Dissertation for Degree of Ph. Application of diffusive gradient in thin films technique for mercury bioavailability prediction in soil Nguyen Huu Viet School of Earth Sciences and Environmental Engineering Gwangju Institute of Science and Technology (GIST) 2021 Application of diffusive gradient in thin films technique for mercury bioavailability prediction in soil Advisor: Professor Seunghee Han By Nguyen Huu Viet School of Earth Sciences and Environmental Engineering Gwangju Institute of Science and Technology (GIST) A thesis submitted to the faculty of Gwangju Institute of Science and Technology in partial fulfillment of the requirement for the degree of Doctor of Philosophy in the School of Earth Sciences and Environmental Engineering Gwangju, Republic of Korea Approved by Professor Seunghee Han Committee Chair Application of diffusive gradient in thin films technique for mercury bioavailability prediction in soil Nguyen Huu Viet Accepted in partial fulfillment of the requirement of the degree of Doctor of Philosophy May 31st, 2021 Dissertation advisor _______________ Prof. Seunghee Han Committee member________________ Prof. Kyoung-Woong Kim Committee member________________ Prof.
Chang-Keun Kang Committee member________________ Prof. Yongseok Hong Committee member________________ Prof. Nguyen Phuoc Dan PhD./EN Nguyen Huu Viet. Application of diffusive gradient in thin films 20144049 technique for mercury bioavailability prediction in soil.
School of Earth Sciences and Environmental Engineering. Advisor: Seunghee Han (한승희). Abstract The technique of diffusive gradients in thin films (DGT) has been shown to be a promising tool to assess metal bioavailability in soils under laboratory conditions. however, its applicability is subject to the type of metal and organism involved.
The theoretical aspect and application of DGT to measure in situ speciation and bioavailability of diverse metal pollutants in soils were introduced in the first chapter. In the second chapter, the accumulated masses of Hg in DGT probes and in the earthworm species Eisenia fetida were monitored for 10 days, to test if the DGT technique can be used as a predicting method for the bioavailability of soil Hg to earthworms. The Hg exposure tests were conducted using freshly prepared artificial soils with different peat moss concentrations of 5, 10, 15, and 20% and aged prepared soils with varying pH values of 4. It is interesting to note that the Hg uptake rates by DGT and earthworms were considerably higher for fresh soils than for aged soils, while pore water (and acid-extractable) Hg concentrations were rather similar between the two types of soils.
DGT-measured Hg flux used to assess bioavailability in earthworm showed a strong positive correlation with steady-state Hg concentration in earthworm ([earthworm Hg] = 354(DGT−Hg flux) − 34, R 2 = 0. The overall results indicate that DGT-measured Hg flux is a better tool than the conventional methods for predicting Hg bioavailability for earthworms inhabiting diverse types of soil. In the third chapter, the critical soil characteristics affecting Hg bioavailability to the earthworm Eisenia fetida were evaluated using DGT technique in the metal-contaminated soils collected from Gumu Creek, a i tributary of the Hyeongsan River. The correlation analysis showed water holding capacity is the key variable of soil properties related to Hg accumulation in the soil, earthworm, and binding gel.
the water-holding capacity played a dual role in the Gumu Creek deposits: increasing the soil Hg concentration and decreasing Hg bioavailability and leachability. DGT–Hg flux showed a positive correlated with the Hg concentration in earthworms (r = 0. The results of this chapter proved that the DGT method is promising for predicting soil Hg bioavailability to the earthworm Eisenia fetida, and the water-holding capacity simultaneously regulates Hg availability to the DGT and the earthworms. In the last chapter, the aging effect of Hg, one of the most important factors controlling Hg bioavailability in soil, was studied using diverse types of field soils.
Surface soil samples were collected from forestry, agriculture, and riverbank sites (Youngsan and Hyeongsan river). The soil samples were spiked with inorganic Hg(II) and incubated for 1, 3, 5, 8, 15, 25, 40, 60 and 90 days. We found that, during the aging process, the proportions of Hg tended to migrate from mobile fraction to the stable binding fractions. Effective Hg concentration (C E) was estimated by DGT and DIFS model, as it represents bioavailable fraction of Hg in soils according to the previous literature.
