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Total organic carbon or COD/3


SPRI Emission Reporting Threshold
50,000 Kg/yr Pollutant Emissions to Water
50,000 Kg/yr Pollutant Emissions to Waste Water
This sheet is a generic summary, designed to give the reader a basic level of background information about the substance in question. Great care has been taken to represent as effectively and correctly as possible the broad range of (not necessarily consistent) information which is available from a variety of sources. The reader must accept therefore that this sheet has no legal status and cannot be relied upon in any legal proceedings. SEPA disclaims any responsibility or liability whatsoever for errors and omissions in this sheet.
What is it?
Total organic carbon (TOC) describes any organic (carbon-containing) compounds dissolved in natural waters. This constitutes a huge range of compounds with a variety of properties.
What is it used for?
TOC does not have any use. It is simply a term used to describe a class of compounds that classify water quality.
Where does it come from?
TOC is released from both natural and man-made sources. All aquatic life naturally release TOC through their normal metabolism, excretion and eventual decomposition. Soils and peat also leach TOC into water bodies. Man-made sources include sewage treatment plants, farm slurry and silage run-off, leachate from waste disposal landfills, fish farm and food processing effluents and spillage of food stuffs.
How might it affect the environment?
TOC is broken down by aquatic micro-organisms, consuming oxygen in the process. At high TOC concentrations, so much oxygen in the water may be used up that fish and other aquatic animals cannot survive. Low concentrations of TOC encourage the growth of anaerobic bacteria (which do not require oxygen). These can then produce sulfate salts which are toxic to any surviving aquatic life. Anaerobic waters have a distinct smell of bad eggs (due to hydrogen sulfide released from the sulfate salts). This is usually a sign of extreme organic pollution, although anaerobic conditions do occur naturally in some waters (for example very deep lakes). TOC is unlikely to impact on the global environment. Local effects of man-made TOC have however been observed across the globe, extending into coastal waters of the Baltic, Black and Adriatic seas.
How might exposure to it affect human health?
TOC does not directly pose a risk to human health. However in extreme cases where anaerobic (non-oxygenated) conditions result, the toxic salts produced may have adverse effects.
What steps are being taken to limit the potential impacts?
Substances which have a measurable adverse effect on the balance of oxygen dissolved in natural waters are regulated through the European Directive on Integrated Pollution, Prevention and Control (96/61/EC), which has been transposed into UK (and Scottish) law as the Pollution Prevention and Control (PPC) regulations.