While preparing for the Olympics, London invested in new walking and cycling routes for specatators. While such efforts are eco-friendly, many of the shoes pounding that new pavement are not. (CARL COURT/AFP/GETTY IMAGES)

The 2012 Olympics may be the first at which the environment has been a major focus.

The organizers promised that the London Games would be the greenest ever. They invested in new walking and cycling routes for spectators, promised to sell only sustainable fish, and have offered food in compostable or recyclable packaging. Some environmental advocates say the Games have fallen short of their targets — relying more on fossil fuels than originally intended, for example — but they have served as a starting point for thinking about sports and the Earth.

Maybe the Games have inspired you to lace up your sneakers. (Or guilted you into it: There’s nothing like watching chiseled bodies streaking around a track at the outer limits of human capability to make you feel bad about your conditioning.)

But before you buy that new pair of trainers, you might consider your own ecological footprint. What are the environmental impacts of a pair of sneakers, and is there anything you can you do to lighten your impact on the planet while softening the planet’s impact on your joints?

The sheer scale of the shoe industry makes it worth thinking about, even if sneakers haven’t been on your environmental radar. Analysts estimate that global shoe production surpasses 20 billion pairs annually.

Go easy on the leather

Sneakers feature some pretty environmentally unfriendly materials. All of the environmental calamities associated with eating beef — greenhouse gas production, the destruction of the rain forests, the streaming of manure into the Chesapeake Bay and other sensitive waterways — are also associated with wearing leather.

The harmful impacts of manufacturing leather extend beyond the raising of cattle. Many tanneries rely on hexavalent chromium to toughen rawhide into leather because it works faster than traditional, vegetable-based materials.

Hexavalent chromium is a probable carcinogen, though, made famous in the film “Erin Brockovich.” In 2010, the Environmental Working Group reported the presence of the chemical in the water supplies of Bethesda, Washington and 33 other cities in the country.

In purchasing a sneaker, therefore, one of the best things a consumer can do for the environment is to select a model with little or no leather.

A group of graduate students from the University of California at Santa Barbara demonstrated the point in 2008 when they analyzed the environmental impacts of Simple Shoes, a brand that emphasizes its green credentials.

The group found that a kilogram of leather was responsible for about 10 times as much greenhouse gas production as synthetic alternatives or natural options such as hemp, jute and wool felt. In fact, Simple Shoes models with less leather performed significantly better than more-leather sneakers in almost every environmental impact category, including acid rain production, eutrophication of waterways and human toxicity.

It’s easy these days to find non-leather running shoes. Major manufacturers such as Saucony, Merrell and New Balance offer completely synthetic options, and some online retailers sell vegan shoes.

The cotton in a sneaker’s upper and its laces is also a concern, because cotton production requires large amounts of chemicals.

According to the advocacy group World Wildlife Fund, cotton accounts for 24 percent of global insecticide use and 11 percent of pesticides, even though less than 3 percent of farmland is planted with cotton.

You can lighten your cotton impact if you use a shoe made with organic cotton, which uses none of these synthetic chemicals and requires about half as much energy to produce as the conventional version, according to a 2005 report from the Stockholm Environment Institute. (Organic cotton is not without costs, though: It takes more land to grow organic than conventional cotton.)

The trouble with rubber

Then there’s the ingredient that makes sneakers special: the rubber outsole. Rubber-soled sneakers were first marketed in 1917, and Bill Bowerman helped rocket the Nike company to prominence in 1972, when he sculpted new soles by pouring rubber into a waffle iron. Most of today’s sneaker outsoles are made from synthetic rubber.

According to the World Wildlife Fund, the manufacture of synthetic rubber results in the release of more waste than the volume of rubber produced. That waste includes several forms of volatile organic compounds, some of which are suspected carcinogens.

Unfortunately, it’s tough to avoid synthetic rubber in sneakers. Some companies sell models with recycled car tires rather than virgin synthetic rubber, but few are suitable for serious running. Natural rubber is also better for the environment than synthetic, but few shoemakers use it.

If all of this has you ready to throw your hands up and plop your backside down on the couch for good, some footwear companies have begun rating the environmental impact of their products.

Timberland, for example, ranks its products on a scale of zero to 10. Such scales are a big step, but keep in mind that most of them are done by the manufacturer, not by a disinterested third party.

In 2011, Puma won some green cred by becoming one of the first major corporations to quantify its overall impact on the environment, but quantifying overall corporate impact doesn’t help consumers choose between shoe models.

Of course, you could just forget the shoes and join the ranks of the barefoot running movement. Although its impact on your joints is still a matter of debate, its impact on the environment is unquestionably lighter.