12 просмотров
от (230 баллов) в категории Другие предметы

Given the concerns pulling us in different directions—our health, the environment, climate change—what’s an environmentally responsible, health-conscious shopper to do? Let’s compare the main bag choices—plastic, paper and cotton—to try to answer that question.

Life Cycle Analysis

To understand the full spectrum of impacts and benefits of a particular bag, we need to analyze its life cycle. A life cycle analysis (LCA) looks at how much energy is used and how many environmental impacts a product is responsible for at every stage of its life, from cradle to grave. This includes extracting the raw materials, refining them, manufacturing the product, packaging it for shipment, transporting and distributing it, its use and possible reuse, recycling and final disposal.

In any LCA, the total environmental impact also depends on how efficient each process is, and how many protective environmental measures are implemented at every stage. Energy use is also subject to variables such as the source of raw materials, the location of manufacturing and processing, how long a product is used and the final disposal method.

Life cycle studies done in Europe and North America have determined that, overall, plastic bags are better for the environment than paper or reusable bags unless the latter are used many times. Most, however, did not consider the problem of litter, which we know is a major drawback of plastic bags.

Plastic bags

Plastic bags were invented in 1967, but only became widely used in stores in the 1970s. The most commonly found thin plastic shopping bags given out at cash registers are usually made of high-density polyethylene (HDPE), but some are made of low-density polyethylene plastic (LDPE).

The energy embodied in plastic bags comes initially from the mining of the raw materials needed to make them—natural gas and petroleum—whose extraction requires a lot of energy. The raw materials must then be refined, which requires yet more energy. Once at a processing facility, the raw materials are treated and undergo polymerization to create the building blocks of plastic. These tiny granules of polyethylene resin can be mixed with recycled polyethylene chips. They are then transported by truck, train or ship to facilities where, under high heat, an extruder shapes the plastic into a thin film. The film is flattened, then cut into pieces. Next, it is sent to manufacturers to be made into bags. The plastic bags are then packaged and transported around the world to vendors. While polyethylene can be reprocessed and used to make new plastic bags, most plastic bags are only used once or twice before they end up being incinerated or discarded in landfills. The Wall Street Journal estimated that Americans use and dispose of 100 billion plastic bags each year; and the EPA found that less than five percent are recycled.

A 2014 study done for the Progressive Bag Alliance, which represents the U.S. plastic bag manufacturing and recycling industry, compared grocery bags made from polyethylene (HDPE), compostable plastic, and paper with 30 percent recycled fibers. It found that the HDPE bags ultimately used less fuel and water, and produced less greenhouse gas gases, acid rain emissions, and solid waste than the other two. The study, which did not consider litter, was peer-reviewed by Michael Overcash, then a professor of chemical engineering at North Carolina State University. Because the carrying capacity of a plastic and a paper bag are not the same, the study used the carrying capacity of 1,000 paper bags as its baseline and compared their impacts to the impacts of 1,500 plastic bags. The plastic bags used 14.9kg of fossil fuels for manufacturing compared to 23.2kg for paper bags. Plastic bags produced 7kg of municipal solid waste compared to 33.9kg for paper, and greenhouse gas emissions were equivalent to 0.04 tons of CO2 compared to paper’s 0.08 tons. Plastic bags used 58 gallons of fresh water, while paper used 1,004 gallons. Energy use totaled 763 megajoules for plastic, and 2,622 megajoules for paper.

Sulfur dioxide, a type of sulfur oxide, and nitrogen oxide emitted from coal-fired power plants that produce the energy for processing bags contribute to acid rain. The plastic bag produced 50.5 grams of sulfur oxides compared to 579 grams for the paper bag; and 45.4 grams of nitrogen oxides, compared to 264 grams for paper.

A 2011 U.K. study compared bags made of HDPE, LDPE, non-woven polypropylene, a biopolymer made from a starch polyester, paper and cotton. It assessed the impacts in nine categories: global warming potential, depletion of resources such as fossil fuels, acidification, eutrophication, human toxicity, fresh water toxicity, marine toxicity, terrestrial toxicity and smog creation. It found that HDPE bags had the lowest environmental impacts of the lightweight bags in eight of the nine categories because it was the lightest bag of the group.

Cotton totes

Cotton bags are made from a renewable resource and are biodegradable. They are also strong and durable so they can be reused multiple times.

Cotton first needs to be harvested, then cotton bolls go through the ginning process, which separates the cotton from stems and leaves. Only 33 percent of the harvested cotton is usable. The cotton is then baled and shipped to cotton mills to be fluffed up, cleaned, flattened and spun. The cotton threads are woven into fabric, which then undergoes a chemical washing process and bleaching, after which it can also be dyed and printed. Spinning, weaving and other manufacturing processes are energy intensive. Washing, bleaching, dyeing, printing and other processes use large amounts of water and electricity.

To be safe, wash reusable bags in warm or hot water after shopping, which can reduce the bacteria by 99.9 percent and kill COVID-19. Only use the bags for groceries and ideally, put meats into a separate bag since meat juices left in bags can enable bacteria to grow quickly. Don’t leave reusable bags in the car because when it gets hot, bags become an ideal place for bacteria to grow.

Paper bags

Paper bags are made from a renewable resource and are biodegradable. In the U.S., over 10 billion paper bags are consumed each year, requiring the felling of 14 million trees.

Once the trees are cut down, the logs are moved to a mill where they can wait up to three years until they dry out. Once ready, bark is stripped off and the wood is chipped into one-inch cubes that are subjected to high heat and pressure. They are then mixed with limestone and sulfurous acid until the combination becomes pulp. The pulp is washed with fresh water and bleach then pressed into paper, which is cut, printed, packaged and shipped. As a result of the heavy use of toxic chemicals in the process, paper is responsible for 70 times more air pollution and 50 times more water pollution than plastic bag production according to a Washington Post analysis, resulting in more toxicity to humans and the environment than HDPE bags. 

Whichever way you respond, you probably have your reasons. Maybe you’re planning to recycle or reuse that paper bag, or maybe you use those plastic grocery shopping bags for cleaning around the house. Maybe you think your choice, whether it’s paper or plastic, is the more environmentally friendly option. But in reality, whatever you’re choosing between paper and plastic, no matter your intentions, you’re still choosing “wrong” — because there’s a better option out there: a reusable grocery bag.

Reusable grocery bags, including drawstring bag, can be used for a lot more than carrying groceries. A nice reusable bag is essentially a structured tote bag, and can be used for many of the things you’d use a tote bag for. You can pack your lunch in them, use them to carry snacks on a road trip, take books to and from the library, etc.

Пожалуйста, войдите или зарегистрируйтесь чтобы ответить на этот вопрос.

Похожие вопросы

0 ответов
спросил 10 Сен от asdfaas598 (220 баллов) в категории Українська мова
0 ответов
спросил 13 Авг от asdfaas568 (200 баллов) в категории Українська мова
0 ответов
спросил 13 Окт от asdfaas17 (200 баллов) в категории Українська мова
0 ответов
спросил 08 Сен от asdfaas595 (220 баллов) в категории Українська мова
0 ответов
спросил 27 Авг от asdfaas583 (200 баллов) в категории Українська мова

Топ рейтинг сайтов! Статистика посещаемости сайтов Stata.Me
...