Cross-Species Evaluation of Bioaccumulation Thresholds for Air-Breathing Animals

In air-breathing organisms, an organic chemical's susceptibility to elimination via urinary excretion and respiratory exhalation can be judged on the basis of the octanol-water partition ratio (K-OW) and the octanol-air partition ratio (K (OA)), respectively. Current regulations specify that chemicals with K (OW) values of K (OA) values of <10(5) may be screened as non-bioaccumulative in air breathers. Here we used a model-based approach to evaluate whether these thresholds are consistent with a biomagnification factor of 1 for 141 different mammals, birds, and reptiles. Animals with lower rates of respiration (e.g., manatees and sloths) and those ingesting high-lipid diets (e.g., polar bears and carnivorous birds) were predicted to be able to biomagnify persistent chemicals with K (OA) values of K (OA) thresholds were determined to be <10(4.85) for mammals, <10(4.60) for birds, 25 ?, and <10(3.95) for reptiles at =25 degrees C. For all animals, urination alone was not efficient to prevent the biomagnification of any organic chemical. For chemicals with K (OW) values of <10(1), we found that biomagnification of persistent chemicals was constrained by the water-air partition ratio (K (WA)) rather than K (OA). Differences in physiology may need to be considered in bioaccumulation assessments of air-breathing species.

Automated summary

The susceptibility of organic chemicals to elimination in air-breathing organisms can be assessed using the octanol-water partition ratio (K-OW) and the octanol-air partition ratio (K (OA)). According to regulations, chemicals with K (OW) values <10(5) and K (OA) values <10(4.85) are considered non-bioaccumulative in air breathers.