Importantly, the toxic measurements obtained by the in vitro method, such as the amount of a contaminant needed to inhibit cell growth, mirror well-established lethal values obtained from animal studies - a long-established method in toxicological studies. "In-vitro toxicity tests can improve the scientific, economic, and ethical value of research and play a significant role in the screening of toxic chemicals and the replacement of animals," Dr Hayes says.
This research earned Hayes and her colleagues the 2006 Australian Museum Voiceless Eureka Prize for Research. This prize rewards scientists for work that has reduced the use of animals or animal products in laboratory-based research, education and testing.
Many industrial and environmental air pollutants are already known to have adverse health effects on the respiratory system of workers. Increasingly, new formulations are using tiny nanoparticles and ultrafine particulates in cosmetics, pharmaceuticals and petrochemical products. Little is known about their toxicity and safety to human health but this new category of pollutants poses possible dangers, both medically and environmentally, especially if they get airborne.
Most nanoparticles have a high surface area-to-mass ratio that can make the particles very reactive or catalytic. Being so small, they may also be able to pass through cell walls in organisms, and their reactions inside the body are relatively unknown.
"These tiny new substances are the tip of a huge chemical iceberg," says Hayes, Manager of the Chemical Safety and Applied Toxicology Laboratories at the University of New South Wales.
"Worldwide, there are millions of known chemicals, of which more than 100,000 chemical compounds are in commercial use in an unknown but extremely large number of chemical mixtures.
"Continued conventional animal toxicity testing of this large number of chemicals is simply unachievable from a scientific and economic standpoint," says Dr Hayes. "It's also unethical, given that in Australia alone, more than a million dogs, cats, rabbits, sheep, cattle, pigs and mice are used each year for toxicological testing and research." This is a drop in the ocean, compared with the animal death toll in the rest of the world.
In many inhalation studies, the toxicity of airborne chemicals is tested on laboratory animals by placing them in enclosed chambers and subjecting them to increasing concentrations of the test compounds for specified times until half of the test animals are killed. One type of test commonly used where this occurs is the LD50 test, where LD stands for lethal dose.
This heavy reliance on animal data in toxicology has long been a concern of the scientific community. Predicting the biological activities of toxic chemicals in humans by using animal data always poses uncertainty due to differences between animals and humans.
In a series of published experiments, the UNSW team has demonstrated the feasibility of their in vitro technique for:
formaldehyde, an industrial contaminant linked to human cancer;
The in vitro method "opens new possibilities for toxicity testing of industrial chemicals, environmental contaminants, workplace airborne contaminants, and fire combustion products", says Dr Hayes.
The technique has several advantages over conventional tests: