A mercury spill of between 200ml and 500ml in a building near Alexandra this week was believed to be the second biggest such spill in the country in a decade.
The mercury, stored in a bottle, was spilled in an outbuilding, Alexandra's deputy chief fire officer Mark Hutton said.
The chemical was at the rural property in Waldron Rd because it was used for recreational gold mining.
The house occupants moved out and would stay away until a specialised decontamination unit had completely cleaned up the spill, which happened on Thursday afternoon.
The Alexandra brigade and the Fire Service's specialist hazardous material unit with a pumping appliance were at the site until 2am yesterday.
There was a cordon around the property and the spill was contained, so it was safe.
Health authorities were involved in the decisions about the cleanup and the spill was ''mopped up'' by specialist hazmat officers wearing splash suits.
It was a ''significant'' quantity and believed to be the second biggest mercury spill in the country in the past decade, he said.
The house occupants had been checked by medical staff and were not displaying any adverse health effects from any possible exposure to mercury.
Asked about the health risks from liquid preparations of mercury, National Poisons Centre poisons information officer Christina Needham said the main concern was chronic exposure to the vapour.
When the liquid was spilled it was difficult to clean up.
Tiny beads could seep into soft furnishings such as carpet and chairs and give off vapours over time.
Long-term exposure to the vapour could cause damage, affecting the entire nervous system.
Symptoms were often ''flu-like'' and included muscle tremors and memory loss, she said.
