DEVELOPMENT OF A PASSIVE SAMPLING STRATEGY FOR MONITORING OF ORGANIC POLLUTANTS AND THEIR IMPACTS IN AQUATIC SYSTEMS

Anthropogenic organic compounds are constantly released into the freshwater environment, demanding a better knowledge of the chemical status of our Earth’s surface waters and sediments. Conventional water quality monitoring only provides “snapshots” of information in time and space. Passive sampling has been proposed as an in-situ time integrative sampling technique to offer better monitoring of the chemical status of our environment. In this thesis, the diffusive gradient in thin films (DGT) technique is introduced because the DGT passive sampler allows for assessing time-weighted average concentrations of various organic contaminants with minimal hydrodynamic influence. This thesis first reviewed the available literature on the potential limitations of DGT samplers. This review summarized the current configurations of the DGT samplers for organics, storage stability of analytes in DGT samplers, kinetic desorption of organic contaminants in sediments and at the interface of water and sediment, and combinations of DGT samplers and bioassays. This review identified two critical gaps: (i) there are only limited studies for desorption kinetics of organic contaminants, especially for hydrophilic to moderately hydrophobic compounds, at the interface of water and sediment; and (ii) there are no studies so far for predicting bioavailability in aquatic biota by in situ DGT technique. Based on these gaps, the objectives of this thesis are to (1) develop DGT samplers that can be applied for the monitoring of organic contaminants across the water-sediment interface in the field with an efficient time; (2) describe the kinetic equilibrium of compounds between sediments and overlying water using a dynamic model; and (3) use DGT-derived concentrations to predict bioaccumulation of organic contaminants by invertebrates through in-situ and laboratory-controlled experiments. First, this research conducted a 30-day laboratory simulation experiment, where DGT samplers were tested for adsorption performance and then were deployed in sediments spiked with nine model antipsychotic compounds, i.e., amitriptyline, bupropion, carbamazepine, citalopram, clozapine, duloxetine, fluoxetine, lamotrigine, and venlafaxine. A dynamic model, DGT-induced fluxes in soils and sediments (DIFS), was used to reveal the dynamic resupply processes of organic contaminants from the solid phase to the aqueous phase. This experiment showed that antipsychotics could be continuously depleted from the sediment aqueous phase and captured by the DGT binding gel. The highest resupply ability was observed for lamotrigine and carbamazepine. The adsorption process took control of the spiked sediments under laboratory conditions during incubation time. Second, DGT devices were in situ deployed at the sedimentwater interface and in sediments, downstream of the Saskatoon Wastewater Treatment Plant, on the South Saskatchewan River. Apart from the DIFS model, a dynamic fraction transfer model was also developed to consider the real status of organic contaminants in sediments during field deployment. The field experiment revealed that positive fluxes of antipsychotics were found from sediment to overlying water and the desorption process was dominant within a 15 cm depth of sediments. The results from the three-fraction transfer model can be auxiliary to further explain dynamic desorption kinetics calculated by the DIFS model. Third, another 30-day laboratory-controlled experiment, where the benthic oligochaete Lumbriculus variegatus was exposed to freshwater sediments spiked with nine antipsychotic compounds, and DGT samplers were synchronously deployed, was conducted to develop a numerical model for passive bioaccumulation using DGT-derived concentrations. Passive uptake of antipsychotic compounds by the benthic oligochaetes could be successfully modeled by inputting the diffusion-induced concentrations measured by DGT samplers in water and sediments. Fast desorption to the labile fraction of analytes in a short response time accounted for the process of uptake by oligochaetes. Fourth, DGT devices were in situ deployed at a wastewater-impacted site for 20 days to develop a predictive bioaccumulation model by comparison between the modeled concentration using DGT-derived concentrations in water and those in resident benthic invertebrates, specifically crayfish (Faxonius virilis). The results showed that targeted antipsychotics could be constantly resupplied to the interstitial water and absorbed by crayfish. DGT techniques with a steady-state uptake model in the current study for crayfish could provide a close prediction compared to the measured concentrations for some compounds while it still needs further developments to predict different organic compounds. This thesis has the potential to transform the DGT technique to efficiently monitor emerging contaminants and evaluate their bioavailability in the aquatic cycle, and help protect the safety of our water resources for human and environmental health

