CHICAGO (CBS) — Investigators have begun examining tiny particles of dust at a northwest Indiana apartment complex contaminated with lead, to determine how widespread the problem is.

Teams were carefully collecting samples from 50 homes at the West Calumet housing complex in East Chicago, Indiana, on Monday, after more than 1,000 residents learned the dirt their children have been playing in has lead levels 10 times higher than the federal safety standard.

It takes 30 minutes to an hour to collect samples from each home, as investigators check each room.

Workers with the U.S. Environmental Protection Agency, the Indiana Department of Health, and the Agency for Toxic Substances and Disease Registry began taking samples from the first home around 9:30 a.m. Monday.

They were collecting dust samples from any flat surfaces, including floors and carpets.

Last week, the EPA announced it had discovered the ground within the housing complex was highly contaminated with lead and arsenic.

East Chicago Mayor Anthony Copeland advised more than 1,000 residents – including about 700 children – they should temporarily relocate from the complex. The EPA also told people there not to play in the dirt, or around the mulch.

Results from the new round of testing should help determine the source of the contamination, and how to remedy the problem, if possible.

“We’re most concerned about young children, so we’re targeting the bedrooms for the children, the play areas, and also at the entrances that they would use coming in and out of the homes,“ said Dr. Mark Johnson, regional director for the Agency for Toxic Substances and Disease Registry.

Joniequa Riley said she’s especially worried, because she’s seven months pregnant.

“They’re still cutting the grass, blowing the dirt everywhere, so you’re really breathing it in,” she said. “I went and got the lead poisoning tests. I’m waiting until this week to pick up the results, but I feel like if something’s wrong with my baby, that’s something that I’m going to have to live with for the rest of our lives, not just mine.”

Teams were testing inside only 50 of the homes at the housing complex, focusing on the ones where the exterior levels were exceptionally high, or homes with children. It could take at least a week before test results are back.