Everything-from the size of raindrops to the height of trees, the speed of wind and the food chain produced in the ocean-is controlled within a magnificent balance. However, due to the unlimited demands of humans, the earth's ecosystem is subjected to immense changes and is gradually being destroyed. Some of the main reasons for this destruction are the fertilizers used in agriculture which contain excessive chemicals, insecticides, and detergents used in the home. These substances are carried into streams, lakes, and the oceans by rainfall, wastewater, and through irrigation, causing pollution. The deterioration in the ecological chain caused by this pollution affects the ecosystem, and thus the human health. Phytoplankton, the productive organisms which are at the base of the food chain in aquatic ecosystems, are microscopic organisms that produce organic nutrients (sugar, protein etc.) through the process of photosynthesis. During the production stage of these nutrients, phytoplankton absorbs the contaminative and toxic elements. As the larger creatures (invertebrates and vertebrates such as fish) feed on phytoplankton, they, in turn, absorb the toxins accumulated in the phytoplankton.

The phosphate and nitrogen compounds found in the waste material that are released into the environment go through some biological processes and are transformed into nourishing salts for the phytoplankton. When there is an increase in temperature, these salts may cause some of the phytoplankton to grow and reproduce excessively. The toxic materials released by some, and the use of excessive oxygen, are harmful to other organisms.

Another example of pollution is related with algae. When the number of microbial plants called algae reaches one million per cubic decimeter (1 million/dm3) of water, the consumption of oxygen required in order to mineralize, and break-down the organic materials found in the water increases, and therefore a compound of toxins which pollute the water, such as hydrogen sulfide (H2S), are released. This pollution can cause the death of fish and other organisms which live in the water. As a result of the reduction in water quality, an increase in the type of algae called cyanobacteria occurs and the biotoxins that they produce threatens human health.

More than forty types of algae produce various toxins. Some of these toxins damage the human liver, some attack the nervous system (particularly the brain), some can cause allergic skin reactions, and some can even induce cancer. The release of domestic, industrial, and agricultural waste and the high percentage of nutrients (such as nitrogen and phosphor compounds) into the aquatic ecosystem can cause an excessive increase of algae in the waters. This algal bloom in fresh water is referred to as eutrophication. In oceans, it is referred to as red tide because the water appears to be a reddish color. Both present a significant environmental problem.

In low doses humans are exposed to these toxins by the consumption of drinking water. In Brazil in 1988, almost 2000 people developed gastroenteritis over a forty day period due to the consumption of drinking water contaminated by these toxins, and eighty-eight of them died. In South Australia, as early as 1878, many sheep, horses, dogs and other animals died as a result of drinking water from Lake Alexandrina, which was covered by scum caused by an aglal bloom called Nodularia spumigena.

Mussels, a delicacy eaten and enjoyed by many, accumulate large amounts of toxins because they feed on phytoplankton. One study found that in fresh water mussels (Mytilus galloprovincialis) that fed on cyanobacteria, almost 10.7 g toxins per gram of bodyweight was accumulated. This is also the case in marine mussels. It has been determined that these toxins in gradually increased concentrations are passed onto organisms higher on the food chain by consumption. Accordingly, we should always consider the potential risk factors before consuming shellfish.

Biotoxins are released into the water after being broken down by algae. Thus, when an algal bloom reaches high levels, there is an increase in the density of toxins in the water. As these toxins dissolve in the water, purifying the contaminated water requires not only expensive, but also advanced technology methods. Unfortunately, it is impossible to remove this waste in many of the existing refining plants. The toxin concentration in drinking and utility water should be reduced in regions where drinking water is obtained from lakes by mixing it with uncontaminated water, particularly during the spring when the algal bloom occurs. Thus, reducing the amount of biotoxins in the water to a level that will cause minimal harm to aquatic organisms should help to reduce the risks to humans.

Many types of waste released into the environment cause damage, which adversely affect humans. Polluting the environment may be easy, but purifying the environment of this pollution is a very difficult task. Indeed, humans were not created to act irresponsibly and destroy the universe in which they are mere guests. On the contrary, the human is a delicate guest with sublime duties. Protecting the natural resources provided for our needs and utilizing these resources in the most productive manner, without disturbing the balance of nature, is a duty of every human on earth.

References

• Pouria S. de Andrade A. 1988. "Fatal microcystin intoxication in haemodialysis unit in Caruaru, Brazil." Lancet 352:21-26.
• Carmichael W.W., Azevedo S.M.F.O. 2001. "Human fatalities from cyanobacteria: Chemical and biological evidence for cyanotoxins." Environ. Health Perspect 109: 663-668.
• Codd G.A., Bell S.G., Kaya K., Ward C.J., Beattie K.A., Metcalf J.S. 1999. "Cyanobacterial toxins, exposure routes and human health." Eur. J. Phycol. 34:405-415.