Integrating and extrapolating the effects of different exposure routes for invertebrates: a case study with honeybees interpreting acute oral, acute contact, glass plate and chronic tests within one single framework

In indirect exposure tests for non-target arthropods, organisms are exposed to a compound on pre-treated glass plates or leaves to mimic exposure in the field. These tests are difficult to generalize because the effective dose that the organism received is unknown. This is unfortunate, because this hampers further interpretation and integration of ecotoxicological tests in general. As proof of principle to show that indirect tests can be integrated with dose-driven tests, an indirect test was carried out with honeybees exposed to imidacloprid and the results were compared with available, more standard chronic oral, acute oral, and acute contact test results. The three standard tests were used to calibrate and validate a ToxicoKinetic ToxicoDynamic model to obtain the toxicity parameters that link the dose to effects. Subsequently, the validated parameter set was used to calculate the dose of imidacloprid needed to obtain the effects observed in the indirect exposure test. This exercise showed that the model can be used to calculate the dose in a glass plate test, which implies that any of the tests can be used to predict the outcome of any other test. This is a first step in the development of a "criss-cross risk assessment model, where both effect endpoints and exposure endpoints, can be combined." This first step has great potential to use this predictive power to reduce bee testing and non-target arthropod testing in general.