METALS - Marine Pollution: What Everyone Needs to Know - page 90

marinas looked abnormal. They grew very thick shells, became
ball-shaped with very little meat inside, and were unmarket-
able. As a result of some excellent detective work, scientists
traced the deformity back to the paint used on the boats that
were concentrated in the marinas. A second observation was
that dog whelk snail populations were crashing and female
snails near marinas throughout Europe were growing penises.
This condition was termed “imposex,” and when severe, the
male structures imposed on the female ones and blocked
the oviduct so that eggs could not be deposited and females
could not reproduce, as found by Peter Gibbs and Geoff Bryan.
This effect was due to increased amounts of male hormones,
which caused male reproductive structures to develop in the
females. This abnormality, which rendered females sterile, led
to drastic population declines. It also spurred the development
of regulations, restrictions, and ultimately bans on the use of
TBT on recreational boats. Imposex in female snails was dis-
covered and studied several years before the term endocrine
disruption was coined to describe such effects. Endocrine
disruption will be discussed in greater detail in the chapter
on organic contaminants (Chapter 6), since far more of them
cause endocrine effects. Mollusks are not the only animals
affected by TBT; they just are much more sensitive than oth-
ers. They were affected at concentrations that were too low for
the instruments in the late 1980s to measure, which spurred
development of more sensitive instrumentation.
Early life stages are generally more susceptible to environ-
mental contaminants than later stages. Embryos can be exposed
to developmental toxicants such as meHg during egg develop-
ment (oogenesis) in females, during the brief period between
shedding of gametes into the water and fertilization, and after
fertilization. Chemicals that are incorporated into the egg
during oogenesis can produce malformations in the embryos
that later develop from these eggs. Subsequently, embryos can
be exposed to chemicals after fertilization. Exposures can be
throughout embryonic development or during shorter time