Three cardinal numbers to safeguard bees against pesticide exposure: LD₅₀ , NOEC (revised) and the Haber exponent

Regulators often employ cardinal indicators to justify measures to protect the health of farmland bees from pesticides used in crop protection. Previously, in evaluating the likely hazard of a compound, they have made extensive use of its LD50 (‘lethal dose to 50% of exposed subjects’), and NOEC (‘no observable effect concentration’). Here, I argue that regulators should also use a third indicator, namely the Haber exponent. The Haber exponent qualifies the meaning of the LD50 by revealing the relative hazard of environmentally relevant exposures longer than that used to determine the LD50 originally. Additionally, I show how the experimental protocol used to determine the Haber exponent will also produce a well-founded, parametric value of the NOEC. Taken together, these three numbers establish a strong foundation on which to evaluate the potential impact of an agrochemical on bees.