Effects of Toxic Chemicals and Other Pollutants on Aquatic Ecosystems - Freshwater Ecology: Concepts and Environmental Applications - page 287

radioactive compounds on aquatic habitats has occurred downstream from
nuclear power-generation plants. Perhaps the greatest concern is with bio-
magnification; many radioactive isotopes are retained in body tissues, and
concentrations increase with each increase in trophic level.

ORGANIC POLLUTANTS

There are millions of known organic compounds; more than 10,000 have
been created and used by humans. Several hundred new chemicals are created
each year. The large number of compounds makes regulation difficult. Mod-
ern society has a consistent record of releasing toxic organic compounds into
the environment only to determine afterwards that they have negative effects
on ecosystem and human health. A recent concern is the release of compounds
that serve as biological signals, the endocrine-disrupting compounds (Sidebar
14.2). Another general concern is the widespread increases in human medici-
nal drugs that enter the aquatic environment through sewage (Ternes, 1998).
The effects of unregulated release of pollutants into a large ecosystem are
exemplified by the experiences in the Great Lakes of North America. Prob-
lems associated with pollution of these lakes peaked in the 1960s, and the
slogan “Lake Erie is dying” served as a rallying point for concerned citizens
(Sidebar 14.3). Fortunately, the problems have been mitigated to some degree.
The use of organic compounds in agriculture is widespread (Nowell et
al., 1999). Worldwide, about 2.3 million met-
ric tons of pesticides are used yearly, and in
the United States about 630 different active
compounds are employed. Corn, cotton,
wheat, and soybean crop management ac-
counts for about 70% of the insecticide use
and 80% of the herbicide use in the United
States, but about 25% of the pesticides are
used in urban settings, such as on lawns and
golf courses (Miller, 1998). Annual costs as-
sociated with the use of pesticides include $1.8
billion for cleaning groundwater, $24 million
in fishery losses, and $2.1 billion in losses of
terrestrial and aquatic birds (Pimentel et al.,
1992). Effects may extend to microbial com-
munities (De Lorenzo et al., 2001).
Although biomagnification of toxic or-
ganic compounds is a serious problem, com-
pounds that do not biomagnify can be of
concern as well. Atrazine is a chemical that
is used to control weeds in cropland. It is
fairly water soluble (Nowell et al., 1999),
persists 6-9 months, and only bioconcen-
trates minimally. It has seen widespread use
in the midwestern United States, with 32 mil-
lion kg applied annually. The chemical prop-
erties of atrazine lead to efficient transfer
through the environment (Pang and Close,

Sidebar 14.2.
Ecoestrogens: Compounds That Mimic
Natural Hormone Activities

Numerous organic compounds can mimic nat-
ural metabolic compounds, leading to en-
docrine disruption (Stahlschmidt-Allner et al.,
1997; Sonnenschein and Soto, 1997). An exam-
ple of this form of pollution is the release of
compounds that mimic estrogen (variously
called oestrogens, ecoestrogens, or environ-
mental estrogens). These compounds include
pesticides and even ingredients in sunscreens
(Schlumpf et al., 2001).
Exposure to the pesticide DDT has recently
been linked to nonfunctional testes in male
alligators, and other reports of feminized
wildlife have begun to surface. In this case,
DDT behaves like estrogen; this adds a new di-
mension to the documented effects of organic
compounds intentionally released into the
environment (McLachlan and Arnold, 1996).
Endocrine-disrupting compounds have been
demonstrated to influence reproduction of fish,
birds, mollusks, mammals (Colborn et al., 1993),
and reptiles (Crain et al., 1998). Other possible