Plastic bags, the more sustainable choice? Break it down please...
May 28, 2019 11:35 AM   Subscribe

Like many municipalities, my town and state are both in the process of trying to pass a ban on single-use plastic bags. Opposers of the ban keep putting forward a handful of life cycle analysis studies of paper vs. plastic vs. cloth reusable bags that find that plastic bags had the least impact on the environment. While I understand the complexities of LCA study and recognize these are mostly government studies and not likely plastic-lobby bias, my strong feeling is that when all forms of impact are considered, plastic is still a net negative. I want to be able to point out the limitations of these studies. What do they miss or exclude?

One of the main things that bothers me is that readers of these studies (or more likely the articles about them) read a line like "you have to reuse a tote bag 200 times to achieve any improvement over plastic bags!" ...which, to me, is not a huge deal, given that most Americans use well more than 200 plastic bags a year (10-15 average for each grocery store run).

Can you help me find succinct, scientifically accurate responses that show that these studies might not be the sole determinant of what we should allow to enter the waste stream?

And though I appreciate hearing about personal experiences, I am looking for contextualization for these studies that deal directly with their findings. Anecdotes will be less useful for these purposes. (If I had a dollar for everyone crowing on Facebook about how people reuse their plastic bags to pick up dog poop, well, I'd have enough to buy them all a year's supply of biodegradable bags designed for that purpose instead of subsidizing them at the expense of our shared environment so they can get them for free).

posted by Miko to Science & Nature (30 answers total) 6 users marked this as a favorite
I don't have science for you, but I will say that my reusable bag holds as much as 3 grocery plastic bags.

Also: continued reliance on this old technology -- plastic grocery bags -- inhibits innovation. That will sound great, and it's true.

The trivializing of counterarguments is a huge deal, and I hope you, or someone, addresses that directly.
posted by amtho at 11:44 AM on May 28, 2019 [3 favorites]

I think many of these studies assume that people are going out and buying brand new canvas (or whatever) totebags to replace their plastic bags, which to me invalidates a big part of the argument. Who doesn't already have a handful of reusable totes around their house? Or if you don't, you can find them at a thrift store for $1. So the cost/value assumption to me is wrong - there wouldn't actually need to be a lot of reusable bags produced in order for people to switch from plastic, making the net impact of cloth over plastic much more equitable.
posted by peanut_mcgillicuty at 11:49 AM on May 28, 2019 [7 favorites]

There are also a lot of options for reusable bags that are not cotton. Some of which are recycled products. A person can also use a backpack or a purse or just carry a small item like a soda or a candy bar without a plastic bag.

Furthermore, many stores have adhesive plastic straps that function as handles for bulkier items like large packages of diapers.

The idea that every plastic bag will be replaced by a cloth bag is short sighted.

As for the science of how long/many times a canvas bag must be reused, are these people operating on the assumption that the bag gets washed between each use? (Which, no, not in my world.) Is that going into the water calculation? If so, are they pretending that that load of laundry contains only that bag and not a lot of jeans or towels that would otherwise be getting washed?
posted by bilabial at 11:57 AM on May 28, 2019 [5 favorites]

Reusable bags don't get mistaken for jellyfish & eaten by turtles killing them if they eat enough of them. A study in 2015 estimated that 52% of sea turtles had eaten plastic bags.

Also bags do not have to be made out of plastic making all their arguments about number of uses invalid. There are hemp, cotton, burlap, & string bags as well as cane baskets for a start, all of which will biodegrade & don't use petroleum products. Most of the tote bags sold in supermarkets around here are made from recycled plastic, actually removing waste from the trash stream where it is reused.
posted by wwax at 12:00 PM on May 28, 2019 [8 favorites]

Every study I've seen looks only at the environmental cost of producing bags, not the disposal cost or the litter. Thin-film plastic is a huge recycling headache.

I seldom wash the bags, most of my groceries are packaged and pretty clean. Somebody in a similar discussion worried that the conveyor belt at the grocery must be filthy, but they do clean them regularly, and I have other worries. If the chicken package is leaking, I'd wash the bag, or if it is clearly grotty.

