Dynamic exposure and body burden models for per- and polyfluoroalkyl substances (PFAS) enable management of food safety risks in cattle.

With increasing global focus on planetary boundaries, food safety and quality, the presence of per- and polyfluoroalkyl substances (PFAS) in the food chain presents a challenge for the sustainable production and supply of quality assured food. Consumption of food is the primary PFAS exposure route for the general population. At contaminated sites, PFAS have been reported in a range of agricultural commodities including cattle. Consumer exposure assessments are complicated by the lack of validated modelling approaches to estimate PFAS bioaccumulation in cattle. Previous studies have shown that PFAS bioaccumulation in livestock is influenced by environmental, spatial and temporal factors that necessitate a dynamic modelling approach. This work presents an integrated exposure and population toxicokinetic (PopTK) model for cattle that estimates serum and tissue concentrations of PFAS over time. Daily exposures were estimated from intakes of water, pasture, and soil, and considered animal growth, seasonal variability (pasture moisture content and temperature) and variable PFAS concentrations across paddocks. Modelled serum and tissue estimates were validated against monitoring data from Australian and Swedish cattle farms. The models were also used to develop and test practical management options for reducing PFAS exposure and to prioritise remediation for farms. Model outputs for exposure management scenarios (testing cattle rotation and targeted supplementation of feed and water) showed potential for marked reductions in consumer exposures from cattle produce.

Dissolution Mechanism of Eutectic and Hypereutectic Mg-Sn Alloy Anodes for Magnesium Rechargeable Batteries.

Magnesium rechargeable batteries (MRBs) are presently attracting much attention due to their low cost, high safety, and high theoretical volumetric capacity. Traditionally, pure magnesium metal has been used as an anode for MRBs, but its poor cycle performance, modest compatibility with conventional electrolytes, and sluggish kinetics limit the further development of MRBs. In this work, eutectic and hypereutectic Mg-Sn alloys were designed and studied as anodes for MRBs. Scanning electron microscopy (SEM) and transmission electron microscopy (TEM) results confirmed that these alloys contained unique microstructures consisting of α-Mg, Mg2Sn, and eutectic phases. The dissolution processes of the Mg-Sn alloys were studied in an all-phenyl-complex (APC) electrolyte. A multiple-step electrochemical dissolution process and a special adsorption interface layer were established for the Mg-Sn alloy anodes with an eutectic phase. Hypereutectic alloys with mixed phases showed better battery performance than the eutectic alloy owing to their superior mechanical properties. In addition, the morphology and Mg dissolution mechanism of the Mg-Sn alloys during the 1st dissolution process were characterized and discussed.

Spatio-temporal trends in livestock exposure to per- and polyfluoroalkyl substances (PFAS) inform risk assessment and management measures.

The migration of per- and polyfluoroalkyl substances (PFAS) onto agricultural properties has resulted in the accumulation of PFAS in livestock. The environmental determinants of PFAS accumulation in livestock from the grazing environment are poorly understood, resulting in limited capacity to manage livestock exposure and subsequent transfer of PFAS through the food chain. Analytical- (n = 978 samples of soil, water, pasture, and serum matrices), farm management/practice- and livestock physiology data were collated and interrogated from environmental PFAS investigations across ten farms, from four agro-ecological regions of Victoria (Australia). Statistical analysis identified perfluorooctane sulfonate (PFOS) and perfluorohexane sulfonate (PFHxS) as key analytes of concern for livestock bioaccumulation. PFOS and PFHxS concentrations in livestock drinking water were positively correlated with serum concentrations while other intake pathways (pasture and soil) had weaker correlations. Seasonal trends in PFAS body burden (serum concentrations) were identified and suggested to be linked to seasonal grazing behaviours and physiological water requirements. The data showed for the first time that livestock exposure to PFAS is dynamic and with relatively short elimination half-lives, there is opportunity for exposure management. Meat from cattle, grazed on PFAS impacted sites, may exceed health-based guideline values for PFAS, especially for markets with low limits (like the European Commission Maximum Limits or EC MLs). This study found that sites with mean livestock drinking water concentrations as low as 0.003 µg PFOS/L may exceed the EC ML for PFOS in cattle meat. Risk assessment can be used to prioritise site cleanup and development of management plans to reduce PFAS body burden by considering timing of stock rotation and/or supplementation of primary exposure sources.

