Toxic Pollutants includes
substances, which are toxic to living organisms, either lethally or sub
lethally. Most of these are not a natural part of aquatic ecosystem, rather,
only introduced through human activities. Examples include chemical compounds
from industries, pesticides, detergents, heavy metals, oil and radioactive
materials.
It is estimated that every year around 300 billion kilograms of synthetic
compounds from agricultural, industrial and consumer products are routed to
natural freshwater.
Many industrial chemicals, metals and pesticides are toxic to aquatic animals
and humans, often affecting sensitive organs and the neuroendocrine system.
Moreover, many of these are responsible for developmental anomalies by
interfering with the developmental processes in various types of animals and
humans.
Most of these substances are non-biodegradable, thereby persisting in the
environment for a long time and accumulating in the bodies of exposed animals.
Their route of exposure to humans is by drinking contaminated water and/or
consuming contaminated food, such as fish and shellfish.
Detergents, mainly introduced through sewage water, alter the physical
characteristics of water and affect aquatic animals as well. Detergents lower
the surface tension of water causing an increased uptake of other toxins by
aquatic animals, exposing them to a greater risk of mortality. On the other
hand, detergents themselves are directly lethal to fish by damaging their gills
and by destroying the protective mucus layer on their external surface.
Detergents may also kill fish eggs. Most of the detergents release phosphates
upon breakdown, resulting into formation of nuisance algal blooms.
Oil is mainly considered a problem of marine waters, but many freshwater bodies
also suffer from this kind of pollution due to oil spills, natural leakage of
oil from rocks or from recreational activities of humans. Oil floats on the
surface of water and prevents the dissolution of oxygen, a critical feature for
the sustenance and productivity of an aquatic ecosystem. It also deteriorates
the drinking and aesthetic qualities of water. Oil-contaminated water is
detrimental for almost all forms of aquatic life from plants to fishes.
Radioactive isotopes accumulate in the food chain. They emit radiations upon
decay, which cause damage to body tissues and DNA, often leading to cancer and
certain developmental malformations.