Risk Assessments Are Missing Harmful Effects of Neonics on Honey Bees

A central question confronting scientists investigating the causes of bee decline is the impact of the low concentrations of neonics now widespread in the environment that honey bees are likely to encounter. A new review paper by Henk A. Tennekes and Francisco Sanchez-Bayo in the journal Toxicology (Volume 309, July 5, 2013, pages 39–51, attached) suggests that very low concentrations of neonics can have devastating effects on bees and—here’s the most important part—that conventional risk assessment approaches can miss or underestimate those effects.

According to the paper, neonics are in a group of chemicals, called time-dependent chemicals, whose toxic effects build up during long exposure times. The paper suggests that time-dependent phenomena occur when an insecticide binds very tightly or irreversibly to critical receptors in the target organism. Given a long enough exposure, even very low levels of time-dependent chemicals can kill.

Standard toxicity tests, which focus on the concentration of toxins for relatively short time periods, do not pick up time-dependent effects because they fail to expose target organisms to very low concentrations of a toxin over long enough periods of time.

Tennekes and Sanchez-Bayo use imidacloprid as a test case to demonstrate how standard risk assessment protocols can miss the harmful effects low levels of the chemicals can have on honey bees.

The paper assessed the impact of imidacloprid on honey bees by determining the time it took for 50 percent of the bees to die (t50) when exposed for varying time intervals to low doses of the chemical. It then related the exposure data to the pesticide concentrations typically found as plant residues under field conditions and calculated that 50 percent of worker bees would die within seven to ten days if they fed on a such a field. By contrast, the authors assert that standard risk assessments suggest field concentrations of imidacloprid pose no risks at all to honey bees.

Tennekes and Sanchez-Bayo propose a new risk assessment protocol based on t50s to evaluate the effects of time-dependent chemicals and recommend that going forward regulatory agencies employ such protocols to assess the harmful effects of neonics.

Regulators should consider these recommendations. Pollinators are too important to agriculture and other ecosystems, and neonics too widely used, for regulators to be ignorant of the threats low levels of these pesticides pose.

Source: Union of Concerned Scientists, June 7, 2013
http://blog.ucsusa.org/harmful-effects-of-neonics-on-honey-bees-149