Development of a novel DGT passive sampler for measuring polycyclic aromatic hydrocarbons in aquatic systems.

Polycyclic aromatic hydrocarbons (PAHs) are priority pollutants and need to be measured reliably in waters and other media, to understand their sources, fate, behaviour and to meet regulatory monitoring requirements. Conventional water sampling requires large water volumes, time-consuming pre-concentration and clean-up and is prone to analyte loss or contamination. Here, for the first time, we developed and validated a novel diffusive gradients in thin-films (DGT) passive sampler for PAHs. Based on the well-known DGT principles, the sampler pre-concentrates PAHs with typical deployment times of days/weeks, with minimal sample handling. For the first time, DGT holding devices made of metal and suitable for sampling hydrophobic organic compounds were designed and tested. They minimize sorption and sampling lag times. Following tests on different binding layer resins, a MIP-DGT was preferred - the first time applying MIP for PAHs. It samples PAHs independent of pH (3.9 -8.1), ionic strength (0.01 -0.5 M) and dissolved organic matter < 20 mg L-1, making it suitable for applications across a wide range of environments. Field trials in river water and wastewater demonstrated that DGT is a convenient and reliable tool for monitoring labile PAHs, readily achieving quantitative detection of environmental levels (sub-ng and ng/L range) when coupled with conventional GC-MS or HPLC. ENVIRONMENTAL IMPLICATIONS: PAHs are carcinogenic and genotoxic compounds. They are environmentally ubiquitous and must be monitored in waters and other media. This study successfully developed a new DGT passive sampler for reliable in situ time-integrated measurements of PAHs in waters at the ng/L level. This is the first time to use passive samplers for accurate measurements of hydrophobic organic contaminants in aquatic systems without calibration, a big step forward in monitoring PAHs. The application of this new sampler will enhance our understanding of the sources, fate, behavior and ecotoxicology of PAHs, enabling improved environmental risk assessment and management of these compounds.

Genetic Advancements in Infantile Epileptic Spasms Syndrome and Opportunities for Precision Medicine.

Infantile epileptic spasms syndrome (IESS) is a devastating developmental epileptic encephalopathy (DEE) consisting of epileptic spasms, as well as one or both of developmental regression or stagnation and hypsarrhythmia on EEG. A myriad of aetiologies are associated with the development of IESS; broadly, 60% of cases are thought to be structural, metabolic or infectious in nature, with the remainder genetic or of unknown cause. Epilepsy genetics is a growing field, and over 28 copy number variants and 70 single gene pathogenic variants related to IESS have been discovered to date. While not exhaustive, some of the most commonly reported genetic aetiologies include trisomy 21 and pathogenic variants in genes such as TSC1, TSC2, CDKL5, ARX, KCNQ2, STXBP1 and SCN2A. Understanding the genetic mechanisms of IESS may provide the opportunity to better discern IESS pathophysiology and improve treatments for this condition. This narrative review presents an overview of our current understanding of IESS genetics, with an emphasis on animal models of IESS pathogenesis, the spectrum of genetic aetiologies of IESS (i.e., chromosomal disorders, single-gene disorders, trinucleotide repeat disorders and mitochondrial disorders), as well as available genetic testing methods and their respective diagnostic yields. Future opportunities as they relate to precision medicine and epilepsy genetics in the treatment of IESS are also explored.

Evaluating the Current State of Epilepsy Care in the Province of Ontario.

There are numerous challenges pertaining to epilepsy care across Ontario, including Epilepsy Monitoring Unit (EMU) bed pressures, surgical access and community supports. We sampled the current clinical, community and operational state of Ontario epilepsy centres and community epilepsy agencies post COVID-19 pandemic. A 44-item survey was distributed to all 11 district and regional adult and paediatric Ontario epilepsy centres. Qualitative responses were collected from community epilepsy agencies. Results revealed ongoing gaps in epilepsy care across Ontario, with EMU bed pressures and labour shortages being limiting factors. A clinical network advising the Ontario Ministry of Health will improve access to epilepsy care.

Comprehensive Assessment of Environmental Emissions, Fate, and Risks of Veterinary Antibiotics in China: An Environmental Fate Modeling Approach.

