Back Accumulation of Diffusive Gradients in Thin-Films Devices with a Stack of Resin Discs To Assess Availability of Metal Cations to Biota in Natural Waters.

Determining species, concentrations, and physicochemical parameters in natural waters is key to improve our understanding of the functioning of these ecosystems. Diffusive Gradients in Thin-films (DGT) devices with different thicknesses of the resin or of the diffusive disc can be used to collect independent information on relevant parameters. In particular, DGT devices with a stack of two resin discs offer a simple way to determine dissociation rate constants of metal complexes from the accumulation of the target metal in the back resin disc. In this work, simple approximate expressions for the determination of the dissociation rate constant are reported and applied to a model Ni nitrilotriacetic complex as well as to Zn complexes in the Mediterranean Osor stream. Once the physicochemical parameters are known, one can plot the labile fraction of the metal complexes in terms of the thickness of the diffusion domain. These plots reveal a strong dependence on the nature of complexes as well as on the characteristics of the diffusion domain, and they are of high interest as predictors of availability to biota whose uptake is limited by diffusion.

Advances in Understanding Mobilization Processes of Trace Metals in Marine Sediments.

Different mobilization mechanisms control the metal distribution in surface sediments of the Belgium coastal zone (BCZ) and the anoxic Gotland basin (GB). This mobilization was studied using DGT (diffusive gradients in thin films): vertical one-dimensional (1D) profiles of Cd, Co, Cu, Fe, Mn, Ni, Pb, and Zn were measured at 5 mm intervals, while two-dimensional (2D) high-resolution (100 µm) images of smaller zones of the sediment profile were obtained on separate DGT probes. Removal of dissolved Cd, Cu, and Pb in BCZ sediments caused steep vertical gradients at the sediment-water interface that were well replicated in 1D profiles and 2D images. While 1D profiles showed apparent coincident maxima of Co, Mn, and Fe, 2D images revealed mutually exclusive Co and Fe mobilization. Correlation analysis supported this observation and showed a consistent linkage between Co and Mn. Sharp maxima of some metals in the vertical 1D profiles of GB sediment were attributed to localized mobilization in microniches. Examination of an ∼1 mm diameter Cu and Ni maximum in 2D, defined by ∼300 data points, showed that the metals were supplied from localized decomposition of reactive organic material, rather than from reductively dissolving Fe or Mn oxides, and that they were removed as their sulfides.

Exposure to Environmental Pollutants and Their Association with Biomarkers of Aging: A Multipollutant Approach.

Mitochondrial DNA (mtDNA) content and telomere length are putative aging biomarkers and are sensitive to environmental stressors, including pollutants. Our objective was to identify, from a set of environmental exposures, which exposure is associated with leukocyte mtDNA content and telomere length in adults. This study includes 175 adults from 50 to 65 years old from the cross-sectional Flemish Environment and Health study, of whom leukocyte telomere length and mtDNA content were determined using qPCR. The levels of exposure of seven metals, 11 organohalogens, and four perfluorinated compounds (PFHxS, PFNA, PFOA, PFOS) were measured. We performed sparse partial least-squares regression analyses followed by ordinary least-squares regression to assess the multipollutant associations. While accounting for possible confounders and coexposures, we identified that urinary cadmium (6.52%, 95% confidence interval, 1.06, 12.28), serum hexachlorobenzene (2.89%, 018, 5.68), and perfluorooctanesulfonic acid (11.38%, 5.97, 17.08) exposure were positively associated ( p < 0.05) with mtDNA content, while urinary copper (-9.88%, -14.82, -4.66) and serum perfluorohexanesulfonic acid (-4.75%, -8.79, -0.54) exposure were inversely associated with mtDNA content. Urinary antimony (2.69%, 0.45, 4.99) and mercury (1.91%, 0.42, 3.43) exposure were positively associated with leukocyte telomere length, while urinary copper (-3.52%, -6.60, -0.34) and serum perfluorooctanesulfonic acid (-3.64%, -6.60, -0.60) showed an inverse association. Our findings support the hypothesis that environmental pollutants interact with molecular hallmarks of aging.

