Mycology, more specifically work on strains of edible mushrooms to clean up the environment. Paul Stamets has shown that certain variations of P. Ostreatus can be used for cleaning up oil spills and that certain fungi concentrates heavy metals, indicating it could be used to clean up said metals.
Unfortunately he's patented a lot of his research[1] and I don't really know my way around patent law enough to risk finding out if a company dedicated to applying these technologies could get me sued.