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Water: Contaminated Sediments

Major Contaminants

Five major types of pollutants are found in sediments:

Nutrients, including phosphorous and nitrogen compounds such as ammonia. Elevated levels of phosphorous can promote the unwanted growth of algae. This can lead to the amount of oxygen in the water being lowered when the algae die and decay. High concentrations of ammonia can be toxic to benthic organisms.

Bulk Organics, a class of hydrocarbons that includes oil and grease.

Halogenated Hydrocarbons or Persistent Organics, a group of chemicals that are very resistant to decay. DDT and PCBs are in this category.

Polycyclic Aromatic Hydrocarbons (PAHs), a group of organic chemicals that includes several petroleum products and byproducts.

Metals, such as iron, manganese, lead, cadmium, zinc, and mercury, and metalloids such as arsenic and selenium.

Metals, PAHs, and organics listed above can be toxic to various plants and animals, depending on the level of contamination. Some can also be toxic to humans depending on their levels. Many persistant organic contaminants and some metals biomagnify as they travel up the food chain.

Sources of Contaminants

The origins of sediment contamination can be divided into point and nonpoint sources of pollution. Point source pollution comes from a specific, identifiable source such as a pipe. Nonpoint source pollution cannot be traced to a specific spot.

Point sources include municipal sewage treatment plants, overflows from combined sanitary and storm sewers, stormwater discharges from municipal and industrial facilities, and waste discharges from industry.

Nonpoint sources include stormwater runoff from hazardous and solid-waste sites; runoff from croplands, livestock pens, mining and manufacturing operations, and storage sites. Atmospheric deposition is another source of nonpoint pollution.

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