Identifying toxicity epidemiology

The emphasis in this chapter is on the use of animal tests, or bioassays as they are sometimes called, to identify toxicity. Epidemiology has been important in uncovering the effects of subchronic and chronic exposures to some very important chemicals, including those capable of causing cancer. Carcinogens are a special breed of chronic... 

Polyalphaolefin Hydraulic Fluids. No human studies for polyalphaolefin hydraulic fluids were located. Polyalphaolefin hydraulic fluids are used in U.S. military aircraft hydraulic systems thus, there is a potential for occupational exposure. Animal studies were insufficient for determining the primary targets of toxicity. Epidemiology studies examining a number of end points would be useful for identifying targets of toxicity. 

Epidemiology studies are, of course, useful only after human exposure has occurred. For certain classes of toxic agents, carcinogens being the most notable, exposure may have to take place for several decades before the effect, if it exists, is observable - some adverse effects, such as cancers, require many years to develop. The obvious point is that epidemiology studies cannot be used to identify toxic properties prior to the introduction of a chemical into commerce. This is one reason toxicologists were invented ... 

Case-Control Study—A t5q)e of epidemiological study which examines the relationship between a particular outcome (disease or condition) and a variety of potential causative agents (such as toxic chemicals). In a case-controlled study, a group of people with a specified and well-defined outcome is identified and compared to a similar group of people without outcome. 

Assessment of whether a chemical has the potential to cause adverse effects in humans arises usually from direct observation of an effect in animals or humans, such as the acute poisoning episodes that have occurred when potatoes contain high levels of glycoalkaloids. Epidemiological studies have also been used to infer a possible relationship between intake of a particular type of food, or constituent of that food, and the potential to cause an adverse effect. Such observations led to the characterisation of the aflatoxins as human carcinogens. However, natural toxic substances that occur in plant foods have often been identified through observations in animals, particularly farm animals. It was observations of adverse effects in farm animals that led to the further characterisation of the phytoestrogens and the mycotoxins. In other instances, the concern arises from the chemical similarity to other known toxins. 

Epidemiological studies carried out on humans are very useful because a hazard can be directly characterized without need for extrapolation. Unfortunately, the statistical power of this methodological tool is too weak to identify with the required accuracy the adverse effects of lower quantities of residues unlikely to produce acute toxic effects. The evidence of allergic effects in humans from penicillin residues is a fortunate exception. More frequently, useful information can be obtained for drugs also used in human medicine. 

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