Risk assessment of pesticides on bees: evaluating risk coefficients for assessing acute and chronic toxicity

Background: Risk coefficients are the key in the way how a pesticide active substances or formulated products will go through the risk assessment scheme dichotomy. Defining them is thus one of the main challenges of a risk assessment scheme design. In the light of the scientific publications on the subject, the existing risk coefficients and methodologies used for the toxicity evaluation under international guidelines result questionable. Results: LD50 values have shown to be variable. Prolonged effects following single contact can sometimes be observed when measuring the acute toxicity. The trigger value (10) of the risk coefficient results as inadequate. The toxicity derived from the exposure to substances continuously available for bees at sub-lethal doses needs to be evaluated separately, given the wide differences between acute and chronic lethal effects of pesticides. Conclusions: The observation period of the mortality tests should be lengthened as long as mortality increases, and while control mortality remains acceptable. Whenever active substances can pollute bees’ food sources, first tier tests should include laboratory tests: (1) on adult bees with: (a) acute toxicity tests; (b) chronic toxicity tests; (c) behavioural tests; and (2) larvae toxicity tests. Consequently, the decision to run higher tier tests should depend on four different risk coefficients. Keywords: honeybees, risk assessment, acute toxicity, chronic toxicity, risk coefficient, TER