Bioremediation

Bioremediation is the cleanup of polluted places with the help of living things. The usual workers are bacteria and fungi that can use a contaminant as food or as an energy source, breaking harmful compounds such as oil hydrocarbons, solvents and pesticides into simpler, safer substances. When plants do the job by taking up or breaking down toxic material, the approach is called phytoremediation.

Treatment can happen in place, called in situ, or after soil or water has been dug up or pumped out to a treatment area, called ex situ. Engineers may feed the microbes already living at a site with oxygen or nutrients, known as biostimulation, or add microbes known to degrade the pollutant, known as bioaugmentation. Success depends on temperature, pH, moisture and how easily the microbes can reach the contaminant, and very high concentrations can poison the microbes themselves.

A well-known example is the cleanup after major oil spills such as the Exxon Valdez in Alaska in 1989, where naturally occurring oil-degrading bacteria helped break down the oil. Some bacteria can also convert dissolved mercury into a less toxic form.