Blood transcriptional and microRNA responses to short-term exposure to disinfection by-products in a swimming pool

Formation and control of disinfection by-products during the trichloroisocyanuric acid disinfection in swimming pool water

The increasing demand for trichloroisocyanuric acid (TCCA) in swimming pool disinfection highlights the need to evaluate its applicability in terms of disinfection by-product (DBP) formation. Nevertheless, there is limited understanding of DBP formation and control during TCCA disinfection, particularly concerning the effects of various management parameters. This study aimed to fill this knowledge gap by comprehensively investigating DBP formation during TCCA chlorination, with a particular focus on assessing the contribution and interaction of influencing factors using Box-Behnken Design and response surface methodology. Results indicated that the concentrations of trichloroacetaldehyde, chloroform, dichloroacetic acid, trichloroacetic acid, and dichloroacetonitrile produced by TCCA disinfectant were 42.5%, 74.0%, 48.1%, 94.7% and 42.6% of those by the conventional sodium hypochlorite disinfectant, respectively. Temperature exhibited the most significant impact on chloroform formation (49%), while pH played a major role in trichloroacetaldehyde formation (44%). pH2 emerged as the primary contributor to dichloroacetic acid (90%) and trichloroacetic acid (93%) formation. The optimum water quality conditions were determined based on the minimum total DBPs (pH = 7.32, Temperature = 23.7 °C, [Cl-] = 437 mg/L). Chlorine dosage and contact time exhibited greater influence than precursor concentration on chloroform, dichloroacetonitrile, trichloroacetaldehyde, trichloroacetic acid, and total DBPs. Although the interaction between water quality parameters was weak, the interaction between disinfection operating parameters demonstrated substantial effects on DBP formation (8.56-19.06%). Furthermore, the DBP predictive models during TCCA disinfection were provided for the first time, which provides valuable insights for DBP control and early warning programs.

Occupational exposure to potentially toxic elements alters gene expression profiles in formal and informal Brazilian workers

Chemical elements, such as toxic metals, have previously demonstrated their ability to alter gene expression in humans and other species. In this study, microarray analysis was used to compare the gene expression profiles of different occupational exposure populations: a) informal workers who perform soldering of jewelry inside their houses (n = 22) in São Paulo (SP) State; and b) formal workers from a steel company (n = 10) in Rio de Janeiro (RJ) state, Brazil. Control participants were recruited from the same neighborhoods without occupational chemical exposure (n = 19 in SP and n = 8 in RJ). A total of 68 blood samples were collected and RNA was extracted and hybridized using an Agilent microarray platform. Data pre-processing, statistical and pathway analysis were performed using GeneSpring software. Different expression was detected by fold-change analysis resulting in 16 up- and 33 down-regulated genes in informal workers compared to the control group. Pathway analysis revealed genes enriched in MAPK, Toll-like receptor, and NF-kappa B signaling pathways, involved in inflammatory and immune responses. In formal workers, 20 up- and 50 down-regulated genes were found related to antimicrobial peptides, defensins, neutrophil degranulation, Fc-gamma receptor-dependent phagocytosis, and pathways associated with atherosclerosis development, which is one of the main factors involved in the progression of cardiovascular diseases. The gene IFI27 was the only one commonly differentially expressed between informal and formal workers and is known to be associated with various types of cancer. In conclusion, differences in gene expression related to occupational exposure are mainly associated with inflammation and immune response. Previous research has identified a link between inflammation and immune responses and the development of chronic diseases, suggesting that prolonged occupational exposures to potentially toxic elements in Brazilian metal workers could lead to negative health outcomes. Further analysis should be carried out to investigate its direct effects and to validate causal associations.

Research Recommendations for Selected IARC-Classified Agents: Impact and Lessons Learned

BACKGROUND

The International Agency for Research on Cancer (IARC) Monographs program assembles expert working groups who publish a critical review and evaluation of data on agents of interest. These comprehensive reviews provide a unique opportunity to identify research needs to address classification uncertainties. A multidisciplinary expert review and workshop held in 2009 identified research gaps and needs for 20 priority occupational chemicals, metals, dusts, and physical agents, with the goal of stimulating advances in epidemiological studies of cancer and carcinogen mechanisms. Overarching issues were also described.

OBJECTIVES

In this commentary we review the current status of the evidence for the 20 priority agents identified in 2009. We examine whether identified Research Recommendations for each agent were addressed and their potential impact on resolving classification uncertainties.