Kinetic model of PFAS removal by semi-batch foam fractionation and validation by experimental data for K-PFOS.

Adsorptive bubble separation techniques such as foam fractionation have recently been applied for the extraction of per- and polyfluoroalkyl substances (PFAS) from waters at both laboratory and operational scales. However, few authors have developed mathematical models of their removal of PFAS. This study presents a theoretical framework for the kinetics of PFAS removal from fresh and monovalent saline waters by a semi-batch foam fractionation process, by the mechanisms of adsorption, entrainment and volatilization, as a function of pertinent parameters including PFAS air-water adsorption, bubble radius, electrolyte concentration and ionic strength, PFAS volatility, and flow and geometric parameters. The freshwater model is validated for the removal of potassium perfluorooctane sulfonate (K-PFOS) using published experimental data (Meng, P. et al., Chemosphere, 2018, 203, 263-270). The proposed models provide quantitative tools for process design and the optimization of individual PFAS removal by semi-batch adsorptive bubble separation techniques such as foam fractionation.

Confinement free energy for a polymer chain: Corrections to scaling.

Spatial confinement of a polymer chain results in a reduction of conformational entropy. For confinement of a flexible N-mer chain in a planar slit or cylindrical pore (confining dimension D), a blob model analysis predicts the asymptotic scaling behavior ΔF/N ∼ D-γ with γ ≈ 1.70, where ΔF is the free energy increase due to confinement. Here, we extend this scaling analysis to include the variation of local monomer density upon confinement giving ΔF/N ∼ D-γ(1 - h(N, D)), where the correction-to-scaling term has the form h ∼ Dy/NΔ with exponents y = 3 - γ ≈ 1.30 and Δ = 3/γ - 1 ≈ 0.76. To test these scaling predictions, we carry out Wang-Landau simulations of confined and unconfined tangent-hard-sphere chains (bead diameter σ) in the presence of a square-well trapping potential. The fully trapped chain provides a common reference state, allowing for an absolute determination of the confinement free energy. Our simulation results for 32 ≤ N ≤ 1024 and 3 ≤ D/σ ≤ 14 are well-described by the extended scaling relation giving exponents of γ = 1.69(1), y = 1.25(2), and Δ = 0.75(6).

Partition-function-zero analysis of polymer adsorption for a continuum chain model.

Polymer chains undergoing adsorption are expected to show universal critical behavior which may be investigated using partition function zeros. The focus of this work is the adsorption transition for a continuum chain, allowing for investigation of a continuous range of the attractive interaction and comparison with recent high-precision lattice model studies. The partition function (Fisher) zeros for a tangent-hard-sphere N-mer chain (monomer diameter σ) tethered to a flat wall with an attractive square-well potential (range λσ, depth ε) have been computed for chains up to N=1280 with 0.01≤λ≤2.0. In the complex-Boltzmann-factor plane these zeros are concentrated in an annular region, centered on the origin and open about the real axis. With increasing N, the leading zeros, w_{1}(N), approach the positive real axis as described by the asymptotic scaling law w_{1}(N)-y_{c}∼N^{-ϕ}, where y_{c}=e^{ε/k_{B}T_{c}} is the critical point and T_{c} is the critical temperature. In this work, we study the polymer adsorption transition by analyzing the trajectory of the leading zeros as they approach y_{c} in the complex plane. We use finite-size scaling (including corrections to scaling) to determine the critical point and the scaling exponent ϕ as well as the approach angle θ_{c}, between the real axis and the leading-zero trajectory. Variation of the interaction range λ moves the critical point, such that T_{c} decreases with λ, while the results for ϕ and θ_{c} are approximately independent of λ. Our values of ϕ=0.479(9) and θ_{c}=56.8(1.4)^{∘} are in agreement with the best lattice model results for polymer adsorption, further demonstrating the universality of these constants across both lattice and continuum models.

