Quality of a River - Water Quality
Contaminants: Toxins (pg 2
Toxins include a range of poisonous or otherwise
harmful substances, such as heavy metals, road
salts, and pesticides.
Heavy metals, including mercury, cadmium, and
lead, come from a variety of sources, such as
industrial processes, trash incineration,
automobiles, and emissions from power plants.
Concentrations of many of these metals tend to
increase as rivers pass through large cities and
collect urban runoff and industrial point sources.
But some, such as mercury, are also dispersed in
the atmosphere and reach streams through
precipitation and runoff.
Many metals are toxic, even at very low
concentrations. One of the greatest known threats
to human health is the concentration of mercury
(from mines, power plants, and paper mills) in
muscle tissue of fish. Overexposure to mercury
damages the brain, nervous system, kidneys, and
lungs. For fish advisory information, go online and
et al., 1999)