Academic literature on the topic 'DDT (Insecticide) – Toxicity testing'

This chapter focuses on four of the best known and most well characterized EDCs: the polychlorinated biphenyls (PCBs), dichlorodiphenyltrichloroethane (DDT), diethylstilbestrol (DES), and bisphenol A (BPA) as prototypical EDCs. For each compound, historical information regarding use, sources of contamination, descriptions of toxic effects, nature of endocrine disruptive mechanisms, and detailed summaries of critical research findings are highlighted. Each of these chemicals are seminal illustrative examples of EDCs that came to be recognized, defined, and considered seriously by the general pu

The more species are removed from each other in evolutionary development, the greater is the likelihood of differences in response to toxic agents. One obvious difference that affects toxicity is the size of the organisms. Much less toxin is needed to kill a small insect than a considerably larger mammal (everything else being equal). In addition, there is an inverse relationship between the weight of an animal and its surface area; the smaller the animal, the larger its surface area per gram of weight. Thus, the weight ratio of a human being (70 kg) to a rat (200 g) is 350, but the surface area ratio of a human being to a rat is only 55. Roughly, the surface area of an animal (S) can be calculated as follows: S(m2) = weight (kg)2/3/10. This type of calculation is important when one is considering the selective eradication of an uneconomical species, such as certain insects, by spraying an area with insecticide. The goal is to control the insects without harming wildlife, livestock, and human beings. Other factors, such as the rate of percutaneous absorption, also have to be considered. For instance, it has been shown that DDT (dichlorodiphenyltrichloroethane) is about equally toxic to insects and mammals when given by injection, yet when applied externally it is considerably more toxic to insects. This toxicity is due not only to the difference of the surface area:- body weight ratio, but also to the fact that the chitinous exoskeleton of the insect is more permeable to DDT than unprotected mammalian skin (1). Of course, in real-life situations (i.e., outside the laboratory), most mammalian skin is covered by fur, which gives the animals additional protection. The foregoing discussion is not meant to imply that unrestricted spraying with pesticides (especially chlorinated hydrocarbons, which are fat-soluble and poorly biodegradable) is environmentally sound. Problems with their use include lack of selectivity among insect species; leaching into watersheds and groundwater; and bioaccumulation in the food chain. These problems will be discussed in detail in Chapter 11. Metabolic-pathway differences among species may provide another rationale for achieving selective toxicity