Scientists testing burnt soil found an unwelcome ingredient - hexavalent chromium. Hexavalent chromium is known to cause cancer. Scientists think the intense heat from wildfires turns benign metals in soil into the carcinogen. Researchers previously detected dangerous metals from burned out cars and buildings. Now they say, we have to worry about toxic gas spewing into the air during fires containing toxins coming from the soil as well. The study showed that temperatures over 390 degrees can catalyze chemicals and turn them into their cancer causing versions. Researchers are concerned that wildfire smoke is spreading toxic metal pollution.