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Water Pollution and Toxic Levels for Animals

Water pollution is a growing concern around the world, as demand for metals and plastics continually increases. Byproducts of the mining and manufacturing industries are eventually deposited into rivers, lakes and oceans. Many of these byproducts are lethal to animals that either live in the aquatic environments or depend on them for food.

  1. The Toxicity of Mercury

    • Great cormorants, native to Greece, consume large quantities of fish and are, therefore, a good model species to investigate the accumulation of toxic substances deposited in aquatic environments. A study published in the January 2011 issue of "Science of the Total Environment" analyzed the concentrations of mercury from the livers of 80 birds. The study explained that mercury concentrations above four μg per g of dried liver were toxic. The researchers found concentrations of mercury as high as eight μg per g of dried liver weight in highly polluted areas, whereas great cormorants living in non-polluted areas had average levels of only one μg.

    Levels of Cadmium

    • Water pollution by transitional metals, such as cadmium, are a common problem in estuaries close to mining facilities. A study appearing in the January 2011 issue of "Chemosphere" investigated the effects of chronic cadmium exposure on oysters. The study found that cadmium concentrations of 50 μg/L led to significant decreases in tissue glycogen, used as energy storage in animals and an increase in free glucose levels. The increased amount of cadmium also led to a significant increase in Vibrio bacteria in the water, which also can increase stress levels and affect the heath of animals in aquatic environments.

    Nitrate-Induced Stress

    • Increased levels of aquatic nitrate, from farming and sewage, can interfere with metabolism, the production of hormones and reproduction in fish. The stress hormone, cortisol, is often employed to monitor the effects of chemical pollutants in aquatic animals. A study published in the October 2010 issue of "Aquaculture Research" reported that nitrate levels of more that 0.5 g/L increased cortisol levels and inhibited the reproduction of koi fish. The authors also reported that these levels were lethal to juvenile koi.

    Toxic Levels of Cadmium and Lead

    • Three bird species, the great grebe, the cormorant and the great kiskadee are indigenous to a lake located in Midwestern Argentina. An article appearing in the November 2009 issue of the "Journal of Environmental Monitoring" investigated the effects of water pollution caused by lead and cadmium on these birds. The study found that lead tended to accumulate in the gonadal, or reproductive, tissues of the animals, whereas cadmium collects in the liver. The authors stated that lead concentrations of over 2 ppm, as found in the bird tissues, were indicative of highly polluted water and generally toxic to several species of aquatic animals.

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