A New York Times report shows the floodwaters left in the wake of Hurricane Harvey contain highly toxic levels of bacteria, heavy metals, and other toxic substances.

The newspaper financed the detailed testing of floodwaters and the leftover sediment in several areas of the city. The samples were gathered by boat, truck, and foot, and the tests were conducted by a state-certified laboratory.

In one instance, the tests revealed the living room of a home near Buffalo Bayou had a concentration of E. coli bacteria that was 135 times the recommended safe level. The tests also revealed high levels of arsenic, lead, and other heavy metals in sediment deposits found in the home’s kitchen.

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Lauren Stadler, an assistant professor of civil and environmental engineering at Rice University, worked with the newspaper on the report.

“There’s pretty clearly sewage contamination, and it’s more concentrated inside the home than outside the home,” Stadler told the Times.

“It suggests to me that conditions inside the home are more ideal for bacteria to grow and concentrate. It’s warmer and the water has stagnated for days and days. I know some kids were playing in the floodwater outside those places. That’s concerning to me.”

The toxic floodwaters and their remaining sediment are already causing an increase in hospital visits. Emergency room workers reported an increase in bacteria-related skin infections, mostly attributed to skin contact with contaminated dirt or water.

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Dr. David Persse, the public health authority for the city of Houston, advised those who care for children, the elderly, and patients with weakened immune systems to stay away from flooded homes until they are cleaned.

“Everybody has to consider the floodwater contaminated,” Persse told the Times.