Cord blood leptin and insulin levels in association with mitochondrial DNA content.

BACKGROUND: The developmental origins of health and disease theory states that a disturbance in the early life environment can contribute to disease risk in later life. Leptin and insulin are anorectic hormones involved in energy homeostasis and are crucial for foetal growth. Disturbances in the levels of these hormones contribute to obesity and diabetes. In adults, altered mitochondrial function is an important hallmark of metabolic disorders, including obesity and diabetes. However, the mitochondrial effects of early life metabolic variation are unexplored. We investigated whether there is an association between metabolic hormones and mitochondrial DNA (mtDNA) content in early life. METHODS: The study included 236 newborns from the FLEHS III birth cohort, Flanders (Belgium). Relative mtDNA content of cord blood leukocytes was determined using quantitative PCR. Cord blood levels of leptin and insulin were determined using immunoassays. We studied the association between these metabolic hormones and mtDNA content using multiple linear regression models, while accounting for covariates and potential confounders. RESULTS: Leptin and insulin levels were positively associated with cord blood mtDNA content. mtDNA content was respectively 4.49% (95% CI 1.15-7.93; p = 0.008) and 1.60% (95% CI 0.31-2.91; p = 0.02) higher for a interquartile range increase of respectively cord blood leptin and insulin levels. In a sensitivity analysis, we observed that insulin and leptin were independently associated to mtDNA content and that insulin was stronger associated to mtDNA content in boys than in girls. CONCLUSION: Neonatal metabolic hormones were associated with cord blood mtDNA content, which suggests that in early life the variation of mtDNA content might accommodate or reflect changes in the metabolic status.

Estrogenic Activity Measurements in Water Using Diffusive Gradients in Thin-Film Coupled with an Estrogen Bioassay.

A novel type of diffusive gradients in thin-film (DGT) was combined with a chemically activated luciferase gene expression bioassay (CALUX) to measure estrogens in aquatic systems. The performance of this novel method was assessed with 17ß-estradiol (E2) as the model steroid hormone, XAD 18 resin gel as the binding phase in the DGT method and VM7Luc4E2 cells (formerly BG1Luc4E2) for the Estrogen Responsive Element (ERE)-CALUX bioassay. The measured effective diffusion coefficient of E2 in agarose diffusive gel was 4.65 ± 0.37 × 10-6 cm2 s-1 at 25 °C. The detection limit of this combined DGT/ERE-CALUX method for 1 day of sampling (0.026 ± 0.003 ng L-1 of E2) is significantly lower than that obtained by spot sampling combined with GC-MS/MS or LC-MS/MS analysis (0.1-7.0 ng L-1). The method is independent of pH (5-8), ionic strength (0.001-0.5 M), and dissolved organic matter (DOM; concentrations up to 30 mg L-1). Field applications of this novel DGT in effluents of three sewage treatment plants in Beijing city (China) showed comparable results to conventional spot (grab) sampling. This study demonstrates that the combined DGT/ERE-CALUX approach is an effective and sensitive tool for in situ monitoring of estrogenic activity in waters and wastewaters.

Environmental exposure to human carcinogens in teenagers and the association with DNA damage.

