Material Use Comparison
In terms of plastics grocery bags the main difference over the period since 1990 has been the move away from LDPE to the tougher paper-like HDPE or MDPE polymer grades. Apart from permitting further downguaging, the most significant result has been a virtual abandonment of the check-out practice of double bagging, caused originally by inexperience in the use of thin plastic bags and the perception that strength or durability correlates with feel or thickness. So, for example, the original Franklin study compensates for this extra use by building in a factor of 1.5 or 2.0 when assessing plastic bag usage per trip. To that extent the weight, energy use, emissions quoted were higher for plastics bags than would be the case for a simple 1:1 comparison. This adjustment was not made in the Winnipeg study on the grounds that supermarket packers frequently double bagged orders even in paper bags. The Winnipeg researchers did however compensate for differences in the volumes of the individual grocery bags used.
They concluded: ”The studies are generally mutually supportive, and validate the general conclusion that for one trip bags, a paper grocery bag unit is about twice as energy intensive as a plastic bag unit”. Similarly the Stage One graphs and tables illustrate that the weight of materials used for paper bags is about four times greater than the weight of materials used for plastic bags. This difference is accentuated further when comparisons are made between the finished bags. The Winnipeg report concludes that “A tonne of plastic one trip bags contains about 105,500 bags. A tonne of paper one-trip bags contains about 18,000 bags i.e. roughly six times heavier per bag. The Franklin study also found that paper bags occupy roughly ten times more space than plastics bags – as with weight, a vital factor in storage, transportation, waste collection and landfill.
Energy Intensity (Energy Content)
Plastics films and plastics feedstock are of course produced from natural gas or crude oil. It is estimated that the whole field of plastics films globally uses about 2 per cent of the oil barrel (cf. transport, heating, power generation etc. using about 85 per cent). Natural gas has a higher energy content per tonne but has differing energy processing requirements. Plastics grocery bags produced from either source material contain a high proportion of this latent energy and have a calorific value nearly twice that of coal. This energy can be recovered via re-use, material recycling or when used to displace oil imports or other fossil fuels via waste to energy systems, as so widely practised throughout the EU.
Any comparison made between paper and plastics bags thus demonstrates the higher energy content per tonne of plastic bags but because plastics bags are so much lighter the energy content per plastic bag is roughly half the energy content of the equivalent paper bag.
Fossil Fuel Use (Energy used in Manufacture)
The comparisons made between the individual reports are clearly not wholly consistent and the Winnipeg researchers found this variability to be due to the power sources assumed i.e. nuclear, hydro, wood waste, fossil fuels. With two of the original studies the energy use between paper and plastics materials is roughly equivalent and in the other two studies the fossil fuel energy use in the manufacture of paper sacks is lower.
Atmospheric and Waterborne Emission
The data on emissions is clearly shown on pages 13 and 14. As the Winnipeg report states there are some statistically significant differences quoted in the original studies but the comparison “validates the conclusion that plastic one trip bags have a lower environmental impact than paper one trip bags”.
Re-use and Recycling
The Winnipeg report makes some very interesting comparisons of energy use for bags that are re-used or recycled – largely based on data from the Franklin study, as the most recent. They also compare both with the possible adoption of a “permanent” nylon bag on the basis of energy per trip.
The comparison well demonstrates the energy saving value of re-use even when compared to high rates of recycling, although it may be questioned whether allowing for 100 or 200 shopping trips per nylon permanent bag is realistic. It also provides excellent environmental justification for the very high level of re-use established by the NOP survey of single-trip plastic carriers.
For obvious reasons the Winnipeg report makes no comment on such issues as convenience, hygiene, check-out efficiency, shoplifting and other aspects that may concern the retailer or the consumer.
For ease of reference a summary of the Winnipeg Project data comparisons is attached.
More recently we have seen great progress in the development of agricultural crop based polymers and there seems little doubt that new and renewable carbon sources of this type will eventually provide a further extension to the range of plastics films commercially available.
Winnipeg Packaging Project - Summary
The Use/Re-Use of Plastic Carrier Bags
As the following extract from a DETR press release shows, more than 4 out of every 5 people interviewed choose to reuse their plastic grocery bags.
Extract from the Press Release issued by the Department of the Environment, Transport and the Regions on 18 October 2000
“According to research out today from the Department of Environment, Transport and the Region’s “Are you doing your bit” campaign, the supermarket carrier bag is the bag that most people would choose to be seen using again and again in public for everything from carrying their gym kit to a stroll down the High Street.
New research has revealed the supermarket carrier bag to be the most popular plastic bag to re-use – even more popular than designer bags such as Harrods or Gucci, and bags from fashionable high street stores like Gap and Next.
And reusing plastic carrier bags is good news for the environment because it helps to reduce the amount of waste we throw away”.
“The survey results showed that when people choose to reuse their plastic bags:
- 52% of people prefer to re-use a supermarket plastic carrier bag for high street shopping.
- 43% of people prefer to re-use a supermarket plastic carrier bag to carry books or materials to work, school or college.
- 39% of people prefer to re-use a supermarket plastic carrier bag to carry their gym kit.
However, despite the many uses of the supermarket carrier bag, the survey showed that we still need to “do our bit” more to cut down on unnecessary waste. On average, nearly 1 in 5 of people in each situation surveyed preferred not to reuse carrier bags.”
(Research conducted by NOP with fieldwork between 21-26 September 2000).
With the exception of the returnable glass milk bottle, it would be very difficult to find any similar form of packaging with such an extraordinary level of re-use, in particular to replace pedal bin liners and, so I am reliably informed, in pursuit of improved canine hygiene on our pavements.
