Shell told state regulators this week that a floating roof over a tank at its oil refinery in Deer Park, Texas, partially sank during the heavy rainfall. The company said 100 pounds of benzene and 100 pounds of toluene were released.
A similar event happened at Exxon Mobil Corp.'s refinery in Baytown, Texas. David Gray, a spokesman for the Environmental Protection Agency, said the company reported the release of 15 pounds of benzene. The EPA classifies benzene as a carcinogen. Toluene, a solvent, is less toxic.
A Shell spokesman did not immediately respond to a request for comment.
"This is an unprecedented storm, and we have taken every effort to minimize emissions and safely shut down equipment," said Exxon spokeswoman Charlotte Huffaker. She said the Irving, Texas-based company was monitoring emission levels and was committed to complying with environmental laws.
Other refinery and chemical plant operators have reported releases due to Harvey, which came ashore as a hurricane but was later downgraded to a tropical storm.
The disclosures highlight the danger posed by flooding in a refinery-rich section of the Gulf Coast that stretches from Corpus Christi, Texas, to Louisiana.
The flooding has caused the shutdown of about 15 percent of the nation's refining capacity, sending gasoline prices higher.
Gasoline futures rose 6 cents, or 4.1 percent, to $1.78 a gallon in trading Tuesday. Retail prices have gained more slowly — up 4 cents in the last week to $2.38 a gallon, according to auto club AAA.
Earlier Tuesday, Motiva Enterprises said that its refinery in Port Arthur, Texas — the biggest in the nation — had cut output to just 40 percent. Motiva, which is owned by Saudi Aramco, the state-owned oil company of Saudi Arabia, said it was dealing with restrictions in the flow of crude oil coming in and products like gasoline going out through pipelines and ports.
A company spokeswoman said there was some water in the plant and local roads were flooded.
The operator of a major pipeline carrying fuel to the East Coast announced it was running at a reduced rate too, compounding pressure on the nation's energy system.
The Colonial Pipeline operator said Tuesday the reduction was due to limited supply from refiners around Houston and storm damage to its facilities in several southeast Texas locations. The company said it dispatched workers to the region.