A holistic approach to understanding the desorption of phosphorus in soils

The mobility and resupply of inorganic phosphorus (P) from the solid phase were studied in 32 soils from the UK. The combined use of diffusive gradients in thin films (DGT), diffusive equilibration in thin films (DET) and the “DGT-induced fluxes in sediments” model (DIFS) were adapted to explore the basic principles of solid-to-solution P desorption kinetics in previously unattainable detail. On average across soil types, the response time (Tc) was 3.6 h, the desorption rate constant (k–1) was 0.0046 h–1, and the desorption rate was 4.71 nmol l–1 s–1. While the relative DGT-induced inorganic P flux responses in the first hour is mainly a function of soil water retention and % Corg, at longer times it is a function of the P resupply from the soil solid phase. Desorption rates and resupply from solid phase were fundamentally influenced by P status as reflected by their high correlation with P concentration in FeO strips, Olsen, NaOH–EDTA and water extracts. Soil pH and particle size distribution showed no significant correlation with the evaluated mobility and resupply parameters. The DGT and DET techniques, along with the DIFS model, were considered accurate and practical tools for studying parameters related to soil P desorption kinetics

A diffusive gradients in thin-films technique for the assessment of bisphenols desorption from soils

Abstract Desorption/adsorption of bisphenols (BPs) in soils affects their mobility and availability. However, the kinetics of these processes have not been well studied, due to the lack of appropriate means of measurement. Diffusive gradients in thin-films (DGT) technique can assess kinetic processes in soils and have recently been developed for measuring three BPs (BPA, BPB and BPF). DGT was deployed for 2.5 h to 20 d in five soils with different soil properties. Non-linear increase in mass accumulation by DGT with time indicated poor resupply of BPs from soil solid to solution phase. By fitting the data with DIFS (DGT-induced fluxes in soils) model, values for the labile partition coefficient (Kdl), response time (tc) and rates of exchange (k1 and k-1) of BPs between soil solid and solution phases were obtained. The derived values of Kdl showed that most of the BPs in the soil could participate in labile exchange. Average response times of 1–2 h implied that the supply of BPs to DGT was limited by their desorption rate. Soils with more binding sites (higher DOM, CEC and Fe oxides) could resupply BPs more quickly, highlighting the danger of just considering partition effects

The Comparison of Olsen, DMT-HFO and DGT Methods for Assessment of Plant Available Phosphorus in Soils

Phosphorus (P) is one of the most important limiting nutrients for crop production in the world soils. Excessive and deficiencies of P in calcareous soils has been reported. Several methods can be used to recognize soil bioavailable phosphorus. Soil P tests involve chemical extraction and ion-sink extractants. The diffusive gradient in thin-films (DGT) is a new technique for measuring available soil phosphorus. This technique attempts to simulate physico-chemical processes influencing the uptake of solutes by plant roots. Also, the dialysis membrane tubes filled with hydrous ferric oxide solution (DMT-HFO) has recently been used to assess P desorption over long-term laboratory studies. The DMT-HFO method acts like the DGT method. Both systems are based on Fick’s law and try to imitate physicochemical uptake of P by plant roots in soils. The aim of this research was to use Fick’s law in the interpretation of DMT measurements and compare it with the Olsen and DGT methods for assessment of corn available phosphorus in some calcareous soils. For this purpose, the diffusion coefficients of P in the DMT membrane and DGT gel were calculated. The DMT-HFOs were located in soil suspensions at 24, 72, 240, and 500 hours and the concentration of DMT-HFO (CDMT-HFO) for P in the mentioned times were compared with those of Olsen and DGT methods on assessing of corn P uptake. Corn (SC 704) were grown in a greenhouse on ten different calcareous soils. Based on the results, the diffusion coefficient of P (H2PO4-) in DMT (5.54*10-8 cm2.s-1)was lower than that of DGT gel (5.8*10-6 cm2.s-1). The linear correlation coefficient(r) between CDMT-HFO and corn P content was increased by the time (24- 500 hours). Based on the r2 values, the lowest and highest correlations were related to CDMT-HFO in 24 hours (r2=0.22, p<0.05) and 500 hours (r2=0.9, p<0.05), respectively. The DMT-HFO provides a more precise correlation with P uptake by corn (r2=0.9 in 500 hours) than Olsen P (r2=0.86) and CE (DGT) (r2=0.76). In roots, the best correlation between CDMT-HFO and corn P uptake was obtained in 250 hours. However, in 24 to 250 hours, the statistical correlations based on r2 values were very similar.

