Monsanto Chemical Company produced more than 18 million kg of Aroclor in 1974 the percentages of the market were as follows: Aroclor 1016, 64%; Aroclor 1242, 17.9%; Aroclor 1254, 17.9%; and Aroclor 1221, 0.1%. From 1930 until 1975 the assessed quantities of produced and consumed PCBs were: total production, 635 million kg; imports, 1.4 million kg; domestic sales, 568 million kg; and exports, 68 million kg. As of 1976 the US government granted the Environment Protection Agency (EPA) all affairs related to PCBs and in 1979 the EPA prohibited the production, export and import, as well as closely monitoring the discharge of PCBs (ATSDR). .
The structure of a Polychlorinated Biphenyl is simply two benzene rings which are carbon to carbon bonded between carbon 1 and 1'and from there they can have a various number of chloride atoms. Normally a Biphenyl is the two cyclic rings attached together with only carbon and hydrogen atoms in the compound, but to produce a PCB some of those hydrogen atoms are displaced by chlorine. As the position and number of chlorine atoms is altered the toxicity of the PCB also changes in response. There are three most common chlorine arrangements: chlorines attached to carbon 2,2' and 6,6' are in the ortho position; chlorines which displase hydrogens in places 3, 3' and 5,5' are said to be in metha position and lastly chlorine atoms in the number 4, 4'positions are para. All sites are in accordance with carbon 1,1' bond. .
In PCBs the location of the chlorine is very important because it is directly related to the toxicity of the compound. If a chlorine substitutes a hydrogen in ortho positions 2 and 2' than that makes the PCB a less toxic one in comparison to a PCB with a coplanar structure meaning there are chlorine atoms in every position except for the ortho ones, these types of PCBs are particularly toxic. Also if a PCB has chlorine in both para positions and at least 2 in any metha they are considered to be dioxin like and very toxic.