ABSTRACT
The study assessed the concentration and bioavailability of Pb, Cd, Zn, Cr and Fe metals in soil from rice fields in Abakaliki, Nigeria. The concentrations of these heavy metals in rice grains were also determined, with a view to assessing their human health risk on consumers. Heavy metal concentrations in soil and rice were determined using FAAS after digestion with 5:1 HNO3:HClO4 while Tessier's sequential extraction method was used to obtain the fractionated soil digests. The mean concentrations (µg/g) of the total heavy metal ranged from 1.036 ± 1.86 (Cd) to 6900.537 ± 734.82 (Fe) in soil while that of rice grains ranged from 0.024 ± 0.07 (Cd) to 101.446 ± 75.26 (Fe).The concentrations of Fe and Cd in most of the soil samples and Pb in rice grains exceeded some Nigerian and International standards. The heavy metal sequential extractions of soil samples showed that lead and zinc were less mobile in the soil and are bioavailable for plant uptake. The estimated daily intake of the metals was below the tolerable daily intake. The hazard quotient and the total hazard index were less than one showing that at present, there is no possible adverse health effect on rice consumers.
Subject(s)
Environmental Monitoring , Metals, Heavy/analysis , Oryza/chemistry , Soil Pollutants/analysis , Agriculture , Food Contamination/analysis , Food Contamination/statistics & numerical data , Humans , Nigeria , Risk Assessment , Soil , Zinc/analysisABSTRACT
Chemical modification of montmorillonite though popular may be expensive and environmentally noxious and can result in secondary contamination. Therefore, there is a need for eco-friendly and efficient treatment techniques. The use of thermally enhanced rice husk montmorillonite combo (TRMC) for aqueous crude oil pollution was evaluated. The physical characterization of the sorbate revealed a light crude oil. Scanning electron microscopy of TRMC and untreated montmorillonite (UM) showed efficient utilization of the pores for crude oil sequestration. Temperatures, pH, initial oil concentration, dosage of sorbent, and time were found to be significant in the batch sorption investigation. The heterogeneous surface nature of TRMC was elucidated by the Freundlich and Scatchard model analyses. The Langmuir monolayer maximum sorption capacity was 5.8 and 9.7 g/g for UM and TRMC respectively and the latter was found to be higher than most reported sorbents. The pseudo-first-order model gave better fit than pseudo-second-order, the Bangham, and the Elovich models in kinetics based on regression and chi-square analysis. Thermodynamics showed a spontaneous, feasible, endothermic, and physical sorption processes. Regeneration and reusability studies using n-hexane as eluent showed TRMC as suitable, environmental friendly sorbents for oil spill remediation.
