Which shopping bags are the most most sustainable?

By Karen Tolkkinen

You would think that deciding which shopping bag is most sustainable would be simple.

A reusable cotton one, right?

Well, not so fast.

A 2011 government study in the United Kingdom found that to be more environmentally sustainable than the standard grocery store plastic bag, that cotton bag would have to be used at least 131 times.

That number goes up if the plastic bag is re-used to line a trash can. If that trash can liner is re-used three times -- suppose the trash is being emptied into a larger receptacle -- you would have to use the cotton bag a whopping 393 times to match the grocery store bag’s level of sustainability.

That seems counterintuitive. After all, the plastic bags are what are choking the whales and blowing in the ditches. And cotton biodegrades.

But the study weighed not just the disposal of various bags, but how the bags are made.

Cotton bags are made of, obviously, cotton, which is generally grown using pesticides and other agrichemicals and which require hefty amounts of water and land..

The study also looked at paper grocery sacks, and determined they would have to be re-used three times to match the plastic bag’s impact. Of course, paper bags tear and get wet and aren’t as likely to be reused as cotton bags. To see the study online, search for “Life cycle assessment of supermarket carrier bags” and “Environment Agency.”

The researchers gave this advice.

Whichever bag you bring to the supermarket, make sure you use it as much as you can. If not for more groceries, then to line your garbage can. Recycling helps, but not nearly as much as reusing.

They didn’t weigh the impact of bags made from jute or hemp, both of which are more sustainable than cotton. They also didn’t consider the impact of making your own bags from recycled fabric. You could turn that old pair of jeans into a handy carrier.

Or, do what my friend Wayne did: Cut the top off a sturdy bird seed bag, stitch on handles, and voila, you have a chic shopping bag that will serve you many, many trips to the store.