Cars sit in a pool of leaked fuel and floodwaters after Harvey smacked Port Arthur, Texas. Thomson Reuters The heart of Texas' oil refining industry was hit by Hurricane Harvey

Storm-related flooding overwhelmed existing safety precautions at many plants , releasing hundreds of thousands of pounds of chemicals

4.6 million pounds of chemicals were released overall, some of which are cancer-causing

While advocates expressed concern about potential health effects, federal and state representatives said there is little reason for alarm

Hurricane Harvey struck the heart of Texas' oil refining industry when it pummeled Houston last week, resulting in the release of 4.6 million pounds of chemicals.

Those chemicals include cancer-causing and potentially lethal gases like carbon monoxide and benzene, among others.

But public health advocates and state and federal regulators are split about whether or not people should worry. While an EPA representative told the New York Times that residents “should not be concerned about air quality issues related to the effects of the storm,” environmental advocates have said the opposite.

“These are cancer-causing compounds, like benzene and butadiene,” Elena Craft, an Environmental Defense Fund senior health scientist, told the Times. “We’re very concerned about people’s long-term health in the area.”

Wei-Chun Chin, a professor of engineering at the University of California, Merced, has conducted research on the after-effects of oil spills like Deepwater Horizon. He told Business Insider in August that although the immediate effects of the pollutants in Texas sounded concerning, he was more worried about the possibility that some of those chemicals might stick around.

"I’m more concerned about things that could have a lingering effect and stay in the soil," said Chin. "Benzene is a known carcinogen. So if that's coming back into the ground that would be very bad."

The Texas Commission on Environmental Quality, the state's pollutant-monitoring agency, said in a statement that most of its air-surveying equipment did not detect emissions at levels that would be harmful to human health. Yet on September 5, Houston officials said they had detected high levels of benzene near one of the refineries that was damaged by the storm. Loren Raun, the chief environmental science officer for the Houston Health Department, told the Times that although the readings varied, officials in the area were seeing “high numbers.”

The EPA is working with Texas state regulators to clean up spills from a dozen industrial facilities, but representatives said it was still too early to estimate the amounts spilled, the Associated Press reported.

Harvey's rising waters overwhelmed existing safety precautions

Shortly after Harvey made landfall, companies including Exxon Mobil and Valero Energy began to shutter local facilities and evacuate workers, taking close to a fifth of the nation's total refining capacity offline.

Yet in many cases, those efforts failed to prevent the release of hazardous pollutants into the environment.

An oil tank damaged by Hurricane Harvey near Seadrift, Texas, August 26, 2017. REUTERS/Rick Wilking Preliminary reports severely underestimated the scope of the leaks, pegging the figure at somewhere around 2 million pounds. A more recent analysis — from the Environmental Defense Fund, Air Alliance Houston, and Public Citizen — suggests the number is closer to 5 million.

In some cases, companies intentionally burned chemicals to dispose of them in anticipation of the storm. This type of burn, called a chemical flare, is a means of relieving pressure on a plant during a shutdown and is considered standard industry practice, according to the American Chemistry Council.

Chevron Phillips, the company that reported the largest release, burned close to 800,000 pounds of chemicals as it shuttered its plant to prepare for Harvey. The colorless, odorless, and potentially deadly gas carbon monoxide made up nearly 300,000 pounds of that total.

At other plants, Harvey's rising waters easily overwhelmed existing safety precautions.

San Antonio-based refiner Valero Energy told local regulators that a floating roof covering a tank at its Houston refinery sank on August 27 due to Harvey-related flooding, and benzene subsequently leaked into the air. Similarly, officials at Kinder Morgan's Pasadena terminal, which released close to 300,000 pounds of chemicals, noted in a filing that several floating roof tanks were "impacted by torrential downpour" from Harvey.

At Exxon's Baytown plant, the floating roof covering one tank also "partially sank during the excess rain event". The company noted the issue in a filing that showed that close to 13,000 pounds of chemicals — including cancer-causing benzene and toxic lung-irritant xylene — were released.

Charlotte Huffaker, a representative for Exxon Mobile, told Business Insider that the company "reported and responded" to the partially submerged tank "as soon as it was identified," and said the container was currently stable and secure.

Still, these impacts may have lingering health effects.

Last week, testing done in the Manchester district near the Valero refinery reveled high levels of the cancer-causing pollutant benzene, the Times reported. The sampling showed concentrations of up to 324 parts per billion of benzene, which is above the level at which federal safety officials suggest workers use special breathing equipment.

Valero did not immediately respond to a request for comment.