticides that kill fungi). I took a look back at Rachel Carson’s book, Silent Spring (Houghton Mifflin, 1962) to see how far we’d come in nearly half a century. Thanks to Carson, DDT was banned, but some of its close, even more toxic relatives, are still in use today. The broader more general pesticides that killed everything in their wake five decades ago have been replaced by more target specific ones, often deadlier, even if they don’t linger as long in the soil. Of particular concern are the ones that mimic sex hormones in the body. And some of the chemicals we have banned or restricted at home are still used in the developing world. Of course, we import fruit and vegetables from those very countries, so we are still getting the effects, served up in a delicious cocktail. But the opposite is also true; some pesticides banned in certain countries are still used here.

In a 2006 Suzuki Foundation Study on International Pesticide Regulations, researchers compared registration data from Canada, the US and Europe. They identified sixty active ingredients still registered for use in Canada and found them in 1,130 pesticide products despite being banned for health and environmental reasons by other western industrialized countries.

The answer to my Facebook friend’s question also depends on whether she’s talking about using the finished product from a backyard or large scale composting system. Backyard compost bins tend to not get very hot, so there is more likely to be residuals if you are not eating a purely organic diet and use some chemicals (pesticides or synthetic fertilizers) on your yard or garden. But you would only know for sure if you had the finished product tested, which can be expensive. If you don’t buy purely organic produce, you may want to start buying at least some. The US-based Environmental Working Group has come up with a list of The Dirty Dozen, the twelve most contaminated fruits and veggies. They include peaches, apples, strawberries, cherries and spinach. They also prepared a list of the least contaminated, many of those have thick skins, like bananas and avocados.

When I worked at City Farmer, I also investigated the inks used for newspapers and magazines to see if they are safe to use as a carbon source in the compost bin. What I found out was even if the inks are soy or canola based, there are plenty of other chemicals contained in the ink composites to be worried about. So I would recommend staying away from any coloured paper and especially the glossy inserts. I would probably avoid putting bleached paper products in the bin, too.

There is less concern for organics composted in industrial scale facilities because the systems get very hot. Also they follow strict quality control measures and conduct regular testing. For example, the Vancouver Landfill regularly tests their finished compost for metals, other contaminants and nutrient levels in accordance with the Ministry of Environment’s Organic Matter Recycling Regulation. However pesticides are not part of their testing regimen. I am told some years ago, a student tested for residuals from commonly used pesticide and herbicides, and no concerns were raised. While many local gardeners use the product on their food gardens, some are leery and prefer to just use their home-made brand.

What can you do? Make sure you practice natural lawn and garden care in your own yard. The City of Vancouver’s Grow Natural web site, the Northwest Coalition for Alternatives to Pesticides and the Pesticide Action Network are great resources. Plant flowers and shrubs known to attract bees and other pollinators. Ask for recommendations from your local garden store. Join or support a group that is working to ban pesticides for both home and agricultural uses.