The effect of Hg aging on CE was evaluated by aging rate constant (k1) obtained by fitting the CE values using pseudo-first order kinetic model. Partial Least Square regression (PLSR) model was used to relate various soil properties to the variations of k 1 in those soils. PLS model constructed by cross-validation and variable selection routines predicted 31% of k 1 when applied to entire soil samples, but 73 – 92% of k1 was predicted when applied to specific soil type. The results showed that variation of k1 was mainly predicted by soil pH and organic matter content.
The overall results indicate that the combination of DGT technique and PLSR method is a useful tool for evaluating the aging effects on bioavailability of Hg in various types of soils using selected soil properties. ii Table of Contents Abstract. i List of Figures. vii List of Tables.
Mercury cycling in the environment. Hg in soil ecosystem. Bioavailability and toxicity of Hg in soil. DGT technique for Hg measurement.
DGT technique to evaluate lability of Hg in soil. DGT application for labile Hg measurement in soil. DGT technique as a bio-mimics surrogate for mercury bioavailability in soil. Modelling approaches for predicting the bioavailability of Hg in soil using DGT.
8 Chapter 2: DGT efficacy tests using earthworm Eisenia fetida grown in artificial soils. DGT probe preparation. Preparation and characterization of soils. Deployment of DGT probes and earthworms.
Hg measurement in DGT probes, earthworms, and soils. Calculation of CDGT and OCM simulation. Results and discussion. Effect of Hg concentration on earthworm and DGT accumulation of Hg.
Effect of peat moss content on earthworm and DGT accumulation of Hg. Effect of soil pH on earthworm and DGT accumulation of Hg. Effect of soil aging on earthworm and DGT accumulation of Hg. Prediction of Hg bioavailability using DGT and conventional methods.
36 Chapter 3: Applying DGT technique for evaluating Hg bioavailability by earthworm Eisenia fetida in natural soils. Materials and Methods. DGT unit and earthworm preparation. Soil sampling and pre-treatment.
Deployment of earthworms and DGT units. Measurement of soil characteristics. Measurement of Hg in resins, earthworms, soils, and headspace air. Accumulation factors and statistical analysis.
Results and Discussion. Hg pollution in soils. Hg accumulation in earthworms. Hg accumulation in DGT.
Prediction of BAF and DAF using PLSR. 67 Chapter 4: Applying DGT techniques for evaluating aging effects of Hg in natural soils. Materials and methods. Soil sampling and preparation.
Measurement of Hg in binding layer and soils. Soil properties measurements. Effective concentration calculation. Kinetic equations for aging and leaching process.
Results and discussion. Correlation analysis among soil properties. Aging effect of Hg on DGT availability and the role of soil properties. Prediction of aging rate k1 and PAF using PLS method.
95 vi List of Figures Figure 2.1 The accumulation of Hg in diffusive gradients in thin films (DGT) resin and earthworm tissue as a function of deployment time for aged soils. The experimental Hg data were fitted by one compartment model (OCM). Soil composition was 69% sand, 20% kaolinite, 10% peat moss, and 1% CaCO3, and the measured Hg concentration was A 5.2 nmol g-1, B 56 nmol g-1, C 105 nmol g-1, and D 262 nmol g-1.2 The accumulation of Hg in diffusive gradients in thin films (DGT) resin and earthworm tissue as a function of deployment time for fresh soils. The experimental Hg data were fitted by one compartment model (OCM).
