Persistent organic pollutants and penile bone mineral density in East Greenland and Canadian polar bears (Ursus maritimus) during 1996-2015

A realistic mixture of ubiquitous persistent organic pollutants affects bone and cartilage development in zebrafish by interaction with nuclear receptor signaling

"Persistent organic pollutants (POPs)" have a plethora of deleterious effects on humans and the environment due to their bioaccumulative, persistent, and mimicking properties. Individually, each of these chemicals has been tested and its effects measured, however they are rather found as parts of complex mixtures of which we do not fully grasp the extent of their potential consequences. Here we studied the effects of realistic, environmentally relevant mixtures of 29 POPs on cartilage and bone development using zebrafish as a model species. We observed developmental issues in cartilage, in the form of diverse malformations such as micrognathia, reduced size of the Meckel's and other structures. Also, mineralized bone formation was disrupted, hence impacting the overall development of the larvae at later life stages. Assessment of the transcriptome revealed disruption of nuclear receptor pathways, such as androgen, vitamin D, and retinoic acid, that may explain the mechanisms of action of the compounds within the tested mixtures. In addition, clustering of the compounds using their chemical signatures revealed structural similarities with the model chemicals vitamin D and retinoic acid that can explain the effects and/or enhancing the phenotypes we witnessed. Further mechanistic studies will be required to fully understand this kind of molecular interactions and their repercussions in organisms. Our results contribute to the already existing catalogue of deleterious effects caused by exposure to POPs and help to understand the potential consequences in at risk populations.

Effects of urinary barium exposure on bone mineral density in general population

Previous studies have reported that exposures to metals are associated with bone health, but are mostly restricted to a few of the most frequent hazardous metals. The effects of barium (Ba) are not fully understood. A cross-sectional study involving 1532 adults from the National Health and Nutrition Examination Survey (NHANES, 2013-2016) was conducted. Generalized linear model (GLM) and restricted cubic spline (RCS) were applied to evaluate the relationship of urinary Ba exposure with BMDs. According to the GLM analyses, urinary Ba was adversely correlated with total BMD (percent change: -0.75; 95% CI: -1.21, -0.29) and lumbar BMD (percent change: -0.76; 95% CI: -1.47, -0.04). Compared with the lowest tertile of Ba levels, the percentage change of T3 was -2.06 (-3.36, -0.73) for total BMD and was -2.39 (-4.51, -0.24) for lumbar BMD, showing a significant linear trend (P trend = 0.014 and P trend = 0.047, respectively). The RCS models showed a monotonically decreasing relationship of urinary Ba with total BMD and lumbar BMD. Moreover, the positive joint effects were observed between Pb (lead) and Ba, and Cd (cadmium) and Ba on BMDs. According to our findings, exposure to Ba may lead to a decrease in BMDs. Possible positive joint effects of Ba and Pb, and Ba and Cd on BMDs were found. Exposure to Ba may contribute to poor skeletal health.

Co-exposures to trace elements and polycyclic aromatic compounds (PACs) impacts North American river otter (Lontra canadensis) baculum

Environmental loadings of polycyclic aromatic compounds (PACs) and trace elements are increasing in areas with marked oil and gas extraction, such as in the Athabasca oil sands region, Alberta, Canada. Some of these chemicals are recognized as potent endocrine disrupting compounds (EDCs). The impacts of co-exposure to PACs and metals on free-ranging wildlife is of considerable concern. River otters (Lontra canadensis) are sentinel species of aquatic ecosystem health. The baculum (penile bone) is an important part of the reproductive system in otters that ensures successful copulation. Although baculum health is critical to male reproductive success and is sensitive to exposure to EDCs, there is no information available regarding the impact of PAC and metal exposures on measures of baculum health. River otter baculum and livers were dissected from carcasses obtained from the fur trade. Trace element and PAC analyses were carried out in liver with matching baculums subjected to dimensional analysis, bone mineral density (BMD) and mechanical loading testing. Trace elements and select PACs exhibited both protective and deleterious effects on baculum bone health metrics. Alkylated four ring PACs were negatively associated with baculum bone material properties (ex: C4-Chrysene and C4-pyrene). The same compounds have been shown to exhibit strong anti-androgenic activities. Few comparable studies exist related to contamination and adverse effects of PACs in wild terrestrial mammals. Baculum health metrics may be an important tool to include in biomonitoring studies as to date, there are limited means to assess male reproductive performance in wildlife biomonitoring programs.

