Inter-varietal variation in elemental uptake by rice and its implications for public health : a case study of Dareta village, Zamfara State, Nigeria

Nigeria is ranked first among the countries affected by Pb poisoning since it was reported in 2010 in Zamfara State. The Pb poisoning epidemic in Zamfara received global attention from various stakeholders and dietary Pb intake through rice which was identified as a major exposure route. There is a need to understand the extent to which different rice varieties accumulate Pb and whether varietal selection could be used to reduce dietary Pb exposure. Whilst the Pb poisoning is having a truly devastating consequence, the dietary transfer of other contaminants in Nigeria also needs to be understood. One group of contaminants that have received very little attention to date in Nigeria is anthropogenic radionuclides. Nigeria is developing nuclear power generation as part of its energy mix, there is a need to understand the potential food-chain transfer of radionuclides released into the environment. Two radionuclides of importance in both operational discharges and emergency (accident) situations are likely to be radio-caesium and radio-strontium. Therefore, in addition to Pb, this thesis provides an evaluation of inter-varietal variation in stable caesium (Cs) and stable strontium (Sr); stable isotopes are assumed to show the same environmental behaviour as their radioisotopes. The uptake of nine essential elements was also evaluated. Site characterisation was conducted first in Dareta village Zamfara Nigeria to select a suitable site for the rice varieties’ field trial; local rice samples were collected from four selected rice farms to examine Pb accumulation and partitioning in different parts of the rice plant (experiment 1). This was followed by the field trial for the 10 most commonly grown Nigerian rice varieties (experiment 2). The field trial was complemented by a pot trial for the same rice varieties at the University of Abuja, Nigeria (experiment 3). At maturity, the rice varieties were harvested together with their respective soil samples and analysed. Experiment 1; Pb accumulation in the rice plant was in the order of root>shoot>seed. Pb accumulation in shoots and rice seeds exceeded the FAO/WHO permissible limits of 10 mg/kg and 0.3 mg/kg respectively. Bisalayi rice, ncro-49, ita-315 and art3-7l demonstrated low uptake and accumulation of Pb in both experiment 2 and 3, whereas nerica-l34, nerica-l19, wita-4 and sipi rice varieties were found to have high Pb uptake and accumulation. Statistically, there were no significant differences (p>0.05) in the uptake and accumulation of the stable Cs and Sr in both trials using the concentration ratio (CR). All the selected rice varieties were good source of the nine essential elements in terms of their percentage contribution to the recommended daily intake (RDI)