BACKGROUND: We investigated whether human environmental exposure to chemicals that are labeled as (potential) carcinogens leads to increased (oxidative) damage to DNA in adolescents. MATERIAL AND METHODS: Six hundred 14-15-year-old youngsters were recruited all over Flanders (Belgium) and in two areas with important industrial activities. DNA damage was assessed by alkaline and formamidopyrimidine DNA glycosylase (Fpg) modified comet assays in peripheral blood cells and analysis of urinary 8-hydroxydeoxyguanosine (8-OHdG) levels. Personal exposure to potentially carcinogenic compounds was measured in urine, namely: chromium, cadmium, nickel, 1-hydroxypyrene as a proxy for exposure to other carcinogenic polycyclic aromatic hydrocarbons (PAHs), t,t-muconic acid as a metabolite of benzene, 2,5-dichlorophenol (2,5-DCP), organophosphate pesticide metabolites, and di(2-ethylhexyl) phthalate (DEHP) metabolites. In blood, arsenic, polychlorinated biphenyl (PCB) congeners 118 and 156, hexachlorobenzene (HCB), dichlorodiphenyltrichloroethane (DDT) and perfluorooctanoic acid (PFOA) were analyzed. Levels of methylmercury (MeHg) were measured in hair. Multiple linear regression models were used to establish exposure-response relationships. RESULTS: Biomarkers of exposure to PAHs and urinary chromium were associated with higher levels of both 8-OHdG in urine and DNA damage detected by the alkaline comet assay. Concentrations of 8-OHdG in urine increased in relation with increasing concentrations of urinary t,t-muconic acid, cadmium, nickel, 2,5-DCP, and DEHP metabolites. Increased concentrations of PFOA in blood were associated with higher levels of DNA damage measured by the alkaline comet assay, whereas DDT was associated in the same direction with the Fpg-modified comet assay. Inverse associations were observed between blood arsenic, hair MeHg, PCB 156 and HCB, and urinary 8-OHdG. The latter exposure biomarkers were also associated with higher fish intake. Urinary nickel and t,t-muconic acid were inversely associated with the alkaline comet assay. CONCLUSION: This cross-sectional study found associations between current environmental exposure to (potential) human carcinogens in 14-15-year-old Flemish adolescents and short-term (oxidative) damage to DNA. Prospective follow-up will be required to investigate whether long-term effects may occur due to complex environmental exposures.

Human biomonitoring from an environmental justice perspective: supporting study participation of women of Turkish and Moroccan descent.

BACKGROUND: Environmental justice research shows how socially disadvantaged groups are more exposed and more vulnerable to environmental pollution. At the same time, these groups are less represented and, thus, less visible in biomedical studies. This socioeconomic participation bias is a form of environmental injustice within research practice itself. METHODS: We designed, implemented and evaluated a targeted recruitment strategy to enhance the participation of socially disadvantaged pregnant women in a human biomonitoring study in Belgium. We focused on women of Turkish and Moroccan descent and developed a setup using personal buddies that enabled information transfer about study conditions in the pre-parturition period as well as support and follow-up with questionnaires in the post-parturition period. RESULTS: We identified four barriers to the participation of women with a vulnerable social and ethnic background which were related to psychosocial and situational factors. Lack of trust in researchers and no perceived study benefits were important personal barriers; the complex study design and difficult self-administered questionnaires were equally significant barriers. CONCLUSION: By investing in direct, person-to-person contact with trusted buddies and supported by practical advice about cultural and linguistic sensitivity, it was possible to increase study participation of socially disadvantaged people. Above all, this required openness and flexibility in the mind-set of researchers so that study design and procedures could be better grounded in the experiences and circumstances of underprivileged groups.

Transcriptome-wide analyses indicate mitochondrial responses to particulate air pollution exposure.

BACKGROUND: Due to their lack of repair capacity mitochondria are critical targets for environmental toxicants. We studied genes and pathways reflecting mitochondrial responses to short- and medium-term PM10 exposure. METHODS: Whole genome gene expression was measured in peripheral blood of 98 adults (49% women). We performed linear regression analyses stratified by sex and adjusted for individual and temporal characteristics to investigate alterations in gene expression induced by short-term (week before blood sampling) and medium-term (month before blood sampling) PM10 exposure. Overrepresentation analyses (ConsensusPathDB) were performed to identify enriched mitochondrial associated pathways and gene ontology sets. Thirteen Human MitoCarta genes were measured by means of quantitative real-time polymerase chain reaction (qPCR) along with mitochondrial DNA (mtDNA) content in an independent validation cohort (n = 169, 55.6% women). RESULTS: Overrepresentation analyses revealed significant pathways (p-value <0.05) related to mitochondrial genome maintenance and apoptosis for short-term exposure and to the electron transport chain (ETC) for medium-term exposure in women. For men, medium-term PM10 exposure was associated with the Tri Carbonic Acid cycle. In an independent study population, we validated several ETC genes, including UQCRH and COX7C (q-value <0.05), and some genes crucial for the maintenance of the mitochondrial genome, including LONP1 (q-value: 0.07) and POLG (q-value: 0.04) in women. CONCLUSIONS: In this exploratory study, we identified mitochondrial genes and pathways associated with particulate air pollution indicating upregulation of energy producing pathways as a potential mechanism to compensate for PM-induced mitochondrial damage.

