The majority of the chemicals which cause environmental problems are synthetic organic compounds, which include the Persistent Organic Pollutants:

1. Polychlorinated biphenyls (PCBs): Used mainly in inks, points,
    plasticisers and electrical components across the world.  Only    
    Europe has stopped the production of PCBs.  Similar chemicals include
    the polybrominated bi-and-di-phenols used as flame retardants in
    electronic circuits, clothing and furniture.

2. Dioxins and furons: not manufactured directly but occur as by-products
    in the production of other chemicals and the burning of wastes
    containing chlorine.

3. Organochlorine pesticides: used widely still in agriculture to protect
    crops from pests.  This group includes DDT, which has been banned in
    the developed world for many years, but is still used in developing
     countries to control mosquitoes.

4. Alkyl phenol ethoxylates: widely used in industries as detergents and
    surfactants.

5. Poly-aromatic hydrocarbons: formed during the burning of fossil fuels
    and other organic substances.

These chemicals enter the water from several sources: point-source discharges, diffuse discharges from agriculture and shipping and atmospheric deposition from waste incineration plants.

Why Toxic Chemicals Are So Nasty for the Environment: 

Acute toxicity is lethal, and chronic toxicity impacts species at a sub-lethal level and only becomes apparent over time.  Example:  Endocrine Disrupting Chemicals which are also known as “gender benders” which interfere with the reproductive, developmental and immune systems of species.

Many synthetic compounds are not able to dissolve in water, so they  dissolve in fats.  This means that these compounds are able to accumulate in the fatty tissues of species and concentrate up the food web, being especially problematic among the top predators.

Impacts of Chemical Pollution upon Marine Life

1. Intersex: when an animal has both female and male intermediary    
    characteristics.  Found in high levels in some tiny Crustacea in coastal
    waters.  In some estuaries of the United Kingdom, some males of the
    bottom-dwelling species such as flounder have begun to produce the
    female egg yolk protein called vitellogenin and has developed egg cells
    in otherwise normal testes.

2. Imposex: when an individual has the sexual characteristics of the
    opposite sex superimposed on its own.   This has been recorded many
    times in the dog whelk species where females have developed male
    genitalia as a result of exposure to the antifouling tribrityltin.

3. Hermaphroditism: where an animal has both male and female
    reproductive organs.  In 1998, 4% of polar bears on two Arctic islands
    were found to be hermaphroditic-high PCB levels were found in their
    fat.

4. Immunosuppression: occurs when a chemical pollutants acts to
    suppress the immune system, which causes an individual to be more
    vulnerable to viruses and diseases.