Marine pollution regulation and prevention

For the purpose of regulation, pollutants in marine environment fall into two categories: nutrients and toxic substances.

• nutrients

  The regulation is placing limits or water quality standards on concentrations of nutrients in aquatic environment. Runoff of nutrients from agricultural fields and forestry areas is best reduced by reducing the application of fertiliser, by planting or leaving wooded buffer zones and by limiting the access of domestic animals to streams. Discharge of nutrients from sewage treatment plans can be reduced by more advanced, tertiary treatment, or by innovations such as constructing wetlands to filter sewage water or using modern composting toilets instead of water-based sewage collection. Some nutrient-rich compounds in emissions from fossil fuel combustion can be trapped and removed by advanced technologies, or the amount of fuel burned can be reduced.

• toxic substances
  

  The problem of toxic substances is very difficult to address. Toxic metals are natural sub-stances that become a problem when they are amassed in high concentrations. This happens regularly with the extraction of metals from the earth. Oil, which gets into the marine envi-ronment through numerous careless actions, presents the same challenge. Synthetic organic pollutants are more insidious because they are numerous and difficult to monitor and in many cases have biological effects at very small doses. Many persist in the environment for long periods of time, causing bioaccumulation and biomagnification in food chains.
  

Policies regarding the introduction of contaminants into the marine environment reflect three general approaches:

• international use of the oceans and seas for disposal of wastes from land via pipelines or dumping from vessels; this approach, very present in the past, declines, but still exists in many countries;
  
• regulation of discharges to maintain "acceptable" levels of contamination - favoured by many governments but rather flawed in practice; and
• prevention of pollution, adopted as a goal internationally, but still far from daily practice.
  

The determination of acceptable levels or standards for toxic chemicals is always controversial. It is described as an attempt to scientifically define how much contamination an ocean or sea system can withstand before it is seriously damaged. This limit, referred to as the "assimi-lative capacity", is based on belief that contaminants are not harmful at low levels and there is a threshold of concentration for each chemical below which no harm is done. This approach is rarely able to incorporate the additive and synergistic effects of a variety of pollutants from a variety of sources.