Is Right-Handed Penflufen Safe to Use? - Chromatography Investigates

Pesticide use is almost ubiquitous in agriculture. Although the ‘organic’ market has grown in recent years, figures suggest that pesticide use has not lessened. And that is a cause of concern for both human and environmental health. In a recent European Union report - the authors acknowledge that ‘Pesticides are a cause of pollution and have a direct effect especially on the state of biodiversity, water bodies, and soils.’

But are all pesticides the same? In fact, are the dangers of the left-handed pesticides the same as the dangers of the right-handed side? Welcome to the world of chirality - where some molecules can be left-handed and some can be right-handed. A recent study published by the Royal Society of Chemistry has investigated whether the chirality of the pesticide penflufen affects its behaviour in plants.

Left and right - not just a political issue

Chirality is a geometric property of some molecules. The word chiral comes from the Greek language and means hand - and is applied to structures that cannot be superimposed on their mirror image. For example, our hands, which have two distinct conformations - left and right. Molecules that are chiral cannot be superimposed on their mirror image.

Chiral molecules occur in nature. One of the simplest chiral molecules is the sugar glyceraldehyde which has two chiral forms, left and right. But sugars that occur naturally in nature are almost exclusively right-handed - which is just as well as humans cannot use the left-handed version. Could chirality play a role in pesticide use?

Are penflufen enantiomers equal?

Penflufen is a broad-spectrum fungicide whose use has grown in recent years. It is also a chiral pesticide with an S-(-) configuration and an R-(+) configuration. These two configurations are non-superimposable on their mirror images - hence they are chiral. The S and R denote different enantiomers. Enantiomers is the name for a pair of chiral molecules.

Penflufen is used for seed borne fungal pathogens on crops such as potato, cereals and some vegetables. In non-chiral environments, the two enantiomers behave the same. But nature is chiral in many respects, it uses only the left- or right-handed molecules, especially in its chemical reactions. In the paper referenced above, the team analysed the residual pollution left on crops after penflufen had been applied.

They used high performance liquid chromatography with tandem mass spectrometry (LC-MS/MS) to analyse the residual enantiomers of penflufen in wheat, spinach and Chinese cabbage. The use of chromatography to analyse agricultural raw materials is discussed in the article, HPLC Analysis of Melamine and Related Substances in Fertilisers. They discovered that in spinach, one of the enantiomers was selectively degraded - suggesting that using chiral pesticides needs more investigation, especially when it comes to human health.