Monitoring approach to detect recent exposure to thiamethoxam-treated seeds in birds

Thiamethoxam (TMX) is a neonicotinoid insecticide that is widely used for seed treatment in a variety of crops. Farmland birds can be exposed to TMX by consuming treated seeds remaining on the soil surface due to either spills or failed implantation during sowing. In the environment, TMX can be metabolized into clothianidin (CLO), another neonicotinoid insecticide that is also toxic to birds. The goal of the present study was to evaluate the feasibility of a non-invasive approach consisting in the analysis of fecal samples to detect recent exposure of wild birds to TMX and CLO. To achieve this, 16 grayish baywings (Agelaioides badius) were exposed for 21 days to seeds coated with four different concentrations of TMX: 0 (control), 0.027 (low), 0.33 (medium), and 4.3 (high) g TMX/kg of seed. These concentrations are within the approved range for seed coating with TMX in typical crops of the Pampa Region in Argentina, where baywings are common. Seed consumption was monitored over 24 h and fecal samples were collected on day 1, 2, 3, 4, 7, and 21 of exposure. Finally, concentrations TMX and CLO were determined in collected feces through LC-MS/MS. Fecal concentrations of both TMX and CLO showed a significant dependence on the treatment dose (p = 0.006). Average concentrations of TMX and CLO were respectively 63, 689, and 2363 ng/g and 75, 735 and 2040 ng/g for low, medium and high dose groups. These results demonstrate that fecal analysis is a reliable non-invasive method for assessing recent bird exposure to TMX. The results also confirm that TMX is metabolized into CLO, and suggest a saturation of the metabolic pathway at high doses. This study supports the use of fecal analysis for pesticide exposure estimation in field monitoring studies of wild birds.