Urinary t,t-muconic acid as a proxy-biomarker of car exhaust and neurobehavioral performance in 15-year olds.

INTRODUCTION: Traffic-related air pollution has been shown to induce neurotoxicity in rodents. Several recent epidemiological studies reported negative associations between residential outdoor air pollution and neurobehavioral performance. We investigated in a population of non-smoker adolescents the associations between the urinary concentration of trans, trans-muconic acid (t,t-MA-U), a metabolite of benzene and used as proxy-biomarker of traffic exposure, and two neurobehavioral domains, i.e. sustained attention and short-term memory. METHODS: In the framework of an environmental health surveillance study in Flanders (Belgium), we examined between 2008 and 2014 grade nine high school students (n=895). We used reaction time, number of omission errors, and number of commission errors in the Continuous Performance Test to evaluate sustained attention, and for the evaluation of short-term memory we used maximum digit span forward and backward of the Digit Span Test. We measured blood lead (PbB) to assess the independent effect of t,t-MA-U on neurobehavioral outcomes. RESULTS: This neurobehavioral examination study showed that a ten-fold increase in t,t-MA-U was associated with a 0.14 SD lower sustained attention (95% Confidence Interval: -0.26 to -0.019; p=0.02) and a 0.17 SD diminished short-term memory (95% CI: -0.31 to -0.030; p=0.02). For the same increment in t,t-MA-U, the Continuous Performance Test showed a 12.2ms higher mean reaction time (95% CI: 4.86-19.5; p=0.001) and 0.51 more numbers of errors of omission (95% CI: 0.057-0.97; p=0.028), while no significant association was found with errors of commission. For the Digit Span Tests, the maximum digit span forward was associated with a 0.20 lower number of digits (95% CI: -0.38 to -0.026; p=0.025) and maximum digit span backward with -0.15 digits (95% CI: -0.32 to 0.022; p=0.088). These associations were independent of PbB, parental education and other important covariates including gender, age, passive smoking, ethnicity, urinary creatinine, time of the day, and examination day of the week. For PbB, an independent association was only found with mean reaction time of the Continuous Performance Test (19.1ms, 95% CI: 2.43-35.8; p=0.025). CONCLUSIONS: In adolescents, a ten-fold increase in the concentration of t,t-MA-U, used as a proxy-biomarker for traffic-related exposure, was associated with a significant deficit in sustained attention and short-term memory. The public health implications of this finding cannot be overlooked as the effect-size for these neurobehavioral domains was about 40% of the effect-size of parental education.

Distinct genotype-dependent differences in transcriptome responses in humans exposed to environmental carcinogens.

Considering genetic variability in population studies focusing on the health risk assessment of exposure to environmental carcinogens may provide improved insights in individual environmental cancer risks. Therefore, the current study aims to determine the impact of genetic polymorphisms on the relationship between exposure and gene expression, by identifying exposure-dependently coregulated genes and genetic pathways. Statistical analysis based on mixed models, was performed to relate gene expression data from 134 subjects to exposure measurements of multiple carcinogens, 28 polymorphisms, age, sex and biomarkers of cancer risk. We evaluated the combined exposure to cadmium, lead, polychlorinated biphenyls, p,p'-dichlorodiphenyldichloroethylene, hexachlorobenzene and 1-OH-pyrene, and the outcome was biologically interpreted by using ConsensusPathDB, thereby focusing on carcinogenesis-related pathways. We found generic and carcinogenesis-related pathways deregulated in both sexes, but males showed a stronger transcriptome response than females. We highlighted NOTCH1, CBR1, ITGB3, ITGA4, ADI1, HES1, NCOA2 and SMARCA2 in view of their direct link with cancer development. Two of these, NOTCH1 and ITGB3, are also known to respond to PCBs and cadmium chloride exposure in rodents and to lead in humans. Subjects carrying a high number of risk alleles appear more responsive to combined carcinogen exposure with respect to the induced expression of some of these cancer-related genes, which may be indicative of increased cancer risk as a consequence of environmental factors.

