In his Correspondence about a recent book review, Ferdinand Engelbeen1 criticizes Joe Thornton2 for failing to distinguish between good and bad organochlorines, without proposing how one might do so at reasonable cost. One of the strengths of Thornton's book3 lies in its account of the exceptional difficulty of this process and the many ways we have failed to understand the implications of synthesizing chemicals that have no part in natural cycles.
Rather than undermining the case for restrictions based on chemical classes, Engelbeen's own example of PVC illustrates why it is so hard to regulate chemical compounds on an individual basis. Thornton argues that organochlorines, as a result of their fundamental chemistry, tend as a class to be greatly more persistent, more toxic and more bioaccumulative than their non-chlorinated relatives. Hence when degradation does occur it usually results in the production only of smaller organochlorines. Even organochlorines that are non-toxic or benign (such as PVC) are end-products of a sequence of reactions that at each stage result in the production of large quantities of toxic, persistent and uncharacterized chlorinated intermediates, by-products and wastes.
To make matters worse, even with the best available methods, organochlorines cannot be disposed of without the production of yet more toxins. PVC, via incineration, is probably ultimately the major environmental source of dioxins4. Nor is PVC always likely to be disposed of by the best methods. Significant quantities (even in the developed world) are disposed of in bonfires, building fires and rubbish-tip fires, and these too are likely to be important sources of dioxins and other chlorinated toxins4.
Engelbeen, F. Nature 407, 445 (2000).
Collins, C. Nature 406, 17–18 (2000).
Thornton, J. Pandora's Poison: On Chlorine, Health and a New Environmental Strategy (MIT, Cambridge, MA, 2000
Thomas, V. & Spiro, C. Toxicology and Environmental Chemistry 50, 1–7 (1995).