The Earth's environment is naturally radioactive. Key sources include cosmic radiation, terrestrial radiation from the earth's crust including radon gas, and potassium-40 which is found in sea water. However, this background radiation is dwarfed by comparison to man-made sources – principally nuclear power stations, nuclear fuel reprocessing plants, military weapons testing, dumped nuclear waste and nuclear accidents.

The Radioactive Substances Act, as amended by the Environment Act 1995, governs  radioactive discharges. Until 1984 sea disposal of solid low level and intermediate level radioactive waste was established practice in the UK. In 1994 the UK signed up to a global ban on the sea disposal of all solid radioactive wastes under the Treaty of London Convention (1972).

However, discharges of low level liquid radioactive waste to the sea continue from a number of European nuclear establishments, the largest being Sellafield in Cumbria and La Hague near Cherbourg on the French coast.

factfile:

• Radiation affects living organisms through damage to genes (DNA). Mutations in the structure of DNA can be lethal or crippling. Excessive radiation exposure in humans commonly causes a variety of cancers and birth defects.  Much less is known about the effect of radioactive pollution on the marine evironment. The current safety regulations assume that limits to protect humans will also protect wildlife.
• Weapons testing: Sea contamination from nuclear weapons testing began during WWII. Halted under treaty by the USA, USSR and UK in 1963, and continued by France and China until 1974. Impacts through the 1970s included contamination of fish stocks (haddock and cod) in Barents Sea, and shellfish (mussels, oysters) on Atlantic, Gulf and Pacific coasts of America. 
• Liquid waste: Continuous discharge by nuclear power and fuel reprocessing plants of low level radioactive waste to the sea. Major sources are Sellafield in Cumbria and La Hague near Cherbourg on French coast. Under 1998 commitments to the OSPAR convention, discharges are expected to be reduced virtually to zero by 2020. 
• Solid waste: Sea dumping began in 1946, and continued until a global ban on sea disposal of all solid waste was introduced in 1994. The environmental impact of historical dump sites is unknown, but leaking containers are to likely contaminate marine sediments with a direct impact on bottom dwelling organisms and filter feeders. 
• Nuclear accident: The Chernobyl nuclear accident in April 1986 dwarfs all other sources of accidental pollution. The Baltic sea, northern Adriatic, North Sea, north west coast of Scotland and Irish sea were all significantly affected by contaminated rainfall. Fish stocks still showed evidence of caesium (134 & 137) contamination in November 1986, and residual contamination is apparent today. 
• Bioaccumulation: In the UK, the principle threat to human health comes from seafood. Shellfish, fish and edible sea weeds can store chemical pollutants as they feed - a process called bioaccumulation - and gradually build up concentrated toxins in their tissues. The Food Standards Agency monitors commercial fish species for signs of radioactive contamination. Sellafield is the most common source.

what you can do:

• Ensure you buy and eat shellfish from reputable suppliers, particularly food sourced from the eastern Irish Sea. 
• Switch to a green energy supplier for electricity.
• Read about MCS’ recommendations for offshore energy development.