METHODS

We reviewed the IARC classifications of each of the 20 priority agents and identified major new epidemiological and human mechanistic studies published since the last evaluation. Information sources were either the published Monograph for agents that have been reevaluated or, for agents not yet reevaluated, Advisory Group reports and literature searches. Findings are described in view of recent methodological developments in Monographs evidence evaluation processes.

DISCUSSION

The majority of the 20 priority agents were reevaluated by IARC since 2009. The overall carcinogen classifications of 9 agents advanced, and new cancer sites with either "sufficient" or "limited" evidence of carcinogenicity were also identified for 9 agents. Examination of published findings revealed whether evidence gaps and Research Recommendations have been addressed and highlighted remaining uncertainties. During the past decade, new research addressed a range of the 2009 recommendations and supported updated classifications for priority agents. This supports future efforts to systematically apply findings of Monograph reviews to identify research gaps and priorities relevant to evaluation criteria established in the updated IARC Monograph Preamble. https://doi.org/10.1289/EHP12547.

Advances and research needs for disinfection byproducts control strategies in swimming pools

The control of disinfection byproducts (DBPs) in swimming pools is of great significance due to the non-negligible toxicity and widespread existence of DBPs. However, the management of DBPs remains challenging as the removal and regulation of DBPs is a multifactorial phenomenon in pools. This study summarized recent studies on the removal and regulation of DBPs, and further proposed some research needs. Specifically, the removal of DBPs was divided into the direct removal of the generated DBPs and the indirect removal by inhibiting DBP formation. Inhibiting DBP formation seems to be the more effective and economically practical strategy, which can be achieved mainly by reducing precursors, improving disinfection technology, and optimizing water quality parameters. Alternative disinfection technologies to chlorine disinfection have attracted increasing attention, while their applicability in pools requires further investigation. The regulation of DBPs was discussed in terms of improving the standards on DBPs and their preccursors. The development of online monitoring technology for DBPs is essential for implementing the standard. Overall, this study makes a significant contribution to the control of DBPs in pool water by updating the latest research advances and providing detailed perspectives.

Impacts of disinfection byproduct exposures on male reproductive health: Current evidence, possible mechanisms and future needs

Disinfection byproducts (DBPs) are a class of ubiquitous chemicals in drinking water and inevitably result in widespread human exposures. Potentially adverse health effects of DBP exposures, including reproductive and developmental outcomes, have been increasing public concerns. Several reviews have focused on the adverse pregnancy outcomes of DBPs. This review summarized current evidence on male reproduction health upon exposure to DBPs from toxicological and epidemiological literature. Based on existing experimental studies, there are sufficient evidence showing that haloacetic acids (HAAs) are male reproductive toxicants, including reduced epididymal weight, decreased semen parameters and sperm protein 22, and declined testosterone levels. However, epidemiological evidence remains insufficient to support a link of DBP exposures with adverse male reproductive outcomes, despite that blood and urinary DBP biomarkers are associated with decreased semen quality. Eight potential mechanisms, including germ/somatic cell dysfunction, oxidative stress, genotoxicity, inflammation, endocrine hormones, folate metabolism, epigenetic alterations, and gut microbiota, are likely involved in male reproductive toxicity of DBPs. We also identified knowledge gaps in toxicological and epidemiological studies to enhance future needs.

Urinary trihalomethane concentrations and liver function indicators: a cross-sectional study in China

While it is known that exposure to disinfection by-products (DBPs), including trihalomethanes (THMs), impairs liver function, few epidemiological studies have explored this association. Here, we determined the concentrations of four urinary trihalomethanes (chloroform [TCM], and three Br-THMs, bromodichloromethane [BDCM], dibromochloromethane [DBCM], and bromoform [TBM]), and nine serum liver function indicators in 182 adults ≥ 18 years of age, examined at a medical examination center in Wuxi, China, in 2020 and 2021. Generalized linear model analysis revealed positive associations between urinary DBCM and alanine aminotransferase (ALT), aspartate aminotransferase (AST), total bilirubin (TBIL), total protein (TP), and albumin (ALB). Urinary Br-THMs and total THMs (TTHMs) were positively associated with ALT, AST, TBIL, indirect bilirubin (IBIL), TP, and ALB (all P < 0.05). Urinary THMs were not associated with alkaline phosphatase (ALP) or glutamine transaminase (GGT) (all P > 0.05). Generalized additive model-based penalized regression splines were used to confirm these associations. In conclusion, THM exposure was associated with altered serum biomarkers of liver function.

