I was very proud when San Francisco in 2007 became one of the first major cities to ban plastic checkout bags. Lightweight and durable, they're almost irresistibly convenient, but these same characteristics make single-use plastic bags so pernicious in marine environments where they persist beyond our lifetimes, traveling currents and endangering marine life. Reusable grocery bags seem like a no-brainer, but continuing buzz based on a couple of university studies now has us concerned reusable bags harbor potentially harmful bacteria. Let's forget the questionable methodology and conflict of interests (one study was funded by the plastic-bag-friendly American Chemistry Council), and assume reusable grocery bags, like just about anything that touches food, can potentially harbor bacteria. Fortunately, it's actually fairly simple to eliminate any threat freeloading bacteria might pose through cleaning (by hand or machine) or by simply letting the inside out bag sit in the sun for a few hours.
While bacteria can generally be managed with a dollop of vigilance, the reusable bag proposition becomes more complex when you consider their production. For example, cotton bags may be biodegradable, but their production requires resource-intensive cotton: an interesting British study found that cotton bags require 131 uses to equal the global warming impact of conventional plastic bags. Repurposing containers as grocery bags is the ideal. The truly committed can even knit their own reusable bag from discarded plastic bags. The bottom line is we should consider the entire life-cycle of reusable bags including production, use/cleaning, and disposal. Beyond that it's a matter of personal preferences and habits: if it's easier to store and bring a certain type of bag on a consistent basis then it's probably a good choice.
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