Non-invasive method to measure the dermal exposure of amphibians to pesticides

Pesticide exposure of amphibians is difficult to assess due to the various possible exposure routes and the movement behavior between aquatic and terrestrial habitats (EFSA, 2018). In particular, little is known about the dermal uptake of pesticides in field, which appears to be very important for amphibian’s exposure risk and survival (Llewelyn et al., 2019). We have used swab samples to measure pesticides on the skin of amphibians which possibly originate from contact to contaminated soil, sediment, water, plants or air. We investigated adult amphibians, nine common toads (Bufo bufo) and one common frog (Rana temporaria), which were trapped in and around maize fields in North Rhine-Westphalia (Germany) in summer 2018. About 10 cm² of the ventral and dorsal side of each animal were swabbed separately using individual sterile Dryswab™ with fine tip rayon buds. The selection of pesticides based on a proposal for a representative monitoring in the framework of the “Implementation of the National Action Plan on the Sustainable Use of Pesticides” (UBA, 2019). The substances were extracted with a solution of water/methanol (1:1, 1% formic acid) from the swabs. The amounts were measured with liquid and gas chromatography-mass spectrometry. We detected terbuthylazine in samples of three animals. Plant protection products containing terbuthylazine may be used in the pre- and post-emergence (BBCH 10-17) of maize with maximal 750 g/ha (BVL, 2018). The highest amount of 75 pg/cm² was found on the ventral side of a toad. This amount corresponds to 0.001% of the maximum application rate permitted for maize fields. The detection of terbuthylazine in swab samples from animals in and around maize fields is an expression of the spatio-temporal behaviour of amphibians.