Toxicity...

Definition

The quality or condition of being toxic

Interested in getting test without leaving your own home, click here!!!

Causes, incidence, and risk factors

The phrase "toxic" chemical is seen frequently in the media and heard often in social settings. Other than suggesting something bad about the chemical, what exactly is meant by saying that a chemical is toxic? Does it mean that it will kill people? cause cancer? affect their children? Are there chemicals that can't cause any harm? To a toxicologist, this last question is easiest to answer. Everything is toxic: in sufficient quantities, every chemical has the capacity to cause adverse effects on human health. It is only the degree and type of toxicity that varies from chemical to chemical.

Even chemicals that are necessary for life such as water and oxygen can be toxic. Human experience has shown that while usual amounts of oxygen and water don't cause adverse effects in humans, higher amounts can. Drinking very large amounts of water in a short period of time can lead to swelling and brain damage, particularly in infants. Breathing pure oxygen can also cause problems in humans, in this case irritation of the lungs. Thus, toxicity assessment is not about determining what is toxic, but rather about how much of a chemical causes what kind of harm.

Dose-response studies are used to establish the relationship between the amount of chemical and the seriousness of the effect. The dose -- the actual amount of chemical -- is gradually increased and the response -- the observed effects -- at each dose are noted. For some chemicals, such as some organophosphate pesticides, increasing the dose slightly leads to a large increase in effect (toxicity). Such a chemical doesn't have a large margin of safety and may be difficult to manage. On the other hand, the effects due to another chemical may increase only very slowly as the dose is increased. Such chemicals, such as alcohol, are easier to manage.

Since toxicity refers to a number of possible adverse effects, there are several ways to deal with it. One way is to divide the effects into categories based on two fundamental characteristics of toxicity: how fast the effects occur and what type they are. Effects that occur very rapidly after exposure has occurred are described as acute toxicity; those that happen only after repeated long-term exposure are known as chronic toxicity. Acute toxicity is the kind that people are familiar with from detective stories. For example, the victim drinks the poisoned wine and dies within minutes. Death is not the only type of acute effect, however; some others are sweating, nausea, and dizziness.

Chronic toxicity also may take many forms. The most well-known chronic effect is cancer. Others are organ damage such as cirrhosis of the liver from long-term alcohol consumption, reproductive effects such as decreased fertility, and effects on the nervous system. An example of a nervous system effect is mental retardation in children who were exposed to high levels of lead over a period of time in early childhood.

Interested in getting test without leaving your own home, click here!!!