China is one of the major global consumers of veterinary antibiotics. Insufficient recognition of emissions and environmental contamination hamper global efforts to prevent antibiotic resistance development. This pioneering study combined empirical data and modeling approaches to predict total 2010-2020 emissions of 80 veterinary antibiotics ranging from 23,110 to 40,850 tonnes/year, after 36-50% antibiotic removal by manure treatment. Following an initial increase of 10% from 2010 to 2015, emissions declined thereafter by 43%. While 85% of emissions discharged into soils, approximately 56%, 23%, and 18% of environmental residue were ultimately distributed in soils, freshwaters, and seawaters under steady-state conditions. In 2020, 657 (319-1470) tonnes entered the ocean from inland freshwaters. Median ∑antibiotics concentrations were estimated at 4.7 × 103 ng/L in freshwaters and 2.9 ng/g in soils, with tetracyclines and sulfonamides as the predominant components. We identified 44 veterinary antibiotics potentially posing high risks of resistance development in freshwaters, with seven exhibiting high risks in >10% of Chinese freshwater areas. Tetracyclines were the category with the most antibiotics exhibiting elevated risks; however, sulfamethylthiazole demonstrated the highest individual compound risk. The Haihe River Basin displayed the highest susceptibility overall. The findings offer valuable support for control of veterinary antibiotic contamination in China.

Development and validation of an in situ high-resolution technique for measuring antibiotics in sediments.

Important biogeochemical processes occur in sediments at fine scales. Sampling techniques capable of yielding information with high resolution are therefore needed to investigate chemical distributions and fluxes and to elucidate key processes affecting chemical fates. In this study, a high-resolution diffusive gradients in thin-films (DGT) technique was systematically developed and tested in a controlled sediment system to measure organic contaminants, antibiotics, for the first time. The DGT probe was used to resolve compound distributions at the mm scale. It also reflected the fluxes from the sediment pore-water and remobilization from the solid phase, providing more dynamic information. Through the fine scale detection, a reduction of re-supply was observed over time, which was concentration and location dependent. Compared to the Rhizon sampling method, antibiotic concentrations obtained by DGT probes were less than the pore-water concentrations, as DGT measures the labile fraction of the compounds. The DGT probe was also tested on an intact sediment core sampled from a lake in China and used to measure the distribution of labile antibiotics with depth in the core at the mm scale. ENVIRONMENTAL IMPLICATION: The abuse of antibiotics and widespread of their residues influences the ecosystem, induces the generation of super-bacteria, and finally poses threat to human health. Sediments adsorbs pollutants from the aquatic environment, while may also release them back to the environment. We systematically developed DGT probe approach for measuring antibiotics in sediment in situ in high resolving power, it provides information at fine scale to help us investigate biogeochemical processes take place in sediment and sediment-water interface.

Indirect Emissions from Organophosphite Antioxidants Result in Significant Organophosphate Ester Contamination in China.

Organophosphite antioxidants (OPAs) have been seriously neglected as potential sources of organophosphate esters (OPEs) in environments. This study utilizes a modeling approach to quantify for the first time national emissions and multimedia distributions of triphenyl phosphate (TPHP)─a well-known flame retardant─and three novel OPEs: tris(2,4-ditert-butylphenyl) phosphate (AO168═O), bis(2,4-ditert-butylphenyl) pentaerythritol diphosphate (AO626═O2), and trisnonylphenol phosphate (TNPP). Emphasis is on the quantitative assessment of OPA source in China. TPHP has 1.1-9.7 times higher emission (300 Mg/year in 2019 with half from OPA sources) than AO168═O (278 Mg/year), AO626═O2 (53 Mg/year), and TNPP (32 Mg/year), but AO168═O is predominant in environments (63-79%) except freshwaters. About 72-99% of the studied OPEs are emitted via air, with 88-99% ultimately distributed into soils as the major sink. OPA-source emissions contribute 9.5-57% and 4.7-56% of TPHP masses and concentrations (except in sediments) in different media, respectively. Both AO168═O and AO626═O2 exhibit high overall persistence ranging between 2 and 11 years. Source emissions and environmental concentrations are elevated in economically developed areas, while persistence is higher in northern areas, where precipitation and temperature are lower. This study shows the significance of the sources of OPA to OPE contamination, which supports chemical management of these substances.