Smoking-related epigenetic modifications are associated with the prognosis and chemotherapeutics of patients with bladder cancer

OBJECTIVE

Epidemiologic studies have linked smoking to various malignancies, including bladder cancer, but its underlying biological functions remain elusive. Currently, we aimed to identify the smoking-related epigenetic modifications and disclose their impacts on prognosis and therapies in bladder cancer.

METHODS

DNA methylation, transcriptome, and clinical profiles were acquired from The Cancer Genome Atlas (TCGA) using "TCGAbiolinks" Differential expression analyses were performed with "limma" and visualized by the "pheatmap" package. Smoking-related interactions were displayed using Cytoscape. Least absolute shrinkage and selection operator (LASSO) algorithm was for generation of a smoking-related prognostic model. Kaplan-Meier analysis with log-rank test was for survival analysis, followed by a prognostic nomogram. The Gene Set Enrichment Analysis (GSEA) was used for functional analysis. The "oncoPredict" package was applied for drug sensitivity analysis.

RESULTS

We recruited all types of bladder cancers and found that smoking was involved in poor prognosis, with the hazard ratio (HR) of 1.600 (95%CI: 1.028-2.491). A total of 1078 smoking-related DNA methylations (526 hypermethylation and 552 hypomethylation) were identified and 9 methylation-driven genes differentially expressed in bladder cancer. Also, 506lncRNAs (448 upregulated and 58 downregulated lncRNAs) and 102 miRNAs (74 upregulated and 28 downregulated miRNAs) were determined as smoking-related ncRNAs. We then calculated the smoking-related risk score and observed that cases of high risk were predicted with poor prognosis. We constructed a prognostic nomogram to predict the 1-, 3-, and 5-year overall survival rates. Several cancer-related pathways were enriched in the high-risk group, and patients with high-risk were more sensitive to Gemcitabine, Wnt-C59, JAK1_8709, KRAS (G12C) Inhibitor-12, and LY2109761. Whereas, those with low-risk were more sensitive to Cisplatin, AZ960, and Buparlisib.

CONCLUSIONS

Totally, we initially identified the smoking-related epigenetic modifications in bladder cancer and constructed a corresponding prognostic model, which was also linked to disparate sensitivities to chemotherapeutics. Our findings would provide novel insights into the carcinogenesis, prognosis, and therapies in bladder cancer.

From trihalomethanes chronic daily intake through multiple exposure routes to cancer and non-cancer health risk assessment: Evidence from public Portuguese indoor swimming pools facilities using a probabilistic approach

This study aimed to estimate chronic daily intake (CDI) and to predict the attributable lifetime cancer risk (LCR) and hazard index (HI) from concurrent exposure to four trihalomethanes (THMs; chloroform, bromodichloromethane, dibromochloromethane and bromoform), via multiple exposure routes (oral ingestion, dermal contact and inhalation), among 238 non-competitive attendees of 10 Portuguese public indoor swimming pools (SPs), using a probabilistic approach based on Monte Carlo simulations. Exposure parameters of study participants were collected via questionnaires and THMs levels in SPs water were determined according the respective normative standards. The CDI for total THMs calculated for male and female participants considering all routes was 7.52 and 8.97 mg/kg/day, respectively. SP attendees presented higher CDI through inhalation than via the other two exposure routes, and chloroform was the compound contributing the most to total THMs CDI. The risk analysis indicated that the total LCR and HI from the targeted THMs were higher than the negligible risk levels (1 × 10^-6 and 1, respectively) in the scenarios examined (central tendency exposure and reasonable maximum exposure), and the health risk for females was slightly higher than for males. This study suggests that there are possible adverse health risks, thus, to protect pool attendees, adequate mitigation measures, and comprehensive regulatory guidelines on individual THMs concentrations are needed.

Exposure to widespread drinking water chemicals, blood inflammation markers, and colorectal cancer

BACKGROUND

Trihalomethanes (THMs) and nitrate are widespread chemicals in drinking water associated with colorectal cancer risk but mechanisms are not well understood.

OBJECTIVES

We explored the association between exposure to THMs and nitrate in drinking water and inflammation markers, and the link with colorectal cancer risk.

