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 <10 2 and 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 <10 5 . This was also observed for several temperate reptiles due to their lower respiration rates and internal temperatures. Protective K OA thresholds were determined to be <10 4.85 for mammals, <10 4.60 for birds, <10 4.60 for reptiles at >25 °C, and <10 3.95 for reptiles at ≤25 °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.