Prenatal exposure to environmental contaminants and body composition at age 7-9 years.

The study aim was to investigate the association between prenatal exposure to endocrine disrupting chemicals (EDCs) and the body composition of 7 to 9 year old Flemish children. The subjects were 114 Flemish children (50% boys) that took part in the first Flemish Environment and Health Study (2002-2006). Cadmium, PCBs, dioxins, p,p'-DDE and HCB were analysed in cord blood/plasma. When the child reached 7-9 years, height, weight, waist circumference and skinfolds were measured. Significant associations between prenatal exposure to EDCs and indicators of body composition were only found in girls. After adjustment for confounders and covariates, a significant negative association was found in girls between prenatal cadmium exposure and weight, BMI and waist circumference (indicator of abdominal fat) and the sum of four skinfolds (indicator of subcutaneous fat). In contrast, a significant positive association (after adjustment for confounders/covariates) was found between prenatal p,p'-DDE exposure and waist circumference as well as waist/height ratio in girls (indicators of abdominal fat). No significant associations were found for prenatal PCBs, dioxins and HCB exposure after adjustment for confounders/covariates. This study suggests a positive association between prenatal p,p'-DDE exposure and indicators of abdominal fat and a negative association between prenatal cadmium exposure and indicators of both abdominal as well as subcutaneous fat in girls between 7 and 9 years old.

Determinants of bisphenol A and phthalate metabolites in urine of Flemish adolescents.

As part of the second Flemish Environment and Health Study (FLEHS II), bisphenol-A (BPA) and different phthalate metabolites were analyzed, for the first time, in the urine of 210 adolescents in Flanders, Belgium. All chemicals had a detection frequency above 90%. For all compounds, except the sum of DEHP, highest levels were detected during spring. Average values for the Flemish adolescents were in an agreement with concentrations found in different international studies, all confirming the ubiquity of BPA and phthalate exposure. There was a significant correlation between BPA and the different phthalate metabolites (r between 0.26 and 0.39; p<0.01). Shared sources of exposure to BPA and phthalates, such as food packaging, were suggested to be responsible for this positive correlation. Different determinants of exposure were evaluated in relation to the urinary concentrations of these chemicals. For BPA, a significant association was observed with household income class, smoking and exposure to environmental tobacco smoke. For phthalates, the following significant associations were observed: age (MBzP), educational level of the adolescent (MBzP), equivalent household income (MnBP), use of personal care products (MnBP and MBzP), wall paper in house (MnBP and MBzP) and use of local vegetables (MnBP and MBzP).

Seaward alteration of arsenic mobilization mechanisms based on fine-scale measurements in Pearl River estuarine sediments.

Identification of key As mobilization processes in estuarine sediments is challenging due to the transitional hydrodynamic condition and the technical restriction of obtaining fine-scale results. Herein, high-resolution (µm to mm) and in situ profiling of As with associated elements (Fe, Mn, and S) by the diffusive gradients in thin-film (DGT) technique were applied and coupled with pore water and solid phase analysis as well as microbial high-throughput sequencing, to ascertain the driving mechanisms of As mobilization in the sediments of Pearl River Estuary (PRE). Significant diffusion fluxes of As from sediment to water were observed, particularly in the upper estuary. With the seaward increase of salinity, the driving mechanism of As mobilization gradually shifted from microbial-induced dissimilatory Fe reduction to saltwater-induced ion exchange. Correspondingly, the dominant Fe-reducing bacteria (FeRB) in sediments changed from the genera Clostridium_sensu_stricto_1 and Bacillus to Ferrimonas and Deferribacter. The presence of dissolved sulfide in deeper sediments contributes to As removal through the formation of As-S precipitates as supported by theoretical calculations. Fine-scale findings revealed seaward changes of As mobilization mechanism in the sediments of a human-impacted estuary and may benefit the understanding of As biogeochemical behavior in estuaries worldwide.

Mercury distribution, mobilization and bioavailability in polluted sediments of Scheldt Estuary and Belgian Coastal Zone.