Gaseous elemental mercury emissions from informal E-Waste recycling facilities in Pakistan.

Detrimental effects of mercury (Hg) on ecosystems and human health have been well-documented. Whereas emissions of gaseous elemental mercury (GEM) from e-waste recycling have been reported in developed countries, much less is known about the situation in the Global South. Using a total of 132 passive air samplers, seasonally resolved concentrations of GEM in air were measured continuously at 32 informal e-waste recycling facilities and background location in Pakistan for a period of one year between September 2020 and December 2021. Annual average GEM concentrations at the studied locations ranged from 1.8 to 92 ng m-3. Among the studied cities, higher concentrations were measured in Karachi (mean ± s.d: 17 ± 22, range: 4.2-92 ng m-3), Lahore (16 ± 4.2, 8.2-22 ng m-3) and Peshawar (15 ± 17, 4.9-80 ng m-3), while lower levels were measured in Hyderabad (6.9 ± 6.2, 3.1-25 ng m-3), consistent with a higher rate of informal recycling activities in metropolitan areas. Seasonally, higher GEM levels occurred during autumn (15 ± 16: 3.3-92 ng m-3) and summer (13 ± 8.7: 1.8-80 ng m-3) than in winter (12 ± 8.4: 2.5-49 ng m-3) and spring (9.2 ± 7.3: 1.8-80 ng m-3), possibly reflecting enhanced volatilization at higher temperatures and/or varying magnitude of recycling operations in different seasons. Policies and strict regulations related to e-waste management should be developed and implemented urgently in the country.

Genetics and SUDEP: Challenges and Future Directions.

Sudden unexpected death in epilepsy (SUDEP) is the leading cause of epilepsy-related deaths in children and adults with epilepsy. The incidence of SUDEP in children and adults is equal, approximately 1.2 per 1000-person years. Although inroads have been made in our understanding of SUDEP, its pathophysiology remains unknown. The most important risk factor for SUDEP is the presence of tonic-clonic seizures. Recently there has been growing interest in the contribution of genetic risk factors to SUDEP deaths. Pathogenic variants in epilepsy-related and cardiac genes have been found in some cases of SUDEP post-mortem. Pleiotropy may occur in which a single gene when altered may cause multiple phenotypes (i.e., epilepsy and cardiac arrhythmia). Recently it has been shown that some developmental and epileptic encephalopathies (DEEs) may also be at heightened risk of SUDEP. In addition, polygenic risk has been postulated to effect SUDEP risk with current models evaluating the additive effect of variants in multiple genes. However, the mechanisms underpinning polygenic risk in SUDEP are likely more complex than this. Some preliminary studies also highlight the feasibility of detecting genetic variants in brain tissue post-mortem. Despite the advances in the field of SUDEP genetics, the use of molecular autopsy remains underutilized in SUDEP cases. Several challenges exist concerning genetic testing post-mortem in SUDEP cases, such as interpretation, cost of testing, and availability. In this focused review, we highlight the current landscape of genetic testing in SUDEP cases, its challenges, and future directions.

The genetic landscape of developmental and epileptic encephalopathy with spike-and-wave activation in sleep.

