The attorney's first job is to determine the source of the toxic exposure and the toxic agent by employing an experienced expert in toxic substances, either toxicologists or a certified industrial hygienists. Of course, the plaintiff must prove not only that the exposure occurred, but also that the negligence of the defendant caused the exposure. In other cases, however, proving that the exposure caused the plaintiff's injury may be more difficult. This is especially so in cases where the injured party was also exposed to toxic substances for which the defendant was not responsible. In many cases, the plaintiff must attempt to provide major scientific evidence based on either clinical tests, animal studies or epidemiological evidence.
Epidemiological evidence is statistical evidence connecting the disease to a particular exposure.
An expert in this area of scientific study is called an epidemiologist. Usually, the epidemiologist will examine the general population, comparing the incidence of the particular disease among those people exposed to the toxic agent in question to those not exposed. The epidemiologist then uses mathematical reasoning to draw a biological inference between particular toxic agent being studied and the disease's etiology. Finally, the attorney must also ensure that qualified experts can establish the extent of damages. The level of damages is intended to put the plaintiff back in the position the plaintiff would have been in if the tort had not occurred.