Industrial waste, including toxic ash from power plants, could also be spread by flooding from the massive storm, which has caused mandatory evacuations of coastal areas in both Carolinas and Virginia, the AP reports.
The hurricane center's projected track had Florence hovering off the southern North Carolina coast starting Thursday night before finally blowing ashore.
As of Tuesday, about 1.7 million people in North and SC and Virginia were under warnings to evacuate the coast, and hurricane watches and warnings extended across an area with about 5.4 million residents.
Georgia Governor Nathan Deal declared a state of emergency in the southern U.S. state on Wednesday ahead of the arrival of Hurricane Florence.
Landfall is expected late Thursday or early Friday, and the National Hurricane Center fears the storm "will slow considerably or stall, leading to a prolonged and exceptionally heavy and risky rainfall event Friday-Sunday".
As millions of people in the Carolinas and Virginia prepare for what could be historic damage from Hurricane Florence, people in space are keeping an eye on it from above.
Florence is rated a Category 4 on the five-step Saffir-Simpson scale.
The NHC said the first tropical storm-force winds of at least 39 miles per hour (63 kph) would hit the region early on Thursday with the storm's center reaching the coast Friday. Jeff Byard of the Federal Emergency Management Agency (FEMA) invoked a former boxing champion to warn residents that it would bring "a Mike Tyson punch to the Carolina coast". At 8 a.m. on Wednesday the storm was located about 855 km southeast of Cape Fear, North Carolina.
"We can only hope it won't hit hard", White said.
"I'm not approaching Florence from fear or panic", said Brad Corpening, 35, who planned to ride out the storm in his boarded-up delicatessen in Wilmington. Some 3,000 people died in the aftermath of that storm.
Michelle Stober loaded up valuables at her home on Wrightsville Beach to drive back to her primary residence in Cary, North Carolina.
"It's been really nice", Nicole Roland said.
"Where else can we go?" she said.
"We're just trying to plan for the future here, not having a house for an extended period of time", David Garrigus said.