Advancing systematic-review methodology in exposure science for environmental health decision making

Associations between airborne pollen, pollen-related allergic rhinitis and blood pressure: A systematic review and meta-analysis

BACKGROUND

Allergic rhinitis (AR) due to pollen affects an estimated 18% of adults globally, but is often trivialized. While there is evidence for an association between high pollen exposure and cardiovascular morbidity and mortality, as well as multiple plausible mechanisms suggesting pathways via blood pressure (BP) elevation, no overview exists to date. This systematic review and meta-analysis aims to investigate whether 1) pollen-related AR and 2) exposure to airborne pollen are associated with BP and/or hypertension. We further evaluated which personal characteristics may modify a potential association and identified research gaps.

METHODS

We searched the PubMed, ScienceDirect, EMBASE, and Web of Science databases and systematically reviewed studies focusing on human populations published between 1 January 1990 and 20 September 2023 that presented data on the association between pollen-related AR or pollen exposure and BP or hypertension. We assessed the risk of bias with a customized version of the Risk of Bias tool by the Office of Health Assessment and Translation of the National Toxicology Program (OHAT), conducted random effects meta-analyses of comparable studies and assessed the certainty of evidence according to OHAT recommendations. We carried out sensitivity analyses, excluding studies with a high bias rating.

RESULTS

We identified 24 studies, ranging in sample size from 41 to 9'548'939 participants. Of these, 23 had a cross-sectional design, and the remaining article included both cross-sectional and longitudinal analyses. Investigated exposures were binary pollen-related AR status (23 studies) and within and outside of pollen season (one study), but no study investigated measured pollen exposure (zero studies). Around half of the studies (13/24) were afflicted with high selection and confounding bias. Data from 22 studies using pollen-related AR status as exposure could be included in meta-analysis, to which eleven studies contributed hypertension data, four studies BP data, and seven studies both. In meta-analysis, we found an adjusted odds ratio of 1.16 (95 % confidence interval (CI): 0.91, 1.47) for hypertension and mean differences of 0.99 (95 % CI: -0.09, 2.07) and 0.40 (95 % CI: -0.41, 1.21) for adjusted systolic and diastolic BP, respectively. Results for crude pooled meta-estimates were similar, and none showed statistically significant differences. We rated the overall certainty in the evidence as very low, mainly due to cross-sectional designs, selection and confounding bias and indirectness of exposure.

DISCUSSION

This review shows that there is insufficient evidence to decide whether pollen-related AR is associated with BP or hypertension to date, and therefore does not support a clear mediating role of BP in the relationship between pollen allergy and cardiovascular events. Studies that 1) investigate BP or hypertension as the main outcome and provide adjusted estimates to avoid selection and confounding bias, 2) define AR as solely triggered by pollen and 3) have longitudinal designs were not identified. The certainty of the evidence is therefore limited by (1) reliance on cross-sectional studies, which prevents conclusions about causality, (2) high risk of selection and confounding biases which could not be adjusted for, (3) heterogeneous and indirect definitions of pollen-related AR, and (4) an exclusively binary exposure assessment (with or without pollen-related AR), which limited the ability to study an exposure gradient. Given these limitations, further cross-sectional studies are unlikely to yield clearer results, whereas repeated measurement designs could offer more valuable insights.

OTHER

This review was primarily funded by the Swiss National Science Foundation (SNSF, grant No. 185864) and the European Research Council (ERC) under the European Union's Horizon 2020 research and innovation programme (grant agreement No. 853568). We pre-published the protocol and search strategy on the PROSPERO website (registration number CRD42022381907).

Spatial indices quantifying exposure to swine farming in North Carolina

Introduction

Proximity to swine farms is often used as a surrogate in exposure assessments, allowing for the relative quantification of potential pollutant dispersion, odor intensity, and health impacts on neighboring communities. However, defining exposure is complex, and the resulting risk profiles can vary depending on the definition used.