Molecular and cellular mechanisms linking air pollution and bone damage

Air pollution is the second most important risk factor associated with noncommunicable diseases after smoking. The effects of pollution on health are commonly attributable to particulate matter (PM), a complex mixture of particles suspended in the air. PM can penetrate the lower respiratory tract and has harmful direct and indirect effects on different organs and tissues. Direct effects are caused by the ability of PM components to cross the respiratory membrane and enter the bloodstream; indirect effects are systemic consequences of the local airway response. Recent work suggests that PM is an independent risk factor for low bone mineral density and osteoporosis-related fractures. Osteoporosis is a common age-related disease closely linked to bone fractures, with severe clinical consequences affecting quality of life, morbidity, and mortality. In this review, we discuss potential mechanisms behind the association between outdoor air pollution, especially PM, and bone damage. The discussion features four main mechanisms: 1) several different atmospheric pollutants can induce low-grade systemic inflammation, which affects bone metabolism through a specific effect of cytokines such as TNFα, IL-1β, IL-6, and IL-17 on osteoblast and osteoclast differentiation and function; 2) some pollutants, particularly certain gas and metal compounds, can cause oxidative damage in the airway and bone cells; 3) different groups of pollutants can act as endocrine disruptors when binding to the receptors in bone cells, changing their functioning; and 4) air pollution can directly and indirectly cause vitamin D deficiency. Characterizing these mechanisms will better define the physiopathology of bone damage, and recognizing air pollution as a modifiable risk factor for osteoporosis will inform environmental policies. Such knowledge will also guide the prevention of fractures due to fragility and help reduce health-related costs.

Aviation, melting sea-ice and polar bears

On 11 May 2019, the Mauna Loa, Hawaii, Earth System Research Laboratory reported the highest CO₂ concentration in human meteorological history. Continuing CO₂ rise will devastate ecosystems, and ice dependent species like polar bears ultimately will disappear. Commercial aviation is presently a relatively small CO₂ contributor, but this CO₂ intensive mode of transportation is projected to increase greatly. Scientists and conservationists are often among the most frequent of flyers, despite their recognition that emissions must be reduced. Here we illustrate the carbon footprint of air travel in terms of its impact on the sea ice habitat necessary for polar bear persistence, and suggest our colleagues reduce their air travel where-ever possible. Each metric ton of CO₂ emitted melts ~3 m² of arctic summer sea ice, and current air travel melts over 5000 m² each year. Each scientist making the short flight from Copenhagen to Oslo to join an IUCN polar bear meeting will melt ~1 m² of Arctic summer sea-ice. Annually hundreds of scientists and conservationists make frequent flights of much greater distances for AMAP, CAFF, IUCN, and other conservation related meetings. Much of this travel could be avoided with better planning and employing internet linkages for remote participation. When air travel, such as for necessary fieldwork, cannot be easily substituted by Web linkage, we all should search for routes and carriers allowing the lowest CO₂ emissions. We encourage all of our colleagues to join 'No Fly Climate Sci' to show their commitment to CO₂ reduction and learn more about doing so. As scientists, if we are serious about preserving polar bears and their Arctic sea ice habitat, we need to walk the talk and show an example for the rest of society by significantly reducing our air travel.

Age-related changes in size, bone microarchitecture and volumetric bone mineral density of the mandible in the harbor seal (Phoca vitulina)

Detailed knowledge of age-related changes in the structure and mineralization of bones is important for interpreting osseous changes in wild mammals caused by exposure to environmental contaminants. This study analyzed mandibular size, microarchitecture and volumetric bone mineral density (vBMD) in harbor seals (n = 93, age range 0.5 months to 25 years) from the German North Sea. Bone microarchitecture and vBMD were assessed using high-resolution peripheral quantitative computed tomography (HR-pQCT). Significant differences were observed between the analyzed age classes (i) young juveniles (0.5–10 months), (ii) yearlings (12–23 months), and (iii) adults (12–25 years) for several of the variables, indicating an overall increase in cortical and trabecular area, cortical thickness and total and cortical vBMD with age. Furthermore, for juvenile animals (≤ 23 months), significant positive correlations with age were observed for mandible length and perimeter, cortical area, cortical thickness, trabecular separation, and total and cortical vBMD. The findings demonstrate a rapid increase in overall size, cortical dimensions and the degree of mineralization of the harbor seal mandible during the first two years after birth. Negative correlations with age existed for trabecular number and thickness as well as for trabecular bone volume fraction in the juveniles. The findings suggest a reduction in trabecular bone volume fraction with age, due to the bone trabeculae becoming thinner, less numerous and more widely spaced. Given the strong age dependence of most analyzed parameters, it is recommended to standardize samples with respect to age in future studies comparing microarchitecture and mineralization of harbor seal mandibles from different populations or different collection periods.

Lactational exposure to dioxin-like polychlorinated biphenyl 169 and nondioxin-like polychlorinated biphenyl 155: Effects on rat femur growth, biomechanics and mineral composition

Exposure to polychlorinated biphenyls (PCBs), which are persistent lipophilic environmental pollutants, has a variety of adverse effects on wildlife and human health, including bone mineralization, growth and mechanical strength. The present study evaluated the effects of lactational exposure to nondioxin-like PCB-155 and dioxin-like PCB-169, individually and in combination, on pubertal rat femur development and its biomechanics. After offspring delivery, Wistar rat mothers were divided into four groups, i.e., PCB-169, PCB-155, PCB-155+169 and control, and were administered PCBs intraperitoneally. Data on bone geometry, biomechanics and mineral composition were obtained by analysis of femurs from 42-day-old offspring by microCT scanning, three-point bending test and inductively coupled plasma mass spectrometry. Decreased somatic mass and femur size, i.e., mass, periosteal circumference and cross sectional area, were observed in the PCB-169 and PCB-155 groups. Additionally, lactational exposure to planar PCB-169 resulted in harder and more brittle bones containing higher amounts of minerals. Combined exposure to structurally and functionally different PCBs demonstrated only mild alterations in bone width and mineralization. To conclude, our results demonstrated that alterations, observed on postnatal day 42, were primarily induced by PCB-169, while toxicity from both of the individual congeners may have been reduced in the combined group.

