One of the greatest dangers to human health is water pollution. After all, people can’t survive without drinking water, and if their freshwater resources are polluted, they can become ill from drinking them. Different types of pollutants affect human health in different ways.
Organisms that cause disease are called pathogens. Pathogens include bacteria, viruses, and parasitic organisms that infect humans and cause illness. Some pathogens occur naturally, and others pollute water when human or animal waste washes into the water. Some of the most common illnesses caused by pathogens in water include
Typhoid
Cholera
Dysentery
Polio
Hepatitis
These illnesses are particularly dangerous for young children; in fact, they account for almost 60 percent of early childhood deaths worldwide. Although sewage treatment plants have reduced the occurrence of water-related illnesses in some nations, less developed nations still struggle to find safe, fresh water. In some regions of the world (parts of India, China, and Africa, for example), water-related illnesses are still a leading cause of death.
In some cases, organisms rather than the water itself carry pathogens. For example, insects whose eggs or larvae live in water carry malaria. Still other diseases are caused by microscopic organisms in the water that infect humans as intestinal parasites — leading to diarrhea, fever, and sometimes death.
Scientists seek to stop waterborne pathogens before they can infect humans and cause illness. Because the pathogens themselves are so difficult to detect, scientists look for an indicator, such as traces of fecal coliform bacteria, instead. Fecal coliform bacteria, such as Escherichia coli, or E. coli, are a common and usually harmless type of bacteria found in human intestines.
But if scientists detect E. coli in a water source, it indicates that some human or animal waste is present in the water and that the likelihood of other dangerous bacteria being present is much greater.
Some water pollutants don’t directly cause illness, but they do damage human health (and the health of other organisms) over the long term. These pollutants, called chemical pollutants, include manmade organic compounds that humans use to make pesticides, prescription drugs, plastics, and other products.
Chemical pollutants enter water sources as runoff from agricultural fields (pesticides) or as drain water (from kitchens and bathrooms) from human homes and businesses. These pollutants also seep into groundwater reservoirs from landfills and underground sewage containers. After these chemicals enter groundwater sources, they contaminate freshwater drinking supplies and are difficult to clean up.
Chemical pollutants usually occur in very low amounts in water supplies, but even at such low levels, they’re still dangerous to human health. Some of these compounds are, at the molecular level, very similar to human hormones and are called environmental estrogens or endocrine disruptors.
Metals, such as mercury, iron, and nickel, pollute water as well. Some of these metals wash into water during mining operations, whereas others, such as mercury, settle into water via the air after being emitted from industrial smokestacks. The small amounts of these metals that scientists measure in water supplies appear almost harmless.
However, after an animal consumes these toxins, they get concentrated and biomagnified up the food chain. (Biomagnification basically means that the negative effects of the toxin are magnified in organisms at the top of the food chain.)