Methods

To quantify the spatially based exposure of surrounding communities to swine farms in North Carolina, three spatially explicit metrics were developed at the census tract-level: IDx1: number of households within 1-mile from a hog farm, IDx2: Co-kriging using the number of hogs and manure lagoons, and IDx3: hog density per square mile. Then, the correlation between these indices and Centers for Disease Control and Prevention (CDC)'s Social Vulnerability Index (SVI) and Environmental Justice Index (EJI), which are generalized vulnerability measures, was evaluated to assess direct impact from swine farms versus multiple stressors.

Results

The three indices differed visually, with IDx3 strongly correlated with IDx1 (0.8) and moderately correlated with IDx2 (0.4). CDC EJI and SVI were not prominently correlated with any of the swine-farm specific indices (≤0.3) indicating limited overlap. The correlation between swine-farm-specific indices and CDC SVI was slightly pronounced in rural areas indicating socially vulnerable populations are more likely to live near swine farming areas in rural census tracts. Having swine farm-specific indices offers a more tailored and nuanced understanding of the potential health and environmental risks. However, the differences between the maps and the varying correlations underscored how different definitions of exposure can yield distinct narratives about which neighborhoods are at risk. Defining and measuring potential exposure, considering factors like proximity, duration, frequency, vulnerability, and cumulative impact, is highly challenging.

Discussion

The study emphasizes the need for a hierarchical framework to quantify and compare environmental exposures, addressing risk-modifying factors and individual-level exposure across space and time before implying direct exposure risks. This approach enables more informed planning for targeted solutions and fosters collaboration among stakeholders, facilitating critical discussions on integrated One Health solutions.

Contribution of environmental determinants to the risk of developing type 2 diabetes mellitus in a life-course perspective: a systematic review protocol

BACKGROUND

Prevention policies against type 2 diabetes mellitus (T2DM) focus solely on individual healthy lifestyle behaviours, while an increasing body of research recognises the involvement of environmental determinants (ED) (cultural norms of land management and planning, local foodscape, built environment, pollution, and neighbourhood deprivation). Precise knowledge of this relationship is essential to proposing a prevention strategy integrating public health and spatial planning. Unfortunately, issues related to the consistency and synthesis of methods, and results in this field of research limit the development of preventive strategies. This systematic review aims to improve knowledge about the relationship between the risk of developing T2DM in adulthood and long-term exposure to its ED during childhood or teenage years.

METHODS

This protocol is presented according to the Preferred Reporting Items for Systematic Review and Meta-Analysis Protocols (PRISMA-P) tools. PubMed, Embase, CINAHL, Web of Science, EBSCO, and grey literature from the Laval University Libraries databases will be used for data collection on main concepts such as 'type 2 diabetes mellitus', 'zoning' or 'regional, urban, or rural areas land uses', 'local food landscape', 'built environment', 'pollution', and 'deprivation'. The Covidence application will store the collected data for selection and extraction based on the Population Exposure Comparator Outcome and Study design approach (PECOS). Studies published until December 31, 2023, in English or French, used quantitative data about individuals aged 18 and over that report on T2DM, ED (cultural norms of land management and planning, local foodscape, built environment, and neighbourhood deprivation), and their association (involving only risk estimators) will be included. Then, study quality and risk of bias will be conducted according to the combined criteria and ratings from the ROBINS-E (Risk of Bias in Non-randomised Studies-of Exposures) tools and the 'Effective Public Health Practice Project' (EPHPP). Finally, the analytical synthesis will be produced using the 'Synthesis Without Meta-analysis' (SWiM) guidelines.

DISCUSSION

This systematic review will summarise available evidence on ED associated with T2DM. The results will contribute to improving current knowledge and developing more efficient cross-sectoral interventions in land management and public health in this field of research.

SYSTEMATIC REVIEW REGISTRATION

PROSPERO CRD42023392073.

