For many years the UK, nicknamed the ‘dirty man of Europe’, has used the sea as a convenient dustbin for sewage, radioactive waste and toxic chemicals. All three categories of waste damage our coastal environment. Pollution by sewage and radioactive waste have recently been of particular public concern.
Raw sewage is broken down in the sea by micro-organisms, which use up a lot of oxygen in the process. Depleted oxygen levels in seawater kill fish and other marine life. Sewage contains 10,000 to 10 million viruses per litre, the hepatitis A virus amongst them, and faecal bacteria - including pathogens. Condoms and cotton swabs flushed down toilets travel with raw sewage into the sea, and - along with faeces - may be washed up onshore. This used to happen on some Devon and Cornwall beaches as recently as the early 1990s. In response, the group ‘Surfers Against Sewage’ (SAS) was set up to campaign for clean, sewage-free coastal waters.
Sewage treatment begins with screening to remove large objects. Primary treatment follows, where raw sewage is left in tanks for 2-6 hours, allowing roughly 55% of solids to settle to the bottom. The liquid contains about 10 million bacteria per litre, and may be pumped into a long coastal outfall pipe or subjected to secondary treatment. The latter involves settling the liquid in another tank, one which contains bacteria that feed on the liquid and sludge. After the secondary stage, the clear liquid contains approximately 100,000 faecal bacteria per litre. The tertiary stage is disinfection of the liquid either by ultraviolet light or microfiltration.
Since the early 1990’s, many water companies adopted tertiary treatment for sewage before discharge into the sea. The Devon town of Croyde obtained planning permission for tertiary treatment of the town’s sewage in 2001, and as a result beaches in North Devon are very clean and receive the coveted Blue Flag awards. Elsewhere the situation is not resolved; at time of writing - July 2005 - untreated sewage from Brighton is discharged into the sea via a long outfall pipe.
In 2004, Southern Water announced plans for a new secondary treatment plant to deal with Brighton’s sewage before discharge into the sea, but not a tertiary treatment facility, meaning that significant amounts of viruses and faecal bacteria would still get into the seawater. Surfers Against Sewage continue to campaign for such a tertiary sewage treatment plant for Brighton.
What about the sewage sludge – what can we do with that? It can be used as fertilizer, but requires further breakdown by bacteria. Data collected by the Department for the Environment, Farming and Rural Affairs (Defra) shows that about half of all sludge was spread on farmland between 1990 and 1998. A drawback for using sludge from industrial areas is that it contains toxic chemicals and heavy metals. About 10% of sludge was disposed to landfill and a further 10 to 20% disposed of at sea. 20% was incinerated, and the remainder disposed of by ‘other means’. Since 1998, the EU’s Urban Wastewater Directive has outlawed dumping of sludge at sea and other methods are used, including composting and use in land reclamation.
Litter is common on beaches and in our coastal waters and most is plastic, cups and supermarket bags, but cans, paper, cardboard, shoes, glass, pottery and munitions also spoil our beaches. The sight of a messy beach puts tourists off from returning, reducing income for local people. Yet tourists themselves contribute to this marine litter, as do people on cargo boats, ferries, fishing boats and oil rigs.
Litter harms wildlife: seabirds and cetaceans are killed by swallowing litter or getting entangled with discarded fishing nets. In turn, fishing nets are ripped by large pieces of debris and the recent ‘Fishing for Litter’ campaign encouraged fishermen to bring to shore for safe disposal any litter caught in their nets. Statutory measures to reduce and prevent marine littering are in place but are obviously difficult to enforce on the open sea.
Nuclear power stations dump liquid radioactive waste - for example water containing the radionuclides tritium, caesium-137, plutonium-239 and strontium-90 - into the sea. The half-lives of some radionuclides are so long that they will persist at significant levels in the coastal environment for hundreds or thousands of years.
Dumping radioactive waste puts it out of sight but the action of the sea and marine food chains returns it to our coast, and into our food. The Sellafield reprocessing plant provides the major input of radionuclides into the Irish Sea, and although the discharges are much lower now than in the 1970s, caesium-137 in seawater is replenished by re-mixing of sediments releasing the isotope back into the water.
Radionuclides move through food chains; mussels and cockles sieve particles out of water and accumulate radionuclides in their bodies. Fish take in the radionuclides by eating contaminated molluscs. When contaminated seafoods are eaten in turn by a person, the radionuclides may be incorporated into the body tissues. Exposure of living tissues to radiation can cause cancer, as energy released by radioactivity damages the genetic material of cells.
So we know it is a bad idea to dump radioactive waste into the sea, but where can we dispose of it safely?
Movement of dumped radioactive isotopes through soils and rocks is poorly understood. The Dounreay prototype fast reactor on the Caithness coast is undergoing decommission but is dogged by problems of leakage of waste. Sand-sized radioactive particles are found regularly on Dounreay and Sandside beaches. The particles may be swarf from cutting aluminium cladding away from nuclear fuel that was dumped into a shaft.
Scotland Against Nuclear Dumping (SAND) feels that the particles are dangerous, in spite of the National Radiological Protection Board’s assessment that ‘the particles have no discernible health effect’.
The Committee on Medical Aspects of Radiation in the Environment (COMARE) suggested that particles may access the beach via movement of water through rock strata and upwelling of fresh water in the sea. COMARE recommended that divers should search for freshwater springs that are spreading the particles into coastal waters.
Currently the UK has 10,000 tonnes of solid long-lived radioactive waste in storage that could rise to 500,000 tonnes as old nuclear power stations are decommissioned. The Committee on Radioactive Waste Management (CoRWM) was set up by the government to look at options for safe storage of this waste.
Unrealistic options such as flying radioactive waste out to space, embedding it in ice sheets, or burial in the sea bed, were discounted immediately. CoRWM provides opportunities for the public and stakeholder groups to take part in the consultation. The four short-listed options are interim storage, near-surface disposal for short-lived wastes and deep underground disposal or phased deep underground disposal that enables waste to be retrieved if necessary.
Recently Nirex, the nuclear waste agency, revealed 12 potential sites for radioactive waste dumps listed in the 1980s and 90s. They are all coastal, and some may be picked in future for deep underground disposal.
However, as sea levels rise, coastal radioactive waste in dumps may leak as water penetrates or erosion occurs. Certainly, the dump for low level radioactive waste at Drigg in Cumbria, located 500m from the coast is identified as being at risk of leaking if the sea level rises.
The practice of pumping raw sewage into the sea is no longer justified as we have technology for cleaning the sewage before discharge into rivers and coastal waters. Some uses have even been found for sewage sludge.
The problem of radioactive waste, one of the most dangerous categories of waste, appears not to have such a straightforward solution. Selecting coastal sites for long-term burial of radioactive waste may not be a realistic option as sea levels rise. CoRWM has a difficult task ahead.