Total Organic Carbon and water quality
Total Organic Carbon
Organic contaminants (natural organic substances, insecticides, herbicides, and other agricultural
chemicals) enter waterways in rainfall runoff. Domestic and industrial wastewaters also
contribute organic contaminants in various amounts. Also, as a result of accidental spills or leaks,
industrial organic wastes may enter streams. Some of the contaminants may not be completely
removed by treatment processes; therefore, they could become a problem for drinking water
sources. For all of these reasons, it is important to know the organic content in a waterway.
Methodology: Total organic carbon (TOC) provides a speedy and convenient way of
determining the degree of organic contamination. A carbon analyzer using an infrared detection
system is used to measure total organic carbon. Organic carbon is oxidized to carbon dioxide before
it is carried by a "carrier gas" into an infrared analyzer that measures the
absorption wavelength of CO2. The instrument utilizes a microprocessor that will calculate the
concentration of carbon based on the absorption of light in the CO2. The amount of carbon will
be expressed in mg/L. Two other test methods that offer organic contamination information are
biochemical oxygen demand (BOD) and chemical oxygen demand (COD). However, TOC
provides a more direct expression of the organic chemical content of water than BOD or COD.
Environmental Impact: By using TOC measurements, the number of carbon-containing
compounds in a source can be determined. This is important because knowing the amount of
carbon in a freshwater stream is an indicator of the organic character of the stream. The larger
the carbon or organic content, the more oxygen is consumed through biodegradation. A high organic content means an
increase in the growth of microorganisms which contribute to the depletion of oxygen supplies.
Both effluent from treatment processes and streams must be monitored for organic
levels. Industrial waste effluent, on the other hand, may contain carbon-containing compounds with various toxicity
levels. This situation can create unfavorable conditions for aquatic life, such as the
depletion of oxygen and the presence of toxic substances.