A highly publicized study sends a misleading message about bioplastics, according to a researcher at Michigan State University, because of several inaccurate assumptions, what the study omits from its life-cycle analysis, and the research team's decision to mix potential impacts and create a weighted average.
The study, from the University of Pittsburgh, concluded that bioplastics are environmentally more taxing to produce than conventional plastics, in part because of the farming and energy-intense chemical processing needed to produce them.
“It simply is not credible to come up with one number for a bioplastic evaluation,” by giving each environmental factor an equal weight and adding them together to come up with “an average number,” said Bruce Dale, Michigan State professor of chemical engineering and associate director of bio-based technologies in East Lansing.
Mixing different impacts of the materials on the environment and public health goes against recommendations for life-cycle analysis from the International Standards Organization, Dale said Nov. 24 by phone.
Specifically, ISO 14044 says that “weighting … shall not be used in any comparison to be disclosed to the public.”
“The conclusions they made are misleading in the sense that you can't actually even make the comparisons they make,” Dale said. “That's like mixing impacts for apples, oranges, pears and bananas. I don't think the study tells us much about which plastics are better for the environment.”
It's impossible to see if their conclusions stand up without analyzing whether those conclusions change when the different factors are weighted differently, he said.
Dale said the research team, led by University of Pittsburgh undergraduate student Michaelangelo Tabone, assumed incorrectly that data for polylactic acid could also be used for polyhydroxyalkanoate, and it excluded the actual use and disposable aspects of bioplastics from its analysis.
“The scope of each life-cycle assessment was 'cradle-to-gate,' [but] including only the impacts resulting from the production of each plastic and not the use or disposal,” the authors said in discussing their report. “The LCAs in this study have a limited scope. To be comprehensive, the use and end of life should be included in future studies. The exclusion of disposal scenarios affects conclusions regarding biodegradable polymers and commonly recycled plastics.”
The research team admitted that it used “the average impact from the PLA scenarios … as substitutes for PHA's impacts on human health, respiratory effects, ozone depletion, and ecotoxicity [because] no life-cycle inventory data were available for PHA within the ecoinvent database.”
“That was one more arbitrary illogical thing they did. They decided not to study the use and disposal aspects,” Dale said. “Another huge flaw is that there wasn't any data for PHAs for them to make estimates for the impact categories, so they assumed that PLA data was appropriate for PHA.”
In addition, the research only looked at specific plastics resins, and not products. That is, researchers performed an LCA on each polymer's pre-production, looking at the environmental and health effects of the use of energy, raw materials, and chemicals to create 1 ounce of plastic pellets. Then they checked each plastic in its finished form against principles of green design, including biodegradability, energy efficiency, wastefulness and toxicity.
“They didn't compare any type of products,” said Steve Davies, global marketing director for NatureWorks LLC in Minnetonka, Minn., which makes PLA. “They just compared the resins and not specific products. It didn't look at how a bioplastics product is used and how it is disposed.”
Davies said a second area where the study is “causing confusion and could be damaging” to bioplastics is that there is “no meaningful way to compare 1 ounce of pellets prior to molding” because it doesn't take into account the density, thickness or stiffness of the final product.
“You need a comparison based on the functional performance of the product, not just a bucketful of chemicals,” he said.
He also criticized the combination of different environmental and health-impact factors to reach “a single, overarching conclusion. They weighed them all equally and just added them up. ISO methodology, in IS0 14044, says you don't do that.”
The research assessed 10 different impact categories: acidification, carcinogenic human health hazards, ecotoxicity, eutrophication, global warming potential, noncarcinogenic human health hazards, ozone depletion, respiratory effects, smog, and non-renewable energy use.
Specifically, the research report and news release from the University of Pittsburgh said conventional plastics are “environmentally less taxing to produce,” that “biopolymers are among the more prolific polluters on the path to production” and that bioplastics are “dirtier to produce” than petroleum-derived plastics because “the farming and energy-intense chemical processing needed to produce [bioplastics] can devour energy and dump fertilizers and pesticides into the environment.”
The University of Pittsburgh study, conducted with support from the National Science Foundation and released Oct. 21, will be published in the environmental journal Environmental Science and Technology.