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Selenium and arsenic speciation in plantsAborode, Fatai Adigun January 2013 (has links)
Selenium and arsenic are important metalloids in the food chain from nutritional and toxicological point of view. These two metalloids are potentially enriched through geogenic processes and anthropogenic activities and they could sometimes co-exist in nature and become available to plants thereby entering the food chain. While selenium is known as an essential element to humans, it could also be toxic. Arsenic on the other hand is a potentially toxic element posing serious health risks to livestock and humans. They have been found to neutralise each other’s effects in animals but their interactions in plants are not well understood. Speciation analysis, which is a set of activities leading to identification and quantification of different forms or species of elements present in an entity, is required for a holistic understanding of the mechanisms and interactions involved in the plants’ metabolism of contaminants and essential elements. Many techniques are currently being used for speciation of selenium and arsenic in plants and they sometimes give contradictory outcomes. The hyphenation of HPLC with MS and synchrotron techniques are the two most commonly used state of the art techniques for speciation of these metalloids. This research therefore sought to access, explore and/ or develop analytical methods appropriate for the speciation of selenium and arsenic in plants. Many selenium and arsenic species have been identified and reported in the literature using well established procedures. The presence of elemental selenium in plants has also been widely reported in plants but to our knowledge this presence has never been experimentally proven and fully quantified. Because this species is non toxic, its proven occurrence in plants will represent a potential detoxification mechanism. Therefore in this study, a method was specifically developed for identification and quantification of elemental selenium. In order to investigate the occurrence of elemental selenium in plants, the newly developed method was applied using Thunbergia alata as a model plant. Arsenic is known to activate the synthesis of PC using glutathione and the complexation of the activating arsenic ions with the synthesised PCs is a well established detoxification mechanism for arsenic. However, very little is known about the role of glutathione and PCs in selenium detoxification. In order to be able to gain better insight into the interaction between selenium and arsenic in plants, the role of glutathione and PCs in selenium metabolism was investigated using Arabidopsis thaliana as a model plant. Sensitivity tests and speciation analysis were carried out on Arabidopsis thaliana WT and the mutants’ one of which is deficient in GSH synthesis and the other deficient in PC synthesis using selenite and arsenate as toxicants. The study revealed that selenium induces the synthesis of glutathione but rather use it as reductant and precursor for transformation and incorporation into peptides and neither GSH nor PCs play any role in selenium detoxification. It was also observed that when selenium and arsenic co-exist there could be competition for PCs between the ions of the metalloids with potentials for increasing arsenic toxicity. Human exposure to inorganic arsenic, a group 1 carcinogen, through Oryza sativa (rice), the staple food for about half the population of the world, has raised serious concerns. Most worrisome are the findings that rice grown in arsenic contaminated areas is characterised by reduced essential amino acids and micronutrients including selenium. A study was therefore conducted to to investigate and understand the interactions between selenium and arsenic in rice. The study confirmed that arsenic could limit the amount of selenium that is taken and translocated to the grains. Selenium was also found to reduce the toxicity of arsenic and most importantly, the study showed that at an appropriate selenium concentration, arsenic uptake and translocation can be reduced.
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Atomic absorption spectroscopic determination of mercury, selenium and arsenic in biological and environmental materials /Dhindsa, Harkirat S. January 1900 (has links)
Thesis (Ph.D.)--University of Western Sydney, Nepean, 1998. / Includes bibliographies.
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Investigation of selenium and arsenic in coal-mining associated rocks and sediments using ultrasonic and sequential extractions techniquesPumure, Innocent. January 1900 (has links)
Thesis (Ph. D.)--West Virginia University, 2008. / Title from document title page. Document formatted into pages; contains xv, 162 p. : ill. (some col.), maps (some col.). Includes abstract. Includes bibliographical references (p. 157-162).
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Determination Of Arsenic, Selenium And Cadmium In Some Turkish Spices By Inductively Coupled Plasma Mass SpectrometrySenol, Feriye 01 July 2010 (has links) (PDF)
ABSTRACT
DETERMINATION OF ARSENIC, SELENIUM AND CADMIUM IN SOME
TURKISH SPICES BY INDUCTIVELY COUPLED PLASMA MASS
SPECTROMETRY
Senol, Feriye
M.Sc., Department of Chemistry
Supervisor: Prof. Dr. O. Yavuz Ataman
July 2010, 106 Pages
The major source of all the nutrient elements for human body is the daily diet
which is affected by age, sex, and health status, geographic and climatic conditions.
It is important to analyze food items in order to determine their elemental contents,
estimate their dietary intakes and compare with recommended or tolerated intake
values in order to limit or increase their consumption. Spices are taken from different
parts of plants and widely used in cooking processes. They are convenient samples to
investigate the distribution of elements among different parts of plants and to
evaluate their daily intakes. Arsenic and selenium are both essential and toxic
elements whereas cadmium is considered to be toxic to human health. The
recommended dietary allowance (RDA) level of selenium ranges from 50 to 200
&mu / g/day. The RDA level of arsenic is set to be 100-200 &mu / g/day for adults to meet the
requirements. The weekly tolerable intake of cadmium and arsenic are 7 and 15
&mu / g/kg, respectively whereas selenium is toxic when intake is greater than 750 &mu / g/day
.
In this study the analysis of a variety of Anatolian spices including daisy
(Chamomillae Vulgaris), bay leaf (Folium Lauri), mint (Folium Menthane), rosehip
(Rosae Caninae), sage (Folium Salviae Officinalis), thyme (Herba Thymi), cumin
(Fructus Cummuni), sumac (Folium Rhois Coriariae), linden flower (Flos Tilliae)
v
and black pepper (Piper Nigrum) were performed and As, Cd and Se levels were
determined by using inductively coupled plasma mass spectrometry (ICP-MS). The
results obtained were evaluated together with the results of previous studies for
determination of Na, K, Mg, Ca, Li, Zn, Fe, Cu, B, Hg, Pb and Mn by inductively
coupled plasma optical emission spectrometry (ICPOES) and atomic absorption
spectrometry (AAS). Samples were digested in microwave oven in optimized
concentrations of HNO3 and H2O2. microwave temperature program was optimized
to maximize digestion efficiency. Samples were analyzed by using direct calibration
method for cadmium and standard addition method for arsenic and selenium
considering the effect of HNO3 concentration on ICP-MS signals. The accuracy of
the methods was checked by using Oyster Tissue 1566b SRM for cadmium and
arsenic and BCR Human Hair, 397 SRM for selenium. The mean arsenic and
selenium levels were found to be in the range of 100-500 &mu / g/ kg whereas cadmium
levels were relatively lower falling in a range of 10-100 &mu / g/ kg with few exceptions.
In order to investigate the effects of spectral and nonspectral interferences on arsenic
signals interference studies were performed by using HCl, NaCl, NaNO3, CsCl,
CsNO3, LiCl and LiNO3. Statistical evaluations were performed on data in order to
detect on significant trends.
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