METHODS

A subset of 198 colorectal cancer cases and 205 controls from the multicase-control study MCC-Spain were included. Average concentration of THMs (chloroform, bromodichloromethane, dibromochloromethane, bromoform) and nitrate in tap water at the residence was estimated from age 18 until 2 years before the interview ("long term") and for a recent period (3 years before diagnosis). Serum levels of EGF, eotaxin, G-CSF, IL-17E, IL-1rA, IL-8, IP-10, MDC, MPO, periostin, VEGF, and C-reactive protein (CRP) were measured. We estimated the linear association between inflammation markers and exposure among controls, and the odds ratio of colorectal cancer associated with THM and nitrate exposure, and inflammation markers. A mediation analysis was conducted to identify inflammation markers in the pathway between THM/nitrate exposure and colorectal cancer.

RESULTS

Serum concentrations of EGF, IL-8, IL-17E and eotaxin increased with recent residential levels of brominated THMs, chloroforom and/or total THM. No associations were observed for nitrate and for long-term residential THM levels. All residential exposures except chloroform were positively associated with colorectal cancer. Serum concentrations of VEGF and periostin were positively associated with colorectal cancer, while EGF was inversely associated. One protein-exposure combination (periostin-recent ingested brominated THMs) slightly mediated the association with colorectal cancer risk.

DISCUSSION

Results suggest that estimated THM exposure is involved in inflammation processes. However, the study design was limited to stablish etiologically relevant associations between the protein levels and colorectal cancer risk. The lack of association between nitrate exposure and inflammation markers suggests other biological mechanisms are involved in the link with colorectal cancer.

What is new in the exposome?

The exposome concept refers to the totality of exposures from a variety of external and internal sources including chemical agents, biological agents, or radiation, from conception onward, over a complete lifetime. It encompasses also "psychosocial components" including the impact of social relations and socio-economic position on health. In this review we provide examples of recent contributions from exposome research, where we believe their application will be of the greatest value for moving forward. So far, environmental epidemiology has mainly focused on hard outcomes, such as mortality, disease exacerbation and hospitalizations. However, there are many subtle outcomes that can be related to environmental exposures, and investigations can be facilitated by an improved understanding of internal biomarkers of exposure and response, through the application of omic technologies. Second, though we have a wealth of studies on environmental pollutants, the assessment of causality is often difficult because of confounding, reverse causation and other uncertainties. Biomarkers and omic technologies may allow better causal attribution, for example using instrumental variables in triangulation, as we discuss here. Even more complex is the understanding of how social relationships (in particular socio-economic differences) influence health and imprint on the fundamental biology of the individual. The identification of molecular changes that are intermediate between social determinants and disease status is a way to fill the gap. Another field in which biomarkers and omics are relevant is the study of mixtures. Epidemiology often deals with complex mixtures (e.g. ambient air pollution, food, smoking) without fully disentangling the compositional complexity of the mixture, or with rudimentary approaches to reflect the overall effect of multiple exposures or components. From the point of view of disease mechanisms, most models hypothesize that several stages need to be transitioned through health to the induction of disease, but very little is known about the characteristics and temporal sequence of such stages. Exposome models reinforce the idea of a biography-to-biology transition, in that everyone's disease is the product of the individual history of exposures, superimposed on their underlying genetic susceptibilities. Finally, exposome research is facilitated by technological developments that complement traditional epidemiological study designs. We describe in depth one such new tools, adductomics. In general, the development of high-resolution and high-throughput technologies interrogating multiple -omics (such as epigenomics, transcriptomics, proteomics, adductomics and metabolomics) yields an unprecedented perspective into the impact of the environment in its widest sense on disease. The world of the exposome is rapidly evolving, though a huge gap still needs to be filled between the original expectations and the concrete achievements. Perhaps the most urgent need is for the establishment of a new generation of cohort studies with appropriately specified biosample collection, improved questionnaire data (including social variables), and the deployment of novel technologies that allow better characterization of individual environmental exposures, ranging from personal monitoring to satellite based observations.

Assessment of exposure of children swimmers to trihalomethanes in an indoor swimming pool

