In Vietnam, soil contaminated with dioxin has been detected in many areas, especially in and immediately surrounding the Bien Hoa, Da Nang, and Phu Cat air bases. Although dioxin concentration in these soil is much lower than before, there are still significant impacts on the environment and ecosystem health. The goal of this project is to develop a framework for site-specific, synergistic bioremediation approaches to decontaminate soils containing low concentrations of dioxin (between 20-1000 ppt) in Vietnam. It aims to accomplish this through investigation and identification of soil limiting factors regulating and preventing successful remediation of dioxins and test biostimulation and biosurfactant strategies to alleviate site-specific limiting factors. Project researchers will collect samples from expected low-level dioxin contaminated soil sites at Phu Cat, Da Nang, and Bien Hoa, with sampling points selected based on previous site history and current vegetative cover. Samples will be analyzed for dioxin congener concentration and bioaccessibility. Soil pH, texture, organic carbon, nitrogen, microbial biomass, particulate organic matter, and biosurfactant synthesizing microorganisms will be determined by using infrared reflectance spectroscopy to identify factors limiting dioxin degradation. Infrared spectra and reference data from the planned analyses will be used to develop models to predict unknown samples as a rapid assessment technique. Biostimulation, organic amendments (sawdust), biosurfactants (rhamnolipids), dioxin-degrading bacteria, and mineral fertilizers will be applied in various combinations in soil microcosms in the lab. The most beneficial treatments will be further tested in three field experiments.
The anticipated outcome of this project is to find out the most limiting factors of soil for dioxin bioremediation and an innovative synergistic approach for in situ dioxin bioremediation. The results of the proposed research will benefit local and regional populations. The success of bioremediation strategies to be developed under this project will provide the local communities and national government agencies with further information on both the soil dioxin levels and bioavailability in the vicinity of Phu Cat, Da Nang, and Bien Hoa air bases, as well as further strategies for managing these soils. These strategies will help to improve this major environmental health issue for local stakeholders by means of soil and water quality improvement, giving the local people the opportunity to use the bio-remediated soils for beneficial uses such as crops, livestock, and forests and eventually increase their income. The data collected from this project will also advance the body of research about the limiting factors of bioremediation strategies of soil dioxin and will be helpful for developing a framework for site-specific bioremediation approaches of biostimulation and biosurfactants.
Summary of Recent Activities
During the first three months of 2023, Dr. Nghia and his team continued working on their project activity 3, which is entitled “Isolation and characterization of biosurfactant producing bacteria from dioxin contaminated soils in Vietnam.” They have tested the biodegradation ability of the various bacterial strains they have isolated in combination with different carrier materials, including biochar and disposed charcoal. They also worked on project activity 4, “Isolation and characterization of dibenzofuran (DF) degrading bacteria from dioxin contaminated soils in Vietnam.” Under that topic, as of April 2023 they had isolated and selected three strains from nine bacterial communities from dioxin-contaminated soil samples collected at Phu Cat, A Luoi – Da Nang, and Bien Hoa air bases.
Field survey activities
As the project moves into its third and final year, in the spring and summer of 2023 the researchers will be focusing on project activity 5, “Comparison of the efficacy of different approaches including the corrected limiting factors of soil after identification by infrared reflectance spectroscopy, organic material and nutritional amendments, biosurfactant producing and dioxin degrading bacteria inoculation on dioxin biodegradation enhancement under laboratory conditions.” The main objective of this work is to compare the efficacy of different approaches, including the corrected limiting factors of soil after identification by infrared reflectance spectroscopy, organic material and nutritional amendment, and biosurfactant producing and dioxin degrading bacteria on dioxin biodegradation enhancement under laboratory conditions. They aim to select the most beneficial treatments to be further tested on the effects of the selected treatment method on in situ bioremediation in field experiments at the three sites (Phu Cat, Da Nang and Bien Hoa air bases).