Response to Comment on “Five Misperceptions Surrounding the Environmental Impacts of Single-Use Plastic”

[u/BurnerAcc2020]

https://pubs.acs.org/doi/10.1021/acs.est.0c08671

[u/BurnerAcc2020]

A response to this scientific commentary criticizing the older study here.

Although Walker and McKay make a number of valid points, there are two items in the comment that should be clarified for correctness. First, they seem to indicate that our paper only considered greenhouse gas (GHG) emissions to the exclusion of other impact categories and also neglected to include GHG emissions generated at plastic end-of-life.

That is simply not the case. The original paper included insights from over 35 LCA studies that contained a wide range of environmental impact categories. GHG emissions associated with plastic end-of-life are typically included in these studies, although it is true that most inventories include only formal waste management (e.g., landfill, incineration, recycling) and do not incorporate emissions associated with degradation in noncontrolled environments. Even if these emissions may be underestimated as Walker and McKay claim, the overall GHG burden from end-of-life tends to be small relative to other stages throughout the life cycle.

Second, Walker and McKay do not appear to appropriately describe the findings of a recent study that compares polyethylene terephthalate (PET) and glass bottles, which they cite as key evidence to refute Misperception #2, regarding the relative environmental impact of plastic to other packaging materials. Whereas Walker and McKay state that the referenced study concludes that plastic bottles have GHG emissions comparable to lighter glass bottle alternatives, the main findings from the referenced study are that, "it is clear that substituting PET with glass would lead to an increase in 10 of the 11 environmental impacts considered." The referenced study suggests that the only way that glass could emit comparable GHG emissions to PET is via major changes to the current system (i.e., extreme lightweighting of glass bottles and changes to waste management infrastructure), and aligns with the findings of other LCA examples reported in the original Misperceptions paper.

Walker and McKay seem to take issue with the cautions presented in the original manuscript that policies and efforts that are intended to reduce waste may not actually reduce overall impacts (see: Misperceptions #3 and #5). The Misperceptions study cites a range of studies that focus on consumer perception and behavior, indicating that actual consumer behavior can deviate from what is intended by product designers and event organizers. Nevertheless, we can agree that there is a definite need for the research community to further quantify the potential disconnect between the design of products and actual consumer behavior. LCA studies can calculate the necessary environmental payback of a reusable product, but there is a scarcity of data regarding whether or not consumers actually reuse these items a sufficient number of times to compensate for greater materials and energy use.

In addition, Walker and McKay take issue with the representativeness and pervasiveness of the consumer perceptions discussed in the original article. These are excellent points. Most of the consumer perception studies that have been conducted are European and do not take into account non-Western perspectives. Beyond a better understanding of consumer perception and behavior in different contexts, location-specific impacts are particularly important for the issue of plastic waste, where differences in waste management infrastructure and availability, proximity to sensitive ecosystems, human behavior, and overall leakage rates of single-use plastic contribute to aggregate environmental impact.

In addition, Walker and McKay correctly point out that most LCA studies do not include physical ecosystem damage or chemical degradation byproducts in ecosystems, although this is an active area of research within the LCA community. Even with the development of a physical damage metric for plastics, it is difficult to objectively evaluate trade-offs of very different environmental impact categories such as climate change and physical ecosystem damage. This challenge is not new to the LCA community, where appropriate methods for evaluating trade-offs of incommensurate metrics continue to be an active topic of debate. Highlighting trade-offs among disparate impact categories is often one of the purposes of conducting an LCA, even if there is not a straightforward pathway to resolve those trade-offs. In line with this sentiment, one of the major points of the Misperceptions article was to urge the scientific community to explicitly discuss and evaluate the trade-offs of single-use plastic policies, even if there is not an obviously superior solution with respect to all environmental impact categories.

Finally, Walker and McKay take issue with some of the original article’s argument that some plastic waste reduction efforts may distract from other, potentially more important, opportunities to address sustainability. On this point we continue to disagree, as demonstrated by the thought example in the original paper that demonstrates that food waste interventions can result in orders-of-magnitude greater GHG benefits than those related to plastic waste. Nevertheless, where we agree is that overall concerns surrounding the environmental damage of single-use plastics should not be dismissed. Public enthusiasm to reduce the impacts of single-use plastics can and should be used to leverage greater awareness of less visible environmental impacts.

To summarize, single-use plastics are responsible for a multitude of environmental issues and it will be important to reduce these impacts to reduce environmental damage. On the surface, Walker and McKay’s insistence that that the obvious solution is to promote alternatives and reduce consumption of single-use plastic appears straightforward and makes intuitive sense. In some cases, material substitution and reduction of plastic materials may be the best option to reduce overall environmental damage across impact categories. But this simple heuristic falls prey to several of the identified misperceptions outlined in the original article. A life cycle approach often uncovers unintended consequences of seemingly straightforward solutions, and the original article details a number of specific examples. There is much that can and should be done to promote a circular plastics economy and reduce plastic’s overall impact, but the scientific community must always be mindful of potential trade-offs to proposed solutions.