In this study, the vertical distribution of mercury (Hg) in estuarine and marine sediment porewaters and solid phases was assessed by conventional and passive sampling techniques in the historically polluted Scheldt Estuary and Belgian Coastal Zone (BCZ). The Diffusive Gradients in Thin-films (DGT) measured labile Hg concentrations (HgLA) were mostly lower than the porewater Hg concentrations (HgPW), and they also presented different vertical distribution patterns. Still high Hg concentrations in the sediment solid phases, comparable to the historical ones, were observed. Even though pH, redox potential and dissolved sulfide concentration could influence the Hg biogeochemical behaviour, organic matter (OM) played a key role in governing Hg mobilization from sediment solid phase to porewater and in its partitioning between porewater and solid phase over depth. In the marine sediments, where OM had a marine signature, higher labile Hg concentrations in the porewater and faster resupply from the solid phase were observed. The DGT technique showed significant potential not only for the measurement of bioavailable Hg fractions in porewater, but also for the assessment of kinetic parameters governing the release of labile Hg species from the solid phase with the assistance of the DGT Induced Fluxes in Sediments (DIFS) model.

Towards a more effective REACH legislation in protecting human health.

There is growing evidence indicating the substantial contribution of man-made products to an increase in the risk of diseases of civilization. In this article, the Belgian Scientific Registration, Evaluation, Authorization and Restriction of Chemicals (REACH) Committee gives a critical view on the working of REACH. The current regulatory framework needs to further evolve taking into account data generated using modern science and technology. There is a need for improved assessment process not only before but also after entering the market. Objectivity, transparency, and the follow-up after market access can be optimized. Additionally, no guidance documents exist for regulation of mixture effects. Further, the lengthiness before regulatory action is a big concern. Decision-making often takes several years leading to uncertainties for both producers and end users. A first proposed improvement is the implementation of independent toxicity testing, to assure objectivity, transparency, and check and improve compliance. A "no data, no market" principle could prevent access of hazardous chemicals to the market. Additionally, the introduction of novel testing could improve information on endpoints such as endocrine disrupting abilities, neurotoxicity, and immunotoxicity. An adapted regulatory framework that integrates data from different sources and comparing the outputs with estimates of exposure is required. Fast toxicology battery testing and toxicokinetic testing could improve speed of decision-making. Hereby, several improvements have been proposed that could improve the current REACH legislation.

Prenatal exposure to mixtures of per- and polyfluoroalkyl substances and organochlorines affects cognition in adolescence independent of postnatal exposure.

BACKGROUND: Studies on cognitive and neurodevelopmental outcomes have shown inconsistent results regarding the association with prenatal exposure to perfluoroalkyl substance (PFAS) and organochlorines. Assessment of mixture effects of correlated chemical exposures that persist in later life may contribute to the unbiased evaluation and understanding of dose-response associations in real-life exposures. METHODS: For a subset of the 4th Flemish Environment and Health Study (FLEHS), concentrations of four PFAS and six organochlorines were measured in respectively 99 and 153-160 cord plasma samples and 15 years later in adolescents' peripheral serum by Ultra Performance Liquid Chromatography-Tandem Mass Spectrometry (UPLC-MS/MS). Sustained and selective attention were measured at 14-15 years with the Continuous Performance Test (CPT) and Stroop Test as indicators of potential neurodevelopmental deficits. Quantile g-computation was applied to assess the joint associations between prenatal exposure to separate and combined groups of PFAS and organochlorines and performance in the CPT and Stroop Test at adolescence. Subsequently, individual effects of each chemical compound were analyzed in mixed effects models with two sets of covariates. Analytical data at birth and at the time of cognitive assessment allowed for off-setting postnatal exposure. RESULTS: In mixtures analysis, a simultaneous one-quantile increase in the natural log-transformed values of PFAS and organochlorines combined was associated with a decrease in the mean reaction time (RT) and the reaction time variability (RTV) in the CPT (ß = -15.54, 95% CI:-29.64, -1.45, and ß = -7.82, 95% CI: -14.97, -0.67 respectively) and for the mixture of PFAS alone with RT (ß = -11.94, 95% CI: -23.29, -0.60). In the single pollutant models, these results were confirmed for the association between perfluorohexanesulfonate (PFHxS) with RT (ß = -17.95, 95% CI = -33.35, -2.69) and hexachlorobenzene with RTV in the CPT (ß = -5.78, 95% CI: -10.39, -0.76). Furthermore, the participants with prenatal exposure above the limit of quantification for perfluorononanoic acid (PFNA) had a significantly shorter RT and RTV in the CPT (ß = -23.38, 95% CI: -41.55, -5.94, and ß = -9.54, 95% CI: -19.75, -0.43, respectively). CONCLUSION: Higher prenatal exposure to a PFAS mixture and a mixture of PFAS and organochlorines combined was associated with better sustained and selective attention during adolescence. The associations seemed to be driven by PFHxS and were not linked to exposure levels at the time of assessment.

