Total Organic Carbon (TOC)

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 is partly broken down by micro-organisms, in the process consuming oxygen. At high TOC concentrations, so much oxygen in the water may be used up that there is not enough to support fish and other aquatic animals, which then die.TOC can be measured directly in samples of water by treating it with chemical oxidants and then measuring the amount of carbon dioxide released. Alternatively it can be measured by determining how much oxygen it uses up during its complete oxidation to carbon dioxide. This is expressed in terms of the Chemical Oxygen Demand (COD). On an average the ratio COD/TOC is about 3:1.