All of my re-usable grocery bags are from thrift shops, and I am now fussy about which ones I like. I keep a couple nylon ones in my daily carry handbag, and sturdy ones in the car.

Most nearby towns (not mine, but I usually shop in a nearby town) have banned free single-use plastic store bags. This leads to good discussion and ideally to better habits.
posted by theora55 at 12:03 PM on May 28, 2019 [4 favorites]

One factor I've always thought was interesting is the reuse of the plastic bags. I know in my house we reuse all plastic bags at least once. So really, take whatever "you'd have to reuse the reusable bag at least 400 times to equate the plastic used compared to the plastic" and double it (800).

Second, I frequently use those plastic bags as an alternative for garbage bags. So, if I was going to use a garbage bag anyway, the plastic bag is virtually "free".

Last, many people think that those reusable bags don't get thrown away. I worked in marketing at trade shows, and they are a common giveaway item, and I know people that have 30-50 of them. Then, they downsize and end up donating/destroying most of the free bags they got. It's kind of like the problem where drug companies are sending more opietes to a city than the population could possibly use - how many bags are being produced compared to the consumption of bags? The purchasing power of the reusable bags is usually as marketing/advertising, whereas grocery stores use every plastic bag they buy. So I think there's a lot more reusable bags that never get a single use outside of a trade show. I've definitely seen pallets of reusable bags just thrown in garbage. Or screen printed incorrectly and landfilled.

I think the question we should be asking is: How many uses do plastic bags get on average? How many uses do reusable bags get on average? Is the total plastic/use more, or less, for either item? Are there other waste factors involved? Which can landfills handle better?

I'm a fan of zero waste. But neither solution is zero waste.
posted by bbqturtle at 12:03 PM on May 28, 2019 [8 favorites]

Reusing bags requires people to remember to bring them. I work as a cashier someplace without a ban, and a good number of the regular customers often vocalize how they wish they'd remembered to bring reusable bags--but they don't. I've also lived in an area with a plastic bag ban, and some stores just sell thicker "reusable" plastic bags for maybe 15-25 cents that might not last 200 times or cost enough to meaningfully dissuade people from just buying them over and over again.

I'm very much in favor of cutting down on plastic bag use, but the human element is complicated.
posted by needs more cowbell at 12:07 PM on May 28, 2019 [3 favorites]

I find that those soft non-woven plastic material bags start falling apart after a year or two, the crunchy-coated plastic reusable bags last longer but are horrible to use and store, while canvas bags are seldom washed and last decades. I'm still using ones I bought in the early '90s.
posted by fimbulvetr at 12:09 PM on May 28, 2019

This Planet Money episode might have some good information -
posted by something_witty at 12:16 PM on May 28, 2019 [1 favorite]

[Couple comments deleted - no harm no foul, but OP isn't looking for individual reports about how we use plastic bags, but for scientific responses/contextualization for these specific studies.]
posted by LobsterMitten (staff) at 12:29 PM on May 28, 2019 [4 favorites]

Reusing bags requires people to remember to bring them. I work as a cashier someplace without a ban, and a good number of the regular customers often vocalize how they wish they'd remembered to bring reusable bags--but they don't.

And until there is a ban or a significant cost for all plastig and paper bags they won't have an incentive to form that habit either. But as with any habit, it doesn't take long to learn to remember to throw a few reusable shopping bags into your handbag or car. I live in a country where there is no such thing as free bags in supermarkets. You pay for all bags including paper. When I moved here, it only took about 10 expensive paper bags, that are clumsy to fold and carry around for re-use before I learned to remember.

I now have a smallish bag that folds extremely small and lives in my handbag. It is too small for a large shopping trip and may not be intended to last a lifetime. But 9 times out of 10 I only pick up a few bits for dinner on the way home from work and it is plenty big enough for that.

If I do a large shop I actually go down a mental checklist before I leave the house. This includes working out if I have enough large bags, if I remembered the reusable produce bags, if I need my cooler, if I need to bag any recycling and swing by the recycling facility en route to the shops etc.

