BALTIMORE, MD — Seven Maryland jurisdictions have filed a lawsuit charging that the largest gasoline suppliers and manufacturers have conspired for years to “needlessly and recklessly” keep a known water contaminant in its formulations, posing a threat to their groundwater.

The towns of Berlin, Sharptown, Aberdeen, Chestertown, Salisbury, Taneytown and the County Commissioners of Worcester County filed the lawsuit naming more than three dozen companies including ExxonMobil, Sunoco and Citgo that are involved in the sale and manufacture of gas containing the additive methyl tertiary butyl ether, or MTBE. The municipalities are asking for more than $20 million in damages on claims of negligence, conspiracy and causing a public and private nuisance.

Attempts to reach legal counsel for the petroleum companies on Friday were unsuccessful.

MTBE is a byproduct of gasoline refining that is added to increase octane. MTBE has not been proven to be a human carcinogen but is a known animal carcinogen. Due to its physical properties, the compound is easily soluble in water and even in small concentrations can leave a foul taste and smell.

The towns claim the petroleum companies have upped the amount of MTBE used in gasoline production from 2 to 4 percent range of the late 1970s to the 11 to 15 percent range today. The lawsuit alleges that spills of gasoline with MTBE are “inevitable” and pose a major environmental threat to their citizens’ drinking water.

“Despite knowing that MTBE has unique characteristics in water, which allows it to contaminate water sources never seen before its addition to gasoline, these defendants chose to make it the second largest chemical manufactured in the United States,” the complaint reads. “In doing so, these defendants have unleashed an unprecedented assault on the water supplied to the citizens of Maryland.”

According to the lawsuit, the companies colluded from the early 1980s on to downplay the risks and hazards of using MTBE as an additive. Despite its potential problems, the plaintiffs said the amount of MTBE used increased drastically after the 1990 Clean Air Act amendments, which required the use of reformulated gasoline that contains MTBE or other additives like ethanol, were passed. The companies allegedly pushed for the use of MTBE primarily because it boosted profits since it was a byproduct of the gasoline refining process.

“MTBE was not the only viable option to achieve higher octane in gasoline,” the complaint reads. “Rather, its use reflected a choice and preference of the defendants, to make money off gasoline refining waste byproducts.”

The case was originally filed in Baltimore County Circuit Court on Jan. 17, but was moved to the U.S. District Court for the District of Maryland, in Baltimore on Friday. Baltimore County Circuit Court was home to other MTBE-related cases stemming from an accident in Jacksonville. Residents sued over a massive gasoline leak that contaminated their water supply in 2006.

In March 2009, a jury in Baltimore County awarded $150 million to 88 households for exposure to MTBE exposure after the leak. In a second lawsuit, now being tried, the plaintiffs are seeking medical monitoring costs.