The Environment - Leading Water Pollutants

The graphic shows the percentage of impaired and not attainable waterways affected by the top 5 water pollutants. For definitions, see previous panel. We did not include data from the Great Lakes shoreline because the shoreline contains pollutants other than those listed here. PCBs, DDT and pesticides are the top pollutants on the Great Lakes shoreline. Ocean shoreline data were not included in the graph because the sample size (5%) was too small to be representative.

Siltation affected more than 111,000 miles of rivers and streams and more than 1 million acres of lakes, reservoirs, and ponds in 1998. When it rains, mineral particles wash off plowed fields, construction and logging sites, urban areas, strip-mined land, and eroded stream banks. Sediment deprives aquatic plant life of sunlight and muddies the water generally. Settling sediment suffocates fish eggs, destroys insect habitats and thus food for fish. Fish population is reduced or fish die out. Excessive sediment also hampers water treatment processes and boating.

Pathogens such as bacteria, viruses, and protozoan affected more than 103,000 miles of rivers and streams and 5,900 square miles of estuaries in 1998. Pathogens can cause illnesses (e.g. typhoid, minor respiratory and skin diseases). Many of us in the summertime probably watch for news reports of beach closings. In 2000, there were 11,270 beach closings or advisories interfered with recreation — up from 6,160 in 1999, and 484 in

1988. Is this due to increased pollution or better monitoring? It's difficult to tell. But in 2001, the National Resources Defense Council urged the Bush administration to implement improved federal water quality standards approved by the Clinton administration. Pathogens enter the waterways through inadequately treated sewage, storm water drains, septic systems, runoff from livestock pens, boats that dump sewage, and wildlife. From 1999 to 2000, there was a 40% jump in the number of beaches reporting pollution from unknown sources.

Nutrients (nitrates and phosphates⁶) occur naturally. Excessive levels stimulate the growth of aquatic weeds and algae. These clog the waterway, use up oxygen as they decompose, and block sunlight from reaching the depths. Fish and other aquatic creatures may suffocate. Swimming is impeded, and boat engines get fouled. Sources of excessive nutrients are agricultural, residential, and urban runoff; sewage treatment plants; and acid rain.

Oxygen-depleting substances have the same effect as excessive levels of nutrients. Untreated wastewater is a source. More than 67,000 miles of rivers and streams; over a million acres of lakes, reservoirs, and ponds; and more than 5,000 square miles of estuaries are affected.

Metals, such as mercury, lead⁷, and cadmium⁸, contaminate around 44,000 miles of rivers and streams; 2 million acres of lakes, reservoirs, and ponds; 3,000 square miles of estuaries. These naturally occurring metals in excessive amounts can pose health risks to both animals and humans. For example, when mercury enters water it turns to methyl mercury, its most toxic form. Aquatic wildlife that consumes mercury-laced plants or fish can suffer neurological damage and have difficulty with reproduction. Although scientists disagree as to what level of mercury is harmful to human health, the effects of mercury can range from paralysis to brain damage to death.

Have things gotten better? In some cases, yes. In others, no. The table on the following page shows comparisons of pullution between 1992 and 1998. Negative percentages mean that the level of the pollutant in 1998 was below the 1992 level. Positive percentages mean that the level of the pollutant in 1998 was higher than the 1992 level. NA means no data were available for one or both years.

Percentage Change of Impaired Waterway Affected By Pollutants, 1992-1998

	Rivers & streams (miles)	Lakes, reservoirs, & ponds (acres)	Estuaries (square miles)
Siltation	-6.8	-7.2	NA
Pathogens	-8.1	NA	5.4
Nutrients	8.6	3.7	-31.9
Oxygen-depleting substances	-0.8	-10.1	7.5
Metals	NA	-20.3	NA

The next panel will discuss the state of our drinking water.

Sources: U.S. Environmental Protection Agency. National Water Quality Inventory, 1992 and 1998. Retrieved June 26, 2002 from http://www.epa.gov/305b/. John Heilprin. "Bacteria-caused beach closings and advisories to nearly double, report says." The Detroit News, August 8, 2001. Guy Williams. National Wildlife Federation. "Mercury Pollution Prevention in Healthcare," July 1997. Retrieved June 27, 2002 from http://www.nwf.org/greatlakes/resources/mercury.html.