CLEMENTON, N.J. (WPVI) -- A Camden County business around for 20 years was shut down after a dangerous, potentially deadly chemical was discovered inside.The Aquarium Center at the Commerce Plaza II in Clementon was shut down May 9 when mercury was discovered inside a fish tank.The toxic substance was spread when employees tried to clean it out along with the dead fish inside."Mercury in itself is a dangerous substance and any elevated exposure to it can cause sickness," Camden County Director of Public Affairs Dan Keashen said.Mercury exposure can cause brain and kidney damage and even death.Employees had to undergo a decontamination process including discarding all of their clothing.Keeshan says acceptable levels of mercury are .05 milligrams per cubic meter. The level on the floor at the fish store was 10,000 times that.Twelve employees at the store are having urine samples sent to the Centers for Disease Control and Prevention (CDC) for testing."My staff, myself, my family, we were walking through it for five days," Siconolfi said. "I can't wrap my head around it. I still can't. We were just tested a couple days ago, I haven't heard anything back from the CDC."Gloucester Township police are leading the criminal investigation into who contaminated the store with mercury and why.The state and county health departments are consulting along with the Department of Environmental Protection (DEP).The store was shut down just as it's about to move to a new location not far from away."This was a criminal act. We are doing the best we can. We are working with the police and the DEP. I don't have any information at this time," Siconolfi said.Siconolfi has been ordered to get a mitigation crew to clean up the mercury.Since nobody has been in the Aquarium Center for a week, it is presumed all of the fish inside have died.