Occurrence of persistent toxic substances in soils, sediments, fishes and human breast milk in southern Vietnam

Global contamination and toxic effects of persistent toxic substances (PTSs) have been an emerging environmental issue and have received considerable attention during the past four decades. The rapid agricultural and industrial growths as well as the expansion of urban areas in Hochiminh City and Mekong River Delta, two of the most densely populated areas in the world with about 26 million peoples, result in the widespread contamination of PTSs in southern Vietnam. Due to adverse effects to human health and environment, more attention has been paid to PTSs in Vietnam since the early 1990s. However, these works mainly focused on PTSs in water, soil and sediment media. PTSs in animals, birds and human (blood, adipose tissue, breast milk, etc.) have drawn less attention due to high cost of research and the need of sophisticated analytical techniques. With the support of Swiss Agency for Development and Cooperation (SDC) project in the frame of a collaboration between Vietnam and Switzerland, we have carried out the research named "Persistent Toxic Substances in southern Vietnam; Development analytical methods, bioaccumulation and modeling". Our research has established suitable analytical methods, which is able to analyze simultaneously PCBs, PBDEs, OCls pesticides and especially, mirex and toxaphene, which are analyzed for the first time in Vietnam, in various matrices such as soil/sediment, fish and human breast milk samples by HRGC/LRMS. The sampling sites (including Hochiminh City, Dongnai – Baria Vungtau province and Mekong Delta) have been selected based on previous studies in Vietnam and collected documents from Vietnam Environment Administration and POPs Project of Vietnamese government. Twenty-one PCB congeners, twelve PBDE congeners and twenty-six organochlorine pesticides were chosen for research due to their high toxicities. Soil, sediment, fish tissue, and human breast milk were selected as the matrices to examine the PTSs residue. The obtained results showed that PTSs levels of soil and sediment samples in southern Vietnam are not so high, e.g. DDTs and PCBs levels are lower than those in previous studies in Vietnam. Endosulfans were found in almost all sites suggesting the widespread contamination due to their large usage in agriculture. Toxaphene was only found in soil close to agrichemical warehouse at high level indicating potential source of toxaphene from the pesticide stockpiles. PBDEs were detected in most of the samples but at the low levels, which shows a possibly atmospheric deposition source. Other PTSs were detected at low levels (< 5 ng/g dry wt.) or below LOD of the analytical method. PTSs concentrations in wild fish samples from Saigon and Tien Rivers are lower than those determined in previous studies in Vietnam and in the world. However, unlike DDTs, PCBs showed a slow decreasing in fish samples and this suggests a continuous contamination. Besides, due to large usage in agricultural activities, endosulfans were also found in almost all wild fish samples from Saigon and Tien River (23.9 and 8.3 ng/g lipid wt., respectively). Other PTSs were detected at low levels (< 5 ng/g dry wt.) or below LOD of the analytical method. PTSs levels in human breast milk of HCMC residents are lower than those in previous study (except PCBs and CHLs). The higher PCB residues observed in human breast milk from HCMC suggest continuously high exposure to PCBs via the food chain to human. In this study, PTSs levels in human breast milk of primiparous mother higher than those in multiparous mothers. This trend well agrees with previous study in Hanoi and HCMC. By using statistic methods for obtained results (cluster analysis and PCA), we have shown the similarity of PTSs profiles pattern between landfill soil, TN-SG River sediments and Saigon River fish samples. Logically, we might suggest that there is a transfer of PTSs compounds from landfill and TN-SG River to fish samples collected from Saigon river. Our results clearly demonstrate that municipal and industrial waste from landfill and urban activities of HCMC could be considered as PTSs pollution sources. The results of the present study have contributed to the improvement of PTSs research capability of Vietnam. This research also efficiently supports and serves the projects of monitoring, studying and evaluating impacts of PTSs on South Vietnam ecosystem during the implementation of NIP under Stockholm Convention.

