Arizona College of Osteopathic Medicine at Midwestern University Phoenix, Arizona, United States
Abstract Body : The detrimental effects of heavy metal exposure on health have long been a subject of concern and while these effects on various organ systems have been extensively studied, their impact on bone health, specifically bone porosity, remains unknown. In addition, organisms exposed to high levels of heavy metals often exhibit bone asymmetry due to stresses imposed during development. Using the North American river otter, Lontra canadensis, a bioindicator of environmental contamination, this study explored the relationships between heavy metal exposure, bone porosity, and cranial symmetry.
We microCT scanned limb elements (tibiae, femora, and radii) of 19 L. canadensis specimens and the skulls of 24 L. canadensis specimens collected from areas in the US with varying degrees of manganese (Mn) and lead (Pb) soil concentrations: low (Florida), intermediate (Tennessee), and high (Alaska). We calculated total bone porosity percentage of each limb element using Avizo 3D. We found no significant differences in bone porosity between geographic regions; however, when regressed, we noted that bone porosity increases with decreasing concentrations of heavy metals. We quantified fluctuating asymmetry in the cranium using 3D geometric morphometrics. We found that all populations exhibited asymmetry in the cranium, particularly around the zygomatic arches, and that this was most exaggerated in specimens from Tennessee. The degree of asymmetry did not significantly differ, however, between geographic regions.
The results of our study suggest that exposure to high concentrations of certain heavy metals causes increased bone mineralization, which is in contrast with much of the previous literature. In addition, degrees of fluctuating asymmetry seem to be unaffected by exposure to heavy metals. River otters may, therefore, be adapting to these higher concentrations within their environments in a unique manner that should be investigated further. Future studies will seek to analyze changes in bone mineral density to further assess the impact of heavy metals on bone strength, which may shed light on the potential risks posed by heavy metal exposure to bone health and development. This will be essential to informing preventative measures in public health aimed at preserving bone integrity in vulnerable populations.
