More Amateur Science?

I know I'm not the most savvy science guy, and my interests and"expertise" is very limited, but this new one really made me say, "wait a minute". I stumbled upon this story about a kid coming up with a nice solution to the problem of discarded plastic shopping bags. It's a little old (May of 2008), and I hadn't heard of this. It's a pretty cool idea for a science fair to identify strains of bacteria that can degrade plastic shopping bags in months instead of years. I don't know how feasible it is on a large scale, but it is a nice proof of concept at the very least.

It sounds like a wild, new, "why wasn't this thought of before" kind of thing. On the surface that may be true, but I recall a discussion of bacteria being used to clean up oil spills in a biology text book from a class I took in the late 90's. Seeing how plastic shopping bags are petroleum products, it isn't completely unheard of. Regardless, this is still some really nice work done by a high school student, and the win was well deserved.

The place where the story breaks down and becomes amateur science is in the statement that it will do the job in 3 months. That is stated early on, but a careful reading suggests the author doesn't know what she is talking about. Toward the end when describing the results of the project, she says that after 6 weeks roughly half of the plastic in the test group is gone. A logical conclusion might be that half gone at 6 weeks means that all will be gone at 3 months (or 6 weeks x2). The problem is that this is a fallacy. The 6 weeks suggests an estimation of a half life. If that is the case, it would take the bacterial culture 6 weeks to "consume" half of the plastic. At that point it will take another 6 weeks to "consume" half of what is left. Half life is kind of a fixture in science. Without experimentally establishing a linear decay, and that is not reported in the text of the article, I cannot help but read that 6 weeks as a half life.