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Science Spin September 2009
Toxicity testing, without killing
By Sean Duke
The current methods of testing for the presence of toxic substances in the environment is crude, slow, expensive, and is still based - somewhat incredibly - on couting the number of dead animals exposed to specfic toxins over time. But, there is a better method.
Professor Dimitri Papkovsky, UCC, is using Daphnia (pictured here), a small, aquatic crustacean, commonly called a 'water flea', as a new 'experimental model' for testing for environmental toxins. This is superior to the traditional method of toxicity testing, which involves exposing larger animals to toxins, and counting the number of dead bodies that mount up over a given time period.
A researcher based in UCC has come up with a new approach to testing for toxins in the environment. It is faster, cheaper and more sensitive than existing methods, and - something that is increasingly important on many levels - it doesn't involve killing animals.
Professor Dimitri Papkovsky has developed new methods for conducting toxicity tests, simply by adapting and applying some existing testing technology.
Sensitive tests can be carried out on cell cultures or on tiny organisms such as the water flea, above, and best of all, there is no scientific need to kill them.
REACH
The context for this work is the EC REACH (Registration, Evaluation, Authorisation and Restriction of Chemical Substances) Directive which became law on 1 June '07. Under REACH a long list of chemicals including heavy metals, organic solvents, pesticides and aromatic hydrocarbons, must be closely monitored and controlled.
At the moment, toxicity testing involves a number of tests that make use of animal 'models' including fish, and mice. There is a drive in the EU now, however, to phase out these type of animal tests and move to something more ethical and humane.
As well as involving the killing of animals, the current tests, said Professor Papkovsky, are not very fast, and do not allow a high throughput of samples - something that's required more and more these days. Also, they are also based on subjective assessments that can be inaccurate, such as determining an animal is dead when it might simply be immobile.
"People, for example, maintain cultures of fish, like trout or zebra fish, in large tanks and then they receive (toxic water) samples," explained Prof Papkovsky. "They put fish in these samples, they incubate for 24, 48 and 72 hours. Basically they are counting the number of dead, and the number of alive animals to determine the level of toxicity."
In contrast, Prof Papkovsky uses cells and small organisms - such as Daphnia 'the water flea' - to develop his toxicity tests. This is ethically more desirable than doing toxicity testing on higher animals like mice. Furthermore, the strategy is set up to test 'sub-lethal' effects of toxicity, so organisms and cells are not killed in any case. The approach is to look at respiration and oxygen consumption as a measure of toxicity.
"We don't need to kill the animals," said Prof Papkovskyi, "we just need to detect changes in respirations, so potentially this approach is more sensitive. It is more humane and it can be automated and miniaturised. We do it on a standard micro-plate, with 100 samples analysed simultaneously over a period of one hour. Then you have your toxicity data pretty much straight away."
The samples are sealed off from the outside inside the microplate. This is important because oxygen levels are being measured and contamination from air is a threat.
"The microplate serves as a small container where we can expose the organism to the toxicant," said Prof Papkovsky. "Clinical tests are (already) done in these type of microplates. So, we don't need to develop a new instrument, we don't need to develop these plates, we're just adopting our assays and system to what is already available."
Under REACH there is a list of in the region of 30 'priority' industrial chemicals, said Prof Papkovsky, which now need to be monitored and assessed for their toxicity. To achieve this Ireland will require a national monitoring system, and he said that his technology would be well suited to be applied to that system by providing a range of simple tests.
There is a follow-on project, said Prof Papkovsky, where a specific group of chemicals, as defined by REACH, are being targeted. Furthermore he is working closely with the EPA, as well as an industrial partner, Luxcel Biosciences - a company working in environmental monitoring - to bring this testing technology into more widespread use.