Behaviour of carbon-14 containing low molecular weight organic compounds in contaminated groundwater under aerobic conditions

Aislinn Ann Boylan

Short chain carbon-14 (C-14) containing organic compounds can be formed by abiotic oxidation of carbides and impurities within nuclear fuel cladding. During fuel reprocessing and subsequent waste storage there is potential for these organic compounds to enter shallow subsurface environments due to accidental discharges. Currently there is little data on the persistence of these compounds in such environments. Four C-14-labelled compounds (acetate; formate; formaldehyde and methanol) were added to aerobic microcosm experiments that contained glacial outwash sediments and groundwater simulant representative of the Sellafield nuclear reprocessing site, UK. Two concentrations of each electron donor were used, low concentration (10(-5) M) to replicate predicted concentrations from an accidental release and high concentration (10(-2) M) to study the impact of the individual electron donor on the indigenous microbial community in the sediment. In the low concentration system only similar to 5% of initial C-14 remained in solution at the end of experiments in contact with atmosphere (250-350 h). The production of (CO2)-C-14(g) (measured after 48 h) suggests microbially mediated breakdown is the primary removal mechanism for these organic compounds, although methanol loss may have been partially by volatilisation. Highest retention of C-14 by the solid fractions was found in the acetate experiment, with 12% being associated with the inorganic fraction, suggesting modest precipitation as solid carbonate. In the high concentration systems only similar to 5% of initial C-14 remains in solution at the end of the experiments for acetate, formate and methanol. In the formaldehyde experiment only limited loss from solution was observed (76% remained in solution). The microbial populations of unaltered sediment and those in the low concentration experiments were broadly similar, with highly diverse bacterial phyla present. Under high concentrations of the organic compounds the abundance of common operational taxonomic units was reduced by 66% and the community structure was dominated by Proteobacteria (particularly Betaproteobacteria) signifying a shift in community structure in response to the electron donor available. The results of this study suggest that many bacterial phyla that are ubiquitous in near surface soils are able to utilise a range of C-14-containing low molecular weight organic substances very rapidly, and thus such substances are unlikely to persist In aerobic shallow subsurface environments.

ELSEVIER SCI LTD2018

Analysis of microbial community structures and functions in heavy metal-contaminated soils using molecular methods

