Development of exposure limits for sodium fluoroacetate based on chronic health effects

Sodium fluoroacetate, better known as 1080, is a vertebrate toxin used for predator elimination in New Zealand. Sodium fluoroacetate itself is non-toxic but is readily converted by the body into highly toxic fluorocitrate, a metabolic poison known to impair mitochondrial function through inhibition of the enzyme aconitase, a key step in the citric acid cycle. The New Zealand workplace exposure standard of 0.05 mg/m3 is unlikely to protect workers from chronic exposure health risks. The chronic protective airborne exposure limit presented herein was derived from a NOAEL of 0.075 mg/kg/day via application of an uncertainty factor of 3,000. A UF of 3,000 was chosen based on 3 for toxicodynamic differences between species; 10 for intraspecies variation; 10 for extrapolation from a short-term duration study; and 10 for database limitations. The resulting reference dose of 0.025 µg/kg/day was converted to an inhalable 8-h equivalent TWA assuming a conservative 60 kg person and a ventilation rate during medium metabolic activity of 6 L/min. This gave a workplace exposure limit for sodium fluoroacetate of 0.52 µg/m3, which should be protective of chronic health risk resulting from quantal myocardial and testicular toxicity. A corresponding BEI of 0.15 µg/L was derived using methodology previously described by Beasley et al. (2009).