- Plastic bags billed as "biodegradable" or other categories may not break down as quickly as expected, according to a three-year study conducted by the University of Plymouth in the UK. The study exposed five types of bags to the natural environment to examine how their chemical composition and tensile strength changed.
- All bags broke down within nine months when exposed to air. After three years in seawater, the biodegradable, oxo-biodegradable and conventional HDPE bags were able to carry a load of groceries successfully. The compostable bag broke down in water after three months, but survived in soil for 27 months.
- The study calls into question whether biodegradable or oxo-biodegradable products have clear effects in reducing littler or marine pollution because they don't deteriorate any faster than conventional plastic.
These findings come from a paper published in the peer-reviewed scientific journal Environmental Science & Technology (owned by American Chemical Society) that calls out plastic retail bags as "an iconic symbol of our 'throw away' society," citing that "approximately 50% of plastics are discarded after a single-use."
Researchers set out to test degradability claims for five common bag varieties starting in July 2015 in four specific environments (soil, sea, outdoor air and an indoor control sample). In addition to measuring tensile strength, the researches also noted changes in surface appearance and performed molecular analysis to compare rates of degradation.
As might be expected, the assorted bags demonstrated varying rates of deterioration and functionality. While the bags exposed to open air did not deteriorate completely, they were so brittle they could not be tested for strength. The compostable bag that survived 27 months also was not weight-bearing. In addition to surviving three years in the ocean, the biodegradable, oxo-biodegradable and conventional bags placed in soil were also still able to hold about five pounds of weight without compromising structural competency.
Based on these results, researchers recommended terms for describing product degradation be explicitly defined with labels that define intended end-of-life destinations and timeframes by which a claim of decomposition would occur. Only then, as the study team states, can we achieve the "maximum benefit from materials with enhanced rates of degradability."
This work is the latest in a series of news items questioning the role of single-use plastic bags, given the burden they can place on consumers, haulers and processors for their ultimate disposal. The pervasiveness of plastic bags, in combination with their renowned ability to decompose slowly, has spurred research into alternative products and calls for innovative ideas to combat the issue. Other recent research by Oregon's Department of Environmental Quality, which questioned whether products with labels such as "compostable" and "biobased" always had positive environmental outcomes, found that was not always the case.
This points to the value of continuing study into creating a circular economy system where product packaging is aligned with infrastructure capabilities for processing and disposal, more so than manufacturers adjusting to regulatory trends.