As a point on the longevity of reusable bags - I have a small cotton bag that is at least 30 years old now. Was it in constant use over that time, no. Will it have been used at least 200 times before it goes to bag heaven, absolutely.
posted by koahiatamadl at 12:39 PM on May 28, 2019 [4 favorites]

Yes, thanks for the mod note. I am looking for holes/omissions in the methodology of these studies, not personal behaviors. I am also looking for ways to push back against these studies, not ways to support them. A few "best answers" marked for comments that have provided some perspective on the study framing. Thanks.
posted by Miko at 12:55 PM on May 28, 2019

I'm sorry I don't have actual articles to link to, but I definitely think the road you want to go down to research this is the fallacious premise of "...plastic grocery bags, which have the smallest carbon footprint for a single use" glossed over in the Planet Money piece.

1) Not every plastic bag is being replaced by a reuseable tote,
2) it's not noted how many plastic bags are being used in a "typical" store trip (think bag capacity, double-bagging, separate bags for food and non-food items, bags for single purchases) and
3) the environmental cost they are factoring in for canvas totes is simply not clear in these articles (are they assuming every canvas bag is being washed each use?). bilabial points to this and some other related issues above.

I think critiquing the pro-plastic bag articles is as valid as trying to find anti-plastic bag articles.
posted by queensissy at 12:57 PM on May 28, 2019 [2 favorites]

I go grocery shopping about once a week and even the flimsiest cloth bags I've had have lasted at least 4 years. Doing the math, that's over 200 shopping trips. My family have had some of the same canvas ones for decades. Even if it takes 131 uses to be more environmentally sound, I'm way, way past that point on all the bags I have.
posted by Zalzidrax at 1:02 PM on May 28, 2019 [1 favorite]

If not a ban, charging for the bags can help. I think the biggest issue is considering the effect on the environment as an externality that you don’t have to pay for. The charge for plastic bags could be used for XYZ. It helps with the push bag that “i need them for ABC!” Ok, you can have them for ANC but ya gotta pay for it.
posted by raccoon409 at 1:25 PM on May 28, 2019

Yeah, I aways smdh when I read these stats - I must be an *extreme* outlier, because I have carried/used (nearly daily) a small, foldable, reusable bag for 30 years - it's got a hole in one corner of the pocket it folds into, but is otherwise solid. I also have a canvas tote I've used less religiously for nearly 40 years - I think the math works on both of these.
Something in the Planet Money report gave me pause - when 'free' grocery store bags stop being free, sales of (heavier, so they use more plastic) trash bags go way up!
posted by dbmcd at 1:28 PM on May 28, 2019 [2 favorites]

There are probably technical bases for critique of these articles (e.g., boiling down all post-use environmental issues to one number must require some pretty big assumptions), but they're really nothing anyone should struggle with seeing the limitations of?

The science shows that plastic shopping bags have a much lower carbon footprint and global warming potential than paper and reusables, if the reusables are not re-used multiple times.

I mean, honestly, just look at that sentence (from one of the articles linked from your link)! Yes, if you assume that people do not take advantage of the very feature which would make it superior, it won't be superior.

The same article says that LDPE bags would need to be used all of *four* times to match the real use case of the HDPE bag. Nonwoven PP bags, *eleven*. I'm not the most organized person, but I've had the same Tom Bihn grocery bag (which I think counts as an LDPE bag, as it's woven) for four-ish years. If you make a weekly grocery run, that's all of three months' use.

The most "expensive" one is cotton bags. Even there, there's an obvious caveat: a cotton bag can carry heavier items without double-bagging (and doubling the cost).
posted by praemunire at 1:39 PM on May 28, 2019 [4 favorites]

As I've understood it, the problem with plastic has always been what happens to it after it's done being used, not what goes into creating it.

Single use plastic bags are so flimsy and lightweight they blow away and pollute the environment without people littering deliberately. Products with corners easily tear them. And because they're given away for free, lots of people think nothing of receiving a bunch of new bags every time they go shopping and then just tossing them out.