Small-scale heterogeneity in sediments:experimental and modelling investigations

This thesis consists of several studies relating to small-scale heterogeneity in sediments. The principal aim was to further our understanding of processes occurring at microniches. The individual studies consist of: 1) a critical review of previous studies of microniches that used probes with high spatial resolution and modelling approaches; 2) an experimental study of analysis of oxyanions in sediment at high resolution that applied a newly developed preparation method for a combined AgI/FeOOH binding phase, to investigating processes occurring at a sulphidic microniche within a freshwater sediment; 3) analysis of the relationship between trace metal (cobalt) and iron and manganese in a marine sediment using DGT, although this is not directly related to microniches, these data are useful in modelling the release of microniche trace metal from authigenic oxides; 4) the development and application of a three-dimensional diagenetic model to investigate conceptually the geochemical behaviour of microniches under different conditions, and to interpret modelled observations in terms of data from the literature and known trace element geochemistry. The key results/conclusions from both the laboratory and modelling studies are: 1) for a freshwater sediment, depletions in anions (of P, V, As) at a microniche of elevated sulphide were observed and the behaviour of phosphate at this niche was attributed to uptake associated with elevated activity of sulphate reducing bacteria; 2) modelled scenarios, with varying microniche properties, were shown to be relevant to experimental observations reported in the literature. The preferential deposition of FeS at the edge of microniches (with lifetimes of 2.5-5 days), forming ‘crustal’ deposits was demonstrated. The modelled data indicated that microniches may be significant in terms of the formation of some trace element sulphides. This thesis also contains an assessment of the significance of microniche processes and a discussion of priorities for future work

DGT estimates cadmium accumulation in wheat and potato from phosphate fertilizer applications

Cadmium is a common impurity in phosphatic fertilizers and may contribute to soil Cd accumulation. Changes in total and bioavailable Cd burdens to agricultural soils and the potential for plant Cd accumulation resulting from fertilizer input was investigated. Three year field studies were conducted using three dose levels of cadmium-rich, commercial, phosphate fertilizers applied at four agricultural sites. Labile Cd concentrations, measured using the passive sampling device Diffusive Gradients in Thin Films (CdDGT), increased with increasing fertilizer application rates. Cd also accumulated in the edible portion of wheat and potato crops grown at the sites, and showed strong positive dose response with fertilizer treatment. Regression models were calculated for each site, year, and for individual crops. Model comparisons indicated that soil physical and chemical parameters in addition to soil Cd fractions, were important determinants of CdDGT. Significant factors contributing to CdDGT concentrations were Cd from fertilizer input (Cdₑᵣₜᵢₗᵢₑᵣ), pH, cation exchange capacity (CEC), and total recoverable Cd (Cdₜₒₜₐₗ). Important factors used to determine Cd concentrations in wheat grain (Cdₕₑₐₜ) and in potato (Cdₚₒₜₐₜₒ) were as follows: Cdₕₑₐₜ:Cdₑᵣₜᵢₗᵢₑᵣ, and CdDGT; and Cdₚₒₜₐₜₒ:Cdₑᵣₜᵢₗᵢₑᵣ, CdDGT, % O.M. The effective concentration, CE, calculated from DGT did not correlate well with Cdₕₑₐₜ or with Cdₚₒₜₐₜₒ. Direct measurements of CdDGT correlated better with Cd found in edible plant tissue. The modeling approach presented in this study helps to estimate Cd accumulation in plant tissue over multiple years and in distinct agricultural soil systems. Keyword

Assessing the bioavailability of the radionuclides technetium-99, selenium-79 and uranium-238 in contaminated soils using the diffusive gradients in thin-films (DGT) technique

