this definitive review, Francoiçe Brucker-Davis assembles
literature up to 1997 from laboratory experiments, wildlife observations
and human epidemiology on possible thyroid disruption by a diversity
of chemicals, including DDT, amitrole, thiocarbamates, polyhalogenated
hydrocarbons (e.g., PCBs), phenol derivatives and phthalates.
begins her review by observing that it is vitally important to distinguish
between potential impacts on fully-grown individuals vs.
impacts via exposure in utero. This is because the thyroid
gland in adults is able, within reason, to compensate for mild or
moderate disruption (e.g., caused by hyperplasia or goiter). In
contrast, the fetus in the womb is highly sensitive to alterations
in thyroid hormones, especially its developing brain.
table compiled by Brucker-Davis summarizes data on over 90 chemicals
known to be thyroid disruptors (from laboratory experiments in animals
in vitro). It turns out that only a tiny fraction of the
70,000+ chemicals in commercial use have been tested for thyroid
activity, even fewer for transgenerational effects examining the
consequences of exposure in the womb.
classifies the main mechanisms of action by which thryoid disruption
occurs into four specific categories--thryoid hormone synthesis,
transport, metabolism, and tumor--and a catch-all "other."
Most of the main synthetic chemicals influence the thyroid system
via multiple mechanisms.