Novel Application of Machine Learning Algorithms and Model-Agnostic Methods to Identify Factors Influencing Childhood Blood Lead Levels.

Blood lead (Pb) poisoning remains a global concern, particularly for children in their early developmental years. Broken Hill is Australia's oldest operating silver-zinc-lead mine. In this study, we utilized recent advances in machine learning to assess multiple algorithms and identify the most optimal model for predicting childhood blood Pb levels (BLL) using Broken Hill children's (<5 years of age) data (n = 23,749) from 1991 to 2015, combined with demographic, socio-economic, and environmental influencing factors. We applied model-agnostic methods to interpret the most optimal model, investigating different environmental and human factors influencing childhood BLL. Algorithm assessment showed that stacked ensemble, a method for automatically and optimally combining multiple prediction algorithms, enhanced predictive performance by 1.1% with respect to mean absolute error (p < 0.01) and 2.6% for root-mean-squared error (p < 0.01) compared to the best performing constituent algorithm (random forest). By interpreting the model, the following information was acquired: children had higher BLL if they resided within 1.0 km to the central mine area or 1.37 km to the railroad; year of testing had the greatest interactive strength with all other factors; BLL increased faster in Aboriginal than in non-Aboriginal children at 9-10 and 12-18 months of age. This "stacked ensemble + model-agnostic interpretation" framework achieved both prediction accuracy and model interpretability, identifying previously unconnected variables associated with elevated childhood BLL, offering a marked advantage over previous works. Thus, this approach has a clear value and potential for application to other environmental health issues.

Study protocol for a randomised controlled trial examining the effect of blood and plasma donation on serum perfluoroalkyl and polyfluoroalkyl substance (PFAS) levels in firefighters.

INTRODUCTION: Perfluoroalkyl and polyfluoroalkyl substances (PFAS) are a diverse group of compounds that have been used in hundreds of industrial applications and consumer products including aqueous film-forming foam (AFFF) for many years. Multiple national and international health and environmental agencies have accepted that PFAS exposures are associated with numerous adverse health effects. Australian firefighters have been shown to have elevated levels of PFAS in their blood, specifically perfluorooctane sulfonic acid (PFOS) and perfluorohexane sulfonic acid (PFHxS), due to the historical use of AFFF. While PFAS concentrations decline over time once the source of exposure has been removed, their potential adverse health effects are such that it would be prudent to develop an intervention to lower levels at a faster rate than occurs via natural elimination rates. METHODS AND ANALYSIS: This is a randomised controlled trial of current and former Australian firefighters in the Metropolitan Fire Brigade/Fire Rescue Victoria, and contractors, with previous occupational exposure to PFAS and baseline elevated PFOS levels. The study is investigating whether whole blood donation every 12 weeks or plasma donation every 6 weeks will significantly reduce PFAS levels, compared with a control group. We have used covariate-adaptive randomisation to balance participants' sex and blood PFAS levels between the three groups and would consider a 25% reduction in serum PFOS and PFHxS levels to be potentially clinically significant after 12 months of whole blood or plasma donation. A secondary analysis of health biomarkers is being made of changes between screening and week 52 in all three groups. ETHICS AND DISSEMINATION: This trial has been approved by Macquarie University Human Research Ethics Committee (reference number: 3855), final protocol V.2 dated 12 June 2019. Study results will be disseminated via peer-reviewed publications and presentations at conferences. TRIAL REGISTRATION NUMBER: Australian New Zealand Clinical Trials Registry (ACTRN12619000204145).

Effects of macromolecular crowding on the folding of a polymer chain: A Wang-Landau simulation study.