The increasing global inventory of 99Tc, 79Se and 238U as components of nuclear waste, coupled with the legacy of contaminated sites, means that increasing attention has been centred on understanding the environmental behaviour of these radionuclides. Over the last 15 years, the technique of diffusive gradients in thin-films (DGT) has emerged as a promising tool for assessing bioavailability based on its demonstrated ability to successfully predict plant uptake for a range of metals and metalloids in soil (Zhang and Davison, 2015). It is therefore utilised in this thesis to address a substantial knowledge gap regarding the bioavailability and aging of Tc, Se and U in soils. Initially, the performance of a Chelex-ferrihydrite mixed binding layer (MBL) DGT for the novel simultaneous measurement of Se and U was investigated to validate its suitability for subsequent use. An assessment of the availability and aging of all three elements was centred on an 18-month laboratory incubation of a suite of spiked soils, throughout which time a series of DGT deployments were made. Lastly, the ability of DGT to predict ryegrass uptake of Tc across a range of soil types was investigated. The experimental work presented in this thesis reveals that the MBL DGT is an acceptable method for determining labile Se and U in soil, although at higher pH (> 7) and with increasing concentrations of HCO3 - , uptake of both elements was impaired. The availability and aging of Se and Tc within soil is governed by soil organic carbon, in addition to the Al and Fe oxide content for Se. Quantitatively, the aging of Tc could be best described by a pseudo-secondorder model, yet a natural exponential function provided the best fit for Se. U was found to be particularly resilient to aging within soils exposed to a fluctuating wet-dry moisture regime, where changes in pH were hypothesised to alter the solubility of key U binding phases, namely Fe and Al oxides and dissolved carbonate ligands. DGT was unable to reliably predict the extent of uptake of Tc within ryegrass across a range of soil types, although in situ deployments whilst the ryegrass was actively growing did yield encouraging results. Remedial efforts to reduce the soil-to-plant radionuclide transfer following a contamination event should look to utilise the complexing capacity of Corg in the case of Tc and Se, or prevent the exposure of the soil to wetting/drying events in the case of U. Where possible, DGT measurements of bioavailability within Tc-contaminated soils should be made in situ, although in a field setting this is logistically challenging and introduces significant uncertainties to the data. In practice, to reliably ascertain the bioavailability of Tc, it would seem that the best approach is to directly measure the accumulated activity within the plant

Metals Transport in the System Soil/Plant. Comparison of the Active and Passive Sampling Method (The Diffusive Gradients in Thin Films Technique)

