In a column on this site, dated 21 August, Lucas Reijnders is of the opinion that presently available bioplastics are more environmentally harmful than the most common fossil-based plastics. He refers to the ‘Pittsburgh Study’, a heavily criticized source with a contestable methodology. On the basis of our own research we reach different conclusions: bioplastics require less energy, and emit less greenhouse gases, although they possibly cause more eutrophication and ozone layer depletion. Moreover, the environmental effect of plastics production from biomass is less than that of biofuel production. Lucas Reijnders’ conclusion is based upon inconclusive evidence.
Lucas Reijnders’ principal source is an article from ‘Environmental Science and Technology’ (Tabone et al., 2010), commonly called the ‘Pittsburgh Study’. From the publication onwards, this study caused much irritation. Criticism concerns both methodology and the data used; consequently, the conclusions cannot be maintained.
Criticism
The most important points of criticism are the following (see a.o. Dale, 2011 en Murphy et al., 2011):
– Use of incorrect data. For PLA and PET, the data used are not up-to-date. For instance, the authors quote a source for PLA resulting in 54 MJ/kg fossil fuel use, whereas according to recent publications this amounts to 42 MJ/kg for PLA from maize (Vink et al.), and to 30.5 MJ/kg for PLA from sugar cane (Groot and Borén, 2010). Data for PET are not in line with recent data, e.g. from PlasticsEurope.
– Irresponsible extrapolations. Because of a lack of data, the Pittsburgh Study assumes PHA data for the categories ‘human health’, ‘respiratory effects’, ‘ozone depletion’, and ‘ecotoxicity’ to be equal to PLA data. For a study which subsequently ranks those effects, such an assumption is clearly not acceptable.
– Methodically incorrect ranking. The study compresses the total environmental effect of each of the polymers to a single value. This is not in agreement with the ISO-directive commonly adhered to in LCA-studies. This study takes the score of the plastic under consideration for each category (human health, ecotoxicity etc.), and subsequently adds these scores. The plastics are only weighed against each other, and not against some external reference. This may cause a category in which environmental effects of all plastics are small, to have a disproportionate weight in the end result. This may have major consequences in the ranking.
We could illustrate our conclusions with more points of criticism, such as found in the publications of Murphy at al. (2011) and van Dale (2011). As a matter of fact, under better scrutiny the study would not have passed peer review.
Lower energy use
From our own work and that of others we conclude that the environmental effect of bioplastics is much more diverse. Major reductions in energy use and greenhouse gas emissions result from substitution of Bio-PE for fossil-based PE (as marketed by Braskem and others), and from substitution of PLA for PET (Bos et al., 2012). And, although not simply exchangeable on a one-to-one basis in most applications, also substitution of PLA for petrochemical PE results in a reduction in energy use and greenhouse gas emissions (Bos et al., 2012). Recently, Chen and Patel (2012) published an exhaustive review of energy use and greenhouse gas emissions from biotechnologically produced bioplastics, compared to their fossil-based counterparts. Of course, for a full-scale picture one should include effects of biomass production on eutrophication and possible land use changes. Weiss et al. (2012) took a critical look at bio-based and fossil-based materials, including the effects on primary energy use, greenhouse gas emissions, eutrophication, acidification, and photochemical ozone formation. According to this meta analysis, bio-based materials cause less primary energy use and greenhouse gas emissions, but possibly more eutrophication and ozone layer depletion. Weiss et al. could not reach general conclusions on acidification and photochemical ozone formation.
Another important overall conclusion is that it is more sustainable to produce bioplastics from biomass, than biofuels (Patel, 2008). We need more research in order to judge all environmental effects of bioplastics; Lucas Reijnders’ conclusion is based upon inconclusive evidence.
Bos, H.L.; Meesters, K.P.H.; Conijn, S.G.; Corré, W.J.; Patel, M.K.: Accounting for the constrained availability of land: a comparison of bio-based ethanol, polyethylene, and PLA with regard to non-renewable energy use and land use. Biofuels, Bioproducts & Biorefining 6 (2012), pp. 146-158
Chen, G.-Q.; Patel, M. K.: Plastics Derived from Biological Sources: Present and Future: A Technical and Environmental Review. Chemical Reviews (Chem. Rev.) 2012, 112, pp. 2082–2099
Dale, B.E.: Comment on “Sustainability Metrics: Life Cycle Assessment and Green Design in Polymers”. Environ. Sci. Technol. 2011, 45, p. 5057
Groot, W.J.; Borén, T.: Life cycle assessment of the manufacture of lactide and PLA biopolymers from sugarcane in Thailand. International Journal of Life Cycle Assessment, Volume 15, Issue 9, November 2010, Pages 970-984
Murphy, R.; Detzel, A.; Guo, M.; Krüger, M.: Comment on “Sustainability Metrics: Life Cycle Assessment and Green Design in Polymers”. Environ. Sci. Technol. 2011, 45, pp.
Patel, M.K.: Understanding bio-economics. European Plastics News, March 2008, pp.28-29
PlasticsEurope: Ecoprofiles of plastics and bulk chemicals. Published by the European association of plastics manufacturers (PlasticsEurope), http://www.plasticseurope.org/plastics-sustainability/eco-profiles.aspx, various years
Tabone, M.; Cregg, J.J.; Beckman, E.J.; Landy, A.E.: Sustainability Metrics: Life Cycle Assessment and Green Design in Polymers. Volume 44, Issue 21, 24 September 2010, pp. 8264-8269
Vink, E.T.H.; Davies, S.; Kolstad, J.J.: The eco-profile for current Ingeo® polylactide production. Industrial Biotechnology, Volume 6, No. 4, August 2010, pp. 212-224
Weiss, M.; Haufe, J.; Carus, M.; Brandao, M.; Bringezu, S.; Hermann, B.; Patel, M.K.: A Review of the Environmental Impacts of Biobased Materials. Journal of Industrial Ecology, Volume 16, Number S1, 2012, page S169-S181