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Bolan, Shiv,Kunhikrishnan, Anitha,Seshadri, Balaji,Choppala, Girish,Naidu, Ravi,Bolan, Nanthi S.,Ok, Yong Sik,Zhang, Ming,Li, Chun-Guang,Li, Feng,Noller, Barry,Kirkham, Mary Beth Elsevier 2017 Environment international Vol.108 No.-
<P><B>Abstract</B></P> <P>The last few decades have seen the rise of alternative medical approaches including the use of herbal supplements, natural products, and traditional medicines, which are collectively known as ‘Complementary medicines’. However, there are increasing concerns on the safety and health benefits of these medicines. One of the main hazards with the use of complementary medicines is the presence of heavy metal(loid)s such as arsenic (As), cadmium (Cd), lead (Pb), and mercury (Hg). This review deals with the characteristics of complementary medicines in terms of heavy metal(loid)s sources, distribution, bioavailability, toxicity, and human risk assessment. The heavy metal(loid)s in these medicines are derived from uptake by medicinal plants, cross-contamination during processing, and therapeutic input of metal(loid)s. This paper discusses the distribution of heavy metal(loid)s in these medicines, in terms of their nature, concentration, and speciation. The importance of determining bioavailability towards human health risk assessment was emphasized by the need to estimate daily intake of heavy metal(loid)s in complementary medicines. The review ends with selected case studies of heavy metal(loid) toxicity from complementary medicines with specific reference to As, Cd, Pb, and Hg. The future research opportunities mentioned in the conclusion of review will help researchers to explore new avenues, methodologies, and approaches to the issue of heavy metal(loid)s in complementary medicines, thereby generating new regulations and proposing fresh approach towards safe use of these medicines.</P> <P><B>Highlights</B></P> <P> <UL> <LI> A first-time comprehensive overview on the health risk assessment of heavy metal(loid)s in complementary medicines </LI> <LI> Ayurvedic medicines contain toxic levels of heavy metal(loid)s including As, Cd, Hg and Pb </LI> <LI> The bioavailability of metal(loid)s in complementary medicines depends on speciation of these metals </LI> <LI> Regular intake of some complementary medicines has caused metal(loid) toxicity in humans </LI> <LI> Health risk assessment can be achieved based on the daily intake of complementary medicines and total metal(loid) content </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>Interactions between heavy metal(loid)s and complementary medicines.</P> <P>[DISPLAY OMISSION]</P>
Remediation of heavy metal(loid)s contaminated soils - To mobilize or to immobilize?
Bolan, N.,Kunhikrishnan, A.,Thangarajan, R.,Kumpiene, J.,Park, J.,Makino, T.,Kirkham, M.B.,Scheckel, K. Elsevier Scientific Pub. Co 2014 Journal of hazardous materials Vol.266 No.-
Unlike organic contaminants, metal(loid)s do not undergo microbial or chemical degradation and persist for a long time after their introduction. Bioavailability of metal(loid)s plays a vital role in the remediation of contaminated soils. In this review, the remediation of heavy metal(loid) contaminated soils through manipulating their bioavailability using a range of soil amendments will be presented. Mobilizing amendments such as chelating and desorbing agents increase the bioavailability and mobility of metal(loid)s. Immobilizing amendments such of precipitating agents and sorbent materials decrease the bioavailabilty and mobility of metal(loid)s. Mobilizing agents can be used to enhance the removal of heavy metal(loid)s though plant uptake and soil washing. Immobilizing agents can be used to reduce the transfer to metal(loid)s to food chain via plant uptake and leaching to groundwater. One of the major limitations of mobilizing technique is susceptibility to leaching of the mobilized heavy metal(loid)s in the absence of active plant uptake. Similarly, in the case of the immobilization technique the long-term stability of the immobilized heavy metal(loid)s needs to be monitored.
Sorption-bioavailability nexus of arsenic and cadmium in variable-charge soils
Bolan, N.,Mahimairaja, S.,Kunhikrishnan, A.,Naidu, R. Elsevier Scientific Pub. Co 2013 Journal of hazardous materials Vol.261 No.-
In this work, the nexus between sorption and bioavailability of arsenic (As) and cadmium (Cd) as affected by soil type, soil pH, ageing, and mobilizing agents were examined. The adsorption of As and Cd was examined using a number of allophanic and non-allophanic soils which vary in their charge components. The effect of pH and ageing on the bioavailability of As and Cd was examined using spiked soils in a plant growth experiment. The effect of phosphate (P)-induced mobility of As on its bioavailability was examined using a naturally contaminated sheep dip soil. The results indicated that the adsorption of both As and Cd varied amongst the soils, and the difference in Cd adsorption is attributed to the difference in surface charge. An increase in soil pH increased net negative charge by an average of 45.7mmol/kg/pH thereby increasing cation (Cd) adsorption; whereas, the effect of pH on anion (As) adsorption was inconsistent. The bioavailability of As and Cd decreased by 3.31- and 2.30-fold, respectively, with ageing which may be attributed to increased immobilization. Phosphate addition increased the mobility and bioavailability of As by 4.34- and 3.35-fold, respectively, in the sheep dip soil. However, the net effect of P on As phytoavailability depends on the extent of P-induced As mobilization in soils and P-induced competition for As uptake by roots. The results demonstrate the nexus between sorption and bioavailability of As and Cd in soils, indicating that the effects of various factors on bioavailability are mediated through their effects on sorption reactions.