At BP’s Texas City refinery, more than 400 pounds a day of benzene — 40 times the state reportable levels — was released during a 40-day period while a subunit of the refinery’s ultracracker unit was offline, according to a company filing with the state’s environmental agency Friday.

In all, BP officials said more than 500,000 pounds of pollutants and nonpollutants were released while the company increased flaring as they tried to repair a compressor on the faulty unit.

Refinery spokesman Michael Marr said in its follow up reporting with the Texas Commission on Environmental Quality, BP estimated 36,000 pounds of nitrogen oxides and 17,000 pounds of benzene were released in the 40 days. State law requires 10 pounds or more of benzene and 200 pounds or more of nitrogen oxide during a 24-hour period must be reported through the commission’s air emissions database.

Benzene is a carcinogen naturally found in oil that has been linked to some forms of cancer, according to U.S. Health and Human Services records. Nitrogen oxides react to sunlight to form ozone and can damage lung tissue and cause respiratory problems.

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The bulk of the emissions during that time included an estimated 189,000 pounds of carbon monoxide and 61,000 pounds of propane, according to the company’s report to the TCEQ.