Toxicity is a measure of the degree to which something is poisonous. The study of poisons is known as toxicology. Toxicity testing ranks as one of the most extreme forms of deliberately-inflicted animal suffering, because death is often the endpoint of the experiment. Animals who do not die in the course of the experiment will be killed anyway, in order to study their tissues. In many tests, very high doses of test compound (often thousands of times more than any conceivable human exposure) are given so as to reveal possible adverse effects. Symptoms may include vomiting, diarrhoea, haemorrhage, breathing difficulties, severe irritation, seizures and, eventually, death. Long-term toxicity tests may result in liver damage, weight loss and tumours.
Toxicity testing is carried out in the UK for purposes of safety or efficacy of pharmaceutical preparations as well as of industrial chemicals. It accounted for nearly half a million animal procedures in 2003, or 16 per cent of the total. Mice, rats and fish were most often used. However, a whole range of animals are killed in such tests, ranging from chickens to rabbits and guinea pigs. In the field of medical drug testing, a rodent and a 'higher mammal' non-rodent species are required for regulatory purposes. The non-rodent species commonly used is the dog, but now, increasingly, monkeys are being used. Toxicity tests usually involve force-feeding animals by gavage (a long tube pushed right down to the stomach - a very unpleasant experience) or injection, or both. In other 'procedures', the animals are forced to inhale vapour by sealing them in an air-tight chamber.
In addition to causing extreme suffering, the use of animals in such tests is exceedingly unreliable as a predictor of human toxicity, which raises serious public health questions regarding the relevance of such tests. During the middle ages, the king would often have his food tested for poison by the court jester - and not by the dogs. Even then, plain common sense was sufficient to recognise the importance of species differences. The animal models used today do not reliably predict human outcomes, because of the vast differences between animal and human metabolism and lifespan. Equally, the sheer number and combinations of chemicals to which humans are exposed simultaneously is something that cannot be duplicated in animals in a laboratory setting. However, there are non-animal methods that could successfully be employed (see Non-animal testing methodologies appropriate for regulatory toxicology).
Today, we live in a sea of chemicals - around 100,000 of them - ranging from pharmaceutical drugs, food additives and pesticides, to air fresheners and deodorants. The potentially deleterious effects that these chemicals have on human health and the environment have not been well studied. Perhaps the most notable reason for this 'oversight' is the enormous economic burden of exposing millions of animals to thousands of individual chemicals over varying lengths of time, even years. Such tests typically involve single chemicals and will therefore not detect the effects of potentially dangerous combinationsof chemicals (the so-called 'cocktail' effect). In addition, it is a well known toxicological phenomenon that a pesticide may exert its most toxic effects at lower doses. Toxicopathologist, Dr Vyvyan Howard, has estimated that,in order to test the commonest thousand toxic chemicals in unique combinations of three, it would requireat least 166 million different experiments (1). Even then,we still would have no way of knowing what of the resulting animal data was relevant to humans.
Animal welfare concerns aside,the current safety testing regime is seriously negligent with regard to its declared purpose of protecting public health.