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Author: Marianne White, Dialogue

If you are a typical Canadian milk consumer, you may drink more than 60 liters of milk each year. A total of approximately 2 billion milk containers are purchased in Canada each year.

The way the milk is packaged depends on your location, and new research shows that one type of milk container is best for the environment.

The range of milk packaging is extremely wide. In Canada, the most common milk containers are rigid high-density polyethylene cans, plastic laminated cartons and "pillow bags", also known as milk bags. Reusable glass bottles are rare, which is good because they have the highest global warming potential of all beverage containers.

My colleagues and I, chemists and physicists engaged in materials research and energy storage, are very interested in consumer issues related to sustainability. We recently evaluated the environmental impact of milk cans, cartons and bags in Toronto and Halifax and found that milk bags are the most environmentally friendly option.

According to a 2010 report by the Food and Agriculture Organization of the United Nations, most milk containers sold in North America are cans (68%), followed by cartons (24%) and bags (7%). On the contrary, the package is dominant in the Mediterranean African countries (72%) and the former Soviet Union (54%).

American chemical company DuPont introduced a milk bag made of thin polyethylene plastic in Canada in 1967. This innovation started in the 1970s when Canada switched to the metric system because their volume was easier to modify than cartons or water bottles.

Our research is to evaluate the life cycle of various milk containers-the types and sizes that consumers in Toronto and Halifax may encounter. We assessed the energy input, greenhouse gas emissions, and water used to produce, transport, and dispose of containers.

We found that the largest energy consumption and greenhouse gas emissions come from the production of plastic polymers and paper, far exceeding transportation and material processing or disposal. These polymers are found in milk jugs, screw caps, laminates of cartons, milk bags and their labels, and paper is part of the cartons.

In these two places, per liter of milk, milk bags require less energy and water than jugs or cartons, and produce less greenhouse gases. This is mainly because the weight of milk bags is only 20% to 30% of the same volume of cans or cartons.

The difference is huge. One liter per liter, compared with a water bottle or a carton, a milk bag consumes only about 20% to 30% of energy, uses about 2% (compared to a carton) to 40% (compared to a kettle) of water, and only Produce 20% 40% of greenhouse gases.

Even if milk bags are discarded in landfills or incinerated—and the cans or cartons are completely recycled—the bags have minimal impact on the environment.

Our investigation overlooked several minor issues, including label-related materials and processes, such as inks and printing. We also excluded the water bottle used to hold the milk bag in use. Another study showed that the impact of supporting tanks is very small. According to my experience, these tanks can last for several years. One of the main issues that our research ignores is the impact of various milk containers on the ocean and marine life.

By comparing with earlier surveys in the UK and several other countries, our research results have been verified. Our energy consumption and greenhouse gas emission calculations are consistent with theirs.

The production, processing and transportation of containers require a lot of water, but a considerable amount of water is recycled through recycling. Net water consumption is a small difference between these large numbers, so it is not very certain. However, we did find that the cartons use a lot of water: each liter of milk requires nearly 20 liters of water to produce the cartons.

One insight drawn from our international comparison is that the UK milk bags consume almost four times as much energy as our results, because the milk bags used in the UK are shipped from Canada. This finding highlights the importance of location in life cycle assessment. However, our results for Toronto and Halifax are basically the same, which shows that the lowest impact of milk bags is related to anywhere in southern Canada.

In other words, if everyone can buy milk bags, the impact of milk bags on Canadian consumers will be the smallest of any milk container. Milk bags are currently not available in Western Canada. Using milk bags in Western Canada can save up to 5,000 tons of plastic each year.

With this new information, will consumers turn to milk bags? In Canada, bagged milk is only sold in a 4 liter capacity, which may be too much for some consumers, resulting in uneaten or spoiled milk. This will obliterate any environmental benefits.

The independent 1-liter milk bag is now available in Germany. Although these are heavier than our bags, they are still better than jugs or cartons.

The impact of milk waste on the environment is even greater than its packaging. In the United States, milk accounts for approximately 13% of food waste, and consumer milk waste generates approximately 10 million tons of carbon dioxide equivalent emissions each year.

Canada's goal is to ban the use of single-use plastic products by 2030, but it is not clear whether milk containers will be included in the ban. Our analysis shows that plastic parts are still the best choice for low-waste milk containers.

If an average Canadian family switched from cans or cartons to bags, the energy saved each week would be equivalent to washing a bucket of clothes in a clothes dryer. For those who care about the environment, this is the beginning. Explore further pasteurization of breast milk to inactivate SARS-CoV-2 provided by The Conversation

This article is republished from The Conversation under a Creative Commons license. Read the original text.

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