Aquatics Pollution

A contaminant is a chemical substance at greater than background levels that has no detrimental effect. A pollutant is defined as chemical substance at greater than background levels that have a detrimental effect. These substances cause damage by interfering with an organism's physical or biochemical processes. An example of a natural pollutant is volcanic eruptions (e.g. sulphuric acid). Anthropogenic pollutants were introduced by human activity such as synthetic organic chemicals (e.g. pesticides).

Chemical pollutants can be divided by inorganic and organic chemical. Inorganic chemical includes nutrients (Nitrate, Phosphate), heavy metals (Hg, Cd, Pb) and radionuclide (Th, U). Chloroform, herbicides and hydrocarbons are example of organic chemical. Types of physical and biological pollutants are thermal effluents and oxygen depleting substances (e.g. sewage).

Chebbi notes that the usual cause of marine pollution is the release of oil spills and hydrocarbon from tanker accidents, conventional shipping or tank cleaning at sea, waste disposal, and oil exploration. Tanker accidents are the most known oil spills because of vicinity to the coast and media coverage. Recovery time after an oil spill takes about 5 to 10 years, dependent on temperature and wave action. In a study, published in the Journal of Chemical Engineering Science, 80% of hydrocarbons are degraded bacterially or evaporated after two months in open sea spills, leading heavy hydrocarbons (long chain) behind. World-wide average contamination in parts per billion (ppb) ranges is considered harmless because toxic effects occur in the parts per million (ppm) ranges. The ecological impact of oil spills depends on location of spill, distance to shore, water temperature, currents, and composition of affected marine communities.

In a new study published in the journal Environmental Management, scientists find that the sewage disposal is the major form of coastal pollution by the release of organic matter, heavy metals, pesticides, detergents, oil, and nutrients. Nutrients can cause algal blooms, among the harmful and toxic blooms which alter the phytoplankton species composition which lead to food chain effects. It also promotes the growth of benthic green algae and cyanobacteria, which overgrow and destroy natural benthic communities. Pathogenic bacteria and viruses can be introduced by sewage.

Eutrophication is known as the excessive growth of aquatic plants caused by high concentrations of nutrients. When the excess nutrients enter an aquatic system, the plants will die and decompose. Meng et al. note that the decomposition uses up the oxygen in the water, causing the aquatic organisms driven out of their prime habitat. Oxygen consumption increases by bacterial degradation of organic matter and sediment phytoplankton, causing hypoxia (anoxic conditions). Agricultural runoff presents another major source of nutrient input into coastal seas, leading to eutrophication effects. Aerial deposition of ammonia from cattle or pig farms also contributes to coastal eutrophication.

Environmental pollution is a universal problem because it is not restricted to developed or undeveloped countries. Unlike the traditional biology, ecology and chemistry sub-disciplines, there are very strong philosophical and ethical reasons for practicing environmental eco-chemistry awareness.

Reference:

Chebbi, R. Profile of oil spill confined with floating boom. Journal of Chemical Engineering Science, Volume 64, Issue 3, February 2009, Pages 467-473

Pei-Jie Meng, Junda Lin, Li-Lian Liu. Aquatic organotin pollution in Taiwan. Journal of Environmental Management, Volume 90, Supplement 1, 15 February 2009, Pages S8-S15