Texas Tech University

Researchers: Flooding Can Have Long-Lasting Impact on Health, Environment

Glenys Young

June 1, 2015

From chemical exposure and mold to mosquitos, problems don’t stop when the rain does.


Flooding of the magnitude recently seen in Houston and Austin has washed away homes, damaged property and even claimed lives, but those aren't the only ways floodwater can be harmful.

Todd Anderson, a professor in Texas Tech University's Institute of Environmental and Human Health, said it's not only the power of the water that can be dangerous, it's also what could be in it.

“In a typical rain event, roads and curbs are used for drainage, so things that are on the road or things that are on lawns and other places are going to run off if there's enough rain,” Anderson said. “Anything that would be there naturally or applied to those surfaces is going to eventually end up in the water.”

That could include fertilizers, lawn chemicals, oil and grease from the road and more.

“When you apply your brakes, things come off the brake pads a little at a time. All of that is on the road surface,” Anderson said. “It ends up in the ditch or the curb. Brake pads contain asbestos, zinc, copper and other types of metals. A lot of those things, including the petroleum products, are naturally occurring. They're used in a lot of products. But that doesn't mean they're potentially less toxic.”

Of course, negative effects from coming in contact with the water are not likely to be immediate.

Todd Anderson

“Unless it's something catastrophic, acute impacts from chemical constituents are not a problem. Most of those are long term,” Anderson said. “That water is dirty, by a variety of definitions. It's not like if you go in the water you're going to fall down dead, but you're going to get an infection probably. You may have other sorts of issues, especially long term, because of being in that environment. Unless there's a waste pond that flooded because of rain and you're coming in contact with that; in that case, there are potentially immediate consequences.”

The important thing to understand is the threat doesn't go away when the water recedes.

“Flooding tends to redistribute things, and sediment gets left behind when the water recedes,” Anderson said. “In some cases, those sediments were contaminated and moved from one place to another. For instance, waste sites have fences up to keep people out, but suddenly there's redistribution. After the water recedes, you potentially have contaminants in places you didn't expect.”

Another risk after flooding is mold.

“Normally we don't have mold issues in West Texas because it's so dry,” Anderson said, “but if you get wood or sheetrock wet, you can end up with various kinds of mold, and some of them are bad.”

David C. Straus, who retired in 2013 as a professor of microbiology and immunology at the Texas Tech University Health Sciences Center, said mold can be a major health issue.

“If one of these houses flooded and mold grew, mold fills the air with its spores and people inhale it,” Straus said. “It causes respiratory problems, wheezing, sneezing, shortness of breath and inflammation of the lungs. That's the most immediate danger.”

When a house floods and building materials – particularly carpeting and sheetrock – get wet, mold starts to grow immediately, Straus said, but it usually takes four to five days before the colony is large enough to be seen with the naked eye.

Steve Presley

“Sheetrock can stay wet for weeks or even months,” Straus said. “What people can and should do is get the material dry immediately, which is very difficult, or just tear it out.”

This is why after natural disasters, the sight of people ripping out carpet and sheetrock and throwing it in the front yard is so prevalent, he said. It's potentially a very expensive problem.

“There are probably 100,000 species of mold. Some are very dangerous, some not so dangerous, but you can't tell what type it is,” Straus said. “All mold should be removed.”

One of the post-flooding threats may not be seen for several weeks, but once it appears it will be obvious.

“With the floodwaters in Houston, Dallas and off the Caprock, mosquito numbers are going to be big this year,” said Steve Presley, a professor in the Texas Tech University Institute of Environmental and Human Health. “Coming out of the drought, they haven't been a big issue for the last several years. They're more just pests right now, but as the season progresses West Nile virus will become more of a concern.”

Mosquitos may also carry a variety of other diseases, including St. Louis encephalitis virus, dengue fever, chikungunya virus and malaria.

While there are a variety of things a person can do to avoid mosquitos, it may be more difficult to avoid floodwaters, especially when rain continues to fall on already saturated ground. Unfortunately, the only way to avoid the threat of flooding is to avoid the flooding altogether.

“There's not much else to do other than avoid it,” Anderson said. “Risk is a function of exposure and effect. So if you eliminate exposure, there is no risk.”