Abstract
Rice production faces significant arsenic and cadmium contamination threats, posing global risks to food safety and agricultural sustainability. This thesis investigates interactions between soil chemistry, microbial communities, and agricultural practice through microcosm experiments, global field sampling, comprehensive chemical analyses, microbial profiling (16S rRNA and ITS sequencing), and subsoil restoration experiments in Bangladesh.
Chapter 2 presents a microcosm experiment with five fertiliser treatments assessing arsenic dynamics and microbial community shifts across the rice life cycle. Inorganic arsenic declined rapidly after flooding, while methylated arsenic species (MMA, DMA) peaked during grain-filling and correlated with anaerobic microbes, including methanogens and sulfate-reducing bacteria. Pig slurry increased Firmicutes abundance and enhanced arsenic mobilisation, highlighting the influence of organic fertilisers on arsenic cycling.
Chapter 3 examines rice paddies from East Africa, Sri Lanka, Vietnam, and Southern Europe to identify microbial and soil chemical drivers of global variation in grain arsenic (As) and cadmium (Cd). Arsenic concentrations were highest in Vietnam and Southern Europe, whereas Sri Lanka showed elevated cadmium. Sulfur-oxidising bacteria, sulfate-reducing bacteria, and methanogenic archaea correlated positively with grain arsenic, while fungi and aerobic bacteria were associated with grain cadmium.
Chapters 4 and 5 address severe topsoil removal in Bangladesh, where soil erosion and brick production expose nutrient-poor subsoils prone to arsenic contamination. Pot and multi-site field studies across Boro and Aman seasons evaluated quick compost, rice husk ash, green manure, and soil test-based fertilisers (STBF). Integrated STBF–organic treatments improved soil fertility, shifted microbial communities, and increased groups associated with nutrient cycling and arsenic methylation. These treatments reduced inorganic arsenic in porewater and grains, especially in Boro because of redox-driven microbial changes.
In conclusion, this thesis provides insights into microbial and geochemical controls over arsenic and cadmium contamination in rice paddies and informs targeted agricultural management practices to reduce contamination risks globally.
Thesis is embargoed until 31 July 2028.
| Date of Award | Jul 2026 |
|---|---|
| Original language | English |
| Awarding Institution |
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| Supervisor | Andy Meharg (Supervisor), Caroline Meharg (Supervisor) & Paul Williams (Supervisor) |
Keywords
- Rice
- grains
- soil
- cadmium
- arsenic
- biogeochemistry
- soil–plant–microbe interactions
- soil amendment strategies
- sustainable rice production
- subsoil restoration
- slurry
- rice husk ash
- soil test-based fertiliser
- sustainable agriculture
Cite this
- Standard