Arsenic speciation and concentration in paddy rice : consequences for dietary exposure

Chapter 1. Introduction. General summary covering the toxicity and environmental distribution of arsenic, rice cultivation in Bangladesh including irrigations practices, previous knowledge of arsenic concentration and speciation in rice and the risk posed to the human food chain. Chapter 2. Variation in arsenic speciation and concentration in paddy rice related to dietary exposure. Arsenic speciation was surveyed in different rice varieties from different rice varieties from different parts of the globe to understand the contribution of rice to arsenic exposure. Pot experiments were utilised to ascertain whether growing rice on arsenic contaminated soil affected speciation and whether genetic variation accounted for uptake and speciation. USA long grain rice had the highest mean arsenic concentration in the grain at 0.26 μg As g-1 (n = 7), and the highest grain arsenic value of the survey at 0.40 μg As g-1. The main arsenic species detected in the rice extract were As(III), DMA(V) and As(V)­. In European, Bangladeshi and Indian rice 64 ± 1% (n=7), 80 ± 3% (n = 11) and 81 ± 4% (n = 15) of the recovered arsenic was found to be inorganic. In contrast DMA(V) was the predominant species in rice from the USA, with only 42 ± 5% (n = 12) of the arsenic being inorganic. Pot experiments show that the proportions of DMA(V) in the grain are significantly dependent on rice cultivar (p = 0.026) and that plant nutrient status is effected by arsenic exposure. Chapter 3. Increase in rice grain arsenic for regions of Bangladesh irrigating paddies with elevated arsenic in groundwaters. Three hundred and thirty of aman and boro rice, nine-four vegetable and fifty pulse and spice samples were analysed for total organic and inorganic arsenic, using HPLC-ICP-MS. Conc. HNO3 was used for total digestion and 2M TFA for extraction. The districts with the highest mean arsenic rice grain concentrations were all from southwestern Bangladesh: Faridpur (boro) 0.51 > Satkhira (boro) 0.38 > Satkhira (aman) 0.36 > Chuadanga (boro) 0.32 > Meherpur (boro) 0.29 μg As g-1. Predicted inorganic arsenic intake from rice is modelled with the equivalent intake from drinking water for a typical Bangladesh diet. Daily consumption of rice with a total arsenic level of 0.08 μg As g-1 would be equivalent to a drinking water arsenic level of 10 μg L-1. Chapter 4. Market basket survey shows elevated levels of As in South Central US processed rice compared to California: Consequences for human dietary exposure. Chapter 5. Greatly enhanced arsenic shoot assimilation in rice leads to elevated grain levels compared to wheat and barley. Chapter 6. General discussion and suggestions for future work.EThOS - Electronic Theses Online ServiceGBUnited Kingdo