Development and application of diffusive gradients in thin films (DGT) for in situ monitoring of emerging contaminants in aquatic environments

There has been increasing concern about the environmental release and dispersal of emerging contaminants (ECs) and their potential risks to human and ecosystem health. The in situ passive sampling tool, diffusive gradients in thin films (DGT), has been developed as a promising alternative to traditional grab sampling in environmental research of ECs, such as pharmaceuticals, endocrine disrupting chemicals (EDCs), and some types of flame retardants. This thesis explored the role of DGT in determining ECs and understanding their sources, fate and impact in aquatic environments. The property range of organic compounds which can be routinely sampled with the present design of DGT device (PTFE membrane filter, agarose gel diffusion layer, and HLB binding layer) was investigated. Sorption experiments and DGT deployment with 9 model chemicals [organophosphate esters (OPEs) with a wide range of log KOW (0.8−9.5), molecular weight (182−435 Da)] and different functional groups showed compounds with high hydrophobicity and aromatic rings are prone to retention on membrane filters, which slows the transport of chemical to the binding resin of the sampler. The limitation of the current DGT device for some trace organics is adsorption in the diffusion layer, mainly in the membrane filter. However, it is possible to extend the DGT technique for a wider range of chemicals, for example, by replacing the current DGT membrane filter with a new type of membrane filter which does not interact with target analytes. The potential effects of biofouling and post-deployment sample storage on DGT measurements were systematically investigated. Biofilms generated at the surface of DGT devices (8-day and 15-day) in summer and winter from a typical urban wastewater treatment plant were tested with 13 ECs; this study showed no effect on DGT measurements for most compounds. Four storage methods up to 2-month were evaluated; this study showed that intact samplers can be kept for up to 2-months at refrigerated temperature (4 °C) without significant effect on the measured concentration of the compounds, but if no refrigerators were available, keeping binding gels in elution solvent at room temperature would achieve comparable results. DGT and grab sampling were used together to study sources and environmental fate of ECs in a dynamic river catchment, the River Thames in the United Kingdom. For chemicals that were relatively stable in the rivers, DGT and grab sampling provided equally good representativeness. For chemicals that showed high dynamic variation in water bodies, the DGT provided a better integral of loadings and exposure than grab sampling. It took a similar time to set up and collect the DGT passive sampling system and to collect grab samples. However, for later storage and sample treatment, DGT is much more space-, cost- and time-effective. DGT, for the first time, was combined with a water quality model (LF2000-WQX) to study sources and environmental fate of ECs, taking trimethoprim as a case study. The model needs the following key input information for the EC: per capita emission, WWTPs and in-river removal rates. DGT measurements in the River Thames network were used to assess the ability of the model to predict reasonable concentrations. This study showed that LF2000-WQX is suitable for predicting point-source ECs; predicted concentrations agreed very well with DGT measurements in winter and the model performance can be improved by improving in-river removal rate, i.e., using different in-river removal rates considering local environmental conditions such as DOC in different river reaches. The work in this thesis is a step forward to understand the current performance of the DGT sampler and to explore its role in studying organic contaminants. It has shown that DGT is an effective tool for studying environmental issues of trace organic contaminants

Investigating Potential Limitations of Current Diffusive Gradients in Thin Films (DGT) Samplers for Measuring Organic Chemicals

The diffusive gradients in thin films (DGT) passive sampler has emerged as a powerful tool for measuring in situ concentrations of organic contaminants in waters with appropriate spatial and temporal resolution at low cost. This study addresses the property range of compounds which can be routinely sampled with the present design of DGT device. Sorption experiments and DGT deployment with 9 model chemicals [organophosphate esters with a wide range of log KOW (0.8–9.5), molecular weight (182–435 Da)] and different functional groups showed compounds with high hydrophobicity and aromatic rings are prone to retention on membrane filters, which slows the supply of chemical to the binding resin of the sampler. The current DGT sampler (PTFE membrane filter, agarose gel diffusion layer, and HLB binding layer) is potentially reliable for measuring hydrophilic [log KOW (0.8–2.6)] and nonaromatic-ring chemicals. For compounds of higher values of KOW or with aromatic rings, knowledge of the lag phase is necessary to optimize sampling times to avoid biasing subsequent laboratory analyses. A standard procedure is used to measure lag times (from minutes to days) by exposing a series of DGT samplers in waters until linear mass accumulation in samplers is achieved. We discuss how monitoring of a wide array of organic contaminants across classes should be possible in the future with a range of validated new DGT devices, optimized for the choice of membrane filter, diffusive material, and binding resin

Random forest model based fine scale spatiotemporal O₃ trends in the Beijing-Tianjin-Hebei region in China, 2010 to 2017

