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

Abstract

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 <102 and K OA values of <105 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 <105. 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 <104.85 for mammals, <104.60 for birds, <104.60 for reptiles at >25 °C, and <103.95 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 <101, 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.

Distribution and trophodynamics of substituted diphenylamine antioxidants and benzotriazole UV stabilizers in a freshwater ecosystem and the adjacent riparian environment

“…It is well established that air-breathing and water-respiring species have different bioaccumulation and biomagnification processes for organic contaminants. 20–22,42 Therefore, air-breathing and water-respiring species were separated for comparisons in this study. Except for the whirligig beetle, air-breathing invertebrates showed 1–2 orders of magnitude higher levels of ΣSDPAs (0.74 ± 0.14–3.5 ± 0.06 ng g −1 , ww) than the concentrations in the muscle of brown bullhead ( Ameiurus nebulosus ; BRBH) (0.11 ± 0.07 ng g −1 , ww), largemouth bass ( Micropterus salmoides ; LMBS) (0.13 ± 0.04 ng g −1 , ww) and rock bass ( Ambloplites rupestris ; RCBS) (0.02 ± 0.01 ng g −1 , ww) (Fig.…”

“…Different K oa thresholds (>10 3.95 –10 6 ) have been established for bioaccumulation and biomagnification in air-breathing organisms, depending on food webs and species. 20–22 Target SDPAs and BZT-UVs are substances with a K oa (10 9.3 –10 22.9 ) much higher than the specified thresholds. Therefore, although some SDPAs and BZT-UVs may not biomagnify in water-respiring organisms, they may still biomagnify in air-breathers.…”