A flexible polymer chain in the presence of inert macromolecular crowders will experience a loss of configurational entropy due to the crowder excluded volume. This entropy reduction will be most pronounced in good solvent conditions where the chain assumes an expanded coil conformation. For polymers that undergo a folding transition from a coil to a compact ordered state, as is the case for many globular proteins, macromolecular crowding is expected to stabilize the folded state and thereby shift the transition location. Here, we study such entropic stabilization effects for a tangent square-well sphere chain (monomer diameter σ) in the presence of hard-sphere (HS) crowders (diameter D ≥ σ). We use the Wang-Landau simulation algorithm to construct the density of states for this chain in a crowded environment and are thus able to directly compute the reduction in configurational entropy due to crowding. We study both a chain that undergoes all-or-none folding directly from the coil state and a chain that folds via a collapsed-globule intermediate state. In each case, we find an increase in entropic stabilization for the compact states with an increase in crowder density and, for fixed crowder density, with a decrease in crowder size (concentrated, small crowders have the largest effect). The crowder significantly reduces the average size for the unfolded states while having a minimal effect on the size of the folded states. In the athermal limit, our results directly provide the confinement free energy due to crowding for a HS chain in a HS solvent.

All-or-none folding of a flexible polymer chain in cylindrical nanoconfinement.

Geometric confinement of a polymer chain results in a loss of conformational entropy. For a chain that can fold into a compact native state via a first-order-like transition, as is the case for many small proteins, confinement typically provides an entropic stabilization of the folded state, thereby shifting the location of the transition. This allows for the possibility of confinement (entropy) driven folding. Here, we investigate such confinement effects for a flexible square-well-sphere N-mer chain (monomer diameter σ) confined within a long cylindrical pore (diameter D) or a closed cylindrical box (height H = D). We carry out Wang-Landau simulations to construct the density of states, which provides access to the complete thermodynamics of the system. For a wide pore, an entropic stabilization of the folded state is observed. However, as the pore diameter approaches the size of the folded chain (D ∼ N1/3σ), we find a destabilization effect. For pore diameters smaller than the native ground-state, the chain folds into a different, higher energy, ground state ensemble and the T vs D phase diagram displays non-monotonic behavior as the system is forced into different ground states for different ranges of D. In this regime, isothermal reduction of the confinement dimension can induce folding, unfolding, or crystallite restructuring. For the cylindrical box, we find a monotonic stabilization effect with decreasing D. Scaling laws for the confinement free energy in the athermal limit are also investigated.

Estimates of potential childhood lead exposure from contaminated soil using the USEPA IEUBK model in Melbourne, Australia.

Soils in inner city areas internationally and in Australia have been contaminated with lead (Pb) primarily from past emissions of Pb in petrol, deteriorating exterior Pb-based paints and from industry. Children can be exposed to Pb in soil dust through ingestion and inhalation leading to elevated blood lead levels (BLLs). Currently, the contribution of soil Pb to the spatial distribution of children's BLLs is unknown in the Melbourne metropolitan area. In this study, children's potential BLLs were estimated from surface soil (0-2 cm) samples collected at 250 locations across the Melbourne metropolitan area using the United States Environmental Protection Agency (USEPA) Integrated Exposure Uptake Biokinetic (IEUBK) model. A dataset of 250 surface soil Pb concentrations indicate that soil Pb concentrations are highly variable but are generally elevated in the central and western portions of the Melbourne metropolitan area. The mean, median and geometric soil Pb concentrations were 193, 110 and 108 mg/kg, respectively. Approximately 20 and 4% of the soil samples exceeded the Australian HIL-A residential and HIL-C recreational soil Pb guidelines of 300 and 600 mg/kg, respectively. The IEUBK model predicted a geometric mean BLL of 2.5 ± 2.1 µg/dL (range: 1.3-22.5 µg/dL) in a hypothetical 24-month-old child with BLLs exceeding 5 and 10 µg/dL at 11.6 and 0.8% of the sampling locations, respectively. This study suggests children's exposure to Pb contaminated surface soil could potentially be associated with low-level BLLs in some locations in the Melbourne metropolitan area.

Addressing Pollution-Related Global Environmental Health Burdens.

