Plant Growth Response to Compost Containing Degraded Polylactic Acid (PLA) Cups.

Consumer reliance on petroleum-based plastics has led to a tremendous buildup of plastic waste in landfills. Petroleum-based plastics are problematic because they voluminous and do not degrade at a sustainable rate. To meet consumer needs for convenience that plastics provide, compostable plastic made from polylactic acid (PLA), is now being marketed. Although PLA products are marketed as green because they are compostable, few consumers realize that PLA will only degrade under industrial composting conditions (high volume, high heat, high moisture). Little research has been published about how well PLA degrades or whether compost containing degraded PLA has an impact on plants. From fall 2011 to spring 2012, a study was performed at the University of Wisconsin- Stevens Point that compared the efficiency of PLA degradation in a controlled industrial composting setting. Treatments of 5, 10, 20 and 30% (by weight of feedstock) of PLA cups were tested against equivalent treatments of paper cups. It was found that in all treatments, higher percentages of PLA (over 99%) were degraded than paper (-19.4, 25.38 and 67.89%, respectively). Following the composting trial, a plant study was performed using the aforementioned compost to determine impacts (if any) of PLA-containing compost on plant growth.