Organochlorines, also called chlorinated hydrocarbons, are synthetically formed as complex mixtures of thousands of compounds. Because the most chlorinated by-products remain unidentified and unknown, they are impossible to assess and control on a chemical-by-chemical basis compounds.
Chlorinated hydrocarbons are not water soluble, they tend to accumulate in fatty tissues of by living organisms and may remain in the body indefinitely. There are 11,000 chlorinated compounds created intentionally and thousands more created unintentionally. Furthermore, new chemicals are brought on the market much faster than toxicologists can evaluate their hazards.
DDT, lindane and chlordane have tumour-promoting (though no tumour-initiating) properties.
It makes no sense to presume that the thousands of untested organochlorines are benign, given that virtually every chlorinated compound ever tested causes one or more toxic effects. Chlorination almost always increases the toxicity and the bioaccumulation of organic chemicals. It is therefore logical and consistent with existing knowledge to presume that all chlorinated compounds are hazardous unless specific information suggests otherwise.