MTBE (Methyl Tertiary-Butyl Ether)
MTBE·Affects liver, kidneys, brain
A gasoline oxygenate used heavily from 1979 through the mid-2000s that contaminated thousands of US groundwater supplies through leaking underground storage tanks. No federal MCL; many states regulate.
MTBE
EPA limit
No federal MCL (CA: 13 µg/L)
Most at risk
Households near current or former gas stations and refineries, well-water households downgradient of leaking tank sites
Found in
City water · Well water · Industrial areas
AquaOx filters
YesActivated carbon (coconut shell + Centaur catalytic)
What it does to you
Health effects
MTBE is classified by the IARC in Group 3, not classifiable as to its carcinogenicity to humans, reflecting limited and mixed evidence from animal studies. Some chronic rodent bioassays have produced tumors, but human epidemiological data is sparse because MTBE exposure is relatively recent and widespread chronic exposure is hard to isolate from other gasoline components.
What is well-established is that MTBE causes liver and kidney effects at chronic exposure, nervous system effects including dizziness, headache, and disorientation at acute exposure, and the most consumer-visible problem: an extraordinarily strong turpentine-like taste and odor detectable by most people at concentrations below 15 ppb. That sensory threshold is the basis of EPA's advisory level for drinking water.
The compound is highly water-soluble and does not biodegrade quickly. Once it reaches an aquifer it spreads quickly and persists for years, often longer than the parent gasoline plume itself.
Where it comes from
How it gets into your water
MTBE was added to US gasoline starting in 1979 to boost octane and reduce emissions, and use expanded sharply after the 1990 Clean Air Act Amendments required oxygenates in winter fuel in many cities. By 2000 it was the second-most-produced organic chemical in the US. Most states phased it out between 2002 and 2008 after widespread groundwater contamination became impossible to ignore.
The contamination route is almost always leaking underground storage tanks at gas stations. MTBE dissolves into groundwater far more readily than other gasoline components and travels in plumes that can extend a mile or more downgradient. Surface spills, marine engine exhaust into reservoirs, and pipeline leaks are secondary sources.
Even though MTBE is largely out of US gasoline today, legacy contamination remains widespread because the compound persists in groundwater for decades.
Leaking gas station tanks
Primary source: USTs near or under stations
Refineries and pipelines
Storage and transfer point releases
Contaminated wells
Plumes travel a mile or more downgradient
Two-stroke boat motors
Reservoir and lake contamination from older marine engines
Find out for yourself
Is it in your water?
MTBE has no federal Maximum Contaminant Level. EPA issued a drinking water advisory of 20 to 40 µg/L in 1997 based on taste and odor thresholds, not health. Several states set their own enforceable limits: California regulates at 13 µg/L (primary) and 5 µg/L (secondary), New York at 10 µg/L, and many others between 13 and 40 µg/L.
Because MTBE is not federally regulated, monitoring varies by state. Many utilities test voluntarily and report results in the Consumer Confidence Report. Private well owners within a mile of any current or former gas station should request a specific MTBE test from a state-certified lab. The taste and odor are extremely distinctive: if your well water has developed a turpentine, paint-thinner, or solvent smell, MTBE is one of the first compounds to rule out.
The fix
How AquaOx filters it
Activated carbon is the standard treatment for MTBE at both municipal and home scale. MTBE is harder for carbon to adsorb than most VOCs because of its small, polar molecular structure, so adequate contact time and a high-quality carbon bed matter. The combination of Centaur catalytic carbon and coconut shell activated carbon in The AquaOx provides the bed depth and dwell time needed to reduce MTBE to non-detect levels in typical residential service flow.
For well-water households on a known MTBE plume, we recommend pairing The AquaOx with the under-sink RO at the kitchen tap. RO membranes provide additional rejection of MTBE and protect drinking and cooking water even if carbon performance declines over a long service interval.