Ambient ozone (O₃) concentrations have shown an upward trend in China and its health hazards have also been recognized in recent years. High-resolution exposure data based on statistical models are needed. Our study aimed to build high-performance random forest (RF) models based on training data from 2013 to 2017 in the Beijing-Tianjin-Hebei (BTH) region in China at a 0.01 ° × 0.01 ° resolution, and estimated daily maximum 8h average O₃ (O₃-8hmax) concentration, daily average O₃ (O₃-mean) concentration, and daily maximum 1h O3 (O3-1hmax) concentration from 2010 to 2017. Model features included meteorological variables, chemical transport model output variables, geographic variables, and population data. The test-R² of sample-based O₃-8hmax, O₃-mean and O₃-1hmax models were all greater than 0.80, while the R² of site-based and date-based model were 0.68–0.87. From 2010 to 2017, O₃-8hmax, O₃-mean, and O₃-1hmax concentrations in the BTH region increased by 4.18 μg/m³, 0.11 μg/m³, and 4.71 μg/m³, especially in more developed regions. Due to the influence of weather conditions, which showed high contribution to the model, the long-term spatial distribution of O₃ concentrations indicated a similar pattern as altitude, where high concentration levels were distributed in regions with higher altitude

Optimization of a static headspace GC-MS method and its application in metabolic fingerprinting of the leaf volatiles of 42 citrus cultivars

Citrus leaves, which are a rich source of plant volatiles, have the beneficial attributes of rapid growth, large biomass, and availability throughout the year. Establishing the leaf volatile profiles of different citrus genotypes would make a valuable contribution to citrus species identification and chemotaxonomic studies. In this study, we developed an efficient and convenient static headspace (HS) sampling technique combined with gas chromatography-mass spectrometry (GC-MS) analysis and optimized the extraction conditions (a 15-min incubation at 100 ˚C without the addition of salt). Using a large set of 42 citrus cultivars, we validated the applicability of the optimized HS-GC-MS system in determining leaf volatile profiles. A total of 83 volatile metabolites, including monoterpene hydrocarbons, alcohols, sesquiterpene hydrocarbons, aldehydes, monoterpenoids, esters, and ketones were identified and quantified. Multivariate statistical analysis and hierarchical clustering revealed that mandarin (Citrus reticulata Blanco) and orange (Citrus sinensis L. Osbeck) groups exhibited notably differential volatile profiles, and that the mandarin group cultivars were characterized by the complex volatile profiles, thereby indicating the complex nature and diversity of these mandarin cultivars. We also identified those volatile compounds deemed to be the most useful in discriminating amongst citrus cultivars. This method developed in this study provides a rapid, simple, and reliable approach for the extraction and identification of citrus leaf volatile organic compound, and based on this methodology, we propose a leaf volatile profile-based classification model for citrus

Long-term exposure to ambient fine particulate matter and fasting blood glucose level in a Chinese elderly cohort

Fasting blood glucose level is the primary indicator for the diagnosis of diabetes. We aim to conduct a longitudinal study on the association between long-term fine particulate matter (PM2.5) exposure and fasting blood glucose concentrations. We recruited and followed up 1449 participants older than 65 years of age in 2009, 2012, 2014, and 2017 in eight counties in China. Fasting blood glucose was repeatedly measured 3697 times in total among these participants. Data on annual ground-level PM2.5 concentrations with a 0.01° spatial resolution from 2005 to 2016 were used to assess exposures. An increase of 10 μg/m3 in 3-year average exposure to PM2.5 was associated with an increase of 0.146 mmol/L (95% confidence interval [CI]: 0.045, 0.248) in fasting blood glucose in all participants. The association was more pronounced among the subgroup with diabetes compared to the subgroup without diabetes (P < .05). In conclusion, Long-term PM2.5 exposure was associated with an increase in fasting blood glucose levels among elderly people. Elderly individuals with diabetes are particularly vulnerable to high level exposures of PM2.5. SUMMARY: Long-term PM2.5 exposure was associated with an increase in fasting blood glucose levels among elderly people. Elderly individuals with diabetes are particularly vulnerable to high level exposures of PM2.5. Keywords: elderly; fasting blood glucose; fine particulate matter; long-term exposur

A Random Forest Model for Daily PM2.5 Personal Exposure Assessment for a Chinese Cohort

