Dr Ravi Gooneratne, from Lincoln University, researches the conduction velocity of nerve cell impulses in earthworms and compares worms kept in polluted soil with those kept in clean soil. The response depends on the amount of the pollutant in the soil, how long the worm is kept in the soil and how much that particular pollutant affects the nervous system of the worm.
DR RAVI GOONERATNE
When these earth worms are exposed to pollutants, the speed decreases, and we can detect that… we can take measurements on a daily basis and look at whether the conduction velocity changes, and we can say – if it’s markedly decreased compared to our worms in the control soil – that in this worm, the nervous system has been affected by something in the soil. Now we cannot say what this pollutant is – the only thing we can say is it has something that affects the nervous system in the earthworm. Many chemicals affect the nervous system because the nervous system is very sensitive to chemicals. That means that, even the smallest, slightest increase in concentration, there’ll be a decrease in the conductant velocity of the nervous system. The effect is dependent on the type of chemical – if the chemical is very specific for the nervous system, we might get a reading very quickly, at a very small concentration or small dose, whereas some chemicals we might have to leave for 4 days or 7 days or 14 days. So in toxicology, the important thing is how much you are exposed to and how often you are exposed to and that determines the effect on the organism.