Martha L. López

The biochemistry of environmental heavy metal uptake by plants: Implications for the food chain

Plants absorb a number of elements from soil, some of which have no known biological function and some are known to be toxic at low concentrations. As plants constitute the foundation of the food chain, some concerns have been raised about the possibility of toxic concentrations of certain elements being transported from plants to higher strata of the food chain. Special attention has been given to the uptake and biotransformation mechanisms occurring in plants and its role in bioaccumulation and impact on consumers, especially human beings. While this review draws particular attention to metal accumulation in edible plants, researched studies of certain wild plants and their consumers are included. Furthermore, this review focuses on plant uptake of the toxic elements arsenic, cadmium, chromium, mercury, and lead and their possible transfer to the food chain. These elements were selected because they are well-established as being toxic for living systems and their effects in humans have been widely documented. Arsenic is known to promote cancer of the bladder, lung, and skin and can be acquired, for example, through the consumption of As-contaminated rice. Cadmium can attack kidney, liver, bone, and it also affects the female reproduction system. Cadmium also can be found in rice. Chromium can produce cancer, and humans can be exposed through smoking and eating Cr-laden vegetables. Lead and mercury are well known neurotoxins that can be consumed via seafood, vegetables and rice.

Effect of indole-3-acetic acid, kinetin, and ethylenediaminetetraacetic acid on plant growth and uptake and translocation of lead, micronutrients, and macronutrients in alfalfa plants.

Alfalfa plants germinated and grown for 15 d in soil containing 80 mg Pb kg−1 were treated with ethylenediaminetetraacetic acid (EDTA) at 0.8 mM and indole-3-acetic acid-kinetin (IAA-KN) at 100 μM. Fifteen days after the treatment application, the concentration of lead (Pb), macronutrients, and micronutrients was determined using inductively coupled plasma/optical emission spectroscopy. The chlorophyll content and plant growth were also measured. Roots of plants exposed to Pb alone, Pb–EDTA, and Pb–EDTA-IAA-KN had 160, 140, and 150 mg Pb kg−1 DW, respectively. Pb was not detected in the stems of plants exposed to Pb alone; however, stems of plants treated with EDTA and EDTA–IAA-KN had 78 and 142 mg Pb kg−1 DW, respectively. While the Pb concentration in leaves of plants treated with EDTA and EDTA–IAA-KN was 92 and 127 mg kg−1 DW, respectively. In addition, EDTA and EDTA–IAA-KN significantly increased the translocation of zinc and manganese to leaves. The x-ray absorption spectroscopic studies demonstrated that Pb(II) was transported from roots to leaves without a change in the oxidation state.

The extraction of gold nanoparticles from oat and wheat biomasses using sodium citrate and cetyltrimethylammonium bromide, studied by x-ray absorption spectroscopy, high-resolution transmission electron microscopy, and UV-visible spectroscopy.

Gold (Au) nanoparticles can be produced through the interaction of Au(III) ions with oat and wheat biomasses. This paper describes a procedure to recover gold nanoparticles from oat and wheat biomasses using cetyltrimethylammonium bromide or sodium citrate. Extracts were analyzed using UV-visible spectroscopy, high-resolution transmission electron microscopy (HRTEM), and x-ray absorption spectroscopy. The HRTEM data demonstrated that smaller nanoparticles are extracted first, followed by larger nanoparticles. In the fourth extraction, coating of chelating agents is visible on the extracted nanoparticles.

Lead toxicity in alfalfa plants exposed to phytohormones and ethylenediaminetetraacetic acid monitored by peroxidase, catalase, and amylase activities

This manuscript describes the toxicity of lead in alfalfa plants treated with ethylenediaminetetraacetic acid (EDTA) and the phytohormones indole-3-acetic-acid (IAA), gibberellic acid (GA), and kinetin (KN), on catalase (CAT), ascorbate peroxidase (APOX), and total amylase activity (TAA). In all cases Pb was used at 40 mg/L; EDTA at 0.2 mM (equimolar to Pb); and IAA, GA, and KN at 1, 10, and 100 microM, respectively. An experiment containing Pb at 40 mg/L, 0.2 mM EDTA, and IAA and KN at 100 microM each was performed to determine changes in TAA. A control (plain nutrient solution) also was used for comparison. In all cases the treatments were performed in triplicate. Standard procedures were followed to determine the activity of the respective enzymes. After 10 d of exposure to the treatments, the leaves were harvested, homogenized, and centrifuged, and the supernatants were analyzed for CAT, APOX, and TAA. All determinations were performed in triplicate. The results demonstrated that CAT was reduced significantly (p < 0.05) by all treatments containing Pb, IAA, and GA at 10 and 100 microM. However, only the treatments Pb/EDTA/KN at 1, 10, and 100 microM reduced the APOX. The TAA in leaves of alfalfa plants was increased significantly (p < 0.05) by all treatments. Overall, the results suggest that the CAT tests showed no lead toxicity to the alfalfa seedlings. However IAA at 10 and 100 muM revealed toxicity to the CAT enzyme. In addition, the APOX tests exhibited no toxicity to the peroxidase enzyme with the exception of Pb/EDTA/KN treatments. Finally, the TAA tests showed high Pb/EDTA/phytohormone toxicity to the amylase enzyme in alfalfa seedlings.