Fabienne Gremion

The contamination of agricultural land and groundwater by heavy metals is essentially linked to human activities. A major problem with heavy metals is that they cannot be biodegraded and therefore reside in the environment for long periods of time if they are not removed. Thus, depending of the kind and depth of contamination, different remediation techniques were developed. One of these methods, called "phytoextraction", uses the ability of so-called hyperaccumulating plants to extract high amounts of heavy metals. Accumulation of heavy metals in the environment is a serious concern for animal and human health. At the microscopic scale, heavy metals may have also deleterious effects on bacteria which are the key-players of the different nutrient turnovers in soils. Consequently, ecosystem functioning can be seriously perturbed and the long-term soil fertility may be threatened. The recent development of molecular biology greatly contributed to the discovery of the microbial diversity and its function in the soil. However, to date only a small number of studies used molecular methods to investigate the impacts of heavy metals on the bacterial community. In this thesis, a pot experiment was conducted under controlled conditions with one hyperaccumulating plant (Thlaspi caerulescens) grown in two different soils, a long-term and an artificially heavy metal-contaminated soil. The impact of heavy metals on the microbial community was then investigated with several molecular methods. Moreover, the decrease of the bioavailable heavy metals concentrations in soil due to plant uptake allowed to study the consequences on bacterial community structure and function. Based on the 16S ribosomal RNA and the corresponding gene (16S rDNA), four clone libraries were constructed to retrieve information on the structure of the microbial community and the potentially active part of the microbial community in the rhizosphere of Thlaspi caerulescens grown during three months in a long-term contaminated soil. The data obtained with the two clone libraries (rRNA and rDNA) from the rhizosphere of Thlaspi caerulescens were compared with the bulk soil data to identify any effect of the plant on the soil microbial community structure. Partial sequence analysis of 282 clones revealed that most of the environmental sequences in both soils affiliated with five major phylogenetic groups, the Actinobacteria, α-Proteobacteria, β-Proteobacteria, Acidobacteria and the Planctomycetales. The taxa dominating the bacterial community structure in the bulk soil also dominated the rhizosphere community, indicating that the plant did not exert a major influence on the overall bacterial diversity. However, all dominant taxa, with the exception of the Actinobacteria, were relatively less represented in the rRNA libraries as compared to the rDNA libraries. On the contrary, sequences belonging to the Actinobacteria dominated both bulk and rhizosphere soil libraries derived from rRNA. Seventy per cent of these clone sequences were related to two subgroups of the Rubrobacteria, which was an indication that this group of bacteria was probably metabolically active in heavy metal-contaminated soils. Fluorescence in situ hybridization (FISH) was used for the in situ detection and quantification of selected bacterial groups previously detected in the clone libraries from the rhizosphere of Thlaspi caerulescens. By applying the most general probe EUB338, only 20% of the total rhizosphere microbial community could be detected. Based on this result, it was difficult to conclude with certitude which were the most dominant bacteria in the rhizosphere. However, despite this low detection rate, it was possible to detect the major groups present in the rhizosphere clone libraries using group-specific oligonucleotide probes. As part of our sequences were affiliated to two emerging bacterial groups, the Acidobacteria and the Rubrobacteria, two new probes were designed, Acido228 (specific for the subgroup 1 of the Acidobacterium division) and Rubro198 (specific for the all Rubrobacteria subclass), for the detection of these microorganisms. These two probes were first checked for their specificity with pure cultures and finally applied in the rhizosphere soil allowing for the first time the detection of these organisms in situ. Finally, the impact of heavy metals and a subsequent one-year phytoextraction with Thlaspi caerulescens on the soil microbial community was investigated in an artificially heavy metal-contaminated soil. All the different molecular and culture-dependent techniques used, denaturing gradient gel electrophoresis (DGGE), community level physiological profile (CLPP) and potential ammonium-oxidation measurement showed that the heavy metal addition induced drastic changes in the bacterial community. Moreover, the analysis of the different bacterial DGGE patterns (Bacteria, β-Proteobacteria and ammonia-oxidising bacteria) obtained during this experiment showed that one-year phytoremediation was not sufficient to recover the initial community present in the non-contaminated soil. However, with the CLPP analysis, it was possible to detect a stimulating effect of the plant on a part of the microbial community in both contaminated and non-contaminated soils. The most obvious result was obtained in the contaminated soil where the number of substrates metabolised increased significantly in the presence of the plant as compared to the unplanted contaminated samples. The measurement of the potential ammonium-oxidation was used as a criterion for soil quality. Although this test showed that the ammonia-oxidising bacteria were significantly stimulated in the planted non-contaminated soil samples, the positive effect of the plant on these bacteria was not sufficient to overcome the inhibition induced by the presence of the heavy metals in the contaminated soil, even after one year phytoremediation. To conclude, molecular methods in combination with culture-dependent techniques have proven in this study to be very useful for the detection of the changes induced by the heavy metals in the structure and the function of the microbial community. Moreover, the molecular techniques contributed to the identification of bacteria which could be potentially used for the bioremediation of contaminated soils thus offering new perspectives of investigation and technology development.

