Imidacloprid seed coating poses a risk of acute toxicity to small farmland birds: A weight-of-evidence analysis using data from the grayish baywing Agelaioides badius

POLISERPI, MARÍA BELÉN; CRISTOS, DIEGO SEBASTIÁN; BRODEUR, JULIE CÉLINE

THE SCIENCE OF TOTAL ENVIRONMENT

Elsevier

Año: 2021

0048-9697

The aim of this study was to estimate the risk posed by imidacloprid (IMI) seed coating to passerine birds of thePampa Region of Argentina using data specifically generated with the grayish baywing (Agelaioides badius). Medianlethal dose (LD50) of the IMI-based formulation tested was 57.11 mg IMI/kg body weight (bw), with intoxicationsigns starting from 20.6 mg IMI/kg bw. The feed intake rate (FIR) was estimated experimentally as4.895 g/day per bird, representing 12.43% of bw. It was calculated that the ingestion of 7?10% of the FIR as treatedseeds would be enough to achieve the LD50 for sorghum, corn, sunflower, and alfalfa,whereas consumption of 31and 54% of FIRwas necessary for oat andwheat, respectively. Based on spill data values available in the literature,it was calculated that, for most crops, a baywing would have to forage an area of field corresponding to less than60 m2 to obtain the number of seeds required to reach the LD50. It was also shown that this number of seeds iscoherent with the amount of seeds ingested in a bout. In a pilot study, all grayish baywings fed with milletseeds treated with 3 g IMI/kg died within three to five days of exposure. In Tier I risk assessment, the triggervalue was achieved for all crops except soybean and a weight-of-evidence risk assessment was performed. Alllines of evidence examined are consistent with the view that grayish baywings, and probably other small farmlandbirds, are exposed to a risk of acute toxicity and mortality under bothworst-case and mixed-ration exposurescenarios. The possible impacts on bird species calls for an urgent reconsideration of IMI seed coating practicescurrently approved in the Pampa Region of Argentina and the various parts of the world where this practice isstill in use.