New Biological Test for Pollutants in Water

Lüneburg. Researchers at Leuphana University Lüneburg have developed a new biological test for pollutants in waste and drinking water. The detection method is based on an already established procedure, however it delivers significantly more information. Additionally, the new test is considerably more sensitive for certain substances - up to a factor of 1000 or more. The cost-effective test can be easily automatized, which makes it extraordinarily well-suited for screening large numbers of probes of toxic contents, according to researchers in the journal, Chemosphere.

The researchers work with so-called luminescent bacteria in their testing. The microorganisms with the scientific name, Vibrio fischeri, occur naturally in the oceans. Under the right conditions, these tiny living organisms can emit light - they start to glow.  How intensively they do so, depends very much on the water quality. This is why toxicologists have used luminescent bacteria for decades to test water for dangerous substances: they place a few drops of the sample they want to test into a test tube of Vibrio fischeri and then, thirty minutes, later assess how much the light intensity has changed. If at this point the bacteria glow only a little or not at all, then it is likely that the water sample contained poisonous substances. 
     
This classical test is simple, delivers quick results, and functions well for many substances. It has, however, one big disadvantage: the measurement has to be concluded within 30 minutes, because at that point the ability of the microbes to emit light increasingly diminishes even in clean water. “Many chemicals release their toxic effect only after a long exposure time, for example, only after several hours delay,” explained Jakob Menz from the Institute for Sustainable and Environmental Chemistry at Leuphana University Lüneburg. “Among other substances, this includes numerous medicines and their decomposed products,” Professor Dr. Klaus Kümmerer, the director of the working group, elaborated.  “These long-term effects cannot be detected with the conventional methods.”        

Microbes on Food Supplements

In order to change this, Menz improved the test in three points: he fortifies his luminescent bacteria by introducing a particularly rich nutrient solution. That way they can survive the test not simply for 30 minutes, but up to 24 hours, or more, without problems. The microscopically small organisms do not just survive during this periodthey actually start to reproduce themselves aggressively. This causes the solution to grow more and more cloudy over the course of the test.

Menz therefore measures not only the light emissions produced by the bacteria, but also the turbidity of the nutrient solution - as second decisive improvement. In particular, there are toxic substances, which in low concentrations can influence the bacteria’s luminosity, but which do not hinder their reproduction. These include, for example, many antibiotics. “Our test can now show at which concentrations a substance impairs the organisms’ metabolism yet still allows it to reproduce unhindered,” the graduate student explained. “These so-called subinhibitory effects are, for example, of great interest in antibiotic resistance.”

The third point concerns the handling procedure: the original test required a great deal of work by hand. This has been greatly reduced in this new variation of the test. Researchers use microtiter plates instead. On a surface area the size of a CD-cover, they can have close to 100 wells for storing the luminescent bacteria.  This makes it possible for almost 100 probes to be studied and evaluated automatically.


A thousand times more sensitive 

The new detection method has withstood its baptism by fire: “We examined a mixture of substances that had been already detected, in the same composition, in the operation of waste water treatment plants,” said Menz. “Our method already sounded the alarm at a thousand times lower concentration than the traditional luminescent bacteria test did.”
 
The working group around the environmental chemist, Professor Dr. Klaus Kümmerer, has for years now investigated the dangers represented by medicines and their decomposed products in food and water. Antibiotics in water, for example, can lead to resistance in pathogens, thereby weakening one of medicine’s most effective weapons. Antibiotics and other wastewater contents can cause also significant damage in sewage treatment plants: after all bacteria are also used in biological sewage treatment. If these are hindered by harmful substances in the wastewater, then the overall water quality suffers. “There has been, until now, a lack of quick, sensitive, as well as cost-effective, screening procedures for such environmental pollutants,” Menz point out.

Such tests are important also in order to improve the quality of wastewater treatment. Hazardous substances are often neutralized these days with the use of ultraviolet light. This procedure is however not always successful. Jacob Menz: “With our method, we have discovered that the toxicity of medical substances following an ultraviolet procedure sometimes actually increases.”
 
Title of the original publication: Toxicity testing with luminescent bacteria – Characterization of an automated method for the combined assessment of acute and chronic effects; J. Menz, M. Schneider, K. Kümmerer; Chemosphere (in Press; online: http://dx.doi.org/10.1016/j.chemosphere.2013.05.067)




Contact:
 Jakob Menz

Prof. Dr. Klaus Kümmerer

Sustainable Chemistry and Material Resources

Institute for Sustainable and Environmental Chemistry,
Leuphana University Lüneburg

Telephone: 04131/677-2863

E-Mail: jakob.menz@uni.leuphana.de