Selection of Toxic Endpoints

Some effects, such as the OP insecticides inhibiting acetylcholinesterase, are relatively consistent across a large group of organisms these can be used without much uncertainty to assess potential toxicity to a target species. Indeed, we use the results of OP studies in chickens to identify a target level of enzyme inhibition in humans that might lead to toxic effects. 

Many times, rather than selecting a specific effect, maximum concentrations that cause no effects are used. In this way, it can be ensured that toxic effects will not occur as long as allowable concentrations remain below this threshold. These issues are further discussed in the next chapter, which explains how such concepts are used to establish safe levels of exposure in humans. 

Hodgson, E., and F. E. Guthrie. 1984. Introduction to Biochemical Toxicology. New York Elsevier Science Publishing Co., Inc., 437 pp. 

To use toxicity information on animals to set gnidelines and regnlations, as well as to evaluate health hazards in hnmans, data collected on animals is often adjusted to equivalent levels in hnmans. This estimation of valnes in one species (humans) from data on another species is referred to as extrapolation. This chapter discusses how this process works, amd what it means to an average consumer. In addition, toxicity in other animals is also expected to vary among species. If we want to establish a safe concentration of PAHs in soil to protect bald eagles from skin exposure, the results of skin painting stndies on rodents would also need to be extrapolated because we shouldn t expect the same sensitivity for such different animals. The extrapolation process for nse in wildlife species will also be discussed in this chapter. 

---

There are several dozen different types of enzymes that metabolize specific types of chemicals. For example, alcohol dehydrogenase is an enzyme that specifically metabolizes alcohol, and acetylcholinesterase is an enzyme that specifically metabolizes one of our neurotransmitters and is affected by organophosphorus insecticides (see the Selection of Toxic Endpoints section below). 

---