Bag Job

Cherry picking is a econometric sport, and figuring out the cost of things is often not as simple as a bunny might wish.  Brian had a few posts on fluoridation discussing the fact that there are not only pros, but also cons, and coming to the conclusion that on balance, and with care in application, the pros win.  Eli's attention was drawn to the question of are non-reusable or reusable bags better, and if so which sort and on what basis.  This, as Eli said, is not as straightforward as a bunny might wish.

There is an obvious part of the answer, the more times a bag is used, the cheaper it is, but how many more times is a good question and what are the problems with reusing a bag is another.

The last has an interesting answer, if you put meat, fish, and milk products into a bag, you have to worry about bacteria, and some of the bacteria, E. coli, for example can be nasty.  Well, you can wash the bags (something Eli has never done, but might start) and doing so reduces the risk of contamination, but increases the amount of water and electricity used.

So what is a Rabett to do?  Well Google is a friend and a quick search turned up Life Cycle Assessment of Reusable and Single-use Plastic Bags in California by Joseph Greene from Cal State Chico.  Besides his own life cycle analysis, Greene presents the results of several others, which pretty much agree with his, each within their own limits.

The first step is to figure out what bags one is talking about and how to compare them.  On the non-reusable side the running is pretty much made by High Density Polyethylene (HDPE) and paper, on the reusable side we got woven Low Density Polyethylene (LDPE) and non-woven polypropylene (PP) and cotton.  To compare all of these, the general agreement is to look to carrying capacity, in which case you need about 1500 HDPE bags to carry about the same amount as 1000 of the others.  Of course, HDPE, bags being very thin often spill the carrots.

Impact indicator	1500 HDPE single- use bag	1000 Reusab le PP non- woven single- use	1000 Reusable PP non- woven 8 times	1000 Reusable PP non- woven 52 times	1000 Reusable LLDPE bag with 40% PCR single- use	1000 Reusable LLDPE with 40% PCR bag 8 times	1000 Reusable LLDPE with 40% PCR bag 52 times	1000 Paper bag single -use
Non-renewable energy, GJ	763	3736	467	72	2945	368	57	2620
GHG emissions, CO2 eq	0.04	0.262	0.033	0.005	0.182	0.023	0.003	0.08
Solid Waste, kg	7.0	34.3	4.29	0.7	34.1	4.3	0.7	34
Fresh water consumption, gal	58	426	85	216	250	40	57	1000
Mass, g	6	42	42	42	44	44	44	52

The amount of water includes that used in washing and manufacture.

While the number of times a bag is used is the major issue, such things as the amount of recycled materials, the cost of disposal, the cost of transportation,  biodegradeability, litter and the effects on fauna and flora are also significant in any decision to tax or eliminate different types of bags. It turns out that  cotton or canvas bags are not a good choice because of their weight and the energy needed to grow the cotton and make the bags.  HDPE bags can be recycled and, with a bit of luck, used one or two times, in Eli's experience maybe 1.5 (breaks the other .5).

So, on balance, multiple use woven bags made from LDPE with 40% recycled polyethylene are the best choice.