“Where did you come from, where did you go?” — An analytical study of pyrethroid insecticides.
You will likely have heard that European forests are currently faced with quite an unprecedented infestation of bark beetles. You can imagine that outbreaks of these tree-killing insects have wide-ranging ecological and economic impacts. The question is, what to do about it?
Methods to deal with bark beetle infestations include sanitation harvests and chemical treatment of infested trees. As far as chemical treatment is concerned, pyrethroids, synthetic analogues of naturally occurring pyrethrins, are currently the only available pesticides for agricultural and forest protection applications in the Czech Republic.
But… When these compounds are exposed to the environment, they undergo degradation through several pathways involving both photochemical and biochemical reactions. In other words, they are broken down by chemical processes as well as by sunlight. This means that the concentration of insecticides present on the treated surface gradually decreases.
Understandably, for the insecticides to be effective against bark beetles, they must be present in sufficient amounts. To ensure this, it is necessary to develop a method of determining their concentration in samples of treated wood.
A frequently used technique for the detection of these types of compounds is gas chromatography (GC). In this procedure, compounds from the analysed sample are vaporised and passed through a long narrow tube, a so-called column. Simply put, different compounds take different lengths of time to pass through the column. As the mixture travels along, its constituent compounds are separated and can be detected as individual components of the mixture.
This technique can also be used to determine the amount or concentration of a compound in a sample.
At the Czech University of Life Sciences, we plan to adapt this analytical process to the detection of pyrethroid insecticides and develop a method that will reliably tell us how much of the initial dose of insecticide is present on the treated material.
When we use the term ‘method’, we usually refer to the specific experimental setup using a chosen analytical technique. This can include the extraction method used to liberate our compounds of interest from the rest of the sample (the so-called matrix), the type of column used, the parameters of the detector and many more variables.
A finely tuned analytical method can allow us to detect our chosen compounds with great precision and to study the processes by which they decompose in the environment.
Since the environment is a very complex system, many variables need to be considered when it comes to determining which factors influence the degradation of pyrethroids (e.g., length of sunlight irradiation, moisture, rainfall, temperature etc.).
We must, therefore, carry out a set of experiments that will reasonably model at least some of these natural conditions. Working directly in an outdoor location is also an option which we would like to make use of.
Ideally, we should not only be able to detect pyrethroids in samples of treated tree bark but also predict the rate of their degradation based on environmental factors.
The results of our research will provide a valuable tool for analytical chemists, private companies or forestry personnel to monitor the correct usage of pyrethroids in forest protection applications. Furthermore, the optimisation of pyrethroid application protocols by accounting for their natural degradation will be made possible. This will lead to a more controlled and environmentally friendly application of these compounds. Considering the extensive usage of pyrethroids in connection with recent bark beetle outbreaks, any details on their chemical behaviour which will allow for optimisation of their application procedures can be very useful.
