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In July 1, 2000 most large grocery stores in the state of California legally required a recycle plastic shopping bags. In Europe, even stricter anti-plastic measures are gaining traction. Retailers in Modbury, England, for example, recently committed to an outright plastic bag ban. News reports have cited a statistic that the ubiquitous receptacles take 5000 years to break down in landfills. How do we know?
Actually, we don’t. Plastic bags have only been around for about 50 years, so there’s no firsthand evidence of their decomposition rate. To make long-term estimates of this sort, scientists often use respirometry tests. The experimenters place a solid waste sample—like a newspaper, banana peel, or plastic bag—in a vessel containing microbe-rich compost, then aerate the mixture. Over the course of several days, microorganisms assimilate the sample bit by bit and produce carbon dioxide; the resultant CO2 level serves as an indicator of degradation