Pesticide contamination patterns in Montagu's harrier (Circus pygargus) chicks

Biomonitoring of persistent pesticides in birds of prey has been carried out for decades, but few studies have investigated their relevance for the monitoring of non-persistent pesticides. Herein, we determined the contamination patterns of multiple pesticides in Montagu's harrier (Circus pygargus) chicks in an intensive farming area of southwestern France. Blood samples from 55 chicks belonging to 22 nests in 2021 were assessed for 104 compounds (herbicides, fungicides, insecticides, safeners and synergists). All chicks had at least one herbicide in their blood, and half had at least two compounds. The 28 compounds detected comprised 10 herbicides, 12 fungicides, 5 insecticides and 1 synergist. Mixtures in blood were predominantly composed of herbicides, and six chicks presented a mixture of the three pesticide classes. The most prevalent compounds were sulcotrione (96% of chicks), tebutam (44%) and chloridazon (31%), of which the latter two had been banned in France for 19 and 3 years, respectively, at the time of sampling. Most compounds are considered non-acutely toxic, but sulcotrione is potentially carcinogenic, mutagenic and reprotoxic, raising questions about the effects on the health of nestlings. Biomonitoring of multiple pesticides through Montagu's harrier chicks in agroecosystems is clearly relevant because it reflects the general pattern of agricultural pesticide use in the study area. It also raises questions about exposure pathways in chicks, and further investigations are needed to disentangle the roles of dietary routes and maternal transfer for the established pesticide contamination patterns.