Total Organic Carbon (TOC)

The substance
All of the organic (carbon-containing) substances in natural waters may be termed TOC. There are many natural and man-made substances that all contribute to TOC. TOC may be broken down by micro-organisms, in the process consuming oxygen. TOC can be measured directly in water samples measuring the amount of carbon dioxide that is liberated after treatment with chemical oxidants.

TOC is used as a convenient parameter for assessing water quality associated with the aqueous discharge of organic chemicals.

Major emissions
All plants and animals in natural waters contribute to TOC as a result of their normal metabolism and excretion of waste products and their eventual death and decomposition. In addition, TOC is also leached out of the surrounding soil or peat. Man-made sources include any organic substance released to natural waters.

Impacts on human health and environment
No health concerns can be identified for such a diverse group of chemicals. High TOC effluent can cause natural waters to be uninhabitable by fish and other aquatic life as a result of oxygen depletion. Anaerobic waters may emit an objectionable odour of hydrogen sulphide and are indicators of gross organic pollution. TOC is unlikely to be an issue on the truly global scale. However, regional examples of coastal waters becoming anaerobic at depth due to man's activities are seen in the Baltic Sea, the Black Sea, the Adriatic Sea and coastal waters around Thailand. It should be mentioned however, that anaerobic conditions also occur naturally in some waters, including enclosed or partially enclosed seas and especially in deep lakes.

Emission to water reporting threshold: 50000 kg/year

Data source: European Pollutant Emission Register