Errors in air pollution exposure assessment are often considered as a major limitation in epidemiological studies. However, it is difficult to obtain accurate personal level exposure on cohort populations due to the often prohibitive expense. Personal exposure estimation models are used in lieu of direct personal exposure measures but still suffer from issues of availability and accuracy. We aim to establish a personal PM2.5 exposure assessment model for a cohort population and assess its performance by applying our model on cohort subjects. We analyzed data from representative sites selected from the subclinical outcomes of polluted air in China (SCOPA-China) cohort study and established a random forest model for estimating daily PM2.5 personal exposure. We also applied the model among subjects recruited in the project mentioned above within the same area and study period to estimate the reliability of the model. The established model showed a good fit with an R2 of 0.81. The model application results showed similar patterns with empirically measured data. Our pilot study provided a validated and feasible modeling approach for assessing daily personal PM2.5 exposure for large cohort populations. The promising model framework can improve PM2.5 exposure assessment accuracy for future environmental health studies of large populations

Novel Method for in Situ Monitoring of Organophosphorus Flame Retardants in Waters

Widespread use of organophosphorus flame retardants (OPFRs) and their ubiquity in water results in the need for a robust and reliable monitoring technique to better understand their fate and environmental impact. In situ passive sampling using the diffusive gradients in thin-films (DGT) technique provides time-integrated data and is developed for measuring OPFRs here. Ultrasonic extraction of binding gels in methanol provided reliable recoveries for all tested OPFRs. Diffusion coefficients of TCEP, TCPP, TDCPP, TPrP, TBP, and TBEP in the agarose diffusive gel (25 °C) were obtained. The capacity of an HLB binding gel for OPFRs was >115 μg per disc, and the binding performance did not deteriorate with time up to 131 days. DGT performance is independent of typical environmental ranges of pH (3.12-9.71), ionic strength (0.1-500 mmol L -1 ), and dissolved organic matter (0-20 mg L -1 ), and also of diffusive layer thickness (0.64-2.14 mm) and deployment time (3-168 h). Negligible competition effects between OPFRs was found. DGT-measured concentrations of OPFRs in a wastewater treatment plant (WWTP) effluent (12-16 days) were comparable to those obtained by grab sampling, further verifying DGT's reliability for measuring OPFRs in waters

Critical Curves for A Coupled System of Fast Diffusive Newtonian Filtration Equations

This paper deals with the large time behavior of solutions to the fast diffusive Newtonian filtration equations coupled via the nonlinear boundary sources. The result of Fujita type is obtained by constructing various kinds of upper and lower solutions. Particularly, we show that the critical global existence curve and the critical Fujita curve are the same for the multi-dimensional system, which is quite different from the known results for corresponding one-dimensional problem. 10.1017/S000497271200038

Comparative studies of the response of larch and birch seedlings from two origins to water deficit

Abstract Background Early developmental stages of plants are expected to be a major bottleneck to recruitment. Information on the response of seedling to anticipated water availability is urgently needed in regions where tree seedlings may experience more frequent water deficits. In this paper, we focused on the influence of water deficit on different species (larch vs. birch) and origins (xeric vs. mesic). Methods Prince Rupprecht’s larch (Larix gmelinii var. principis-rupprechtii (Mayr) Pilg.) and white birch (Betula platyphylla Sukaczev) from northern China were selected to represent the xeric origin. Eastern larch (Larix laricina (Du Roi) K. Koch) and paper birch (Betula papyrifera Marshall) from eastern Canada were selected to represent the mesic origin. For each species, half of seedlings were assigned to a well-watered treatment (WW, 75% water holding capacity (WHC) and the other half to a low-watered treatment (LW, 35% WHC). After 20 weeks of treatment, we collected data on morphological indexes of shoot height, root collar diameter, total leaf area and total root area; measured photosynthetic rate (A sat), transpiration rate (E), photosynthetic water-use efficiency (WUE) and apparent chlorophyll concentration (Chl); harvested seedlings and measured biomass allocation of leaf, stem and root. Results We found that reduced photosynthetic rate, transpiration rate and increased water-use efficiency were physiological responses of the four species to drought, and the responses varied among the species. All larch seedlings appeared no leaf shedding, survived through the drought treatment and showed a longer duration and high tolerance to drought. In low-watered conditions, survival rate, biomass, shoot height, root collar diameter, total leaf area, total root area and chlorophyll concentration of birch seedlings were significantly decreased. The response of seedlings to water deficits also differed according to the seed origins. Xeric origin of Prince Rupprecht’s larch was more affected than mesic origin of eastern larch, mainly because Prince Rupprecht’s larch originated in a narrower range of mountainous regions, resulting in lower adaptation of this species to water deficits, whereas eastern larch was distributed widely along coastal regions, contributing to higher phenotypic plasticity to variable soil conditions. Similarly, higher plasticity of paper birch may be responsible for its better performance in the low-watered treatment than white birch. Conclusions Larch seedlings were less sensitive to water deficit than birch seedlings. Larch seedlings were characteristics of a conservative water-use strategy, whereas birch seedlings responded with a profligate water-use strategy. Plasticity or adaptation of seedlings outweighs the seed origins in determining their drought responses