Organic substances

TOC (Total Organic Carbon)

According to Wikipedia, the number of known organic compounds is estimated at 40 million. Reason enough to monitor these in water as well. Our water can contain an exceedingly large number of organic, i.e. carbon-containing substances. These can be natural substances (e.g. humic acids, carbohydrates, amino acids), but also pollutants (e.g. wastewater, mineral oil, pesticides, cyanides). To test a water sample for the presence of all individual organic substances would be neither practical nor affordable. However, it is possible to examine a specific group of substances. The determination of TOC, i.e. the measurement of organically bound carbon, is such a cost-effective analytical method.

TOC analysis is mainly used for groundwater/well water, pond water and water treatment control.

The TOC content of water is an important indicator of the purity of the water or of the contamination of the water with undesirable and possibly health-endangering organic substances of human origin. An increased TOC content does not immediately indicate a health hazard.

The causes of abnormal changes must be investigated by individual substance analyses.

The TOC measurement is anchored in the drinking water ordinance without a limit value, i.e. the TOC value of a water should not increase compared to previous measurements.

In clean drinking water, TOC values below 1.5 mg C/l are normal.

What are the effects of elevated TOC levels?

• Microorganisms can use elevated concentrations of organic matter as a nutrient substrate for their reproduction, and contamination of the plumbing system is more likely.
• Increased TOC concentrations promote the formation of undesirable, sometimes toxic by-products from disinfectants, e.g. volatile trihalomethanes. Therefore, testing is recommended for well water used to fill a pool.
• TOC impairs the effect of water filters. For example, the removal of iron from well water is disturbed because organic compounds significantly increase the solubility of iron. TOC analysis is therefore advisable when operating water treatment plants.
• TOC concentrations above 1.5 mg C/l promote corrosion of copper pipes at a pH below 7.4. The use of copper pipes is then not recommended.

Typical TOC concentrations in waters:

• Sea water approx. 0.5 mg C/l
• Ground water 0.5 - 1.5 mg C/l
• Rainwater 0.5 - 2.5 mg C/l
• River water slightly polluted below 5 mg C/l
• Ecologically dead water over 40 mg C/l

The measurement is carried out according to DIN EN 1484:2019-04