OBJECTIVE: Epileptic Encephalopathy / Developmental Epileptic Encephalopathy with spike-and-wave activation in sleep (EE/DEE-SWAS) is defined as an epilepsy syndrome characterized by neurodevelopmental regression temporally related to the emergence of significant activation of spike-wave discharges in EEG during sleep. The availability of genetic testing has made it evident that monogenic and chromosomal abnormalities play an aetiological role in the development of EE/DEE-SWAS. We sought to review the literature to better understand the genetic landscape of EE/DEE-SWAS. METHODS: In this systematic review, we reviewed cases of EE/DEE-SWAS associated with a genetic aetiology, collecting information related to the underlying aetiology, onset, management, and EEG patterns. RESULTS: One hundred and seventy-two cases of EE/DEE-SWAS were identified. Genetic causes of note included pathogenic variants in GRIN2A, ZEB2, CNKSR2 and chromosome 17q21.31 deletions, each of which demonstrated unique clinical characteristics, EEG patterns, and age of onset. Factors identified to raise suspicion of a potential genetic aetiology included the presentation of DEE-SWAS and onset of SWAS under the age of five years. Treatment of EE/DEE-SWAS due to genetic causes was diverse, including a combination of anti-seizure medications, steroids, and other clinical strategies, with no clear consensus on a preferred or superior treatment. Data collected was significantly heterogeneous, with a lack of consistent use of neuropsychology testing, EEG patterns, or use of established clinical definitions. CONCLUSIONS: Uniformity concerning the new definition of EE/DEE-SWAS, guidelines for management and more frequent genetic screening will be needed to guide best practices for the treatment of patients with EE/DEE-SWAS.

SUDEP: Living with the knowledge.

OBJECTIVE: To understand how knowledge of sudden unexpected death in epilepsy (SUDEP) impacted the lives of adult persons with epilepsy (PWE) and primary caregivers of both adults and children with epilepsy. METHODS: The principles of fundamental qualitative description guided this descriptive and exploratory qualitative study to document patients' and caregivers' perceptions and experiences. A purposeful sample of individuals (18 years or older) diagnosed with epilepsy or primary caregivers of PWE completed a single in-depth, semi-structured, one-to-one telephone interview. Categories of findings were developed using directed content analysis. RESULTS: A total of twenty-seven participants completed the study. This consisted of eight adult females and six adult males with epilepsy, ten female caregivers, and three male caregivers of PWE. All participants had become aware of SUDEP at least 12 months before their interview. Most were not informed about SUDEP by their treating neurologist and instead learned about SUDEP via alternative sources (e.g., the internet). All participants believed that knowledge of SUDEP outweighed the risks of being informed about it. Anxiety/fear related to SUDEP disclosure was generally not long-lasting. Caregivers of PWE were more directly impacted by SUDEP disclosure than adult PWE. Caregivers were more likely to make lifestyle/management changes due to learning about SUDEP (e.g., increased supervision and co-sleeping). Participants agreed that follow-up clinical support should be provided after SUDEP disclosure. CONCLUSIONS: Disclosure of SUDEP risk may have more significant impacts on caregivers of PWE than adult PWE in the form of lifestyle changes and epilepsy management. After SUDEP disclosure, follow-up support should be offered to PWE and their caregivers, which should be incorporated into future guidelines.

SUDEP counseling: Where do we stand?

Sudden unexpected death in epilepsy (SUDEP) is the leading cause of epilepsy-related death in children and adults living with epilepsy. Several recent clinical practice guidelines have recommended that all individuals living with epilepsy and their caregivers be informed about SUDEP as a part of routine epilepsy counseling. Furthermore, several studies over the last two decades have explored the state of SUDEP counseling. Patients with epilepsy and their families want to be informed about the risk of SUDEP at or near the time of diagnosis, and preferably in person. Despite guideline recommendations, many pediatric and adult neurologists do not routinely inform individuals with epilepsy and their families about SUDEP. Some neurologists discuss SUDEP with only a subset of patients with epilepsy, such as those with risk factors like frequent generalized or focal to bilateral tonic-clonic seizures, nocturnal seizures, noncompliance, or medically refractory epilepsy. Proponents of routine SUDEP counseling argue that patients with epilepsy and their families have a "right to know" and that counseling may positively impact epilepsy self-management (i.e., behavioral modification and risk reduction). Some neurologists still believe that SUDEP counseling may cause unnecessary stress and anxiety for patients and their families (although this is erroneous) and that they also have a "right not to know." This narrative review explores the current gaps in SUDEP counseling, patients' and caregivers' perspectives of SUDEP counseling, and SUDEP prevention.

Co-occurrence of macroplastics, microplastics, and legacy and emerging plasticisers in UK soils.