Antimicrobial resistance in southeast Asian water environments: A systematic review of current evidence and future research directions

Antimicrobial resistance has been a serious and complex issue for over a decade. Although research on antimicrobial resistance (AMR) has mainly focused on clinical and animal samples as essential for treatment, the AMR situation in aquatic environments may vary and have complicated patterns according to geographical area. Therefore, this study aimed to examine recent literature on the current situation and identify gaps in the AMR research on freshwater, seawater, and wastewater in Southeast Asia. The PubMed, Scopus, and ScienceDirect databases were searched for relevant publications published from January 2013 to June 2023 that focused on antimicrobial resistance bacteria (ARB) and antimicrobial resistance genes (ARGs) among water sources. Based on the inclusion criteria, the final screening included 41 studies, with acceptable agreement assessed using Cohen's inter-examiner kappa equal to 0.866. This review found that 23 out of 41 included studies investigated ARGs and ARB reservoirs in freshwater rather than in seawater and wastewater, and it frequently found that Escherichia coli was a predominant indicator in AMR detection conducted by both phenotypic and genotypic methods. Different ARGs, such as blaTEM, sul1, and tetA genes, were found to be at a high prevalence in wastewater, freshwater, and seawater. Existing evidence highlights the importance of wastewater management and constant water monitoring in preventing AMR dissemination and strengthening effective mitigation strategies. This review may be beneficial for updating current evidence and providing a framework for spreading ARB and ARGs, particularly region-specific water sources. Future AMR research should include samples from various water systems, such as drinking water or seawater, to generate contextually appropriate results. Robust evidence regarding standard detection methods is required for prospective-era work to raise practical policies and alerts for developing microbial source tracking and identifying sources of contamination-specific indicators in aquatic environment markers.

A Scoping Assessment of Implemented Toxicokinetic Models of Per- and Polyfluoro-Alkyl Substances, with a Focus on One-Compartment Models

Toxicokinetic (TK) models have been used for decades to estimate concentrations of per-and polyfluoroalkyl substances (PFAS) in serum. However, model complexity has varied across studies depending on the application and the state of the science. This scoping effort seeks to systematically map the current landscape of PFAS TK models by categorizing different trends and similarities across model type, PFAS, and use scenario. A literature review using Web of Science and SWIFT-Review was used to identify TK models used for PFAS. The assessment covered publications from 2005-2020. PFOA, the PFAS for which most models were designed, was included in 69 of the 92 papers, followed by PFOS with 60, PFHxS with 22, and PFNA with 15. Only 4 of the 92 papers did not include analysis of PFOA, PFOS, PFNA, or PFHxS. Within the corpus, 50 papers contained a one-compartment model, 17 two-compartment models were found, and 33 used physiologically based pharmacokinetic (PBTK) models. The scoping assessment suggests that scientific interest has centered around two chemicals-PFOA and PFOS-and most analyses use one-compartment models in human exposure scenarios.

Biological plausibility in environmental health systematic reviews: a GRADE concept paper

BACKGROUND

"Biological plausibility" is a concept frequently referred to in environmental and public health when researchers are evaluating how confident they are in the results and inferences of a study or evidence review. Biological plausibility is not, however, a domain of one of the most widely-used approaches for assessing the certainty of evidence (CoE) which underpins the findings of a systematic review, the Grading of Recommendations Assessment, Development and Evaluation (GRADE) CoE Framework. Whether the omission of biological plausibility is a potential limitation of the GRADE CoE Framework is a topic that is regularly discussed, especially in the context of environmental health systematic reviews.

OBJECTIVES

We analyse how the concept of "biological plausibility", as applied in the context of assessing certainty of the evidence that supports the findings of a systematic review, is accommodated under the processes of systematic review and the existing GRADE domains.

