Shoes, bags, sports equipment, upholstery, your favorite jacket… chances are you own leather goods in some form. Traditional animal leathers date back to around 7 000 years ago, when humans first discovered strategies for preserving and using animal skins leftover from the food they would consume. Now, advances in improving leather’s durability and flexibility have led it to be incorporated in a wide variety of consumer goods, accounting for 340 billion dollars (CAD) in global trade every year.
Animal leather is obtained from the hides or skins of animals that have gone through a process known as tanning. Tanning gets its name from the use of molecules known as tannic acids, which bind to the proteins in animal skins and prevent them from decaying. This chemical transformation is ultimately what provides leather with the durability that we know and love. Tanning agents can be derived from plant sources, fish or animal oils, mineral salts (chromium sulphate), or synthetic molecules such as glutaraldehyde or formaldehyde. Although plant or animal derived tanning agents have significantly lower toxicity and environmental impact, they are much less powerful than other available options, leading to longer processing times and reduced durability of the leather. For these reasons, chromium sulphate and aldehydes are the most popular options, despite their known carcinogenic and mutagenic properties.
Besides tanning, many other steps are included in transforming animal skins into a final product. Each step serves a purpose in providing a soft, flexible, uniform leather, but generally relies on the use of more toxic chemicals. Hydrogen sulfide and ammonia are commonly used to prepare leathers for tanning and are linked to irritation of the eyes and skin, damage to respiratory and nervous systems, and digestive issues. Hydrogen sulfide can also contribute to acid rains. The use of these chemicals is especially hazardous for those working in the leather industry, but poses risks to everyone worldwide through the pollution of water and air, and bioaccumulation in our food, whether plant or animal-based.
Leather production requires a good amount of other resources. For one kilogram of leather, 17.5 to 25.5 liters of wastewater are produced (this does not include the amount of water needed to raise an animal from birth to slaughter). This wastewater is mostly left untreated before being dumped back into the environment, contaminants and all. The carbon footprint of leather isn’t negligible either, with one pair of animal leather shoes representing 40.7 kg of carbon dioxide emissions. This number climbs to an average of 100.6 kg for a leather tote bag or 176 kg for a leather jacket. This carbon footprint considers the entire life cycle of the item, from animal agriculture (from which the leather is obtained) to final processing steps.
Animal leathers are vey diverse in origin. While some come from animals such as lizards, snakes, eels, fish, ostriches, and kangaroos, leathers most commonly come from seven main groups. These include cattle (cows, calves, and oxen), sheep and lambs, goats and kids, equine animals (horses, mules, and zebras), buffalo, pigs and hogs, and aquatic animals (seals, walruses, whales, crocodiles, and alligators). In the early days of leather, transforming animal hides and skins was a way to value the by-products of eating meat. Today, the industries are separate and animals are raised for the sole purpose of being killed for their skins. For cattle-leather alone, an estimated global heard of one billion animals currently exists, 290 million of whom are killed each year. This is a significant contributor to leather’s high carbon footprint. Animal cruelty and carbon emissions from animal agriculture are the two main concerns driving the rise of vegan leathers in recent years. But, besides the question of animal ethics, are vegan leathers truly more sustainable?
Vegan leather can be derived from a number of natural and synthetic sources. Pineapple leaves, cork, apple peels, mushrooms, and cotton are all examples of plant materials that can be transformed into vegan leathers. However, synthetics are by far the most common types of faux leathers, with polyurethane (PU) and polyvinyl chloride (PVC)-based options taking the lead. These synthetics are plastics derived from the petrochemical industry, which has its own important environmental impact. They begin as non-renewable resources (fossil fuels) and are transformed using chemicals of varying toxicities (examples of which include organic solvents, phthalates, dioxins, dimethyl formamide, and concentrated acetic acid). As is the case for animal leathers, many of the chemicals used in the production of synthetic leathers are carcinogenic and mutagenic, or impact the respiratory, nervous, and reproductive systems.
Although the precise impact of water-consumption from the production of plastic leathers is unknown, data does exist on their carbon footprint. This is much lower than for animal leathers, as a pair of PU-leather shoes represents 5.8 kg of CO2, a tote bag accounts for 14.4 kg of CO2, and a PU synthetic leather jacket is responsible for 9.9 kg of CO2 emissions. However…
One of the main advantages of animal-leather is its superior durability. These leathers tend to last significantly longer than their petrochemical counterparts, meaning that they don’t need to be replaced as often. Another advantage is that natural leathers will eventually biodegrade, taking anywhere from 25 to 40 years to decompose in the appropriate conditions. Plastic-based vegan leathers don’t last nearly as long with regular use, can release carcinogenic and mutagenic molecules during wear, and ultimately never fully decompose. Instead, these leathers break down into micro and nano plastics, which accumulate in the environment. These particles end up being ingested by animals and humans alike. It is estimated that it would take over 500 years for synthetic leather to no longer be detectable.
New plant-based leathers are the most promising option, although they still require a fair amount of research and development to be produced at a large scale. While they are vegan and can sometimes be produced from carbon-neutral crops or from plant waste, they are not yet fully biodegradable as they need to be mixed with or coated with plastic in order to be sufficiently durable. Industry representatives and scientists alike are excited to see how they can be improved upon to hopefully bring about a fully biodegradable, sustainable option in the coming years.
Until then, existing methods for leather production can be improved upon. Unfortunately, not much can be done to mitigate the risks associated with synthetic vegan leathers, but there are several proposed strategies to reduce the toxicity and environmental impact of animal leather goods. Low waste and cleaner technologies have been developed over the past decades, as well as methods for the treatment and management of solid waste and wastewater. By exploring environment and human-friendly chemical alternatives, converting solid waste into useful products, and recycling and reusing wastewater, the downsides can be significantly reduced. Another way to reduce the environmental impact of animal leather would be to only use the skins of animals otherwise killed for their meat. As for consumers, the standard five Rs of sustainability still apply: refuse to buy leather products altogether, reduce your consumption of new leather goods, reuse and repurpose leather goods by shopping second-hand, and as a final step, recycle old, unusable items.
Note: this article does not discuss the human ethics of leather production, which is an entire topic of its own. If choosing to buy new leather goods, look for options that are not produced in sweatshops. B Corporation certification is a great indicator that your product has been manufactured to the highest standard of human and environmental ethics. Many high-end designer brands still use child or forced labor to produce their products, so don’t rely on price point alone as an indicator of more ethical business practices.