Endocrine Disrupting Chemicals: A Conceptual Framework

Summary

To comprehend the complexity of the environmental hormone disrupter problem, it is important to have a conceptual framework within which to interpret detailed scientific information. This chapter attempts to provide such a framework, with the intention of making the more technical chapters and their references understandable by decision-makers, journalists, lawyers and other people who have an interest but who do not necessarily come from a scientific background.

In this chapter, we discuss the endocrine system and the time scale over which this system evolved, compared to the rapid introduction of millions of tonnes of completely novel organic man-made chemicals into the biosphere on a global scale, in less than a century. Next, we look at the apparent equilibrium between species at any one time-point in evolution, with respect to the ‘chemical warfare’ that they wage with one another. A major consequence of this is the virtual absence of the phenomenon of ‘bioaccumulation’ of natural compounds. We then consider the reasons why some anthropogenic synthetic chemicals bioaccumulate, and discuss the consequences for the functioning of the endocrine system and consequences for the effective regulation of hormone-disrupting chemicals. Finally, we undertake a brief comparison of the regulation of pharmaceuticals, agrochemicals and bulk chemicals to illustrate how comparatively little testing is required for bulk chemicals. In view of their possible and often foreseeable negative impacts on the environment and health, this is unsatisfactory, as it leaves the burden of proof to regulatory bodies or affected people. To illustrate the fact that foreseeable problems with these compounds are not adequately dealt with, we compare the time-scale for research into toxic effects and the eventual regulation of an ‘old’ problem, polychlorinated biphenyls (PCBs) with the unfolding of a more recent but very similar problem, polybrominated diphenyl ethers (PBDEs). Comparison of PBDEs to PCBs and polybrominated biphenyls (PBBs) show they have very similar structural, physical and chemical characteristics, and in addition their environmental fate and toxicology is similar. Despite this, only very limited research on PBDEs was performed before bulk production was started. As will be shown, research only commenced in earnest after detection of their global occurrence in the environment and dramatically increasing levels in mother’s milk.

Difficulties with attributing adverse effects in humans and wildlife to specific chemicals or chemical groups are experienced because of the mixtures of thousands of pollutants to which we are all exposed. This has consequences for the regulatory authorities and the speed at which they might be able to prove causal relationships and react.