Investigation of the distribution of anticoagulant rodenticide residues in red fox (Vulpes vulpes) livers to ensure optimum sampling protocol

The lobular distribution of 9 different anticoagulant rodenticide (AR) residues in the liver of a sentinel predator/scavenger i.e. the red fox (Vulpes vulpes) was determined following multi-residue analysis using Ultra (High) Performance Liquid Chromatography tandem Mass Spectrometry (UHPLC-MS/MS). The aim of the study was to address concerns that if distribution of AR residues in the liver was significantly heterogeneous, analysis of random sub-samples or finite remnants of liver could result in false negatives or lead to incorrect toxicological diagnoses. Intact livers excised from animals shot as part of routine legal pest control activities in Scotland during 2018 and 2019 were sub-sectioned and the lobular concentration of AR residues was investigated. Analysis of individual lobes from 10 different fox livers revealed that AR residues initially detected in a randomly selected small portion of liver tissue were present throughout the liver. Also, in cases where AR residues were not found in the initial randomly selected portion, they were not found in the subsequent more detailed examination. The limit of quantitation was 3 μg kg‐1 and AR residue concentrations ranged from 3 to 885 μg kg−1. Statistical analysis of variance (ANOVA) was performed on the eight and six out of ten livers that tested positive for bromadiolone and brodifacoum, respectively. No statistical evidence was found of differences in mean residue levels of bromadiolone throughout the liver i.e. within and between liver lobes. However, brodifacoum showed a statistically significant difference (p < .001) in mean residue concentration between the lobes but there was no statistical evidence of mean differences within the lobes.