INTRODUCTION TO THE MARINE ENVIRONMENT AND POLLUTION - Marine Pollution: What Everyone Needs to Know - page 12

reproduction can be affected by many chemicals, now called
“endocrine disruptors.” Exposures during early life may cause
effects that do not appear until later, sometimes many years
later. Thus, long-term delayed effects and indirect effects are
important. There has been some progress toward greater eco-
logical realism, but advances have been mainly in freshwater
ecosystems.
The effects of chemicals on individuals may cause
changes in populations and result in reduced population
growth rate, lower population size, reduced birth rates, and
higher death rates, producing a population dominated by
younger, smaller individuals with reduced genetic variability.
Reduced genetic variability happens when the more suscep-
tible individuals disappear from the population and the more
pollution-tolerant ones become predominant, as has been
seen with insecticide-resistant insects or antibiotic-resistant
bacteria.
Toxic effects appear first at the biochemical level, and later
at the cellular level, then the level of the whole organism, the
population, and eventually the ecological community as a
whole. Initial biochemical changes observed can be altered
enzymes, changes in DNA and RNA, or the production of par-
ticular proteins that can detoxify the chemical. At the cellular
level, chromosome damage, cell death, abnormal structures,
or cancer can occur. Some chemicals affect the immune system
and increase susceptibility to infectious diseases. At the level
of the whole organism, changes in physiology, development,
growth, behavior, or reproductive capacity may occur, and at
high concentrations, the animal or plant can die.
Fortunately, we have seen in many locations that when the
input of pollutants decreases or toxic waste sites are cleaned
up, the incidence of diseases and other problems dimin-
ishes. Tolerance to the contaminants may be lost as well. In
a contaminated marsh near a former battery plant close to
the Hudson River that released cadmium for decades, Jeffrey
Levinton and colleagues from Stony Brook University showed