By definition, a pesticide is any chemical used to kill or control and unwanted population.  The pesticide aims to work at the target organism, or the species that is trying to be killed.  However, in most situations, it is nearly impossible to kill off or control just the target organism, and usually, many other species are affected as well.  There are two main types of pesticides, and these are non-persistent pesticides which break down quickly (such as the commonly used brand, Roundup), and persistent pesticides which remain in their original form for a very long time (such as the infamous DDT).  I want to address the pros and cons as well as types of each, and s the problems associated with biomagnification and bioaccumulation.