After exhaustive discussion, I’ve been deputed to inform our readers of Troppo’s plastic bag policy. We’re in favour of single-use plastic bags. In fact, we’re making them compulsory.
I was recently in Book Grocer and was refused a plastic bag, though they were prepared to give me a paper bag which on thinking about it, I’ve always thought was probably worse for the environment because I’d have assumed it was more energy intensive. The two supermarket chains are phasing out free single-use bags and replacing them with paid multi-use bags. Thing is, they’re unlikely to be used often enough to improve the environment. I’ve no problems in them being charged for – nor do I have problems with them being free – but all other interventions, all other preferences to get back to granma’s time with cloth and paper bags, are probably actually bad for the environment. Whodda thunk?
From this British Government “Life cycle assessment of supermarket carrierbags” conducted in 2011.
The paper, LDPE, non-woven PP and cotton bags should be reused at least four, five, 14 and 173 times respectively to ensure that they have lower global warming potential than conventional HDPE carrier bags.
Here’s the rest of it in table form:
Here are the study’s conclusions regarding individual carrier bags:
The following sections outline the results shown in figure 7.1 for each of the bag types considered in this study. The comparisons include the secondary reuse of 40 per cent of lightweight bags (HDPE, HDPE prodegradant and starch-polyester) as bin liners.
8.1.1 Conventional HDPE bag
The conventional HDPE bag had the lowest environmental impacts of the lightweight bags in eight of the nine impact categories. The bag performed well because it was the lightest bag considered. The lifecycle impact of the bag was dictated by raw material extraction and bag production, with the use of Chinese grid electricity significantly affecting the acidification and ecotoxicity of the bag.
8.1.2 HDPE bag with prodegradant additive
The HDPE prodegradant bag had a larger impact than the HDPE bag in all categories considered. Although the bags were very similar, the prodegradant bag weighed slightly more and therefore used more energy during production and distribution.
8.1.3 Starch-polyester bag
The starch-polyester bag had the highest impact in seven of the nine impact categories considered. This was partially due to it weighing approximately twice that of the conventional HDPE bags but also due to the high impacts of raw material production, transport and the generation of methane from landfill.
8.1.4 LDPE bag
The LDPE bag has to be used five times to reduce its GWP to below that of the conventional HPDE bag. When used five times, its impacts were lower in eight of nine of the impact categories. The impact was also substantially lower than the HDPE bag in terms of acidification, aquatic ecotoxicity and photochemical oxidation due to lower shipping distances and the use of grid electricity which is less reliant on coal.
8.1.5 Non-woven PP bag
The non-woven PP bag had to be used fourteen times to reduce its GWP to below that of the conventional bag. With this level of reuse it was also superior to the conventional HDPE bag in five of the nine categories. However, the PP bag was significantly worse than the baseline in terms of terrestrial ecotoxicity due to the emissions associated with use of a heavy fuel oil in an industrial furnace. When recycling was considered global warming potential and abiotic depletion impacts were reduced similar to the HDPE bag.
8.1.6 Paper bag
The paper bag has to be used four or more times to reduce its global warming potential to below that of the conventional HDPE bag, but was significantly worse than the conventional HDPE bag for human toxicity and terrestrial ecotoxicity due to the effect of paper production. However, it is unlikely the paper bag can be regularly reused the required number of times due to its low durability.
8.1.7 Cotton bag
The cotton bag has a greater impact than the conventional HDPE bag in seven of the nine impact categories even when used 173 times (i.e. the number of uses required to reduce the GWP of the cotton bag to that of the conventional HDPE bag with average secondary reuse). The impact was considerably larger in categories such as acidification and aquatic & terrestrial ecotoxicity due to the energy used to produce cotton yarn and the fertilisers used during the growth of the cotton.