Exchange-traded funds offer a convenient way to invest in sectors or niches that interest you. If you're interested in the waste management industry because of its seemingly inevitable growth due to a growing population, the Global X Waste Management ETF (NYSE: WSTE) could save you a lot of trouble. Instead of trying to figure out which companies will perform best, you can use this ETF to invest in lots of them simultaneously.

The basics
ETFs often sport lower expense ratios than their mutual fund cousins. The waste-focused ETF's expense ratio -- its annual fee -- is 0.65%, which is a bit higher than many ETFs, but also considerably lower than the typical stock mutual fund.

This ETF doesn't have much of a performance to assess, as it's extremely young. Year to date, it's ahead of the S&P 500, but as with most investments, of course, we can't expect outstanding performances in every quarter or year. Investors with conviction need to wait for their holdings to deliver.

The ETF is very tiny, too, so if you're thinking of buying, beware of occasionally large spreads between its bid and ask prices. Consider using a limit order if you want to buy in. Or just keep it on your watchlist for a while.

What's in it?
Several waste-management companies had strong performances over the past year. Clean Harbors (NYSE: CLH), gained 42%, cleaning up messes such as oil spills. It collected $42 million from ExxonMobil's Yellowstone spill, for example. It's unfortunate that our planet suffers from occasional hazardous-waste disasters, but it's good news for Clean Harbors and its peers.

Darling International (NYSE: DAR), meanwhile, specializing in food industry waste recycler, gained 11%. Among other initiatives, it's partnering with Valero Energy (NYSE: VLO), which will accept the renewable diesel fuel it's creating from used cooking oil and animal fats.

Other companies didn't do as well last year, but they could see improvement in the years to come. EnergySolutions (NYSE: ES), for instance, shed 32%, but it sports government contracts and is poised to benefit from needed cleanups of nuclear facilities and from the decommissioning of various nuclear facilities.

The big picture
Demand for waste management isn't going away anytime soon. A well-chosen ETF can grant you instant diversification across any industry or group of companies -- and make investing in and profiting from it that much easier.

Learn about the 5 ETFs That Could Soar in 2012. And if you're looking for some great investments beyond ETFs, consider these 12 Dividend Stocks for 2012.