New analyses are revealing the scale of pollution on global health, with a disproportionate share of the impact borne by lower-income nations, minority and marginalized individuals. Common themes emerge on the drivers of this pollution impact, including a lack of regulation and its enforcement, research and expertise development, and innovative funding mechanisms for mitigation. Creative approaches need to be developed and applied to address and overcome these obstacles. The existing "business as usual" modus operandi continues to externalize human health costs related to pollution, which exerts a negative influence on global environmental health.

Reducing risk and increasing confidence of decision making at a lower cost: In-situ pXRF assessment of metal-contaminated sites.

This study evaluates the in-situ use of field portable X-ray Fluorescence (pXRF) for metal-contaminated site assessments, and assesses the advantages of increased sampling to reduce risk, and increase confidence of decision making at a lower cost. Five metal-contaminated sites were assessed using both in-situ pXRF and ex-situ inductively coupled plasma mass spectrometry (ICP-MS) analyses at various sampling resolutions. Twenty second in-situ pXRF measurements of Mn, Zn and Pb were corrected using a subset of parallel ICP-MS measurements taken at each site. Field and analytical duplicates revealed sampling as the major contributor (>95% variation) to measurement uncertainties. This study shows that increased sampling led to several benefits including more representative site characterisation, higher soil-metal mapping resolution, reduced uncertainty around the site mean, and reduced sampling uncertainty. Real time pXRF data enabled efficient, on-site decision making for further judgemental sampling, without the need to return to the site. Additionally, in-situ pXRF was more cost effective than the current approach of ex-situ sampling and ICP-MS analysis, even with higher sampling at each site. Lastly, a probabilistic site assessment approach was applied to demonstrate the advantages of integrating estimated measurement uncertainties into site reporting.

Estimates of potential childhood lead exposure from contaminated soil using the US EPA IEUBK Model in Sydney, Australia.

Surface soils in portions of the Sydney (New South Wales, Australia) urban area are contaminated with lead (Pb) primarily from past use of Pb in gasoline, the deterioration of exterior lead-based paints, and industrial activities. Surface soil samples (n=341) were collected from a depth of 0-2.5cm at a density of approximately one sample per square kilometre within the Sydney estuary catchment and analysed for lead. The bioaccessibility of soil Pb was analysed in 18 samples. The blood lead level (BLL) of a hypothetical 24 month old child was predicted at soil sampling sites in residential and open land use using the United States Environmental Protection Agency (US EPA) Integrated Exposure Uptake and Biokinetic (IEUBK) model. Other environmental exposures used the Australian National Environmental Protection Measure (NEPM) default values. The IEUBK model predicted a geometric mean BLL of 2.0±2.1µg/dL using measured soil lead bioavailability measurements (bioavailability =34%) and 2.4±2.8µg/dL using the Australian NEPM default assumption (bioavailability =50%). Assuming children were present and residing at the sampling locations, the IEUBK model incorporating soil Pb bioavailability predicted that 5.6% of the children at the sampling locations could potentially have BLLs exceeding 5µg/dL and 2.1% potentially could have BLLs exceeding 10µg/dL. These estimations are consistent with BLLs previously measured in children in Sydney.

On the Pseudo Phase Diagram of Single Semi-Flexible Polymer Chains: A Flat-Histogram Monte Carlo Study.

Local stiffness of polymer chains is instrumental in all structure formation processes of polymers, from crystallization of synthetic polymers to protein folding and DNA compactification. We present Stochastic Approximation Monte Carlo simulations-a type of flat-histogram Monte Carlo method-determining the density of states of a model class of single semi-flexible polymer chains, and, from this, their complete thermodynamic behavior. The chains possess a rich pseudo phase diagram as a function of stiffness and temperature, displaying non-trivial ground-state morphologies. This pseudo phase diagram also depends on chain length. Differences to existing pseudo phase diagrams of semi-flexible chains in the literature emphasize the fact that the mechanism of stiffness creation matters.

VegeSafe: A community science program measuring soil-metal contamination, evaluating risk and providing advice for safe gardening.