Origin and partitioning of mercury in the polluted Scheldt Estuary and adjacent coastal zone.

Estuaries and coastal zones are areas with complex biogeochemical and hydrological cycles and are generally facing intense pollution due to anthropogenic activities. An emblematic example is the Scheldt Estuary which ends up in the North Sea and has been historically heavily contaminated by multiple pollutants, including mercury (Hg). We report here Hg species and their levels in surface waters of the Scheldt Estuary and the Belgian Part of North Sea (BPNS) from different sampling campaigns in February-April 2020 and 2021. Along the estuary, Hg concentration on suspended particles ([HgSPM]) progressively decreased with increasing salinity and was strongly correlated with organic matter content (%Corg) and origin (identified with δ13Corg). While [HgSPM] drives total Hg concentration in the estuary (total dissolved Hg, HgTD is only 7 ± 6 %), annual and daily variations of total Hg levels were mostly attributed to changes in SPM loads depending on river discharge and tidal regime. In the BPNS, a significant fraction of total Hg occurs as HgTD (40 ± 21 %) and the majority of this HgTD was reducible (i.e. labile Hg), meaning potentially available for microorganisms. Compared to the '90s, a significant decrease of [HgSPM] was observed in the estuary, but this was not the case for [HgTD], which can be due to (1) still significant discrete discharges from Antwerp industrial area, and (2) higher Hg partitioning towards the dissolved phase in the water column relative to the '90s. Our results highlight the important contribution of the Scheldt estuary for the Hg budget in North Sea coastal waters, as well as the need for seasonal monitoring of all Hg species.

Investigation on metal geochemical cycling in an anthropogenically impacted tidal river in Belgium.

The geochemical behavior of metals in water and sediment was investigated in the tidal section of the Zenne River in Belgium. Twelve-hour sampling campaigns were performed in October 2013 and March 2021 at the mouth of the Zenne River, under dry and rainy weather conditions respectively. Water samples were collected every hour while the passive samplers of Diffusive Gradients in Thin-films (DGT) were deployed continuously during a tidal cycle. In addition, bottom sediments were sampled at the tidal station and water samples were taken upstream and downstream of that station to identify the metal sources. The highest concentrations of Fe, Mn, Pb, Cr, Ni and Zn appear at low tide, indicating the Zenner River as a main source. However, for Co, Cd and Cu, other sources including upstream transport may explain their behavior during a tidal cycle. Fe, Pb and Cr are essentially transported in the particulate phase (<10 % dissolved) while the other metals in the dissolved phase (20 to 90 %). Rainfall and wind gust events also play an important role in trace metal distribution, increasing sediment resuspension and metal desorption. A good agreement was found between the time-averaged dissolved and DGT-labile metal concentrations with the exception of Cu and Fe, which form strong organic Cu complexes and Fe colloids respectively. The sediments of the tidal Zenne are contaminated by trace metals, thus acting as a secondary pollution source to the river. The reductive dissolution of Mn and Fe oxyhydroxides and the release of associated trace metals are the main mobilization mechanisms. Knowledge of the upstream and downstream levels in the water column, the benthic fluxes, which are based on turbulent diffusion, and the partitioning between dissolved and particulate phases allow to explain the metal concentration variations during the tidal cycle.

Human urinary arsenic species, associated exposure determinants and potential health risks assessed in the HBM4EU Aligned Studies.

