Abstracts Category : Other

Arsenic in rice: genotypic variation and its bioavailability with respect to human health risk assessment

by Shofiqul Islam

Research Doctorate - Doctor of Philosophy (PhD) 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 worlds 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 g/kg and 107 g/kg, respectively, ranging between 3680 g/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 11502 g/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 g/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 0.5410-3 to 2.1210-3 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 predictAdvisors/Committee Members: University of Newcastle. Faculty of Science, Global Centre for Environmental Remediation.