Předkládaná dizertační práce se zabývá porovnáním příjmu mědi ředkví setou (Raphanus sativus L.) s množstvím mědi stanoveným technikou DGT v půdě přirozené a obohacené solemi mědi a s množstvím mědi stanoveným ve výluzích běžně používaných extrakčních činidel (HNO3, NaNO3, deionizovaná voda) a půdním roztoku. Rostliny byly pěstovány v půdě přirozené i obohacené. Obsah mědi byl stanoven v celé ředkvi i jednotlivých částech rostliny po rozložení v mineralizátoru APION analytickou metodou ET – AAS. Největší množství mědi ukládala rostlina ve své podzemní části, především v kořenech a slupce kořenové bulvy, což svědčí o vazbě mědi v buněčných stěnách kořenového systému. Rostlinami přijaté množství mědi nepřekračuje ani na obohacených půdách povolené hygienické limity a konzumace ředkví není zdravotně závadná. Celková množství mědi přijatá rostlinami korelovala s obsahem mědi v půdách stanoveným z výluhů všech použitých extrakčních činidel a půdního roztoku. Výluh 2M HNO3 potvrdil, že celkové množství přidané mědi v obohacených půdách zůstalo stabilní po dobu všech vegetačních experimentů. Experimenty s DGT ukázaly, že obohacené půdy jsou schopny úbytek měďnatých iontů vázaných jednotkou DGT doplňovat uvolňováním z pevné fáze do půdního roztoku stálou rychlostí a jejich koncentrace je v blízkosti vzorkovací jednotky DGT konstantní, zatímco uvolňování mědi z půdy neobohacené po 24 hodinách klesá. Měď přidaná do půdy ve formě měďnaté soli se tak i po měsíční době ekvilibrace nachází v půdě i v jiných formách než měď přirozeně se v půdě vyskytující. Obsah mědi v půdách stanovený DGT se lišil od obsahu stanoveného extrakcí dusičnanem sodným. Lze usoudit, že o dva řády nižší koncentrace mědi zjištěná pomocí DGT techniky lépe odpovídá skutečnému biodostupnému podílu mědi v půdě. Vysoké hodnoty korelačních koeficientů (R2 > 0,9) byly nalezeny mezi obsahem mědi v rostlinách ředkve seté a obsahem mědi v půdě stanovené z analýzy půdního roztoku a mezi obsahem mědi v rostlinách ředkve a obsahem mědi v půdě změřené technikou DGT. Hodnoty obsahu mědi v půdě zjištěné pomocí půdního roztoku byly třikrát vyšší než ty, změřené technikou DGT. Půdní roztok tedy obsahuje i specie mědi, které nejsou měřitelné DGT a dle předpokladu i rostlině dostupné. Koncentrace mědi stanovená DGT technikou je v porovnání s výsledky získanými extrakčními postupy a analýzou půdního roztoku blíže ke skutečnému obsahu biodostupných forem kovů přítomných v půdě a prokazatelně koreluje s obsahem mědi v těle rostliny ředkve seté. Je proto možno techniku DGT doporučit jako techniku pro stanovení biodostupných forem mědi v půdách.The doctoral thesis deals with comparison between copper uptake by radish (Raphanus sativus L.) and concentration of copper measured by a DGT-device and concentration of copper obtained by extraction with generally used extraction agents (HNO3, NaNO3 and water). Plants were cultivated in pot experiments on a tested non-treated and gradually spiked soil. The amount of copper was determined in various part of radish (whole plant, above- and below-ground part) after mineralization in the APION mineralizer by ET – AAS. The highest concentration was in belowground part, especially in root tissues and sheel of root bulb. It confirms copper is associated with cell walls. The amount of copper taken by radish up does not pass beyond sanitary standards not even in spiked soils and consummation of radish is not unhealthy. Good correlations were found between copper concentration in radish and the amount of copper extracted with HNO3, NaNO3 and water and the amount found in soil solution. Results of extraction with HNO3 confirmed the amount of copper was stable in spiked soils during the pot experiments. The DGT experiments have shown that the rate of resupply from the solid phase to soil solution is constant during the deployment time. Whereas the release of copper decreases after 24 hours in natural soil. Copper added to soil in form of cupric ions is present in the different form after one month-equilibration than copper present in unspiked soils. The results obtained by DGT measurements were approximately up to two orders of magnitude lower than copper concentration obtained by leaching with sodium nitrate. The extraction with sodium nitrate does not provide true reflection of metal availability to plant root system and soil microorganism. High values of correlation coefficients (R2 > 0,9) were found between concentration of copper in radish plant and the concentration of copper in soil solution measured by DGT technique. Concentration of copper in soil solution was three times higher than concentration measured by DGT technique. Soil solution contains species of copper that are not measured by DGT technique and available to plants. Concentration of metals obtained by DGT measurements is more closely to real concentration of bioavailable forms of metal in soil. Therefore it is possible to recommend the DGT technique as a technique for determination of bioavailable forms of copper in soils.

Lessons from a large scale deployment of DGT in the Seine basin

Diffusive Gradient in Thin film (DGT) is a speciation technique now commonly used in the scientific literature to assess metallic contamination in water. However applications usually take place in a same watercourse or in neighbouring sites. We propose here to present the first results of a large scale deployment of DGTs. The main objective of the project, which is supported by the French water agency of the Seine-Normandie basin, is to evaluate the potential of passive samplers as monitoring tools. DGT devices were deployed in 45 sites, on 30 locations in the entire Seine river basin. The sampling area was 500 km long and 200 km wide around Paris. The total sampling period lasted over the whole 2009 year. Restricted gels of 0.78 were used to measure labile Cd, Cr, Co, Cu, Mn, Ni, Pb and Zn. In parallel, raw and filtered water samples were collected to measure total and dissolved metals. General physico-chemical parameters were also measured. The whole set of measurements constitute a rich dataset including large and small rivers, and reference as well as impacted sites. The results first allow us to draw a map of total, dissolved and labile metal concentrations, representing the spatial variability of metal contamination in the Seine basin. Moreover, considering the temporal variability, different behaviours, depending on the metal, can be identified. The large scale deployment of DGT in the Seine river basin was successful: all the samples have been interpreted and are exploitable, whereas the dissolved metal samples are sometimes under the detection limit. We have then built a representative data set on the water contamination in labile metal of an urban impacted basin. The results are also interpreted as labile percentage, showing the operationally possible values of lability in contrasted environmental conditions. A first approach of the factors influencing the lability highlights the significance of the nature of the organic matter to interpret the lability of the metals