The common kestrel as an environmental bioindicator of toxic chemicals on Tenerife Island (Canary Islands, Spain).

Indirect effects of toxic chemicals, such as persistent organic pollutants (POPs), affect non-target species like apex predators due to bioaccumulation in food webs. The common kestrel (Falco tinnunculus canariensis), an endemic subspecies from the Canary Islands and Madeira, was evaluated as a bioindicator to assess contamination by organic pollutants in Tenerife. A total of 390 liver samples, collected between 2003 and 2021, were analysed for 341 toxic compounds including pesticides, pharmaceuticals, and POPs like PCBs, PBDEs, PAHs and OCPs. Results revealed widespread contamination: 97.7% of kestrels had DDE, and 94.6% had PCB, with congener #180 being the most prevalent. BDE-153 was detected in 32.3% of samples and PAH, predominantly naphthalene, in 36.9%. Additionally, we identified four fungicides, five insecticides, one herbicide, and the acaricide tetradifon, marking the first report of these substances in raptors globally. Generalised Linear Models (GLM) and Linear Models (LM) indicated that adults had significantly higher levels of OCP and PCB, and PBDE exposure. Males exhibited significantly higher levels of PCBs and were more likely to be exposed to PBDEs. A decline in the concentrations and presence of OCPs, PCBs, and PBDEs was observed during the second study period (2003-2009 vs. 2017-2021). For PAHs, the null model was the best fit, indicating that the factors examined (sex, age, human density, cultivated area or period) did not have a significantly influence on exposure. This comprehensive, long-term study, represents a pioneering investigation in the Canary Islands, demonstrating the utility of the common kestrel as a bioindicator of environmental pollution.