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  Pollutants are waste materials that pollute either the water, air or soil around them. Human activities can often be responsible for increasing the occurrence and incidence of pollutants in the environment. Different kinds of pollutants include sediment, inorganic nutrients, thermal pollution, exotic species of animals and plants, heavy metals, toxic organic chemicals, ocean pollution, and oxygen-demanding organic wastes.
  
  

Ocean Pollution

• Ocean pollution can be attributed to human activities. Dredge spills, sewage, plastic and oil are the common pollutants found in the ocean and can cause many problems with natural ocean wildlife.
  
  

Sediment pollution

• Sediment pollution refers to the loss of top soil caused by the removal of vegetation. Sediment pollution occurs most often due to road construction, urban construction sites, farmland and strip-mining operations. Sediment pollution is harmful because toxic compounds can be absorbed onto particle surfaces, can bury fish breeding ground, and can reduce reservoir lifespan.
  
  

Inorganic nutrient control

• Inorganic nutrient control can be harmful to aquatic ecosystems and can occur naturally, but is often accelerated by human activities, such as the use of phosphate detergents and some fertilizers. Inorganic nutrient control can lead to a rise in algal blooms, which is accompanied by a lake being covered with green slime. This can be harmful, as well, because some algae release poisons.
  
  

Thermal pollution

• Thermal pollution is caused by heated water from nuclear power plants. Thermal pollution is dangerous because it can decrease dissolved oxygen in water, interferes with reproduction, increases the vulnerability to disease, induces direct mortality, and increases the metabolic rate of exposed animals.
  
  

Exotic Species of Animals and Plants

• Exotic species of animals and plants are imported by humans either on purpose or accidentally. Zebra mussels are one example of an exotic species that was accidentally imported in the ballast of a ship and has been known to cause many problems. Zebra mussels can grow so thickly that they can obstruct pipelines and clog water intakes.
  
  

Toxic Organic Chemicals

• Toxic organic chemicals, such as solutes and solvents, are released by factories into the environment, often into streams and other water surfaces. Toxic organic substances are very harmful and can be linked with the occurrence of sudden infant death syndrome, childhood leukemia and stillbirths.
  
  

Heavy Metal Pollution

• Heavy metal pollution refers to toxic substances like mercury, lead, cadmium and arsenic. Heavy metal can leach into the groundwater from mines. Heavy metals are dangerous because they can cause brain damage, birth defects and kidney failure.
  
  

Oxygen-Demanding Organic Wastes

• Oxygen-demanding organic wastes can accumulate in the environment and diminish the oxygen in the water, which affects fish and other species that there. The degradation process is increased by sewage treatment plants.