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 ( NYS: 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 ( NYS: DAR ), meanwhile, specializing in food industry waste recycler, gained 11%. Among other initiatives, it's partnering with Valero Energy ( NYS: 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.