BIOAVAILABLE FORMS OF HEAVY METALS FROM RICE SAMPLES AND ITS POTENTIAL HEALTH RISK ASSESSMENT

Food crops grown in contaminated soils have a greater accumulation of heavy metals and the consumption of food crops grown in the contaminated soils are the source of metals that enters into the human body. Rice being a major food crop, the presence of heavy metals should be monitored regularly for reducing health risk. The analysis of total heavy metal always overestimates the content which leads to misinterpretation of results; however, bioaccessible heavy metal analysis projects the actual health risk. Hence, the present study aims to assess the bioavailable form of heavy metals in rice. The rice samples were collected from 20 different places and used for the inherent and bioavailable metal estimation. In vitro simulated digestion method was applied for bioaccessible metal analysis. Metal concentration in polished rice ranged from 0.10 to 0.82, 0.10 to 1.07, 0.11 to 0.56 and 0.23 to 1.09 mg  kg-1 for Lead (Pb), Nickel (Ni), Cadmium (Cd) and Chromium (Cr), respectively. Twenty five percent of the samples recorded less than 0.028, 0.01, 0.01, and 0.03 mg kg-1 of bioaccessible Pb, Ni, Cd, and Cr, respectively. A significant negative correlation was observed between total metal concentration and bioaccessibility percentage. Targeted Hazard Quotient (THQ) of all the metals were less than one for adults indicating that there were no health risks, which undoubtedly reveals the importance of bioaccessible metal analysis. Hence, regular monitoring of heavy metals is essential to reduce the intensive accumulation in the human food chain.  Also, the present study has opened up a wide scope on human health risk assessment using an in vitro digestion model

Metal(loid) speciation and transformation by aerobic methanotrophs

Abstract: Manufacturing and resource industries are the key drivers for economic growth with a huge environmental cost (e.g. discharge of industrial effluents and post-mining substrates). Pollutants from waste streams, either organic or inorganic (e.g. heavy metals), are prone to interact with their physical environment that not only affects the ecosystem health but also the livelihood of local communities. Unlike organic pollutants, heavy metals or trace metals (e.g. chromium, mercury) are non-biodegradable, bioaccumulate through food-web interactions and are likely to have a long-term impact on ecosystem health. Microorganisms provide varied ecosystem services including climate regulation, purification of groundwater, rehabilitation of contaminated sites by detoxifying pollutants. Recent studies have highlighted the potential of methanotrophs, a group of bacteria that can use methane as a sole carbon and energy source, to transform toxic metal (loids) such as chromium, mercury and selenium. In this review, we synthesise recent advances in the role of essential metals (e.g. copper) for methanotroph activity, uptake mechanisms alongside their potential to transform toxic heavy metal (loids). Case studies are presented on chromium, selenium and mercury pollution from the tanneries, coal burning and artisanal gold mining, respectively, which are particular problems in the developing economy that we propose may be suitable for remediation by methanotrophs. 6g_ZKsLH11vt1AExshJzH4Video Abstrac

Long-term tannery waste contamination: effect on chromium chemistry / by Avudainayagam Subramanian.

Corrigenda inside front cover.Includes bibliographical references (leaves 205-232)xii, 232, [27] leaves : ill., plates ; 30 cm.Thesis (Ph.D.)--University of Adelaide, Dept. of Soil and Water, 200

Separation of chromium (III) and chromium (VI) by capillary electrophoresis using 2,6-pyridinedicarboxylic acid as a pre-column complexation agent

A simple method was developed for the simultaneous determination of Cr(III) and Cr(VI) by capillary zone electrophoresis (CZE), where Cr(III) was chelated with ligands to form anionic complexes. Nitrilotriacetic acid, N-2-hydroxyethylenediaminetriacetic acid, ethylenediaminetetraacetic acid, diethylenetriaminepentaacetic acid, and 2,6-pyridinedicarboxylic acid (PDCA) were investigated as Cr(III) complexing ligands. Of all the ligands studied, 2,6-PDCA with Cr(III) gave the largest UV response and high selectivity for Cr(III). In addition, the condition for pre-column derivatization, including pH, concentration ratio [Cr(III)/2,6-PDCA] and the stability of Cr(III) complexes were also examined. The separation of anionic forms of Cr(III) and Cr(VI) was achieved using co-CZE with UV detection at 185 nm. The electrolyte contained 30 mM phosphate, 0.5 mM tetradecyltrimethylammonium bromide, 0.1 mM 2,6-PDCA and 15% (v/v) acetonitrile at pH 6.4. The detection limits were 2 μM for Cr(III) and 3 μM for Cr(VI) and linear plots were obtained in a concentration range of 5–200 μM. The utility of the method was demonstrated for the determination of Cr(III) and Cr(VI) in contaminated soils.Zuliang Chen, Ravendra Naidu and Avudainayagam Subramania

Microbial role in the failure of natural attenuation of chromium(VI) in long-term tannery waste contaminated soil

Bioremediation of Cr(VI) in long-term contaminated soil environment has not been very successful due to the known reoxidation of Cr(III) to Cr(VI). Microbial role on the presence of Cr(VI) in soil samples from a long-term tannery waste contaminated site, even 25 years after cessation of waste disposal was examined. The contaminated soil, unamended or amended with 6.6% (w/w) cow manure, was incubated under 70% water holding capacity and saturated conditions. Water-soluble and exchangeable Cr(VI) declined to undetectable levels within 20 days only in saturated soil, irrespective of the presence or absence of cow manure. When the saturated soil with no Cr(VI) present was subjected to drying, Cr(VI) reappeared in cow manure-amended and unamended soil within 10 days of drying, but at levels far less than that present in the soil before saturation. When the saturated soil was autoclaved and then dried, Cr(VI) was not formed. Evidently, microorganisms are involved in the reoxidation of chromium and the resulting negligible attenuation of Cr(VI) at the long-term tannery waste contaminated site