Leather, as a material, hasn't made a big splash here at TreeHugger; aside from one lonely post, we haven't given it much time. Yet, it remains a very popular material for clothing, accessories, furniture, luggage and shoes, from the runways in Milan and Paris to just about every mall in the US. So, what's the deal?
It's true: from a TreeHugger's standpoint, it's best if leather is simply avoided. Why? First of all, it's dead animal skin, which means that animal has to be raised: fed, watered, pastured, and eventually slaughtered. Most leather (about 66% of it) comes from cows, and it takes 8 acres of land, 12,000 pounds of forage, 125 gallons of gasoline & other petroleum derivatives for fertilizer, 2,500 pounds of corn, 350 pounds of soybeans, 1.2 million gallons of water & 1.5 acres of farmland (to grow the crops for feed), plus various insecticides, herbicides, antibiotics & hormones to grow one cow from an 80 pound calf to its full size, when it can be slaughtered and the hide harvested. Something like bison, on the other hand, takes less land and less water, and they're primarily pasture-raised, meaning they aren't stuck in feedlots getting fat for half their natural lives. Since they're on the pasture, and their hooves are smaller and sharper, they help till and fertilize the soil (with their waste as fertilizer), and though they require more feed per pound, they aren't picky about where the food comes from; it can be prairie grass or whatever they happen across. Regardless, the point remains: it takes a ton of resources to grow cows.Once the animal skin becomes available (usually as a byproduct of the beef industry), it doesn't get much prettier. Before tanning, the skins are unhaired, degreased, desalted and soaked in water over a period of 6 hours to 2 days. To prevent damage of the skin by bacterial growth during the soaking period, biocides, such as pentachlorophenol (a synthetic fungicide that is toxic to humans), are used. Hides are then either vegetable tanned or mineral tanned. Vegetable tanning employs tannin, from which tanning gets it name, which occurs naturally in tree bark; the primary barks used these days are chestnut, oak, tanoak, hemlock, quebracho, mangrove, wattle, and myrobalan. Hides are stretched on frames and immersed for several weeks in vats of increasing concentrations of tannin. Vegetable tanned hide is flexible and is used for luggage and furniture; Q Collection, one of TreeHugger's favorite sustainable designers, uses vegetable-tanned leathers in their furniture (this gorgeous chair is an example).
Mineral tanning, on the other hand, usually uses chromium and is a fairly chemistry-intensive process. The hides are "pickled," raising the pH to a high acidity level (about 3) and enabling chromium tannins to enter the hide. For preservation purposes, fungicides and bactericides are also applied (yum). After pickling, when the pH is low, chromium salts are added. To fixate the chromium, the pH is slowly increased through addition of a base of magnesium oxide and more fungicide -- sounds like something you'd really want to snuggle up against, no? Chrome tanning is faster than vegetable tanning -- less than a day for this part of the process -- and produces a stretchable leather which is preferred for use in handbags and garments.
Chromium is not very nice stuff for people; studies have clearly established that inhaled chromium is a human carcinogen, resulting in an increased risk of lung cancer. While people aren't as likely to inhale once it's been ingrained in the leather hide, it doesn't bode as well for the people tanning the leather, and, on the whole, isn't something that will really benefit you by rubbing up against your skin all the time.
For the most part, cow leather is a bi-product of the beef industry; this is a double-edged sword. Cows raised for beef aren't going anywhere any time soon, so beef-eating TreeHuggers will note that we may as well use as much of the animal as possible, but tanning leather is a dirty, energy-intensive, potentially toxic process. Further, the synthetic "versions" of leather include vinyl and other plastics, which aren't really very good for anybody either (but that's another post).
Unfortunately, there aren't any regulations or certifications for "organic" or "certified humane raised & handled" leather, as there is with beef and some other leather-producing animal meat, so there is no easy way to insure that your leather products came from an ethical and/or planet and animal-healthy environment, short of raising the animal yourself. So, in the end, the best thing is to avoid it altogether; replacing a leather product with a vinyl one won't be doing anyone any good, so for those who simply must have it, we recommend finding it repurposed or second-hand or otherwise reused, rather than buying a virgin product, and if you absolutely, positively have to have new leather, vegetable-tanned is the only way to go.