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Unformatted text preview: t reduces the probability of exposure where the
endocrine modulating substances are not persistent and not released on a continuous basis. Thus,
for endocrine modulating substances that are not persistent and are released into the environment
on a sporadic basis only, the probability of exposure coinciding with sensitivity is reduced and
the risk is thus smaller (Figure 3-27). Endocrine modulating responses from non -persistent
substances have not been as well documented as those from the persistent organic pollutants.
Because of their lack of persistence, these substances present a special case with respect to
endocrine modulation as consideration of the probability of exposu re and sensitivity becomes
Sensitivity Persistent endocrine modulating substances or continuous release 184.108.40.206 EFFECTS ON WILDLIFE: THE
EXAMPLE OF THE GREAT L AKES
Time Higher probability of response Sensitivity Exposure Non-persistent endocrine modulating substances, noncontinuous release Time Lower probability of response Figure 32
Illustration of the relationship between cyclical sensitivity and
exposure to endocrine modulating substances As recently as last year, wildlife in
the great lakes was thought to be
affected by pesticides.
―Eagles, cormorants, and other
birds residing near the Great Lakes
have been born with crossed beaks
abnormalities. Abnormal nesting
observed.‖(USEPA 1996) The Great Lakes are an interesting
case in point. Wildlife in the Great
Lakes did suffer declines and near -extinctions as a r esult of exposure to pollutants. Similar
observations were made elsewhere. These observations of population -level effects on birds and
other organisms exposed to persistent and bioaccumulative substances lead to regulatory action
to reduce production a nd release. Many of these substances was restricted or banned, starting in
the early 1970s. Much of this activity was initiated in North America, where considerable
attention was focused on persistent substances released into the Great Lakes. Regulation of these
types of substances has since spread to other jurisdictions. Environmental concentrations have
declined since regulations were implemented. Thus, while the Great Lakes were heavily polluted with persistent organic pollutants, such as PCBs, DDT, hexachlorobenzene, mirex,
dieldrin, chlordane, nonachlor, toxaphene, and PCDD/PCDFs from the 1950s through the 1960s,
concentrations of these in the ecosystem peaked in the late 1960s and early 1970s and have
declined in sediments, water, air and biota. The rates of these decreases differ from lake to lake
but the downward trend is consistent.
Consistent with decreases in concentrations of persistent organic pollutants in the Great Lakes,
several bird species also have shown r eductions in effects. A case in point is the Double -crested
Cormorant ( Phalacrocorax autitus), a non-native species that first colonized the Great Lakes in
the early 1900s. Starti...
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This document was uploaded on 04/07/2014.
- Fall '14
- The Land