Despite a theoretical link between plastic and plasticiser occurrence in the terrestrial environment, there are few empirical studies of the relationship between these contaminants in soils. We carried out a field study to assess the co-occurrence of plastic waste, and legacy and emerging plasticisers in UK soils (n = 19) from various land uses (woodlands, urban roadsides, urban parklands, landfill-associated). Surface plastics and soil microplastics were quantified and characterised using ATR-FTIR and µ-FTIR. Eight legacy (phthalate) and three emerging (adipate, citrate, trimellitate) plasticisers were quantified using GC-MS. Surface plastics were found at higher prevalence at landfill-associated and urban roadside sites, with levels significantly (2 orders of magnitude) greater than in woodlands. Microplastics were detected in landfill-associated (mean 12.3 particles g-1 dw), urban roadside (17.3 particles g-1 dw) and urban parkland (15.7 particles g-1 dw) soils, but not in woodland soils. The most commonly detected polymers were polyethene, polypropene and polystyrene. Mean ∑plasticiser concentration in urban roadside soils (3111 ng g-1 dw) was significantly higher than in woodlands (134 ng g-1 dw). No significant difference was found between landfill-associated (318 ng g-1 dw) and urban parkland (193 ng g-1 dw) soils and woodlands. Di-n-butyl phthalate (94.7% detection frequency) and the emerging plasticiser trioctyl trimellitate (89.5%) were the most commonly detected plasticisers, with diethylhexyl phthalate (493 ng g-1 dw) and di-iso-decyl phthalate (96.7 ng g-1 dw) present at the highest concentrations. ∑plasticiser concentrations were significantly correlated with surface plastic (R2 = 0.23), but not with soil microplastic concentrations. Whilst plastic litter seems a fundamental source of plasticisers in soils, mechanisms such as airborne transport from source areas may be as important. Based on the data from this study, phthalates remain the dominant plasticisers in soils, but emerging plasticisers are already widespread, as reflected by their presence in all land uses studied.

The epilepsy phenotype of ST3GAL3-related developmental and epileptic encephalopathy.

OBJECTIVE: ST3GAL3-related developmental and epileptic encephalopathy (DEE-15) is an autosomal recessive condition characterized by intellectual disability, language and motor impairments, behavioral difficulties, stereotypies, and epilepsy. Only a few cases have been reported, and the epilepsy phenotype is not fully elucidated. METHODS: A retrospective chart review of two siblings with ST3GAL3-related DEE was completed. In addition, we reviewed all published cases of ST3GAL3-related congenital disorder of glycosylation. RESULTS: Two brothers presented with global developmental delay, motor and language impairment, hypotonia, and childhood-onset seizures. Seizures started between 2.5 and 5 years and had tonic components. Both siblings had prolonged periods of seizure freedom on carbamazepine. Tremor was present in the younger sibling. Whole exome sequencing revealed two novel pathogenic variants in ST3GAL3, (a) c.302del, p.Phe102Serfs*34 and (b) c.781C>T, p.Arg261*, which were inherited in trans. Magnetic resonance imaging showed T2 hyperintensities and restricted diffusion in the brainstem and middle cerebellar peduncle in the older sibling, also described in two reported cases. A review of the literature revealed 24 cases of ST3GAL3-related CDG. Twelve cases had information about seizures, and epilepsy was diagnosed in 8 (67%). The median age of seizure onset was 5.5 months. Epileptic spasms were most common (67%). Four children were diagnosed with Infantile Epileptic Spasms syndrome and Lennox Gastaut syndrome (57%). Most children (n = 6, 75%) had seizures despite anti-seizure medication treatment. SIGNIFICANCE: Seizures related to ST3GAL3-related DEE often occur in infancy and may present as epileptic spasms. However, seizure onset may also occur outside of infancy with mixed seizure types and show good response to treatment with prolonged seizure freedom. Tremor may also be uniquely observed in this condition.

Epilepsy surgery outcomes in patients with GATOR1 gene complex variants: Report of new cases and review of literature.

