ABSTRACT
Animal studies occur under controlled conditions. This control refers to exact doses, and specific lengths and times of exposure. By controlling the amount, the timing, and the duration of exposure, scientists can obtain increased quantity and quality of information on a chemical’s health effects. For example, altering the amount, timing, or duration of a dose in a study can alter the chemical’s opportunity to inflict damage. Large doses may cause one type of response; small doses, another. Timing of a dose may also be critical. For example, if exposure is timed to occur during a “window of vulnerability” in a fetus, minuscule amounts of an agent may cause severe damage. Outside this “window,” this amount would be harmless to the fetus. Clearly, control of the dose provides tremendous influence over the types of health effects seen. In addition, this control allows for variability in study design. Toxicology studies can occur over short, medium, or long periods of time. Shortterm, or acute exposure studies, occur over 2 weeks and generally involve high doses of the chemical substance. Medium-length or subchronic studies involve lower chemical doses over a longer time period, from 5 to 90 days. Long-term or chronic
studies can last 2 years and use much smaller doses of chemicals. This variability improves understanding of a chemical’s activity under a different conditions.
