TORONTO — Thirty per cent of Canadian dentists missed a voluntary 2007 target to better control how they release mercury into the environment, but the dentists insist they're making good progress in cleaning up their act, even though they say they can't stop using the toxic substance.

Environmentalists, however, say the lack of any real standards is a major concern since low exposure to mercury can lead to learning disabilities in children, while more significant exposure can cause neurological damage or even death in severe cases.

The Canadian Council of Ministers of the Environment endorsed a set of voluntary Canada-wide standards in 2000 and 2001 to limit mercury emissions from base-metal smelters, coal-fired power plants, waste incinerators, mercury-containing lamps and from dental amalgam waste, which is a byproduct of dental fillings.

While all those emissions are decreasing, only 70 per cent of dentists hit their targets set for 2007 and the council said the industry has a long way to go before it reaches the goal of reducing mercury waste by 95 per cent.

Environmentalists say it's no surprise that the target was missed by so many dentists since it was only voluntary, and carried no penalty for non-compliance.

"My view is you need to have a stronger system, any dentist that is not using proper approaches, one thing to do it is to fine them ... it's theoretically possible under the Canadian Environmental Protection Act,'' said Ken Ogilvie, executive director of Pollution Probe.

It's estimated that as much as 1,046 kilograms of mercury was released by dentists into the wastewater stream in 2003, while the amount dropped by 57 per cent to 452 kilograms in 2007.

Mercury that's released into the environment can be absorbed in fish and wildlife and then transferred to humans when they eat those creatures, said Ogilvie.

"It doesn't go away, it doesn't biodegrade in the environment the way an organic pollutant might, so you do want to limit mercury as tight as possible,'' he said.

There are alternatives to using mercury in fillings, the most common being composite resins, which are growing more popular because they're white and blend in better with teeth.

But Ogilvie said composite filings could also carry a possible health risk since they contain bisphenol A, a chemical that's commonly found in plastic bottles. Some studies have suggested bisphenol A is unsafe and Health Canada is currently conducting its own study on the substance.

Fillings are also available in ceramics or gold but those options are considerably more expensive.

Outlawing mercury fillings would have a disastrous effect on public health by making dental care too costly for many Canadians, said Benoit Soucy, the Canadian Dental Association's director of membership and professional services.

"Changing to those two types of materials is definitely an economic problem,'' he said, and added that it's not easy to find an alternative for mercury because of the complex inner workings of the mouth.

"Getting materials that respond well in that environment is extremely difficult,'' he said. "There is no better alternative, definitely.''

But he said dentists are reducing the mercury they use -- in part because of the appeal and demand for composite fillings -- and are getting better at how they deal with its waste.

The most significant component of the voluntary standards involve the use of an amalgam separator, a device which filters the mercury before it can be released into the environment. Soucy said dentists must choose a separator that is 95 per cent effective but most are actually 98 per cent effective.

A study by Environment Canada estimated that only 16 kilograms of mercury would have been released into the environment in 2003 had all dentists used separators.

Kevin Mercer of the environmental group Riversides said any discharge of mercury is significant and every dentist in the country should be using a separator -- and ideally thinking of how to reduce the use of mercury.

"It's dark-ages thinking that we'd allow only 70 per cent of any industry to knowingly discharge a known neurotoxin into the ecosystem,'' he said.

"It's appalling, it boggles the mind -- they're like any other polluter and if anything, we should actually hold them to higher standard of care.''