AIM: To report seizure outcomes in children with GATOR1 gene complex disorders who underwent epilepsy surgery and perform a systematic literature search to study the available evidence. METHODS: The records of children with pathogenic/likely pathogenic variants in GATOR1 gene complex who underwent epilepsy surgery were reviewed. Clinical, radiological, neurophysiological, and histological data were extracted/summarized. The systematic review included all case series/reports and observational studies reporting on children or adults with genetic (germline or somatic) variants in the GATOR1 complex genes (DEPDC5, NPRL2, NPRL3) with focal epilepsy with/without focal cortical dysplasia who underwent epilepsy surgery; seizure outcomes were analyzed. RESULTS: Eight children with pathogenic/likely pathogenic variants in GATOR1 complex genes were included. All had drug-resistant epilepsy. Six children had significant neurodevelopmental delay. Epilepsy surgery was performed in all; clinical seizure freedom was noted in 4 children (50%). Systematic literature search identified 17 eligible articles; additional 30 cases with patient-level data were studied. Lesional MRI brain was seen in 80% cases. The pooled rate of seizure freedom following surgery was 60%; FCD IIa was the most encountered pathology. INTERPRETATION: Epilepsy surgery may be effective in some children with GATOR1 complex gene variants. Seizure outcomes may be compromised by extensive epileptogenic zones.

Life after SUDEP: Experiences of traumatic loss and growth.

PURPOSE: To understand the experiences of bereaved relatives of individuals who passed due to sudden unexpected death in epilepsy (SUDEP) and to explore the impacts of death in their lives. METHODS: The principles of fundamental qualitative description informed all design decisions. Stratified purposeful sampling included 21 bereaved relatives (parent, sibling, or spouse/partner), aged at least 18 years, of persons who passed away because of SUDEP. In-depth one-to-one interviews were conducted. Directed content analysis was used to code, categorize, and synthesize the interview data. RESULTS: There was some criticism of emergency response and medical professionals involved in providing insensitive or poor care immediately after SUDEP occurred. Personal hardships described by participants following SUDEP included loss of personal identity, feeling depressed, experiencing guilt, having panic attacks, requiring therapy, as well as having difficulty with anniversaries, dates, and cleaning up a child's room. Bereaved spouses and parents in particular spoke of experiencing challenges in maintaining other relationships following the death. Some participants spoke of experiencing increased financial hardships. Ways of coping included keeping oneself busy, honoring the memory of the loved one, relying on friends and families, and engaging in advocacy/community work, including raising awareness on epilepsy and SUDEP. CONCLUSIONS: Sudden unexpected death in epilepsy affected several aspects of the day-to-day lives of bereaved relatives. Though methods of coping were similar to the usual strategies adopted by all bereaved relatives, advocacy work related to raising awareness about epilepsy and SUDEP was unique to this group. Guidelines on SUDEP should ideally include recommendations for trauma-informed support and assessment for depression and anxiety to the bereaved relatives as well.

The neuroimaging spectrum of SLC13A5 related developmental and epileptic encephalopathy.

BACKGROUND: SLC13A5 related developmental and epileptic encephalopathy (DEE) is an autosomal recessive condition characterized by neonatal seizures, fever sensitivity, status epilepticus, developmental delay and tooth anomalies. The neuroimaging spectrum of SLC13A5 related DEE is not fully known. We present a case of SLC13A5 related DEE with distinct neuroimaging findings and review the neuroimaging findings of all published cases of SLC13A5 related DEE. METHODS: A retrospective case review and focused review of the literature was completed. RESULTS: A 16-month-old male with a clinical phenotype consistent with SLC13A5 related DEE and a previously reported pathogenic variant in SLC13A5, c.655G>A, p.Gly219Arg and a novel likely pathogenic variant in SLC13A5, c.202C>T, p.Pro68Ser was identified. MRI at day 5 of life revealed wide spread punctate white matter lesions (PWMLs) affecting the subcortical white matter, periventricular white matter, splenium of the corpus callosum, posterior limb of the internal capsule, corticospinal tracts, midbrain, pons and medulla, mimicking a metabolic/infectious etiology. MRI at one month showed atrophy and evolution of white matter necrosis. One hundred and five cases of SLC13A5 related DEE were identified. Initial MRI was completed in 62 cases (59%). MRI was normal in 41 cases (66%) and abnormal in 21 (34%). White matter abnormalities were most common (n=15, 71%); PWMLs occurred in 8 cases (38%). CONCLUSION: Neuroimaging abnormalities may exist in a third of SLC13A5 related DEE cases. White matter abnormalities such as PWMLs appear most common. It remains unknown why some are susceptible to these lesions and how they affect long-term neurodevelopmental outcomes in SLC13A5 related DEE.

