Geoffrey B. Saupe

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.

Kinetin increases chromium absorption, modulates its distribution, and changes the activity of catalase and ascorbate peroxidase in Mexican Palo Verde

This report shows, for the first time, the effectiveness of the phytohormone kinetin (KN) in increasing Cr translocation from roots to stems in Mexican Palo Verde. Fifteen-day-old seedlings, germinated in soil spiked with Cr(III) and (VI) at 60 and 10 mg kg(-1), respectively, were watered every other day for 30 days with a KN solution at 250 μM. Samples were analyzed for catalase (CAT) and ascorbate peroxidase (APOX) activities, Cr concentration, and Cr distribution in tissues. Results showed that KN reduced CAT but increased APOX in the roots of Cr(VI)-treated plants. In the leaves, KN reduced both CAT and APOX in Cr(III) but not in Cr(VI)-treated plants. However, KN increased total Cr concentration in roots, stems, and leaves by 45%, 103%, and 72%, respectively, compared to Cr(III) alone. For Cr(VI), KN increased Cr concentrations in roots, stems, and leaves, respectively, by 53%, 129%, and 168%, compared to Cr(VI) alone. The electron probe microanalyzer results showed that Cr was mainly located at the cortex section in the root, and Cr distribution was essentially homogeneous in stems. However, proven through X-ray images, Cr(VI)-treated roots and stems had more Cr accumulation than Cr(III) counterparts. KN increased the Cr translocation from roots to stems.

Potential of Chilopsis linearis for gold phytomining: using XAS to determine gold reduction and nanoparticle formation within plant tissues.

This study reports on the capability of the desert plant Chilopsis linearis (Cav.) Sweet (desert willow) to uptake gold (Au) from gold-enriched media at different plant-growth stages. Plants were exposed to 20, 40, 80, 160, and 320 mg Au L−1 in agar-based growing media for 13, 18, 23, and 35 d. The Au content and oxidation state of Au in the plants were determined using an inductively coupled plasma/optical emission spectrometer (ICP/OES) and X-ray absorption spectroscopy (XAS), respectively. Gold concentrations ranging from 20 to 80 mg Au L−1 did not significantly affect Chilopsis linearis plant growth. The concentration of gold in the plants increased as the age of the plant increased. The Au concentrations in leaves for the 20, 40, 80, and 160 mg Au L−1 treatments were 32, 60, 62, and 179 mg Au kg−1 dry weight mass, respectively, demonstrating the gold uptake capability of desert willow. The XAS data indicated that desert willow produced gold nanoparticles within plant tissues. Plants exposed to 160 mg Au L−1 formed nanoparticles that averaged approximately 8, 35, and 18 Å in root, stem, and leaves, respectively. It was observed that the average size of the Au nanoparticles formed by the plants is related to the total Au concentration in tissues and their location in the plant

Use of chemical modification and spectroscopic techniques to determine the binding and coordination of gadolinium(III) and neodymium(III) ions by alfalfa biomass

Metal pollution in the aqueous environment has become an important issue in the past few decades leading to extensive research in the area of pollution remediation. Most of the recent research in this area has been in bioremediation including phytofiltration and phytoextraction. Although there has been a lot of research done in the field of metal interactions with plants, the actual mechanism(s) and ligands involved are not well understood. Through a series of batch experiments, including pH profiles, time dependency studies, and capacity experiments, we have investigated the binding of Gd(III) and Nd(III) to alfalfa biomass. Batch pH studies showed that the optimum binding was at pH 5.0 for both elements. The time dependency experiments showed that the binding occurs within the first 5min of contact and remains constant for up to 60min. In addition, chemical modifications to the alfalfa biomass were performed to indirectly determine the ligands on the biomass responsible for metal binding. For Gd(III) binding, it was shown that the carboxyl groups on the biomass play the most important role in metal ion binding. However, for Nd(III), not only was it found that the carboxyl groups play an important role in the binding, but in addition, the amino groups on the biomass also play an important role in the binding of the metal ions. Further studies using X-ray absorption spectroscopy (XAS) showed that the Gd(III) and Nd(III) ions were bound to the alfalfa biomass through oxygen (or nitrogen ligands), which were coordinated to carbon atoms. The lanthanide complexes within the biomass included some coordinated water molecules.

Using New Porous Nanocomposites for Photocatalytic Water Decontamination

Heterogeneous catalysts that accelerate the photolytic destruction of organic contaminants in water are a potentially inexpensive and highly effective way to remove both trace-level and saturated harmful compounds from industrial waste streams and drinking water. Porous photocatalytic materials can have the combined qualities of high surface area and relatively large particle sizes, as compared with nanoparticulate catalyst powders like titanium dioxide . The larger particle sizes of the porous materials facilitate catalyst removal from a solution, after purification has taken place. We have synthesized new kinds of photocatalytic porous oxide materials that can be used to purify contaminated water by accelerating the photodegradation of any kind of organic pollutant. The new materials have very large open pore structures that facilitate the diffusion, the surface contact of contaminants, and solvent flow through the catalyst. These qualities enhance surface reactions important to the process. The new catalysts have shown robust physical and chemical properties that make them candidates for real applications in polluted water decontamination.

Use of Plasma-Based Spectroscopy and Infrared Microspectroscopy Techniques to Determine the Uptake and Effects of Chromium(III) and Chromium(VI) on Parkinsonia Aculeata

Chromium uptake and tolerance by Mexican Palo Verde (Parkinsonia aculeata) (MPV) was studied in a six-month experiment with Cr(III) and Cr(VI) at 60 and 10 mg kg−1, respectively. Chromium and nutrient uptake were determined by ICP-OES and changes in macromolecules were studied by infrared microspectroscopy (IMS). In the Cr(VI)-treated plants, chromium concentration increased in the roots only through the third month, while translocation to stems increased constantly throughout the six months. Cr(III) applications decreased the amount of Zn in leaves and stems (p ≤ 0.05). Cr(VI) increased P and S in all plant tissues and increased Ca in roots, but decreased Ca in stems and leaves, and Mg in roots and stems. Cr(III) decreased P in stems and leaves, while both Cr ions decreased K in all MPV tissues. Relative to untreated plant tissue, the IMS revealed significant changes at 1730 cm−1 and 845 cm−1. Changes at 1730 cm−1 indicated that the cortex and xylem of Cr-treated plants were more proteinaceous. Changes at 845 cm−1 revealed higher lignifications in cortex. However, at the stem level, Cr(VI) decreased lignin deposition in xylem. The data showed that MPV could be useful in the phytoremediation of Cr in moderately impacted soils.

Getting past the first year: Retaining engineering majors

Peer Led Team Learning (PLTL) is a nationally recognized curriculum enhancement strategy adopted in various forms by over 150 universities and colleges across the United States. Consistent with the outcomes and the vision of ABET Engineering Criteria 2000 and the National Academy of Engineering Engineer 2020, PLTL prepares students to work in teams; apply knowledge of mathematics, science, and engineering to solve problems; communicate effectively; engage in life-long learning; and develop leadership skills. Published PLTL program data have shown that using peer leaders in small group workshop settings boosts performance in critical first-year courses including core math, science and engineering courses. The PLTL model promotes the growth of critical workplace skills for students and peer leaders such as working in teams, listening, critical thinking and leadership. This paper will present the basics of the PLTL instructional model, including sample materials developed for engineering workshops. Consideration of the practicalities of the six critical components will be discussed: integration of the workshop component into the course structure, involvement of the teaching faculty, training and supervision of the peer leaders, creation of challenging materials, and provision of appropriate institutional resources.