In the mid-1920s physicians reported workers in polychlorinated naphthalene manufacturing suffering from chloracne and later  it was discovered  that workers exposed to PCNs (polychlorinated naphthalene) could die from liver disease . By the 1950s, there had been several reports and investigations of hazards involving PCNs. For example, after testing hydraulic oils containing PCBs (polychlorinated biphenyl), the U.S. Navy found that skin contact caused fatal liver disease in animals and the PCNs were banned from being used in submarines.

       A book by  Rachel Carson (biologist) began a major conflict about environmental pollution. This book first focused on DDT and other pesticides, some of them also halocarbons. These concerns became more evident when a Swedish chemist Soren Jensen reported bioaccumulation of PCBs among Arctic and sub-Arctic fish and birds. DDT is known to be poisonous to birds and fish although it does not seem to affect mammals.

     In 1930, the DuPont company manufactured Freon, a chlorofluorocarbon, CF2Cl2(g). However, it was discovered that there were large"ozone holes"  in the polar regions.  Although CFC's did not cause any problems in the lower atmosphere, they were reactive in the upper atmosphere. In the presence of unltraviolet light, CFC molecules realease highly reactive chlorine atoms. Chlorine destroys the ozone molecules in the stratosphere, which allows an unsafe amount of UV light to pass through the atmosphere.

    Perfluorooctanoic acid (PFOA), used in the most common manufacturing process for Teflon and also used for food packaging as well as fabric coating, has also become a health and environmental concern. PFOA is a carcinogen, a liver toxicant, a developmental toxicant, an immune system toxicant, and also has the ability to  alter the thyroid hormone levels which can lead to many health problems.

     Another problem is that halocarbons, even if some of them are not hazardous, can present waste disposal issues. Because they do not degrade in natural environments, halocarbons tend to accumulate.

The DDT Conflict

Ozone Depletion

1]"DDT.button." ActionOutdoors.org 6 Mar 2010. <http://www.actionoutdoors.org/edres/images/DDT.jpg>.

2] "chlorofuorocarbons." theozonehole.com 6 Mar 2010. <http://www.theozonehole.com/images/cfc.gif>.

3]"pfoa." Exponent. Exponent.com 6 Mar 2010. <http://www.exponent.com/files/Uploads/Images/toxicology/pfoa.jpg>.

1] "DDT Conflict." Youtube.com 6 Mar 2010. <http://www.youtube.com/watch?v=kyYpwOTtaLI&feature=related>.

2] “Ozone Depletion.” Youtube.com 6 Mar 2010. <http://www.youtube.com/watch?v=eSraEkgdRfM&feature=related>.