New Methods For Determining Unknown Pollutants - Jens-Uwe Schroeter

When determining unknown pollutants, it should be considered that it is impossible to detect all possible trace substances. The analysis of all known substances within a single sample is too expensive and time consuming. However, there must be a process to determine the existence of pollutants in water or sewage water promptly or at least within a few minutes.

Therefore, quantitative parameters have been introduced to increase the efficiency of water analysis. Normally these parameters cannot differentiate between unwanted or harmful substances. Typically, unwanted substances are any water pollutants that do not result in significant harmful effects.

In comparison, harmful substances have direct or long-term poisonous effects on the environment, even in very low concentrations. We could, in this respect, use the terms toxic and less toxic substances. In this article we will focus on the possibilities for determining unknown substances by quantitatively measuring toxicity.

Background Information
Harmful substances should preferably be detected with responding on-line analysis equipment as soon as possible after their discharge into a given medium. Most of the known parameters are available as on-line measurement today. The appropriate combination of parameters such as TOC, TN, TP and others with adequate toxicity measurement is of great significance. It is essential that the toxicity measurement is as manageable and representative as possible.

The collection of toxicity parameters, being quantitative, should be relatively simple without requiring a specialised laboratory for growing test organisms. By combining TOC, DOC, TN, (optional TP) with ammonia and nitrate as well as an UV-spectrum or UV-absorption and by using adequate evaluations and comparisons, it is possible to draw conclusions on the pollution by harmful substances and their possible origin. However, it is still difficult to detect toxic substances in low concentrations. They do not necessarily stand out by a significant concentration increase of the parameters stated above even though there may have been toxic effects already.

As a simple example we may consider cyanide, a well-known highly toxic substance which is toxic even at low concentrations. At low concentrations it would not be easily detected by the above-mentioned parameters. Suitable toxicity measurement methods, however, detect cyanide even at low concentrations immediately.