NEW YORK ( TheStreet) -- For more than a month, BP ( BP) has considered top hats, top kills and junk shots as ways to halt the flow of oil pouring from the sight of the Deepwater Horizon rig off the coast of Louisiana.This disaster, which is expected to surpass the Exxon Valdez oil spill from the late 1980s as being the worst oil spill in U.S. history, threatens not only the surrounding area's fishing and tourism industries but also the lives of numerous different animal species that call the affected land and ocean home. Cleaning up after this mess is sure to be a monumental task, but it's unlikely to be the last spill as new sources of energy are needed and companies search for oil in difficult areas. That's not good news, but it's good for business for a diverse collection of companies dedicated to this and other types of environmental efforts. Investors can track diverse baskets of these clean-up firms using both the Market Vectors Environmental Services Index ETF ( EVX) and the Fidelity Select Environmental Portfolio ( FSLEX ). EVX passively tracks the NYSE Arca Environmental Services Index. Twenty-one companies comprise EVX's index, with top holdings Stericycle ( SRCL), Republic Services ( RSG) and Waste Management ( WM) together representing nearly one-third of the fund's portfolio. FSLEX tracks a basket of 22 different companies. Pall Corp ( PLL), Ecolab ( ECL), and SRCL represent the fund's three largest positions, accounting for 14%, 13% and 10% of the fund respectively. EVX and FSLEX attempt to track a similar slice of the market. However, only a small number of holdings aside from SRCL are common across both funds. Nalco ( NLC), a water treatment firm held by Warren Buffett and directly involved in the current Deepwater Horizon clean-up efforts, is held by both, representing nearly 9% of FSLEX and 4% of EVX. Other holdings found in both instruments include Darling International ( DAR), Clean Harbors ( CLH)and WM. The main difference in the portfolios is that FSLEX's manager has more room to stray from the environmental services sector, for instance there are small holdings in solar power companies. FSLEX, like most mutual funds, carries a considerably higher expense ratio than EVX: 1.08% versus 0.55%. Aside from providing investors with exposure to companies which will benefit from the current BP clean-up efforts and future environmental issues, environmental services funds like FSLEX and EVX are also defensive plays which maintain stability in times of market stress. Over the past month, EVX and FSLEX have taken hits, losing 9% and 10% respectively. However, in both cases, they have managed to outperform the broad S&P 500.