For many years Lindane was used as an insecticide in Germany. In 2003 the use of Lindane in agriculture was banned throughout the EU due to its strongly toxic effect and its long-term persistence. However, in some areas soil and groundwater are still heavily contaminated with this substance. To implement efficient environmental management, it is important to know whether the pollutant is being degraded and how quickly. Researchers at the Helmholtz Centre for Environmental Research (UFZ) have now developed a method that makes it possible to quantify the biodegradation of Lindane and estimate the length of time required for the chemical to safely decompose. The study appears in the current edition of the Journal of Environmental Science and Technology.

Lindane belongs to a group of chemicals known as HCHs (hexachlorocyclohexanes). These substances are slow to degrade, accumulate in the food chain and are believed to have hormonal effects. The use of Lindane in agriculture has been banned in the Federal Republic of Germany since 1977 and it continued to be used in East Germany until 1990. Using groundwater and soil samples from former manufacturing and landfill sites in the Bitterfeld region of Saxony-Anhalt, the UFZ team led by biogeochemist Dr. Hans-Hermann Richnow has developed a new concept with which to monitor the biodegradation of HCHs in the environment.

The UFZ researchers’ innovative approach is to combine two detection methods: isotope and enantiomeric fractionation. In laboratory tests, they developed a model that allows the degree of degradation to be measured using specimens taken from the environment. "This means that we now have an elegant way of analysing the biodegradation of Lindane and other HCHs in soil and groundwater with minimal effort," says Richnow. He adds that the method makes it possible to measure the biodegradation of the substance when it is transported in water or with soil particles. This will allow scientists to work out how long the HCHs can be expected to be present in the environment.

Applying isotope fractionation, researchers analyse the ratio of light (¹²C) to heavy (¹³C) carbon atoms in the Lindane molecules of environmental samples. The ratio of ¹²C to ¹³C is normally about 99:1. "When chemical or biological degradation occurs, the molecules with light carbon atoms break down faster because less energy is required to break the chemical bonds," explains Richnow. When the isotope ratio shifts towards the heavier ¹³C, this is a clear indication that degradation is taking place. Chemical manufacturing produces equal proportions of 'mirror image’ molecules (enantiomers) - rather like a left and a right hand. This provides the basis for enantiomeric fractionation. With this method, researchers can now study the samples and see whether the ratio has changed. "The bacteria that break down the pollutant prefer one enantiomer or the other depending on what enzymes they possess," says Richnow. If a changed enantiomer ratio can be measured in a sample, this provides information about the biodegradation taking place in the location where the sample was collected.

The new method of analysis could also be used in areas other than Bitterfeld. The environmental burden caused by Lindane and other HCHs is a global problem. Richnow says: "We hope that this method will provide a monitoring tool to assess and evaluate the current HCH burden in soil, groundwater and surface water." This in turn could advance the development of suitable methods for efficient environmental management.

The research was supported by data and sampling assistance from Ökologisches Großprojekt Bitterfeld-Wolfen, Landesanstalt für Altlastenfreistellung Sachsen-Anhalt and Chemiepark Bitterfeld-Wolfen GmbH.

Publication:

Yaqing Liu, Safdar Bashir, Reiner Stollberg, Ralf Trabitzsch, Holger Weiß, Heidrun Paschke, Ivonne Nijenhuis, Hans-Hermann Richnow (2017). "Compound Specific and Enantioselective Stable Isotope Analysis as Tools to Monitor Transformation of Hexachlorocyclohexane (HCH) in a Complex Aquifer System". Environ. Sci. Technol., 2017, 51 (16), pp 8909-8916 http://pubs.acs.org/doi/10.1021/acs.est.6b05632

Further information

Dr. Hans-Hermann Richnow
Head of the UFZ Department of Isotope Biogeochemistry
hans.richnow@ufz.de