- Title
- Arsenic in rice: genotypic variation and its bioavailability with respect to human health risk assessment
- Creator
- Islam, Shofiqul
- Relation
- University of Newcastle Research Higher Degree Thesis
- Resource Type
- thesis
- Date
- 2017
- Description
- Research Doctorate - Doctor of Philosophy (PhD)
- Description
- Arsenic (As) is a carcinogenic metalloid that poses a significant health and environmental hazard. Geogenic As-contaminated groundwater has been reported in 150 countries of the world and its used for irrigation purposes for crops especially rice lead to As accumulation in paddy soils and further to elevated As contents in rice plants. Almost half of the world’s population depends on rice for a subsistence diet and it has been considered a significant pathway for human exposure to As. The As bioaccumulation by rice plants has been linked to a number of soil and environmental factors together with the rice genotypes, soil As loading, water and nutrient management practices in soils. The proposed research focuses on reducing As loading in different rice varieties and their bioavailability in relation to human health risk assessment under different management strategies. In this research household survey, market basket survey, pot and field experiments on rice genotypes were conducted to ascertain whether: firstly, soil As concentration, nutrient and water management practices affected rice As concentration and speciation; secondly, genetic variation accounts for uptake and their speciation and finally, the bioavailability of As from different rice genotypes can be employed in human health risk assessment and risk management decisions. An extensive number (965) of rice samples collected by household survey from 73 upazilas in Bangladesh was analyzed to determine regional variation, distribution and associated health risks from As in rice. Results showed that, the variation in As content was dominated by the location (47% among the upazilas, 71% among districts) and rice variety (14%). The mean and median concentrations of total As were 126 µg/kg and 107 µg/kg, respectively, ranging between 3–680 µg/kg. Total As levels of aromatic rice were significantly lower than non-aromatic rice and varied with rice grain size. Coarse grain rice had the highest total As content followed by medium grain and fine grain rice. Irrigated rice had higher As content than the non-irrigated rice. Inorganic As content in rice grain ranged between 11–502 µg/kg (n=162) with the highest fraction being 98.6%. The daily intake of inorganic As from rice ranged between 0.38 to 1.92 µg/kg BW in different districts. The incremental lifetime cancer risk (ILCR) for individuals due to the consumption of rice varied between 0.57× 10-3 to 2.88× 10-3 in different districts, and 0.54×10-3 to 2.12×10-3 in different varieties, higher than the US EPA threshold. The highest average ILCR value of inorganic As for population in Narayanganj district was 2.88 × 10-3 which was 288 times higher than the acceptable limit. The 2-10 years age group experiences higher carcinogenic risks than others and females are more susceptible than males. In a market survey study, fifty-nine rice and rice-based products available on sale in Australian supermarkets were collected for analysis of total and different As species to predict the potential health risk for children and adults. Results show that of the 59 rice-based products, 31 (53 %) exceeded the EU recommended value (100 µg/kg) of As for young children and 13 (22%) samples had higher than maximum level of 200 µg/kg recommended for adults. Arsenic content varies as rice crackers>baby rice>rice cakes>puffed rice>other rice-based snacks>ready-to-eat rice. Of the 6 categories of rice-based products, except ready-to-eat rice, all others exceeded the EU recommended value for young children. Even manufacture recommended servings deliver significant amounts (0.56 to 6.87 µg) of inorganic As. In the field study, ten rice cultivars were evaluated at three locations of Bangladesh having different levels of soil As and irrigation water As to investigate the effect of continuous flooding (CF) and alternate wetting and drying (AWD) irrigation practices on the bioaccumulation of As by rice plants. Results showed that As concentration in different parts of rice plants varied significantly with rice genotypes and irrigation practices. Higher grain As bioaccumulation was detected in plants in areas of high soil As in combination with CF irrigation practice. AWD irrigation practice with suitable genotypes resulted in 17-35% reduction in grain As level with 7-38% increase in grain yield compared to CF irrigation practice. This study advances the understanding that, for moderate to high levels of As contamination, the Binadhan-5, Binadhan-6, Binadhan-8, Binadhan-10 and BRRI dhan47 varieties were quite promising to mitigate As induced human health risk. A greenhouse study was conducted to investigate the effect of water and fertilizer management on the bioaccumulation of As in rice plants under different As-graded paddy soils using an Australian rice variety (cv. Sherpa). Results showed that, arsenite accounted for >80% of the total inorganic As in pore water. AWD irrigation practice with Si fertilization significantly reduced the total As levels in pore water. The addition of As markedly increased the As concentration of grain and straw, with a concomitant reduction in grain and straw yields of rice. Lower levels of As in rice grains were found using AWD (93 µg/kg) than those observed in CF (121 µg/kg) irrigation practice. The addition of Si significantly decreased As uptake by rice plants while adding of P has no significant effect and this is also true for Si and P interaction. AWD irrigation practice with Si fertilization resulted in a reduction of grain As level at around 12% to 21%, while grain yield increased by 13%. Arsenic contaminated rice poses a significant health risk to people. Therefore, assessing the bioavailability of As from rice is crucial for understanding human exposure and as a consequence to reduce the risk of As-related diseases. An in vivo assay using swine was used to measure the absolute bioavailability of As from cooked rice of twelve genotypes usually grown in Bangladesh. The average As concentrations in each rice genotype ranged from 108 ± 4 µg/kg to 580 ± 6 µg/kg. This study demonstrates that rice genotypic characters influenced As bioavailability varied between 25% and 94%. Arsenic in salt tolerant rice genotypes as well as brown rice genotypes has lower bioavailability compared to other rice genotypes. The most commonly cultivated and consumed variety (BRRI dhan28) has As bioavailability of 70%, which poses a significant risk to consumers.
- Subject
- groundwater pollution; bioaccumulation; rice; arsenic poisoning; health risks
- Identifier
- http://hdl.handle.net/1959.13/1351326
- Identifier
- uon:30686
- Rights
- Copyright 2017 Shofiqul Islam
- Language
- eng
- Full Text
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