The European Joint Programme HBM4EU coordinated and advanced human biomonitoring (HBM) in Europe in order to provide science-based evidence for chemical policy development and improve chemical management. Arsenic (As) was selected as a priority substance under the HBM4EU initiative for which open, policy relevant questions like the status of exposure had to be answered. Internal exposure to inorganic arsenic (iAs), measured as Toxic Relevant Arsenic (TRA) (the sum of As(III), As(V), MMA, DMA) in urine samples of teenagers differed among the sampling sites (BEA (Spain) > Riksmaten adolescents (Sweden), ESTEBAN (France) > FLEHS IV (Belgium), SLO CRP (Slovenia)) with geometric means between 3.84 and 8.47 µg/L. The ratio TRA to TRA + arsenobetaine or the ratio TRA to total arsenic varied between 0.22 and 0.49. Main exposure determinants for TRA were the consumption of rice and seafood. When all studies were combined, Pearson correlation analysis showed significant associations between all considered As species. Higher concentrations of DMA, quantitatively a major constituent of TRA, were found with increasing arsenobetaine concentrations, a marker for organic As intake, e.g. through seafood, indicating that other sources of DMA than metabolism of inorganic As exist, e.g. direct intake of DMA or via the intake of arsenosugars or -lipids. Given the lower toxicity of DMA(V) versus iAs, estimating the amount of DMA not originating from iAs, or normalizing TRA for arsenobetaine intake could be useful for estimating iAs exposure and risk. Comparing urinary TRA concentrations with formerly derived biomonitoring equivalent (BE) for non-carcinogenic effects (6.4 µg/L) clearly shows that all 95th percentile exposure values in the different studies exceeded this BE. This together with the fact that cancer risk may not be excluded even at lower iAs levels, suggests a possible health concern for the general population of Europe.

Neurobehavioral function and low-level exposure to brominated flame retardants in adolescents: a cross-sectional study.

BACKGROUND: Animal and in vitro studies demonstrated a neurotoxic potential of brominated flame retardants, a group of chemicals used in many household and commercial products to prevent fire. Although the first reports of detrimental neurobehavioral effects in rodents appeared more than ten years ago, human data are sparse. METHODS: As a part of a biomonitoring program for environmental health surveillance in Flanders, Belgium, we assessed the neurobehavioral function with the Neurobehavioral Evaluation System (NES-3), and collected blood samples in a group of high school students. Cross-sectional data on 515 adolescents (13.6-17 years of age) was available for the analysis. Multiple regression models accounting for potential confounders were used to investigate the associations between biomarkers of internal exposure to brominated flame retardants [serum levels of polybrominated diphenyl ether (PBDE) congeners 47, 99, 100, 153, 209, hexabromocyclododecane (HBCD), and tetrabromobisphenol A (TBBPA)] and cognitive performance. In addition, we investigated the association between brominated flame retardants and serum levels of FT3, FT4, and TSH. RESULTS: A two-fold increase of the sum of serum PBDE's was associated with a decrease of the number of taps with the preferred-hand in the Finger Tapping test by 5.31 (95% CI: 0.56 to 10.05, p = 0.029). The effects of the individual PBDE congeners on the motor speed were consistent. Serum levels above the level of quantification were associated with an average decrease of FT3 level by 0.18 pg/mL (95% CI: 0.03 to 0.34, p = 0.020) for PBDE-99 and by 0.15 pg/mL (95% CI: 0.004 to 0.29, p = 0.045) for PBDE-100, compared with concentrations below the level of quantification. PBDE-47 level above the level of quantification was associated with an average increase of TSH levels by 10.1% (95% CI: 0.8% to 20.2%, p = 0.033), compared with concentrations below the level of quantification. We did not observe effects of PBDE's on neurobehavioral domains other than the motor function. HBCD and TBBPA did not show consistent associations with performance in the neurobehavioral tests. CONCLUSIONS: This study is one of few studies and so far the largest one investigating the neurobehavioral effects of brominated flame retardants in humans. Consistently with experimental animal data, PBDE exposure was associated with changes in the motor function and the serum levels of the thyroid hormones.