Last, many people think that those reusable bags don't get thrown away. I worked in marketing at trade shows, and they are a common giveaway item, and I know people that have 30-50 of them. Then, they downsize and end up donating/destroying most of the free bags they got.

Yes, this is an important point. Just like nearly every other product, way more are produced than anyone needs. Same goes for reusable water bottles and travel mugs. That's our society for you. Regulating promotional items destined for the landfill doesn't seem to be a popular issue yet.
posted by wondermouse at 2:06 PM on May 28, 2019 [3 favorites]

I heard a piece about this on NPR the other day (and perhaps they're citing the studies you mention), but it seems that the impact of bans is really not clearly a net positive. One of the issues is that people often reuse disposable plastic bags (eg for dog poop, or to line trash cans). In the story I heard, it seems that purchases of plastic garbage bags went up dramatically (like > 60%) in places where bag bans were instituted (this was specific to California, I believe). Plastic garbage bags are made of thicker (ie higher environmental impact) plastic than grocery bags, so this is not a good tradeoff.

Here's a link to the NPR story: It doesn't have links to the studies, but it does mention the name of the economist who analyzed the data (Rebecca Taylor), so you could probably find more info by googling her.
posted by number9dream at 2:08 PM on May 28, 2019 [2 favorites]

I've been poking around in these studies myself and a few things I might consider.

This PDF from the American Chemistry Council about plastics and recycling talks about how much HEAVIER non-plastic solid waste is as a way of explaining that it's worse for the environment. However it neglects to mention that this is more of a thing for single-stream solid waste and in many places (notably places with a bottle bill and good scrap recycling) a lot of this stuff doesn't wind up in the main waste stream at all. Glass and metal is heavier than plastic, true. Glass and metal have other, better and environmentally "cleaner" recycling options than plastic, also true.

I also don't see a lot of look at the externalities here. So while the plastics people offer a lot of good studies that can give you numbers on stuff like recycling and paper vs plastic you'll notice that all they have to say about marine debris is that they're "trying to help." Because marine debris plastics are a mess that go past the waste stream (or, rather, out the other side) that they take little to no responsibility for.

Lastly I was hoping I could find something about just how messy the plastic bag production line is, but some cursory Googling didn't take me there. I think you could argue, however, that metal and glass production are, due to weight and recyclability, more likely to be local and somewhere where US environmental regulations matter. The same is not true for plastic bag production in other countries which we should care about as much as our own.
posted by jessamyn at 2:09 PM on May 28, 2019 [2 favorites]

So I just just skimmed the Danish study, and there's a few things to be aware of.

Their baseline bag is the sort of thick plastic bag that Scandinavian grocery stores use. American style plastic grocery bags (LDPE Simple in the study) are smaller, and are counted as 0.5 bag equivalents. They also assume you'll use it as a trash bag, and in Sweden is totally what I used to do. The thicker bags could be re-used a few times and then used for kitchen trash, since the trash cans are tiny there. Here in the U.S. I get way too many grocery bags to do that, and they wouldn't work for kitchen trash can sizes anyway.

So in terms of carbon footprint, they calculate a non-woven polyester sort of re-usable bag (the kind I happen to use) needs to be re-used three times to achieve the footprint of an LDPE Simple bag. For conventionally grown cotton, 26 times, and for organic cotton 75 times.

Where things get more complicated is the second column, the equivalency for "All Indicators". They've tried to compute the cost per bag in 14 other categories of environment indicator, such as air pollution, ozone depletion, water pollution from agricultural pollutants (eutrophication) and total water usage. The result for All Indicators is the maximum of the equivalents in all of these categories. For cotton bags, they note this is ozone depletion, followed by eutrophication and fresh water usage. So since cotton production causes 20,000 times more ozone depletion than making a thin plastic bag, they put 20,000 in that column. Regardless of whether cotton farming is a major concern for the ozone in absolute terms.

So if you re-use your cotton bags only 100 times, you're coming out ahead in carbon footprint, but doing worse in terms of water usage in cotton growing countries like Uzbekistan (think the Aral Sea) or India. At 1000 re-uses maybe cotton bags is better on all indicators other than ozone, water usage and eutrophication. Their method doesn't let us evaluate that tradeoff. It's just telling us the number of re-uses until a bag type is better on every environmental indicator they can think of, which isn't that useful a measure.

