Transport, Transformation, and Fate of MTBE
Once MTBE has entered the air, it may be transported and removed by photochemical reactions or by wet deposition (i.e. rain), because of its solubility in water.  The half life of MTBE in air is dependent upon hydroxyl radical concentration and/or precipitation events and is expected to be about 3 to 4 days near an urban area, varying with season.

MTBE enters surface waters by rain or stormwater runoff.  MTBE enters shallow groundwater by rain, stormwater flow, or leaky storage tanks or associated piping and may be transported into deeper aquifers by infiltration.  MTBE may be transported from the surfaces of lakes to greater depths by vertical mixing.

In shallow surface waters, photochemical reactions may degrade MTBE.  In addition, MTBE may volatilize from shallow waters into the air.  Volatilization is dependent upon temperature, depth and speed of flow. 

In deeper surface waters and in subsurface waters, few mechanisms exist to degrade MTBE.  Recent research indicates that MTBE does biodegrade rapidly in engineered ex situ environments, but at this time it is uncertain whether indigenous aquatic or soil microorganisms will biodegrade MTBE in situ at significant rates.

The estimated half-life of MTBE in flowing surface water is on the order of hours to days, in standing surface water the half-life ranges from days to weeks, and in groundwater the half-life ranges from months to years.

Routes of Exposure
Because it is not thought to be removed readily from aquatic environments, animals and ecosystems may be exposed to MTBE via water supplies.  Exposure can occur through ingestion of potable and recreational water.  Skin absorption and inhalation can occur when showering with contaminated water.  Water suppliers will not purposely deliver water containing MTBE at levels above health, taste or odor guidelines**, so exposure to significant levels of MTBE through potable water supplies is unlikely.  In urban areas where oxygenated fuels are in use, the major route of MTBE exposure is expected to be inhalation of gasoline vapors.

** Regulatory agencies are still deciding upon the range of appropriate levels for water quality guidelines.

Control of MTBE
Examples of source control of MTBE include the following:  1) limited recreational use of vehicles on selected water bodies, 2) reduction of leaks and spills through systematic improvements to the storage, distribution and monitoring systems, 3) treatment of spills and leaks, and 4) treatment of industrial discharges to receiving waters.

Examples of "point of withdrawal" treatment technologies include adsorption (activated carbon), photooxidation (UV light) and/or chemical oxidation (e.g. hydrogen peroxide), air-stripping with or without heating or vacuum assistance and subsequent control of vapors with thermal oxidation, activated carbon or biofiltration.  Biological treatment of water with microorganisms followed by filtration or ultrafiltration of the microorganisms from the water, may be useful in reducing the costs of physico-chemical treatment proccesses.  Studies underway at a number of laboratories, including UCD, will help to determine the level of treatment that can be achieved biologically.