Anticoagulant rodenticide exposure and toxicosis in four species of birds of prey in Massachusetts, USA, 2012-2016, in relation to use of rodenticides by pest management professionals.

Restrictions on second-generation anticoagulant rodenticides (SGARs) in the United States, which were partially implemented in 2011, prohibit the sale of SGAR products through general consumer outlets to minimize use by non-professional or non-agricultural applicators. This study analyzed liver tissue from four species of birds of prey admitted to a wildlife clinic in Massachusetts, USA, from 2012-2016 for residues of anticoagulant rodenticides (ARs). Ninety-four birds were analyzed; 16 were symptomatic for AR toxicosis, and 78 asymptomatic. Ninety-six percent of all birds tested were positive for SGARs: 100% of those diagnosed with AR toxicosis ante-mortem and/or post-mortem and 95% of subclinically exposed birds. Brodifacoum was found in 95% of all birds. Sixty-six percent of all birds contained residues of two or more SGARs. A significant increase in exposures to multiple SGARs occurred in later years in the study. Pesticide use reports (PURs) filed with the Massachusetts Department of Agricultural Resources were reviewed to determine the frequency of use of different ARs by pest management professionals (PMPs) across five years. This study finds that the three SGARs favored by PMPs-bromadiolone, difethialone, brodifacoum-were present in combination in the majority of birds, with increases in multiple exposures driven by increased detections of bromadiolone and difethialone. Continued monitoring of AR residues in nontarget species following full implementation of sales and packaging restrictions in the US is needed in order to elucidate the role of PMP use of SGARs in wildlife exposures and to evaluate the effectiveness of current mitigation measures.