Age and seasonal variation in testis and baculum morphology in East Greenland polar bears (Ursus maritimus) in relation to high concentrations of persistent organic pollutants

Persistent organic pollutants (POPs) are found in high concentrations in the Artic. Polar bears (Ursus maritimus) are one of the most exposed mammals in the Arctic and are thereby vulnerable to reproductive disruption. The aim of this study was to investigate male polar bear reproduction based on a detailed evaluation of testis histology and to assess possible effects of environmental chemicals on male polar bear reproduction. Reproductive groups that were identified based on histology were as follows: actively reproductive (REP), non-reproductive either with degenerated testes (DEG), undeveloped seminiferous tubules (UND), or morphology in-transition (INT). Categorization into these groups was supported by significant differences in testis and baculum measurements among REP, DEG, and UND, as well as differences in the area and diameter of seminiferous tubules among REP, DEG, and UND. These results show that it is possible to identify the reproductive stage in polar bears even if capture date and or age is lacking. Based on testis morphology we suggest that adult male polar bears from East Greenland have active spermatogenesis in February to June, and inactive degenerated testes in August to January. January to February was the main period of reproductive transition, characterised by a shift between inactive and active spermatogenesis. Baculum and testis size measurements decreased significantly with increasing concentrations of the chlordane metabolite oxychlordane, suggesting a potential impact on male reproductive success. Half of the investigated polar bears in REP group displayed signs of disorganization of the spermatogenesis which might be a sign of disrupted reproduction. However, no correlations with levels of the investigated POPs were detected. Reproductive organ measurements in polar bears differed significantly between REP and DEG groups, which cannot be explained by age, and therefore should be considered when investigating the effect of POPs on male reproduction.

State of knowledge on current exposure, fate and potential health effects of contaminants in polar bears from the circumpolar Arctic

The polar bear (Ursus maritimus) is among the Arctic species exposed to the highest concentrations of long-range transported bioaccumulative contaminants, such as halogenated organic compounds and mercury. Contaminant exposure is considered to be one of the largest threats to polar bears after the loss of their Arctic sea ice habitat due to climate change. The aim of this review is to provide a comprehensive summary of current exposure, fate, and potential health effects of contaminants in polar bears from the circumpolar Arctic required by the Circumpolar Action Plan for polar bear conservation. Overall results suggest that legacy persistent organic pollutants (POPs) including polychlorinated biphenyls, chlordanes and perfluorooctane sulfonic acid (PFOS), followed by other perfluoroalkyl compounds (e.g. carboxylic acids, PFCAs) and brominated flame retardants, are still the main compounds in polar bears. Concentrations of several legacy POPs that have been banned for decades in most parts of the world have generally declined in polar bears. Current spatial trends of contaminants vary widely between compounds and recent studies suggest increased concentrations of both POPs and PFCAs in certain subpopulations. Correlative field studies, supported by in vitro studies, suggest that contaminant exposure disrupts circulating levels of thyroid hormones and lipid metabolism, and alters neurochemistry in polar bears. Additionally, field and in vitro studies and risk assessments indicate the potential for adverse impacts to polar bear immune functions from exposure to certain contaminants.

Immunologic, reproductive, and carcinogenic risk assessment from POP exposure in East Greenland polar bears (Ursus maritimus) during 1983-2013

Polar bears (Ursus maritimus) are among the world's highest trophic level marine predators and as such have some of the highest tissue concentrations of organohalogen contaminants (OHCs) among Arctic biota. In this paper we present the results of a three decade (1983-2013) risk assessment of OHC exposure and effects on reproduction, immunity, and cancer (genotoxicity) in polar bears from Central East Greenland. Risk of adverse effects are evaluated using a risk quotient (RQ) approach with derivation from measured OHC concentrations in polar bear tissue and critical body residues (CBR) extrapolated for polar bears using physiologically-based pharmacokinetic modelling (PBPK). The additive RQs for all OHCs in polar bears were above the threshold for all effect categories (RQ > 1) in every year, suggesting this population has been at significant and continuous risk of contaminant-mediated effects for over three decades. RQs peaked in 1983 (RQ > 58) and again in 2013 (RQ > 50) after a period of decline. These trends follow ΣPCB levels during that time, and contributed almost all of the risk to immune, reproductive, and carcinogenic effects (71-99% of total RQ). The recent spike in RQs suggests a major shift in polar bear contaminant exposure from climate related changes in food composition and hereby the increased risk of adverse health effects. In the context of lifetime exposure ΣPCB and PFOS levels showed the interactive importance of year of birth, age, and emission history. In conclusion, the results indicate that East Greenland polar bears have been exposed to OHC levels over the period of 1983-2013 that potentially and continuously affected individual and theoretically also population health, with a peaking risk in the more recent years.