Since the late 1800s the range of synthesized chemicals has increased dramatically to include pesticides, plastics, hydrocarbon fuels, soaps, detergents and other useful substances. The effects in the environment are result of a sequence of processes that depend on the properties of individual chemical. DDT has been the focus of a large amount of early research due to its effects on the endocrine system leading to egg shell thinning and reduced breeding in birds. DDT is a member of chlorohydrocarbons, a family of chemically related insecticides. Chlorohydrocarbons are highly toxic to aquatic organisms, persistent, soluble in fat and have very low solubility in water. They move from water to animals with a large increase in concentration by a process described as bioaccumulation. This group, banned from use in many countries, includes industrial chemicals such as PCBs and combustion products like polycyclic aromatic hydrocarbons, dioxins and furans. In terms of used quantities herbicides are of major importance but their properties differ significantly from chlorohydrocarbons. Herbicides are relatively water soluble but less soluble in fat and less persistent. Thus they don't bioaccumulate and are less toxic having a much lower impact in the environment. Organophosphates, carbamates, pyrethrins and pyrethroids also have, in general, low solubility in fat, relatively high solubility in water but low persistence and are not bioaccumulative. Members of this group can be highly toxic to biota including mammals and aquatic organisms but overall their environmental effects are usually low. Soaps and detergents, containing surfactants, have relatively low toxicity, persistence and bioaccumulation. Although discharged to environment in large quantities their effects are generally low. Plastics differ from other contaminants since these substances enter environment as solid wastes with little toxicity but have other adverse environmental effects. The management of these effects relates to their degradation and removal from the system.