The floodwaters from Hurricane Harvey had to go somewhere.
The storm dumped 50 inches of rain on parts of the Houston area in late August. Much of the water made its way through streets and bayous and eventually drained into the Houston Ship Channel, the busy commercial waterway that allows ships to travel between the Gulf of Mexico and industrial facilities around Houston.
In the weeks since, the water has drained away, but scientists believe many of the contaminants it carried have not.
"The Port of Houston is saying they had up to 10 feet of storm layer deposited in the ship channel," explains Tim Dellapenna of Texas A&M University, Galveston, who is studying the so-called storm layer of sediment that Harvey left in the bottom of the channel.
Sediment can tell scientists a lot about a flood — contaminants get trapped in the mud, and the very amount of mud and sand can reveal things about how the storm played out.
"We're actually going to try to do a full screening for dioxins, heavy metals, polyaromatic hydrocarbons," Dellapenna explains. Mercury is a heavy metal. Polyaromatic hydrocarbons are often released by petrochemical operations, like the ones that line the ship channel.
Water rises in the Houston Ship Channel on Aug. 27. Some of the largest oil refineries in the world line the channel,
which connects Houston to the Gulf of Mexico.
Dioxins, in this case, could come from a Superfund toxic waste site nearby. The San Jacinto Waste Pits upstream flooded during the storm, and the Environmental Protection Agency says dioxins may have washed into the channel.