RESULTS AND DISCUSSION

We argue that "biological plausibility" is a concept which primarily comes into play when direct evidence about the effects of an exposure on a population of concern (usually humans) is absent, at high risk of bias, is inconsistent, or limited in other ways. In such circumstances, researchers look toward evidence from other study designs in order to draw conclusions. In this respect, we can consider experimental animal and in vitro evidence as "surrogates" for the target populations, exposures, comparators and outcomes of actual interest. Through discussion of 10 examples of experimental surrogates, we propose that the concept of biological plausibility consists of two principal aspects: a "generalisability aspect" and a "mechanistic aspect". The "generalisability aspect" concerns the validity of inferences from experimental models to human scenarios, and asks the same question as does the assessment of external validity or indirectness in systematic reviews. The "mechanistic aspect" concerns certainty in knowledge of biological mechanisms and would inform judgements of indirectness under GRADE, and thus the overall CoE. While both aspects are accommodated under the indirectness domain of the GRADE CoE Framework, further research is needed to determine how to use knowledge of biological mechanisms in the assessment of indirectness of the evidence in systematic reviews.

Biological plausibility in environmental health systematic reviews: a GRADE concept paper

BACKGROUND

"Biological plausibility" is a concept frequently referred to in environmental and public health when researchers are evaluating how confident they are in the results and inferences of a study or evidence review. Biological plausibility is not, however, a domain of one of the most widely-used approaches for assessing the certainty of evidence (CoE) which underpins the findings of a systematic review, the Grading of Recommendations Assessment, Development and Evaluation (GRADE) CoE Framework. Whether the omission of biological plausibility is a potential limitation of the GRADE CoE Framework is a topic that is regularly discussed, especially in the context of environmental health systematic reviews.

OBJECTIVES

We analyse how the concept of "biological plausibility", as applied in the context of assessing certainty of the evidence that supports the findings of a systematic review, is accommodated under the processes of systematic review and the existing GRADE domains.

RESULTS AND DISCUSSION

We argue that "biological plausibility" is a concept which primarily comes into play when direct evidence about the effects of an exposure on a population of concern (usually humans) is absent, at high risk of bias, is inconsistent, or limited in other ways. In such circumstances, researchers look toward evidence from other study designs in order to draw conclusions. In this respect, we can consider experimental animal and in vitro evidence as "surrogates" for the target populations, exposures, comparators and outcomes of actual interest. Through discussion of 10 examples of experimental surrogates, we propose that the concept of biological plausibility consists of two principal aspects: a "generalisability aspect" and a "mechanistic aspect". The "generalisability aspect" concerns the validity of inferences from experimental models to human scenarios, and asks the same question as does the assessment of external validity or indirectness in systematic reviews. The "mechanistic aspect" concerns certainty in knowledge of biological mechanisms and would inform judgements of indirectness under GRADE, and thus the overall CoE. While both aspects are accommodated under the indirectness domain of the GRADE CoE Framework, further research is needed to determine how to use knowledge of biological mechanisms in the assessment of indirectness of the evidence in systematic reviews.

Systematic Review Methodologies and Endocrine Disrupting Chemicals: Improving Evaluations of the Plastic Monomer Bisphenol A

BACKGROUND

Endocrine disrupting chemicals (EDCs) are found in plastics, personal care products, household items, and other consumer goods. Risk assessments are intended to characterize a chemical's hazards, identify the doses at which adverse outcomes are observed, quantify exposure levels, and then compare these doses to determine the likelihood of risk in a given population. There are many problems with risk assessments for EDCs, allowing people to be exposed to levels that are later associated with serious health outcomes in epidemiology studies.

OBJECTIVE

In this review, we examine issues that affect the evaluation of EDCs in risk assessments (e.g., use of insensitive rodent strains and absence of disease-oriented outcomes in hazard assessments; inadequate exposure assessments). We then review one well-studied chemical, Bisphenol A (BPA; CAS #80-05-7) an EDC found in plastics, food packaging, and other consumer products. More than one hundred epidemiology studies suggest associations between BPA exposures and adverse health outcomes in environmentally exposed human populations.

FINDINGS

We present support for the use of systematic review methodologies in the evaluation of BPA and other EDCs. Systematic reviews would allow studies to be evaluated for their reliability and risk of bias. They would also allow all data to be used in risk assessments, which is a requirement for some regulatory agencies.

