Dating aroclors new england
Atmospheric concentrations of PCBs tend to be lowest in rural areas, where they are typically in the picogram per cubic meter range, higher in suburban and urban areas, and highest in city centres, where they can reach 1 Volatilization of PCBs in soil was thought to be the primary source of PCBs in the atmosphere, but research suggests ventilation of PCB-contaminated indoor air from buildings is the primary source of PCB contamination in the atmosphere.
In biosphere, PCBs can be degraded by either bacteria or eukaryotes, but the speed of the reaction depends on both the number and the disposition of chlorine atoms in the molecule: less substituted, meta- or para- substituted PCBs undergo biodegradation faster than more substituted congeners.
It is unlikely that a full inventory of global PCB production will ever be accurately tallied, as there were factories in Poland, East Germany, and Austria that produced unknown amounts of PCBs.
PCB's utility was based largely on their chemical stability, including low flammability, and high dielectric constant.
Some PCBs share a structural similarity and toxic mode of action with dioxin.
The bromine analogues of PCBs are polybrominated biphenyls (PBBs), which have analogous applications and environmental concerns. They are hydrophobic, with low water solubilities — 0.0027-0.42 ng/L for Aroclors, Other physical and chemical properties vary widely across the class.
These were sold under trade names followed by a 4-digit number.
In general, the first two digits refer to the number of carbon atoms in the biphenyl skeleton (for PCBs this is 12); the second two numbers indicate the percentage of chlorine by mass in the mixture.
Different Aroclors were used at different times and for different applications.In an electric arc, PCBs generate incombustible gases.Use of PCBs is commonly divided into closed and open applications.As the degree of chlorination increases, melting point and lipophilicity increase, and vapour pressure and water solubility decrease.They can generate extremely toxic dibenzodioxins and dibenzofurans through partial oxidation.