Does freeze-thaw action affect the extractability and bioavailability of Pb and As in contaminated soils?

As global warming intensifies, there will be increased uncertainty as to the environmental behavior and risks from heavy metals in industrial/legacy contaminated sites in permafrost regions. Bioavailability has been increasingly used for human health risk assessment of heavy metals in contaminated soils. Soil heavy metal bioavailability depends on soil physicochemical properties, and freeze-thaw affects soil physical, chemical and biological processes. However it is not clear whether freeze-thaw has an effect on the bioavailability of soil heavy metals. In this study, soils contaminated with Pb and As were collected from 10 industrial sites in northeast China. Extractability and bioavailability of soil Pb and As were determined by the Tessier sequential extraction method and four in vitro gastron-intestinal simulation methods under control and freeze-thaw treatments. The aims were: to compare the results of extraction and bioavailability from laboratory experiments which artificially simulate freeze-thaw conditions against control soils; to explore the correlation between bioavailability of Pb/As and soil properties. Freeze-thaw significantly decreased soil pH, and increased the soil weight surface area. Freeze-thaw decreased the percentage in the residual fraction, and increased the percentage of Pb and As in the exchangeable fraction, carbonate-bound fraction, Fe-Mn oxides-bound fraction and organic-bound fraction, relative to control soils. Freeze-thaw significantly increased Pb and As bioavailability compared to the controls. Pb and As released in the gastric phase of the four methods was significantly higher than that in the intestinal phase. Further analysis of correlations between Pb and As bioavailability and soil properties indicated that total concentrations of Al, Fe and Mn, particle size, and weight surface area significantly correlated to Pb and As bioavailability. Overall, this study demonstrated that freeze-thaw did influence the bioavailability of soil heavy metals. It suggests the freeze-thaw action should be comprehensively considered in the human risk assessment of soil pollutants in permafrost regions.

A bibliometric analysis and assessment of priorities for heavy metal bioavailability research and risk management in contaminated land.

Risk assessment has been recognized as an important tool for evaluating heavy metal pollution and providing risk-based information for decision makers. In order to accurately assess the risk of heavy metals in contaminated soil to human health, it is necessary to conduct bioavailability studies on heavy metals in soil. Bioavailability of heavy metals in soils and the implications for risk assessment and land management/remediation has evolved over the decades and now has considerable practical and economic implications internationally. This article aims to explore its evolution by undertaking a bibliometric analysis of the research fields which have addressed heavy metal bioavailability in soils, with a focus on the risk assessment of contaminated land and human exposure to soil-borne metals. Bibliometric analysis techniques are applied to monitor and assess the changing research literature on the bioavailability of heavy metals in contaminated soils. Over 5000 articles were found for the period 1979-2020. The purpose was not to perform an exhaustive literature review, but to draw out trends and patterns in the literature, and to make observations on past and current priorities. Key words were extracted from the analysis and the roles of different countries in driving the research literature identified. Three phases in literature/subject development were identified. Between 1979 and 2000 (initial phase, 213 articles), studies used extraction procedures and solubility studies to investigate the roles of soil properties on metal form/speciation and focused on bioavailability to (crop) plants in agricultural soils. Between 2001 and 2010 (slow development phase, 1105 articles), attention switched to metals introduced in soil amendments and wastes, metal impacts on soil microbial processes, and incorporating bioavailability in risk assessment. More rigorous techniques were being used, such as the diffusive gradients in thin films technique, to better understand kinetic and metal speciation in soils and the quantitative relationship to bioavailability. By 2011-2020 (rapid development phase, 3137 articles), research was being conducted in many countries (site specific, often industrially contaminated and urban sites), with a focus shift to health risk assessment, remediation, and bioavailability to various ecological receptors (e.g., humans and animals), with the development of many methods of bioavailability (e.g., simulated gastrointestinal tract enzymolysis methods). Some priorities for research on soil heavy metal bioavailability are identified.