This study aimed to understand the exposure levels of trihalomethanes (THMs) in an indoor swimming pool and calculate the risks of exposure to THMs, based on the presence of each THM species, of children swimmers aged 6-17, in Beijing, China. We obtained exposure factors for the children through questionnaires and measured THM concentrations through laboratory tests, and we combined the results with an exposure model to calculate the risks, with consideration of different exposure routes (oral ingestion, inhalation and dermal absorption). In terms of exposure factors for the swimmers aged 6-17, the average body weight, exposure duration, exposure frequency, swimming time, shower time, changing time, warm-up exercise and rest time, skin surface area and ingestion rate of pool water were 40.46 kg, 2.70 years, 96 events/year, 64.03 min/event, 17.04 min/event, 15.31 min/event, 12.71 min/event, 1.37 m² and 48.93 ml/event, respectively. The THM concentrations in swimming pool water, shower water, swimming pool air and locker room air were 67.17 μg/L, 12.64 μg/L, 358.66 μg/m³ and 40.98 μg/m³, respectively. The average cancer risk of THMs was 5.44 × 10^-6, which is an unacceptable risk according to the United State Environmental Protection Agency (USEPA) Guidelines. The average hazard index was 0.007, i.e., less than 1, indicating that the noncancer risk was acceptable. Chloroform (TCM) was the main substance in four species of THMs and inhalation exposure was the main exposure pathway. The risk of cancer and noncancer from inhalation exposure to THMs accounts for 97-99% of the total risk. As a result, the disease control authorities and administrative department should pay attention to the health and safety of swimming facilities and, at the same time, establish standards for THMs in the air through further research.

Making evidential claims in epidemiology: Three strategies for the study of the exposome

How is scientific data used to represent phenomena and as evidence for claims about phenomena? In this paper, I propose that a specific type of claims - evidential claims - is involved in data practices to define and restrict the representational and evidential content of a dataset. I present an account of data practices in the epidemiology of the exposome based on the notion of evidential claims, which helps unpack the approaches, assumptions and warrants that connect different stages of research. I identify three different strategies to generate different types of evidential claims in this case. The macro strategy, which individuates the dataset that serves as the initial evidential space for research. The micro strategy, which is used to generate evidential claims about the microscopic and individual component of target phenomena. The association strategy, that uses evidence from the other strategies to identify a dataset as representation of the different levels and relations of exposure and disease. Differentiating between these strategies sheds light on the multi-faceted landscape of biomedical research on environment and health; and the roles of data and evidence in the process of inquiry.

Trihalomethanes in Drinking Water and Bladder Cancer Burden in the European Union

BACKGROUND

Trihalomethanes (THMs) are widespread disinfection by-products (DBPs) in drinking water, and long-term exposure has been consistently associated with increased bladder cancer risk.

OBJECTIVE

We assessed THM levels in drinking water in the European Union as a marker of DBP exposure and estimated the attributable burden of bladder cancer.

METHODS

We collected recent annual mean THM levels in municipal drinking water in 28 European countries (EU28) from routine monitoring records. We estimated a linear exposure-response function for average residential THM levels and bladder cancer by pooling data from studies included in the largest international pooled analysis published to date in order to estimate odds ratios (ORs) for bladder cancer associated with the mean THM level in each country (relative to no exposure), population-attributable fraction (PAF), and number of attributable bladder cancer cases in different scenarios using incidence rates and population from the Global Burden of Disease study of 2016.

RESULTS

We obtained 2005-2018 THM data from EU26, covering 75% of the population. Data coverage and accuracy were heterogeneous among countries. The estimated population-weighted mean THM level was 11.7μg/L [standard deviation (SD) of 11.2]. The estimated bladder cancer PAF was 4.9% [95% confidence interval (CI): 2.5, 7.1] overall (range: 0-23%), accounting for 6,561 (95% CI: 3,389, 9,537) bladder cancer cases per year. Denmark and the Netherlands had the lowest PAF (0.0% each), while Cyprus (23.2%), Malta (17.9%), and Ireland (17.2%) had the highest among EU26. In the scenario where no country would exceed the current EU mean, 2,868 (95% CI: 1,522, 4,060; 43%) annual attributable bladder cancer cases could potentially be avoided.

DISCUSSION

Efforts have been made to reduce THM levels in the European Union. However, assuming a causal association, current levels in certain countries still could lead to a considerable burden of bladder cancer that could potentially be avoided by optimizing water treatment, disinfection, and distribution practices, among other possible measures. https://doi.org/10.1289/EHP4495.

Maternal swimming pool exposure during pregnancy in relation to birth outcomes and cord blood DNA methylation among private well users

Swimming in pools during pregnancy may expose the fetus to water disinfection by-products (DBP). As yet, our understanding of the impacts on DBPs on the fetus is uncertain. Individuals with public water systems are typically exposed to DBPs through drinking, showering and bathing, whereas among those on private water systems, swimming in pools may be the primary exposure source. We analyzed the effects of maternal swimming on birth outcomes and cord blood epigenetic changes in the New Hampshire Birth Cohort Study, a cohort of pregnant women with households on private water systems. Information about swimming in pools during pregnancy was obtained from 1033 women via questionnaires. Swimming pool use and duration were modeled using linear regression with newborn weight, length, and head circumference (z-scores) and genome wide cord blood DNA methylation as the outcomes and with adjustment for potential confounders. Overall 19.7% of women reported swimming in a pool during pregnancy. Among swimmers, duration of swimming was inversely related to head circumference (-0.02 z-score per 10% increase in duration, P = 0.004). No associations were observed with birth weight, length or DNA methylation modifications. Our findings suggest swimming pool exposure may impact the developing fetus although longer-term studies are needed.