So I think this study is only really useful for the climate change equivalence numbers, which are actually smaller than the what some others have claimed. Also none of their environmental indicators seem to include the effect of ocean-borne plastic on wildlife, which is one of the biggest concerns people have with it.
posted by serathen at 2:29 PM on May 28, 2019 [6 favorites]

I think a lot of the analyses—especially the ones that come out pro-plastic—also assume that for each plastic bag that's not used, a tote will be used instead.

And that's just... not consistent with reality. When bags cost money or aren't provided, people carry out a lot of goods unbagged. Stores stop using bags as a de facto anti-shoplifting indicator. People stack or nest purchases so they can carry them without bags. Lots of solutions.

So I would be wary of studies that assume that a bag = a bag, without taking into account behavioral changes. And, presumably because of the difficulty of studying that, most lifecycle analyses don't really go there.

That might or might not be something you want to argue in public, though, because those "behavioral changes" are, to some people, a sign of the coming Apocalypse, an obvious harbringer of the decline of civilization, an insult to American values, and a personal affront to their God-given right to carry out every gallon of milk in its own individual disposable bag. It starts to cut right to the heart of the issue, in other words.
posted by Kadin2048 at 2:36 PM on May 28, 2019 [4 favorites]

Hi, I was looking at some point for something similarish but about plastic bags vs textile totes. Here are some of the things I have bookmarked:

Macro and micro plastics sorb and desorb metals and act as a point source of trace metals to coastal ecosystems

Great Pacific Garbage Patch

From the above article (Nat Geo):

While many different types of trash enter the ocean, plastics make up the majority of marine debris for two reasons. First, plastic’s durability, low cost, and malleability mean that it’s being used in more and more consumer and industrial products. Second, plastic goods do not biodegrade but instead break down into smaller pieces.

In the ocean, the sun breaks down these plastics into tinier and tinier pieces, a process known as photodegradation. Scientists have collected up to 750,000 bits of microplastic in a single square kilometer of the Great Pacific Garbage Patch—that’s about 1.9 million bits per square mile. Most of this debris comes from plastic bags, bottle caps, plastic water bottles, and Styrofoam cups.

Here's more about microplastics.

Here something re. textile decomposition (also not as straightforward as i had hoped):

Biodegradation Behavior of Textiles Impregnated with Ag and TiO2 Nanoparticles in Soil

The one linked above has a good biblio list on the topic.

Here's something on biodegradable plastics - so far not a resounding success.

Somewhat anecdotally - I grew up with bags made of wool/ cotton (a bit like these); they had belonged to my grandparents, and a couple of them still exist, more than 50 years old now and heavily used for heavy carrying etc. Producing them was minimal in terms of environmental cost - other than what the sheep cost. Disposing of them via composting is easy. We never, ever used anything other than these bags when I was a kid, and neither did my dad & family. I was a convert to plastic bags because you can be a much more spontaneous shopper with plastics, until I figured that I probably used more than 1,000 bags in 5 years.

So now I'm searching for a foldable cotton bag.
posted by doggod at 2:46 PM on May 28, 2019 [2 favorites]

As someone who has performed a bunch of life cycle studies, and had to review many more, here's some of things that I would look for. You'll probably need access to the primary study for most of these.

1) Local vs "average" disposal impacts: the average impact of recycling or incinerating a plastic bag across the US or world is likely different from the specific recycling plant/dump/body of water that performs the function for your town.

2) As above, but for production impacts. Less likely to matter in the case of plastic where production which will likely be completely generic, but possibly a big player in the alternative case. As a less absurd example than it might seem: imagine if the average cotton bag factory is coal powered and dumps chemicals in a river, but you happen to have a local organic weaving co-op that makes enough for your city and is the most likely source of the alternative bags. Or vice versa, but assumes your plastic bags are made in the one clean factory in Norway, when in reality they're from some average factory nowhere near as efficiently run.

