By Mike Verespej, Plastics News, a Crain publication
East Lansing, Michigan -- A US researcher has questioned the validity of claims made about bioplastics because of basic faults in a University of Pittsburgh life-cycle study which concluded that bioplastics are environmentally more taxing to produce than conventional plastics.
The highly publicised study sends a misleading message about bioplastics because of what it omitted from their life cycle analysis, says Bruce Dale, professor of chemical engineering and associatedirector of biobased technologies at Michigan State University. It also makes several assumptions that are not accurate, and the decision by the research team to mix potential impacts and create a weighted average is also in error, Dale adds.
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 the materials.
But, Dale says, "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." 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 in a 24 Nov telephone interview.
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," he 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 than others," Dale said.
"It's impossible to see if their conclusions" standing 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 of bioplastics," 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 a LCA on each polymer's preproduction, looking at the environmental and health effects of the use of energy, raw materials, and chemicals to create one 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, which manufactures 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 and that's essential to a life-cycle analysis."
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 one ounce of pellets prior to moulding" 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.
Third, he took umbrage with how the study combined 10 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 nonrenewable energy use.
"The study doesn't tell us much about which plastics were better and they have muddied the waters," Davies said.
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."
"They have made a mess that others now have to clean up," said Michigan State bioplastics professor Dale, based in East Lansing, Mich.
The University of Pittsburgh study, conducted with support from the National Science Foundation and released Oct. 21, is scheduled to published in the environmental journal "Environmental Science and Technology."