MicroRNAs and their role in environmental chemical carcinogenesis

MicroRNAs (miRNAs) are a class of small, noncoding RNA species that play crucial roles across many biological processes and in the pathogenesis of major diseases, including cancer. Recent studies suggest that the expression of miRNA is altered by certain environmental chemicals, including metals, organic pollutants, cigarette smoke, pesticides and carcinogenic drugs. In addition, extensive studies have indicated the existence and importance of miRNA in different cancers, suggesting that cancer-related miRNAs could serve as potential markers for chemically induced cancers. The altered expression of miRNA was considered to be a vital pathogenic role in xenobiotic-induced cancer development. However, the significance of miRNA in the etiology of cancer and the exact mechanisms by which environmental factors alter miRNA expression remain relatively unexplored. Hence, understanding the interaction of miRNAs with environmental chemicals will provide important information on mechanisms underlying the pathogenesis of chemically induced cancers, and effectively diagnose and treat human cancers resulting from chronic or acute carcinogen exposure. This study presents the current evidence that the miRNA deregulation induced by various chemical carcinogens, different cancers caused by environmental carcinogens and the potentially related genes in the onset or progression of cancer. For each carcinogen, the specifically expressed miRNA may be considered as the early biomarkers of the cancer process. In this review, we also summarize various target genes of the altered miRNA, oncogenes or anti-oncogenes, and the existing evidence regarding the gene regulation mechanisms of cancer caused by environmentally induced miRNA alteration. The future perspective of miRNA may become attractive targets for the diagnosis and treatment of carcinogen-induced cancer.

From John Snow to omics: the long journey of environmental epidemiology

A major difference between infectious and non-communicable diseases is that infectious diseases typically have unique necessary causes whereas noncommunicable diseases have multiple causes which by themselves are usually neither necessary nor sufficient. Epidemiology seems to have reached a limit in disentangling the role of single components in causal complexes, particularly at low doses. To overcome limitations the discipline can take advantage of technical developments including the science of the exposome. By referring to the interpretation of the exposome as put forward in the work of Wild and Rappaport, I show examples of how the science of multi-causality can build upon the developments of omic technologies. Finally, I broaden the picture by advocating a more holistic approach to causality that also encompasses social sciences and the concept of embodiment. To tackle NCDs effectively on one side we can invest in various omic approaches, to identify new external causes of non-communicable diseases (that we can use to develop preventive strategies), and the corresponding mechanistic pathways. On the other side, we need to focus on the social and societal determinants which are suggested to be the root causes of many non-communicable diseases.

A multivariate approach to investigate the combined biological effects of multiple exposures

Epidemiological studies provide evidence that environmental exposures may affect health through complex mixtures. Formal investigation of the effect of exposure mixtures is usually achieved by modelling interactions, which relies on strong assumptions relating to the identity and the number of the exposures involved in such interactions, and on the order and parametric form of these interactions. These hypotheses become difficult to formulate and justify in an exposome context, where influential exposures are numerous and heterogeneous. To capture both the complexity of the exposome and its possibly pleiotropic effects, models handling multivariate predictors and responses, such as partial least squares (PLS) algorithms, can prove useful. As an illustrative example, we applied PLS models to data from a study investigating the inflammatory response (blood concentration of 13 immune markers) to the exposure to four disinfection by-products (one brominated and three chlorinated compounds), while swimming in a pool. To accommodate the multiple observations per participant (n=60; before and after the swim), we adopted a multilevel extension of PLS algorithms, including sparse PLS models shrinking loadings coefficients of unimportant predictors (exposures) and/or responses (protein levels). Despite the strong correlation among co-occurring exposures, our approach identified a subset of exposures (n=3/4) affecting the exhaled levels of 8 (out of 13) immune markers. PLS algorithms can easily scale to high-dimensional exposures and responses, and prove useful for exposome research to identify sparse sets of exposures jointly affecting a set of (selected) biological markers. Our descriptive work may guide these extensions for higher dimensional data.