CONCLUSION

Systematic review methodologies can be used to improve evaluations of BPA and other EDCs. Their use could help to restore faith in risk assessments and ensure that all data are utilized in decision-making. Regulatory agencies are urged to conduct transparent, well-documented and proper systematic reviews for BPA and other EDCs.

Improving the quality of toxicology and environmental health systematic reviews: What journal editors can do

Systematic reviews are fast increasing in prevalence in the toxicology and environmental health literature. However, how well these complex research projects are being conducted and reported is unclear. Since editors have an essential role in ensuring the scientific quality of manuscripts being published in their journals, a workshop was convened where editors, systematic review practitioners, and research quality control experts could discuss what editors can do to ensure the systematic reviews they publish are of sufficient scientific quality. Interventions were explored along four themes: setting standards; reviewing protocols; optimizing editorial workflows; and measuring the effectiveness of editorial interventions. In total, 58 editorial interventions were proposed. Of these, 26 were shortlisted for being potentially effective, and 5 were prioritized as short-term actions that editors could relatively easily take to improve the quality of published systematic reviews. Recent progress in improving systematic reviews is summarized, and outstanding challenges to further progress are highlighted.

Human exposure pathways to poly- and perfluoroalkyl substances (PFAS) from indoor media: A systematic review protocol

BACKGROUND

Human exposure to per- and polyfluoroalkyl substances (PFAS) has been primarily attributed to contaminated food and drinking water. However, additional PFAS exposure pathways have been raised by a limited number of studies reporting correlations between commercial and industrial products and PFAS levels in human media and biomonitoring. Systematic review (SR) methodologies have been widely used to evaluate similar questions using an unbiased approach in the fields of clinical medicine, epidemiology, and toxicology, but the deployment in exposure science is ongoing. Here we present a systematic review protocol that adapts existing systematic review methodologies and study evaluation tools to exposure science studies in order to investigate evidence for important PFAS exposure pathways from indoor media including consumer products, household articles, cleaning products, personal care products, plus indoor air and dust.

OBJECTIVES

We will systematically review exposure science studies that present both PFAS concentrations from indoor exposure media and PFAS concentrations in blood serum or plasma. Exposure estimates will be synthesized from the evidence to answer the question, "For the general population, what effect does exposure from PFAS chemicals via indoor media have on blood, serum or plasma concentrations of PFAS?" We adapt existing systematic review methodologies and study evaluation tools from the U.S. EPA's Systematic Review Protocol for the PFBA, PFHxA, PFHxS, PFNA, and PFDA IRIS Assessments and the Navigation Guide for exposure science studies, as well as present innovative developments of exposure pathway-specific search strings for use in artificial intelligence screening software.

DATA SOURCES

We will search electronic databases for potentially relevant literature, including Web of Science, PubMed, and ProQuest. Literature search results will be stored in EPA's Health and Environmental Research Online (HERO) database.

STUDY ELIGIBILITY AND CRITERIA

Included studies will present exposure measures from indoor media including consumer products, household articles, cleaning products, personal care products, plus indoor air and dust, paired with PFAS concentrations in blood, serum or plasma from adults and/or children in the general population. We focus on a subset of PFAS chemicals including perfluorooctanoic acid (PFOA), perfluorooctanesulfonate (PFOS), perfluorobutanoic acid (PFBA), perfluorobutane sulfonate (PFBS), perfluorodecanoic acid (PFDA), perfluorohexanoic acid (PFHxA), perfluorohexanesulfonate (PFHxS), and perfluorononanoic acid (PFNA).

STUDY APPRAISAL AND SYNTHESIS METHODS

Studies will be prefiltered at the title and abstract level using computationally intelligent search strings to expedite the screening process for reviewers. Two independent reviewers will screen the prefiltered studies against inclusion criteria at the title/abstract level and then full-text level, after which the reviewers will assess the studies' risk of bias using an approach modified from established systematic review tools for exposure studies. Exposure estimates will be calculated to investigate the proportion of blood, serum or plasma) PFAS concentrations that can be explained by exposure to PFAS in indoor media.