Effects of Lead, EDTA, and IAA on Nutrient Uptake by Alfalfa Plants

ABSTRACT The element concentrations of alfalfa plants exposed for 10 d to 40 mg lead (Pb) L− 1 from lead nitrate [Pb(NO3)2] alone, or combined with ethylenediaminetetraacetic acid (EDTA) and indole-3-acetic acid (IAA), was determined by inductively coupled plasma-optical emission spectroscopy (ICP-OES). Indole-3-acetic acid at 10 μ M and Pb/EDTA/IAA at 10 μ M increased potassium (K) concentration in roots by 87% and 94%, respectively (P < 0.05). However, IAA at 100 μ M decreased K concentration in leaves (P < 0.05). Plants exposed to 100 μ M IAA, Pb/IAA at 100 μ M, and Pb/EDTA/IAA at 100 μ M had, respectively, 30%, 55%, and 40% more sulfur (S) in leaves than control plants (P < 0.05). Lead and Pb/IAA reduced Ca concentration in stems and leaves (P < 0.05). Conversely, Pb and Pb/EDTA increased Cu concentration in roots and stems. IAA at 100 μ M, Pb, and Pb/EDTA/IAA decreased Zn concentration in roots (P < 0.05). Manganese (Mn) and molybdenum (Mo) concentration in roots and stems was lower in plants treated with Pb and Pb/IAA (P < 0.05). Pb and Pb/IAA reduced (P < 0.05) the iron (Fe) concentration in roots. However, the addition of EDTA and IAA at 10 μ M reduced the negative effects of Pb on Fe absorption.

Concentration and biotransformation of arsenic by Prosopis sp. grown in soil treated with chelating agents and phytohormones

Environmental context. Arsenic (As) is a metalloid found throughout the environment. Although As can be released from natural phenomena, anthropogenic activities account for most As contamination worldwide. The toxicity of As depends on the form (inorganic or organic) and species (AsIII or AsV), among others. Plants have the ability to absorb and bioreduce As, cleaning the soil and reducing the toxicity of As to some extent. The aim of the present research was to study the effects of cysteine, the chelating agents cyclohexylenedinitrotetraacetic acid and nitrilotriacetic acid, and the phytohormone kinetin on the As concentration and speciation in mesquite (Prosopis sp.). The results give an insight about how a desert plant absorbs, bioreduces, distributes and stores this toxic metalloid. Abstract. The aim of the present research was to study the effects of cysteine (Cys), cyclohexylenedinitrotetraacetic acid (CDTA), nitrilotriacetic acid (NTA), and kinetin (KN) on the arsenic (As) concentration and speciation in mesquite (Prosopis sp.) grown in soil containing 30 ppm (parts per million) of AsIII or 50 ppm of AsV. Inductively coupled plasma–optical emission spectroscopy (ICP-OES) determinations revealed that, compared with As alone, roots of plants treated with 2.5 mM CDTA or 0.5 mM of Cys + 100 μM KN increased total As concentration from AsIII by ~20 and 36% and from AsV by 100 and 65%, respectively. Liquid chromatography–inductively coupled plasma–mass spectrometry (LC-ICP-MS) studies revealed that in roots, AsIII remained without change, whereas both AsIII and AsV were found in plants grown with AsV. X-ray absorption spectroscopy (XAS) studies revealed that As within plants was mainly coordinated to three sulfur atoms, with interatomic distances of 2.26 A. Results suggests that Cys + KN increased the mesquite tolerance to AsV, because plants grown in AsV had roots of similar size to plants grown without As.

Arsenic speciation in biological samples using XAS and mixed oxidation state calibration standards of inorganic arsenic

The speciation of elements without pre-edge features preformed with X-ray absorption near edge structure (XANES) can lead to problems when the energy difference between two species is small. The speciation of arsenic (As) in plant samples was investigated using the mixtures As2S3/As2O5, As2S3/As2O3, or As2O3/As2O5. The data showed that the energy separation (eV) between As2O5 and As2S3 was 5.8, between As2O3 and As2O5 was 3.6, and between As2S3 and As2O3 was 2.1. From the intensity of the white-line feature and the concentration of As species, calibration curves showing a limit of detection of approximately 10% were generated. In addition, an error of ±10% was determined for the linear combination–XANES (LC-XANES) fitting technique. The difference between the LC-XANES fittings and calculations from the calibration curves was <10%. The data also showed that the speciation of As in a sample can be determined using EXAFS (extended X-ray absorption fine structure). Finally, it was also shown that both EXAFS and XANES of the sample should be examined to determine the true speciation of an element. Even though there is a difference of 2 eV between As(III) bound to O and As(III) bound to S, in the EXAFS region the As(III)–S and As(III)–O ligands are clearly visible. However, distinction between the As(III)–O and As(V)–O ligands in the EXAFS spectra was not clearly visible in this study.

Study of Calcium(II), Copper(II), Magnesium(II), and Iron(III) Interference on Au(III) Binding to Native Hop Biomass Using ICP-OES

Abstract Biosorption of metals from industrial effluents has been studied widely. The economic advantage of scavenging precious metals such as gold has increased the interest in recovery technologies. Hop biomass has been studied for its capability of uptaking Au(III) ions from aqueous solutions. The interference of Cu(II), Fe(III), Ca(II), and Mg(II) on Au(III) binding to hop biomass was studied using ICP‐OES for metal quantification. Portions of hop biomass were reacted with mixed solutions of Cu(II)–Au(III), Fe(III)–Au(III), Cu(II)–Au(III), and Mg(II)–Au(III) at different concentrations. The analysis of the Cu(II)–Au(III) solution showed that Cu(II) ions do not interfere in Au(III) binding at pH 3, 4, and 5. All Fe(III) concentrations seem to have no effect on the Au(III) binding at the pH that was investigated. The presence of Ca(II) increases about 50% the binding of Au(III) at pH 6 and decreases about 25% at pH 2, while the presence of Mg(II) ions increased the Au(III) binding to native hop biomass almost 10% at pH 2 and more than 30% at pH 6.