- Title
- Managing beryllium contamination in soils: a risk-based approach
- Creator
- Islam, Md. Rashidul
- Relation
- University of Newcastle Research Higher Degree Thesis
- Resource Type
- thesis
- Date
- 2022
- Description
- Research Doctorate - Doctor of Philosophy (PhD)
- Description
- The increasing use of Be and Be products and their environmental emission in the last few decades poses a serious risk to plants, animals, and humans when they are mobilised in the environment. Research on the environmental behaviour of Be is limited, and a better understanding of this behaviour is essential to reduce the risk of mobilisation and potential toxicity. In this study, we investigated the environmental behaviour of Be (sorption-desorption, migration or leaching, bioavailability, bioaccessibility), taking into account a variety of factors to explore the role of Be in soils. Potentially contaminated soils were collected for detailed study from the Little Forest Legacy Site (LFLS), Sydney (Australia), where approximately ~1070 kg Be waste was co-disposed (1960- 1968) with other low-level radioactive waste in unlined trenches in accordance with the standard practice at that time. This site is representative of other Be contaminated sites arising from research, manufacturing, and disposal of waste elsewhere in the world. If Be is exposed to soil either from waste trenches or other sources, it will interact with the host soil, and its sorption-desorption, mobility and bioavailability will primarily depend on the physicochemical properties of the site soils. This study examined the concentration of Be in soil, sediment and grass samples at LFLS, and how the sorption-desorption of Be was influenced by soil physicochemical properties. Results revealed that soil organic matter (SOM), oxyhydroxides of metals, clay minerals, porous surface of soil particles influenced higher sorption and limited desorption of Be. Hydrolysis and precipitation are the prominent features of Be in aqueous solutions, which primarily depend on pH, but this behaviour was influenced by other factors when Be ions were exposed to complex chemical environments in the field soils. Solubilisation and precipitation study revealed Be solubility is limited at pH>7, but chemisorption of Be with SOM is possible at pH>8, which was confirmed by XPS and FTIR analysis. This study suggests SOM is an important entity in soils for specific chemisorption of Be, resulting in 77% and 46% Be being respectively sorbed by separated fulvic and humic acid fractions. Moreover, diverse physicochemical conditions of soils affected environmental behaviour of Be in soils, such as the presence of an electrolyte which showed negative effects on sorption (due to competition); however, different types of electrolytes and ionic strengths indicated only a limited effect. The effects of different competing ions, counter ions, and co-existing ions were predominantly found at low pH<6 and high pH >9, where different organic-inorganic ligands can compete with hydrolysis and precipitation of Be. However, sorption was influenced by both organic and inorganic species, and/or their synergistic effect at pH 5.5 (relevant to the LFLS field soil pH condition). Moreover, the sorption-desorption process was spontaneous, enthalpically and entropically influenced in the temperature range of 288-318 K. Desorption and migration behaviour of Be [from the simulated (spiked) contaminated soil of LFLS] using different batch and sequential leaching techniques revealed that organic leachate composition, and simulated local rain water compositions accelerated Be desorption and migration. Though desorption and migration of Be were affected by several factors, the application of vertisol or clay-rich soil, heat treatment, and increasing the incubation time can reduce the environmental mobility of Be. Based on leaching studies, no ecological risk and human health concerns were suggested from the desorption of Be from LFLS soils based on the current situation. Nevertheless, certain potential risks may result, particularly if Be concentrations increase in the site soil with different metals mobilising factors and exposure routes. Study of Be contamination by different exposure pathways (e.g. inhalation, ingestion, and inhalation-to-ingestion) revealed that inhalation-to-ingestion pathway showed higher bioaccessibility (20.8%) as compared to direct ingestion (4.8%), which suggests increased Be bioaccessibility and toxicity in the gastrointestinal tract when the contamination derives from the inhalation route. The solubility of Be in the biological fluids was influenced by dissolved organic matter (dissolved organic carbon, and nitrogen) at higher pH and by inorganic matter (e.g. oxyhydroxide of metals) at lower pH, which was linked with the solubility of geochemically reactive fractions of soils. Mobilisation and potential toxicity of Be in the LFLS soil was noticed under different soil-solution conditions, which may need potential immobilisation or management in the future if Be is released from waste trenches. Synthesised zeolite Na- P1 (SZ) and modified zeolite/chitosan (MZ) were investigated as potential immobilisers for Be, and results revealed that both SZ and MZ showed excellent sorption of Be, greater than many other sorbent materials. Moreover, the chemisorption process of Be was further increased (up to 99.8%) using soil solution (collected from LFLS soil using simulated acid rain solution) as compared to the ultrapure water, and MZ always showed higher sorption than SZ in the field soil pH. The study of amendment application revealed that the soil with 2% MZ significantly reduced (up to 70.8%) the mobility of Be in pore water (PWBe) but increased PWBe using SZ. These phenomena (decrease of PWBe by MZ or increase of PWBe by SZ) were correlated with the soluble organic-inorganic elements in the PW. Moreover, with increasing Be concentration in soil, microbial toxicity/sensitivity rose, which needed more energy for microbes to survive and led to increase microbial biomass degradation and respiration. The immobilisation study suggests that the application of MZ in both ultrapure water, soil-solution or in the amendment can be an effective candidate for potential immobilisation of Be in an eco-friendly and cost-effective way in the LFLS soil. However, the ramifications of this approach may differ for other Be contaminated site soils depending on the soil physicochemical properties. They may need site-specific investigation, and our results could provide a guide for future research.
- Subject
- beryllium contaminated soil; environmental chemistry; sorption-desorption; bioaccessibuility; management; synthesised zeolite for immobilisation; thesis by publication
- Identifier
- http://hdl.handle.net/1959.13/1505476
- Identifier
- uon:55672
- Rights
- Copyright 2022 Md. Rashidul Islam. This thesis is under embargo until 01.09.2024.
- Language
- eng
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