Introduction to Endocrine Disrupting Chemicals

from one culture plate to the next. Animal work is conducted in a laboratory with
row after row of cages of mice, each genetically identical to the others, with a very
specific type of bedding, food, water, light cycle, and controlled temperature. The
essence of traditional toxicological methods is the administration of a single, pure
chemical in exact dosages, with all other conditions equal to allow comparison of
the chemical to a control (placebo) group.
However, the world is not like a laboratory. Humans are genetically unique (other
than identical twins); they live in very different environments; they migrate to new
environments; each person has his/her own dietary and nutritional exposures, etc.
Each person is exposed to mixtures of EDCs at various developmental periods –
that is, each person has a unique “exposome,” the sum of everything to which he or
she is exposed. The ‘new science’ of EDCs recognizes these realities: that exposure
in nature is chronic; that EDCs are ubiquitous and global; and that there is bioaccumulation
and biomagnification of EDCs up the food chain. Furthermore, with
the exception of occupational exposures, it is rare that environmental exposure
involves pure compounds. Instead, exposures involve mixtures of compounds, as
well as degradation products of single compounds.
Thus, modern science must include studies on effects of single compounds, but
more importantly, their mixtures, to better approximate the additive or synergistic
effects of compounds in the body. There is still some controversy as to whether
EDCs exhibit synergistic activity. The heat of that debate stems from the fact that a
number of EDCs have a lower potency than natural hormones and, when considered
individually, these chemicals may exist in the environment in concentrations
believed to be too low to be of concern. However, in the absence of a so-called
‘safe dose’, these low environmental levels may still have biological actions. Much
debate in this area has been based on the old science of extrapolating low-dose
effects from high-dose experiments, rather than on real life physiology of hormone
actions, or the real-world nature of exposures – the modern paradigm shift that is
needed in understanding biological actions of EDCs.
Introduction to EDCs (December 2014) 31