Many Australians are exposed to a cocktail of toxic substances in their daily lives - but the mixture doesn't necessarily put them more at risk.

The research was presented 25 June 2007 by Professor Jack Ng of the CRC for Contamination Assessment and Remediation of the Environment and University of Queensland at the Contamination 07 conference in Adelaide.

"We are seldom exposed only to a single contaminant in the environment - but more often than not to a cocktail of chemical mixtures," Prof. Ng explains.

"Exposure can take place at a contaminated site or via the food chain. Examples include mixtures of petroleum hydrocarbons, metals and metalloids in mining waste material and pesticides on or in the food we consume".

He cautions that health risk assessment of chemical mixtures can be complex and often very expensive to get sufficient evidence-based data for proper evaluation.

"The urban myth of thinking one exposes to chemical mixtures automatically places one into higher risk category is incorrect. The fact about toxicity remains the same for either a single chemical or a mixture of chemicals: "It is the dose that makes the poison".

The main risk in a chemical mixture is most often that of the most risky component, he says.

An important feature in assessing the riskiness of mixtures is to have a good understanding of how the different contaminants in the mix may interact with one another - and inside any creature, including humans, which absorbs them.  Sometimes these reactions can make the mixture more, or less, toxic.

Professor Ng said the cost of analyzing all the possible interactions and effects of any complex mixture would be immense. Failing this it is best to use a risk-based approach focused on the known kinetics and dynamics of the chemicals in the mix and the risk of human exposure.