假如你买了一些塑料制品，上面标明“可生物降解”。那你就可以放心了，因为你知道将它扔掉后它会无害降解。嗯，不要太快下结论。

“当我们从适合垃圾填埋场的特性这一角度考虑生物降解能力时，会发现它并不是理想的材料属性。原因是，我们在设计生物降解能力时，通常会追求快速的生物降解，然而垃圾填埋场尚未开始收集两年内产生的气体，生物降解产生的如此多的甲烷气体，会在安装气体收集系统之前就被释放到环境中。”莫顿·巴拉兹说到。他是北卡罗莱纳州立大学土木、建筑和环境工程系主任。

So you buy something made of plastic and it's labeled biodegradable. You can rest easy knowing that after you throw it out it will harmlessly break down. Well, not so fast.

"When we look at biodegradability as it pertains to landfills, biodegradability is not a desirable attribute for a material. And the reason for this is that when we design for biodegradability, we're typically designing for rapid biodegradability, and yet landfills do not begin to collect the gas that's produced typically for two years...so much of the gas, the methane, from biodegradability is released to the environment before gas collection systems are installed."

Morton Barlaz. He heads the Department of Civil, Construction and Environmental Engineering at North Carolina State University. And he spoke June 6th on Capitol Hill at the third "Science on the Hill" event, co-hosted by Scientific American and California Congressman Jerry McNerney. The theme of this session: "Solving the Plastic Waste Problem."

"Now I just answered the question from a landfill perspective. If I were to switch hats and say, well, is it desirable from a litter perspective, sure. If it actually biodegrades and is converted to gas, then the litter would disappear, and that's desirable. But let's make sure it's really biodegrading and not just degrading into small pieces that nobody can see. That's degradability, it's not biodegradability."

Also on the panel, Kara Lavender Law, Research Professor at the Sea Education Association in Woods Hole. She studies plastic debris in the ocean. What about biodegradability there?

KL: "I do not think that it is possible to design a material that will do that in the open environment and certainly not in the ocean...my understanding is that a lot of the standards around classifying a material as biodegradable are done under temperatures of 30 C, and for reference the average temperature of the surface ocean spans 0 C to 25 C. With an average temperature of 4 C. So even if you had a magical material that satisfied all the other environmental criteria, it's likely that that kind of breakdown would occur on such slow timescales that waste would build up and probably cause environmental harm. So...we shouldn't think of the ocean or the environment as a magical disposal of our waste."