Other contaminants such as radioactive
waste, pesticides, and other chemicals have cumulative effects,
building up within individuals over time, especially within
species high on the food chain. There have been reductions
in most direct and riverine inputs from the UK to coastal
waters around the UK since 1985, except for zinc, nitrate,
nitrogen and suspended particulates.
Between 1987 and 1991, dolphin and seal deaths were recorded
in the North and Baltic seas, off the eastern coast of the
United States, in the Gulf of Mexico, and in the Mediterranean
Sea. The carcasses of dolphins and seals animals were found
to contain elevated levels of polychlorinated biphenyls (PCBs),
dioxins, and other organochlorines, known to accumulate in
the blubber (or lipid tissues) of large species and predators
at the top of the food chain.
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These
deaths and an epidemic of tumors observed within green sea turtles
have been linked to the cumulative buildup of PCBs and other
chemicals that are believed to weaken immune systems, creating
a vulnerability to viral infections (74).
Other contaminants can trigger ecosystem-wide changes. Runoff
of sewage from cities and of fertilizers from agricultural areas
elevates the levels of nutrients in coastal waters. Certain
algal species feed on these conditions, and have massive population
explosions (known as blooms).
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More on Lethal Blooms
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