Elevated levels of arsenic have been found at seven Detroit sites where buildings were demolished in 2017-18 and filled with soil, a newspaper reported.
The results followed concerns raised by federal inspectors that 200 sites may have been filled with risky dirt.
Tests show unsafe levels of arsenic at seven sites so far and an eighth "did not fully meet quality standards," the city said Thursday.
Detroit ordered a contractor to replace soil at seven sites and test or replace soil at another 127 sites, The Detroit News reported.
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"Whenever we become aware of a breach of contract instance, we require the contractor to address the situation at their own cost," said Raymond Scott of the buildings department.
Arsenic is a natural element found in water, air and soil. Chronic exposure can cause health problems.
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"Scientists, pediatricians, and public health professionals are concerned about subtle and long-range health effects of low-level exposures to arsenic in people," according to the National Institute of Environmental Health Sciences.
Detroit said temporary fences would be installed around the sites.