3) Assumptions based on the status-quo, i.e. assuming that because only x% of people reuse any bags now, only X+5% will reuse cotton bags, instead preferring to throw them in a river on their way home or something. Whereas if these things cost $5 each that's not going to happen (which sadly may be a losing argument for you, "these things are so costly you'll be forced to reuse them").

4) As many have said above, ignoring or handwaving-away effects that are difficult to quantify or compare. E.g. on a strict CO2 equivalent-emissions basis, maybe cotton bags really are worse than plastic. But they don't choke dolphins. And maybe they can be produced locally, creating jobs. How many grams of CO2 is that worth? Things like this are always going to involve some kind of value judgement, there is no strictly-objective overall criteria that can choose a best option for you.
posted by Jobst at 2:51 PM on May 28, 2019 [2 favorites]

Ha, I hope this is not too besinde the point, but this bag is less likely to end up in an ocean. I wish they included more env.-relevant info.
posted by doggod at 2:55 PM on May 28, 2019

Another problem with the Danish study: they seem not have treated conventional and organic cotton the same in terms of eutrophication, which is a direct result of over-application of fertilizers! If I take the number for organic, multiply by 0.7, which is their scaling factor for yield difference, then divide by 2 (the organic cotton bag they used was on the small side, so they counted it as half a bag), then I get the same result for both. I don't seem them mentioning this in their results which seems sloppy.

So yeah, large scale environmental impacts are hard to do science about. Despite their conclusions being reported matter-of-factly by journalists, there are a lot of caveats and limitations involved. I still think that better than not having the science at all, but care needs to be taken when using these results for policy decisions.
posted by serathen at 3:03 PM on May 28, 2019

The problem with these studies - generally funded by grocery or packaging lobbies - is that they never, ever account for two things (that completely destroy their pissant arguments):

1. Where the disposable plastic bags end up - which is all over the place. Here in Aus, plastic bags alone were over 16% of rubbish collected this is often a lot higher in beach and other environments. Garbage bags - as mentioned above - unsurprisingly end up in landfill, which from a waste management perspective, is actually the system working as intended and not so bad (I used to work for Australia's waste management peak body. Although here's a pro tip, line your small household bins with newspaper and just tip them into your outside trash bins directly - nobody really needs garbage bags).

2. The volume of cheap plastic shopping bags - which dwarf every other kind of plastic bag by more than an order of magnitude. People use more disposable plastic bags, way more; they litter with them waaaaaay more.
posted by smoke at 4:05 PM on May 28, 2019 [1 favorite]

Plastic bag bans are very effective at reducing plastic in the ocean- as one example, in San Jose (prior to CA's statewide ban), a plastic bag ban and a fee on paper bags increased reusable use from 4% to 62% and reduced plastic bag pollution in storm drains 89%. In Alameda County, plastic bag pollution in storm drains dropped 44%.

The Danish study notes that a polyester bag (like Baggu) only has to be reused twice to have the same climate impact as a (Danish) plastic bag, and 35x to have the same overall environmental impact. It does not look at the impact of plastic bags on marine life (it also assumes that bags that aren't reused will be recycled or incinerated, whereas in the U.S. they're probably more likely to go to a landfill and possibly blow away into a waterway on the way there).
posted by pinochiette at 7:45 PM on May 28, 2019 [3 favorites]

To put an analytical framework around some of the things mentioned by others, you are talking about a multiple-objective problem. Such things tend to have complicated answers. The bag protocol that uses the least energy may/may not be the protocol that produces the fewest global warming gasses. The bag that seems best looking at production may/may not be the bag that looks best looking at the post-consumer effects. It's not at all clear that any particular study even considered the effects that you are most interested in.

For my money, any product that has very limited useful lifetime but which takes a long time to disappear is a problem. When the beaches of Polynesia are littered with canvas totes, maybe I'll change my mind.
posted by SemiSalt at 3:39 PM on May 29, 2019 [2 favorites]

This was really helpful, so thanks for the boost to my own science literacy and my community's.
posted by Miko at 2:11 PM on June 27, 2019

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