Toxicity in water
Toxicity is described as the direct harmful effect of a substance on organsims. It can refer to the effect on a whole organism or on a substructure of the organism, such as a cell.
The toxic effect depends on the concentration of toxic substances, on the sensitivity of the organisms as well as on the incubation period. Toxicity can already occur at low concentrations. In water toxicity is often calculated as EC50. The Effective Concentration indicates the concentration at which 50% of the test organisms are harmed.
LAR Nitrification Respiration Inhibition Test
The bacteria (nitrifiers) used live on oxygen from the conversion of ammonia to nitrate. The LAR NitriTox and ToxAlarm measure this oxygen consumption. Toxic substances in the sample contents can inhibit the respiration of the bacteria leading to a lowering of the oxygen consumption. Thereby the nitrifiers' oxygen consumption enables to draw conclusions about the toxicity of a sample. The LAR test takes 5-15 minutes and is characterized by its self-regenerating, integrated bacteria culture. Hence, no purchase or external breeding is necessary.
The difference to common methods
The LAR measurement method uses a bacteria culture which constantly and independently produces biomass in a fermenter. This fermenter is separated from the measuring cell. For each measurement a fresh amout of bacteria is used. This guarantees that there is always enough bacteria for new measurements and the risk of the fermenter being contaminated is removed. For this reason, there is no purchase or external breeding of organisms necessary.
This table shows a comparison of the most common toxicity detection methods assessed on four criteria.
|Supply||Purchase / breed||Purchase / breed||Purchase / breed||Purchase / breed||Self-regenerating|
|Duration||72 h||50 min||24 or 48 h||48 h||5 min|
|Sensitivity||very high||middling||very high||high||very high|
|Continuous monitoring after accident||yes||yes||no||no||yes|
Common Toxicity Measurement Methods
Often the unicellular green algae is used to indicate toxicity. This method measures the inhibition of cell division caused by toxic substances. At high toxic concentrations, algaes can die. Hence, new algaes have to be stored and kept in stock to ensure further toxicity measurements after a toxic effect.
The algae test takes 72 hours and the supply of the test organisms must be secured by purchase or breed.
Bioluminescence is the production and emission of light by a living organism. Specific detectors measure the emitted light and draw conclusions on toxicity. Toxic substances cause a reduction of the emitted light.
Commonly, this standard method uses Vibrio fischeri as test organisms. These bacteria glow under optimal growth conditions (bioluminescence). The bioluminescence is reduced by toxic substances in the sample and may lead to death of the organisms.
The bioluminescence test takes 50 minutes. The used test organisms must be purchased or bred.
Daphnia are crustaceans between 0.2 to 5 mm in lenght. Commonly, these small animals called water fleas and are often used for the determination of toxicity. However, for toxicity measurements, they must not be older than 24 hours.
The used Daphnia Magna are very sensitive to heavy metals but less to other substances. Toxic substances cause the death of the organisms, following which the number of surviving organisms are counted.
The daphnia test takes 24 or 48 hours and the organisms must be bred.
The fish test - also known as golden orfe test - describes an animal experiment, which aims to determine at what dilution of waste water all animals survive 48 hours. The result is the smallest integer value of the dilution of the waste water (GF value).
As with the common test methods, the toxic substances cause the death of the organisms. At the end of the test the number of surviving fishes are counted. In Germany the fish test has been replaced since 2005 by the fish egg test.
The fish test takes 48 hours. The used test organisms must be purchased or bred.