Which container is the least worse for the environment?
Rigid high-density polyethylene jugs, plastic-coated cardboard boxes, milk bags or reusable glass bottles & # 8230; there are a variety of different containers to carry our dairy products. We don't always know, but some containers are better for the environment than others.
If you are a Canadian who consumes an average of milk, you probably drink more than 60 liters per year. This represents approximately two billion containers each year.
The packaging for all that milk depends on where you live, and new research shows that one type of container is better for the environment than others.
There is a particularly wide range of containers for milk. In Canada, the most common are rigid high density polyethylene jugs, plastic cardboard boxes and milk bags. Reusable glass bottles are rare, and that's good because they have a higher global warming potential than other beverage containers.
My colleagues and I, all chemists and physicists specialists in research on materials and energy storage, have studied consumption issues linked to sustainability. We recently assessed the environmental impact of plastic jugs, cartons and milk bags in Toronto and Halifax, and found the bags to be the most environmentally friendly option.
According to a 2010 report from the Food and Agriculture Organization of the United Nations, most milk containers sold in North America are plastic jugs (68%), followed by boxes (24%) and bags (7%). Conversely, bags dominate in Mediterranean African countries (72%) and the former Soviet Union (54%).
The American chemical company DuPont marketed polyethylene plastic milk bags in Canada in 1967. This innovation took off in the 1970s, when Canada converted to the metric system because the volume could be changed there. more easily than for cardboard boxes and jugs.
The impact of the container
Our study consisted of a life cycle assessment of a wide variety of milk containers – the types and sizes commonly found in Toronto and Halifax. We assessed energy inputs, greenhouse gas emissions and the water used to produce, transport and dispose of them.
We found that the most energy use and greenhouse gas emissions came from the production of paper and plastic polymers, much more than the transportation and processing or disposal of materials. Polymers are found in milk jugs, screw caps, which plasticize cardboard, milk bags and their clips, and paper is part of the cardboard.
In both cities, the bags require less energy and water per liter of milk and produce less greenhouse gases than jugs or cans. This is mainly due to the fact that the bags weigh only 20-30% of the weight of the jugs or cartons for an equal volume.
The differences are significant. For the same amount of milk, if compared to jugs or cartons, bags only consume about 20-30% of the energy, only use about 2% (compared to cartons) and 40% (relative to the jugs) of the amount of water and produce only 20 to 40% of the greenhouse gases generated by the other containers.
Even when the bags are buried or incinerated and that the jugs or the cartons are entirely recycled, the environmental impact of the bags remains lower.
Exclusions and comparisons
We omitted several small items in our study, including materials and processes associated with labeling, such as inks and printing. We have also excluded the jugs in which the bag of milk is placed in order to be able to use it. Another study showed their impact to be low and, in my experience, they can last for several years. One important issue that we have overlooked is the impact of different containers on the ocean and marine life.
The results of our research were validated by a comparison with previous studies conducted in the UK and several other countries. Our calculations of energy consumption and greenhouse gas emissions were consistent with theirs.
A lot of water is used in the production, processing and transportation of containers, but a considerable amount of water is recovered through recycling. The net water consumption is the small difference between these large numbers and therefore is not very precise. However, we have found that the cartons use a very large volume of water: almost 20 liters of water are needed to produce the carton for each liter of milk.
Our comparison with other countries showed us that the energy consumed by bags of milk in the UK was almost four times our result. This is because the bags used in the UK come from Canada. This prompts us to stress the importance of the location of consumers in a lifecycle assessment. However, our numbers were essentially the same for Toronto and Halifax, indicating that the lower impact for milk bags applies to any location in the southern regions of Canada.
In other words, the milk bag would have the least impact on Canadian consumers of all containers if everyone could buy it. At the moment, they are not found in the west of the country. Using bags in Western Canada could save up to 5,000 tonnes of plastic per year.
Will this new information make people turn to bagged milk? In Canada, it is only sold in four-liter quantities, which may be too much for some and may cause waste, negating any environmental benefit.
Individual one-liter milk bags are now sold in Germany. Although they are heavier than ours, they are still preferable to jugs or cans.
The environmental impact of wasted milk is even greater than that of its packaging. In the United States, milk accounts for about 13% of food loss, and consumer wasted milk produces about ten million tonnes of carbon dioxide equivalent per year.
Canada aims to ban single-use plastic by 2030, but it's unclear whether milk bags will be included in the banned products. Our analysis suggests that plastic remains the best option for low-waste milk.
If the average Canadian household switched from jugs or cartons to bags, the weekly energy savings would be equivalent to a load of laundry in a dryer. For those who care about the environment, this is a start.
Mary Anne White, Professor emerita, Department of chemistry, Dalhousie University
This article is republished from The Conversation under a Creative Commons license. Read the original article.