Waste Reduction & Litter
The Irish Plastic Bag Levy
When introducing this new shopping tax in Ireland, the Minister for the Environment and Local Government, Mr Noel Dempsey TD, stated that he wished to see “a significant reduction in the use of plastic shopping bags and a subsequent reduction in the number of plastic bags which end up as litter”. The note to Editors stated that “Plastic bags are a visible component of litter production in towns, throughout the countryside and along our coastline”.
[In sharp contrast the South African Department of Environmental Affairs advised that new regulations would be issued soon to ease the ban on thin plastics bags, less than four months before it hosts the World Summit on Sustainable Development.]
The Consultancy Study carried out by Fehily Timoney and Company, Dublin, and commissioned by the Department of the Environment and Local Government, was published in January 1999. It deals comprehensively with the consumption and disposal of plastic bags, retail trends and management measures. The author also quotes the Life Cycle Analysis (LCA) studies carried out by the University of Winnipeg and others. Despite this the report appears to advocate a switch to paper bags by assessing the tax necessary per plastic bag to equate with paper bags on price, since consumers would prefer to use one trip bags rather than compromise their ability to shop without the need to pre-plan the trip.
However when communicating specifically on the alleged litter problems the report refers to:
“Anecdotal information suggests that the main problems of plastic bag litter are caused by lighter gauge vest type bags.”
“With total annual packaging waste arisings in the Republic of some 640,000 tonnes, plastics bags account for a small proportion of this at around 2% (Based on UK market data this would suggest that plastics carrier bag waste would be less than 0.5%).
“Although no hard data exist to show the contribution of plastic bags to the litter problem their high visibility in the litter stream is widely recognised”.
“Where a level of tax or charge is sufficiently high to effectively make plastic bags uncompetitive with respect to other types of shopping container, this would not necessarily be deemed discriminatory, even where a large proportion of products are imported” and “Indeed most checkout bags are currently imported”.
“A ban, on say plastic bags under a certain size or weight, would be less likely to be challenged if there was a justifiable environmental reason for the ban.
Such justification would need to take into account
- the scale of the problem
- the contribution to the problem caused by plastic bags
- the costs and effectiveness of alternative means of addressing the issue”.
“As noted above the environmental problems caused by plastic bags are more identifiable and – providing more concrete evidence can be put forward – a regulation designed to limit their use should be less subject to challenge than the Danish initiative” (The Danish Can Ban).
“Because there is incomplete knowledge on how plastic bags get into the environment one is restricted to using bag consumption as an indicator of the environmental disamenity caused”.
“In the UK the Tidy Britain Group measures and collates cleanliness standards across the country”.
“It is difficult to draw any firm conclusions from the above assessment of the litter issue in so far as it affects the matter of plastics shopping bags. Bags are acknowledged as part of a litter nuisance problem – but only a part. They are not the most numerous item recorded in either of the two National Litter Surveys but are certainly one of the most visible – along with plastic bottles and fast food containers. Plastic as a whole accounts for a relatively low percentage of both the household waste stream and the litter waste stream and shopping bags are obviously a sub-set of these data”.
It would appear from any objective reading of the Consultants report that any assessment of a plastic bag litter problem is based on perception and lacks any credible or quantifiable evidence to support the case. However the imposition of the carrier bag tax on plastic bags alone creates a restraint to international trade that cannot be justified in any environmental assessment of paper versus plastic-bag usage.
The UK Environment Agency – Plastics in the Environment
In March 2001 the UK Environment Agency published “Plastics in the Environment” as part of their “Environmental Issues” series. This contains data on surveys conducted by the Marine Conservation Society from 1994-2000 and headed “Plastics Items most frequently found on beaches in the UK” per km. In 1999, the last year quoted, they found 1029 plastic items and of these 46 were bags, in an area where litter is wholly objectionable. The bags were not identified but if we assume that crisp bags, bread bags etc. were a component, it would be difficult to justify even half of these or 2.2% of plastic litter, being composed of carrier bags and a far lower percentage of the total all materials beach litter.
Degradability versus Sustainability
In a world of finite resources it must be in all our interests to use only the minimum amount of energy and resources that our social needs demand and to create the minimum environmental impact by our actions. This should cause us to limit our demands on materials use, consistent with the essential functions that packaging must fulfil in terms of safety, hygiene, avoidance of waste whilst providing variety, choice and convenience at lowest cost. After use we should seek to maximise materials recovery whenever it is environmentally sound to do so and when economically or technically not feasible, we can seek to recover the energy content and greatly reduce the volume of waste for disposal via the adoption of waste to energy systems.
There are undoubtedly specialist areas where degradable materials have a part to play – composting bags, crop covers, mulching films, for example – but all degradability involves the total loss of the basic materials and the creation of both land and airborne pollution in some form. As studies at Columbia University (USA) have shown, modern landfill sites are designed to be stable sealed repositories, said to more often resemble tombs than biological reactors, where plastic products, paper products and even food waste may still be recognisable decades after their disposal. Any gases from chemical decomposition can be dangerous, damaging to the environment, or both. This is well recognised in the new Landfill Directive by which all landfill operators must drastically reduce, or costly pre-treat, all biodegradable wastes including paper and board, accepted for land-filling over the next 15-20 years.
As indicated by data compiled in the Irish Carrier Bag Study, plastics carrier bag waste forms probably about 0.5% of packaging waste arisings and an even smaller proportion of the overall urban waste stream passing to landfill. Plastic films help to stabilise landfill and will not pollute the ground-water system or the atmosphere.
Litter is a social and not a material-specific problem and its overall solution cannot reasonably be found by pursuing degradability which may be environmentally damaging, and contrary to the Landfill Directive. It may also create real problems of materials identification and separation in any scheme for mechanical recycling. But above all the total loss of recoverable energy and finite resources is the antithesis of sustainability.