Soil composition was 59-74% sand, 20% kaolinite, and 1% CaCO3, and the peat moss content was A 5%, B 10%, C 15%, and D 20%.3 The accumulation of Hg in diffusive gradients in thin films (DGT) resin and earthworm tissue as a function of deployment time for fresh soils. The experimental Hg data were fitted by one compartment model (OCM). Soil composition was 69% sand, 20% kaolinite, and 10% CaCO3, and the pH of the soil was A 4.4 A) Hg in earthworm tissue at steady-state and B) Hg uptake rate by earthworm versus porewater Hg concentration. The Hg uptake rate was estimated by k 1×Cs, where Cs is the soil Hg concentration and k1 is the Hg uptake rate constant for earthworm estimated by the one compartment model (OCM), as presented in Table 2.5 A) Hg in earthworm tissue at steady-state and B) Hg uptake rate by earthworm versus acid-extractable Hg concentration.
The Hg uptake rate was estimated by k1×Cs, where Cs is the soil Hg concentration and k 1 is the Hg uptake rate constant for earthworm estimated by the one compartment model (OCM), as presented in Table 2.6 Correlation of A) Hg in earthworm tissue at steady-state and B) Hg uptake vii rate by earthworm with diffusive gradients in thin films (DGT)-measured Hg flux at 24 hours of deployment time. The Hg uptake rate was estimated by k1×Cs, where Cs is the soil Hg concentration and k1 is the Hg uptake rate constant for earthworm estimated by the one compartment model (OCM), as presented in Table 2.1 The location of the sampling sites in Gumu Creek in Pohang, South Korea.2 (a) A setting to measure the accumulation of Hg(0) in a headspace and DGT resin above the air film and (b) Hg(0) concentration accumulated in a headspace after 4 and 6 weeks of incubation at 20℃. Hg concentrations in the DGT resins were under the detection limit. Soil Hg concentrations are found from Table 3.3 The correlation between Hg concentration in earthworm (HgEW) and DGT- measured Hg flux.
The Hg concentrations in earthworms were determined after 6 weeks of earthworm incubation in soils and the DGT-Hg fluxes were measured after 24 hours of DGT deployment after the earthworm collection.4 The partial least squares regression projection of the independent variables (soil properties) and dependent variables (BAF and DAF). The variable importance in the projection (VIP) index of input parameters are found in Table 4. WHC: water holding capacity, CEC: cation exchange capacity, LOI: loss on ignition, and ORP: oxidation reduction potential.1 Location of sampling sites. 2 Grain size classification plot of 7 forest, 6 agricultural, 5 Youngsan river and 3 Hyeongsan river soils.3 Changes in effective concentration (CE) of forest, agricultural, Youngsan river, and Hyeongsan river soils.4 Predictor (red dots) and response (blue dots) loadings on factor 1 and 2 (T 1 viii and T2) in initial partial least squares regression (PLSR) model for k1, 𝐶𝐸0 and PAF in a) entire soil samples, b) forest soils, c) agricultural soils, d) Youngsan river soils and e) Hyeongsan river soils.
89 ix List of Tables Table 2.1 Composition and chemical characteristics of artificial soils for diffusive gradients in thin films (DGT) and earthworm deployment: pH, total organic carbon (TOC), aging period, water content, and maximum water holding capacity (MWHC).2 Output parameters of the one compartment model [i., diffusive gradients in thin films (DGT) and earthworm uptake rate constant, elimination rate constant, DGT-soil accumulation factor (DSAF), and biota-soil accumulation factor (BSAF)], and experimentally determined DSAF and BSAF.1 Conventional properties of the soil samples collected from the Gumu Creek, a tributary of Hyeongsan River. CEC: cation exchange capacity, LOI: loss on ignition, WHC: water holding capacity, and ORP: oxidation reduction potential. The values are the mean and standard deviation of triplicate measurements.2 Pearson’s correlation matrix of the Hg concentrations in soil and earthworm, DGT-Hg flux, bioaccumulation factor (BAF), DGT accumulation factor (DAF), and general properties of the riverbank soils collected from the Gumu Creek. WHC: water holding capacity, LOI: loss on ignition, ORP: oxidation reduction potential, and CEC: cation exchange capacity.05 is shown in bold.