Tests at William Byrd High School in Roanoke County have ruled out several possible causes for strange, seizurelike symptoms in roughly 10 people at the school.

The school system hired environmental consultant ECS Mid-Atlantic to perform the tests. Company official Derek Cooper said tests on surfaces at the school found no evidence of anything abnormal inside the building.

He said they ruled out mold, carbon dioxide and carbon monoxide. While there's no evidence of mercury, pesticides or herbicides, final results are not in.

The surface tests follow earlier tests on the school's air and water supply, which turned up nothing unusual.

The Virginia Department of Health is performing its own epidemiological investigation.