The extent of metal contamination in Sydney residential garden soils was evaluated using data collected during a three-year Macquarie University community science program called VegeSafe. Despite knowledge of industrial and urban contamination amongst scientists, the general public remains under-informed about the potential risks of exposure from legacy contaminants in their home garden environment. The community was offered free soil metal screening, allowing access to soil samples for research purposes. Participants followed specific soil sampling instructions and posted samples to the University for analysis with a field portable X-ray Fluorescence (pXRF) spectrometer. Over the three-year study period, >5200 soil samples, primarily from vegetable gardens, were collected from >1200 Australian homes. As anticipated, the primary soil metal of concern was lead; mean concentrations were 413 mg/kg (front yard), 707 mg/kg (drip line), 226 mg/kg (back yard) and 301 mg/kg (vegetable garden). The Australian soil lead guideline of 300 mg/kg for residential gardens was exceeded at 40% of Sydney homes, while concentrations >1000 mg/kg were identified at 15% of homes. The incidence of highest soil lead contamination was greatest in the inner city area with concentrations declining towards background values of 20-30 mg/kg at 30-40 km distance from the city. Community engagement with VegeSafe participants has resulted in useful outcomes: dissemination of knowledge related to contamination legacies and health risks; owners building raised beds containing uncontaminated soil and in numerous cases, owners replacing all of their contaminated soil.

On the polymer physics origins of protein folding thermodynamics.

A remarkable feature of the spontaneous folding of many small proteins is the striking similarity in the thermodynamics of the folding process. This process is characterized by simple two-state thermodynamics with large and compensating changes in entropy and enthalpy and a funnel-like free energy landscape with a free-energy barrier that varies linearly with temperature. One might attribute the commonality of this two-state folding behavior to features particular to these proteins (e.g., chain length, hydrophobic/hydrophilic balance, attributes of the native state) or one might suspect that this similarity in behavior has a more general polymer-physics origin. Here we show that this behavior is also typical for flexible homopolymer chains with sufficiently short range interactions. Two-state behavior arises from the presence of a low entropy ground (folded) state separated from a set of high entropy disordered (unfolded) states by a free energy barrier. This homopolymer model exhibits a funneled free energy landscape that reveals a complex underlying dynamics involving competition between folding and non-folding pathways. Despite the presence of multiple pathways, this simple physics model gives the robust result of two-state thermodynamics for both the cases of folding from a basin of expanded coil states and from a basin of compact globule states.

Can field portable X-ray fluorescence (pXRF) produce high quality data for application in environmental contamination research?

This research evaluates the analytical capabilities of a field portable X-ray fluorescence spectrometer (pXRF) for the measurement of contaminated soil samples using a matrix-matched calibration. The calibrated pXRF generated exceptional data quality from the measurement of ten soil reference materials. Elemental recoveries improved for all 11 elements post-calibration with reduced measurement variation and detection limits in most cases. Measurement repeatability of reference values ranged between 0.2 and 10% relative standard deviation, while the majority (82%) of reference recoveries were between 90 and 110%. Definitive data quality, the highest of the US EPA's three level quality ranking, was achieved for 15 of 19 elemental datasets. Measurement comparability against inductively coupled plasma atomic emission spectrometry (ICP-AES) values was excellent for most elements (e.g, r(2) 0.999 for Mn and Pb, r(2) > 0.995 for Cu, Zn and Cd). Parallel measurement of reference materials revealed ICP-AES and ICP-MS measured Ti and Cr poorly when compared to pXRF. Individual recoveries of soil reference materials by both ICP-AES and pXRF showed that pXRF was equivalent to or better than ICP-AES values for all but two elements (Ni, As). This study demonstrates pXRF as a suitable alternative to ICP-AES analysis in the measurement of Ti, Cr, Mn, Fe, Cu, Zn, Sr, Cd, and Pb in metal-contaminated soils. Where funds are limited, pXRF provides a low-cost, high quality solution to increasing sample density for a more complete geochemical investigation.