The chemicals that are used are all highly toxic to mammals as the pure product. However, only very small quantities are placed on baits that attract target animals. The adverse effects of rodenticides include killing of some nontarget species and secondary poisoning of predators feeding on poisoned animals. Since no bait is likely to be attractive to the target species only, rodenticides often cause temporary reduction in populations of species other than the offending ones. Because of reproductive potential of most small mammals, such decreases in populations, including that of the target species, are likely to be limited to a year, more or less, unless a very large area is baited.
Many predators feed on a variety of small mammals and other predators.
Substantial reduction in the population of one or even several species of small mammals would not cause a long-term effect on the predator population. Other parts of the forest are affected little by the use of rodenticides. The most common use of fungicides in nurseries is soil fumigation before seeding. The fumigants are general biocides, which are effective in killing seeds, fungi, and the various soil insects. Because of the very limited acreage of forest nurseries, these treatments do not have a general effect on the environment in the broadest sense.