EPFL2003

Fate of volatile fluorinated compounds in the subsurface

Christian Balsiger

Since their discovery around 1930, the synthetic compounds of the class of chlorofluorocarbons (CFCs) have been produced and used worldwide at very large scale. Their physico-chemical properties (non-flammability, chemical inertia, miscibility with water and oil, compatibility with many metals and plastics, solvent capacity) have made them ideal candidates for several applications, such as refrigerant fluids, aerosol propellants, foam blowing agents, or as solvents or intermediates of chemical synthesis. In the 70', it was demonstrated that following their release in the atmosphere, they are implicated in the process leading to the commonly called stratospheric ozone hole. The governments of several industrialised country have thus signed a protocol with the objective to stop the production and use of CFCs. CFCs have been increasingly replaced by compounds with similar structure, the hydrochlorofluorocarbons (HCFCs), but whose reactivity in the lower layers of the atmosphere is quite different from that of CFCs. Due to their chemical inertia, CFCs has been used as tracers for surface and groundwater datation. During such investigations, the biodegradability of these compounds and the existence of punctual pollution sources in soil and groundwater have been evidenced. It has been demonstrated that some of these compounds can be dechlorinated under anoxic conditions producing other compounds with sometimes higher toxicity and higher water solubility, and resulting in a risk linked to the consumption of natural groundwater. The goal of this thesis was to get indications about reductive transformations of CFCs and especially HCFCs in Swiss aquifers and landfills, on the potential of different microbial communities to reductively dechlorinate certain compounds, and under which redox conditions the transformations occur in aquifer systems. Data concerning the production, use, emission, regulation, as well as the biodegradability and toxicity of these compounds are presented in chapter 1 and in the appendix. The analytical methods developed and used during this work are presented in chapter 2. Particularly, a versatile analytical system allowing the measure of trace but also higher concentrations in different media, solid or aqueous, has been set up and used during this work. CFCs and HCFCs were analyzed at 3 sites in Switzerland. Samples were collected from a natural groundwater in which a chloroethene plume had been observed, from an old landfill closed in 1980, and from a more recent bioactive landfill constructed in horizontal layers. In addition, the behaviour of different CFCs and HCFCs was studied in microcosms inoculated with sludge originating from several sewage treatment plants in the canton of Vaud, and with a sediment originating from a contaminated aquifer in Holland. The studied CFCs and HCFCs were furthermore injected at the inlet of a 1.2 m height column filled with the aquifer sediment from Holland. In this quasi natural aquifer, the oxido-reductive conditions were modified during the experiment in order to investigate the conditions at which the biodegradation occurred. The field studies showed that CFCs and HCFCs are present in aquifers and landfills, and there were indications that their transformation also occurs there. Estimations of half-life times indicated that the reductive dechlorination occurred at slow rates. This could be due to the low temperatures of natural groundwater systems and other factors linked to the hydro-geological properties of the natural environment such as dispersion, sorption or partitionning. In the microcosms inoculated with sludge, CFC-11 was transformed to HCFC-21, the latter being further dechlorinated to HCFC-31. HCFC-123a and chlorotrifluoroethene (CTFE) were produced simultaneously from CFC-113. Inhibition of methanogesis with 2 bromoethane sulfonate decreased significantly the degradation rate of CFC-11, emphasizing the importance of the role of methanogens in the degradation process. In the microcosms inoculated with the contaminated sediment, the transformation of CFC-11 also occurred, but was not accompanied with methane production, as it was the case in the suldge microcosms. Moreover, the presence of acetate, lactate and butyrate in the microcosms containing CFC-11 suggested that methanogens were inhibited in the presence of CFC-11. CFC-113 was transformed in the same way as in the microcosms inoculated with the sludge; however, the produced CTFE was further transformed to trifluoroethene (TFE). Production of HCFC-151b from HCFC-141b was also observed. In the column filled with aquifer material, only the transformations of CFC-11 and CFC-113 were observed, which is probably due to the short residence time in the column (~10 days), during which the transformation of the other compounds was not sufficiently pronounced. The increasingly reducing conditions in the column were accompanied with an increase of the degradation rates of CFC-11 and CFC-113, with a maximum reached in presence of methanogenesis. The addition of sulfate in the artificial groundwater decreased the biodegradation rates of the two compounds, and the concentration of their transformation products was simultaneously increased. This suggests that these products become more persistent under sulfate-reducing conditions. Natural attenuation designates all the processes leading to the decrease of the concentration of organic compounds migrating from a pollution source throughout a natural environment. Whereas natural attenuation or enhanced natural attenuation seem adequate for several classes of compounds, the absence of defluorination reaction of CFCs and HCFCs reported in this work suggests the use of other remediation techniques for the decontamination of sites polluted with these compounds. Indeed, the transformation products of CFCs and HCFCs still contain a fluorine atom and are not less harmfull to the environment than the parent compounds. In addition, the use of CFCs as age-dating tracers in groundwater is not recommended under anoxic conditions, as it was demonstrated here that they are not stable in such environments. The HCFCs on the other hand seem to be more persistent, and it is primordial to decrease rapidly their production and release in the environment.

EPFL2004