Copyright (c) 2009 All rights reserved. http://works.bepress.com/jeffrey_weidenhamer Recent documents in Jeffrey D. Weidenhamer en-us Sat, 26 Sep 2009 23:31:36 PDT 3600 http://works.bepress.com/jeffrey_weidenhamer/14 http://works.bepress.com/jeffrey_weidenhamer/14 Fri, 25 Sep 2009 13:40:01 PDT Root exudates are implicated in the chemical defense of plants, but testing such hypotheses has been hindered by the difficulties of quantifying allelochemical concentrations in soil. Here we describe a new, simple method to quantify the dynamics of non-polar root exudates in soil. Novel soil probes were constructed using stainless steel wire inserted into polydimethylsiloxane (PDMS) tubing. Probes were inserted into soil for 24 h, removed and extracted, and analyzed by HPLC. Lipophilic thiophenes produced by roots of Tagetes and Rudbeckia species were chosen as candidate compounds to test the method. Probes recovered microgram quantities of the highly phytotoxic thiophenes 5-(3-buten-1-ynyl)-2,2'-bithienyl (BBT) and alpha-terthienyl per probe per day from the root zone of Tagetes patula, and distribution of thiophenes beneath plants was spatially and temporally heterogeneous. Flux-proportional sampling of soil provides a means to test hypotheses about the role of root exudates in plant-plant and other interactions. Jeffrey D. Weidenhamer Allelopathy -- Research Methods http://works.bepress.com/jeffrey_weidenhamer/13 http://works.bepress.com/jeffrey_weidenhamer/13 Sun, 14 Jun 2009 14:33:50 PDT Inexpensive highly leaded jewelry, much of it imported from China, remains widely available in the United States. The source materials for these items are unknown. Due to the low cost of much of this trinket jewelry, it seems likely that scrap materials may be used in their manufacture. Thirty-nine jewelry items previously determined to contain 90% or more lead by weight were analyzed for antimony content. The average antimony content of these thirty-nine items was 3.0%. The range of antimony content in the samples was from 0.3% to 6.2% antimony by weight, with twenty-seven of the samples in the range of 2-4% antimony by weight. By comparison, battery lead standard reference material obtained from the US National Institute of Standards and Technology contains 2.95% antimony by weight. While the evidence is circumstantial, the similarity in composition of these samples to battery lead is striking and supports the hypothesis that some battery lead is being recycled into highly leaded jewelry items. These results suggest that the recycling of this waste in China needs to be investigated, as the use of lead battery waste as a source material for children's jewelry poses a clear threat to children's health. Jeffrey D. Weidenhamer Lead Contamination http://works.bepress.com/jeffrey_weidenhamer/12 http://works.bepress.com/jeffrey_weidenhamer/12 Sun, 14 Jun 2009 10:11:54 PDT The oily droplets exuded from the root hairs of sorghum are composed of a 1:1 ratio of sorgoleone and its lipid resorcinol analogue. The production of these droplets appears to be suppressed when c. 20 μg of exudate mg−1 root dry weight accumulates at the tip of the root hairs. However, more exudate is produced following gentle washing of the roots with water, suggesting that the biosynthesis of lipid benzoquinones and resorcinols is a dynamic process. Sorgoleone interferes with several molecular target sites, including photosynthetic electron transport, in in vitro assays. However, the in planta mechanism of action of sorgoleone remains controversial because it is not clear whether this lipid benzoquinone exuding from the roots of sorghum is taken up by roots of the receiving plants and translocated to their foliage where it must enter the chloroplast and inhibit PSII in the thylakoid membrane. Experiments designed to test the in planta mode of action of sorgoleone demonstrated that it has no effect on the photosynthesis of older plants, but inhibits photosynthesis in germinating seedlings. Sorgoleone is not translocated acropetally in older plants, but can be absorbed through the hypocotyl and cotyledonary tissues. Therefore, the mode of action of sorgoleone may be the result of inhibition of photosynthesis in young seedlings in concert with inhibition of its other molecular target sites in older plants. Dayan E. Franck Allelopathy -- Research Methods http://works.bepress.com/jeffrey_weidenhamer/11 http://works.bepress.com/jeffrey_weidenhamer/11 Sun, 14 Jun 2009 10:01:50 PDT Lead is a potent neurotoxin and because of this, the US regulatory limit for lead content of paint on items intended for children is 0.06% by weight. There were numerous recalls of name-brand toys in the United States for lead paint contamination during 2007. Most of these items were manufactured in China. Seasonal and holiday items are inexpensive and often directed specifically toward children, yet the use of lead paints in these products has not been widely recognized. The objective of this study was to determine the extent of lead contamination in this product category. Ninety-five samples were tested, including primarily Halloween and Easter products. Twelve of the products were found to contain lead in excess of the current US regulatory limit of 0.06% by weight for lead in paints on items intended for children. The high percentage of products found to be contaminated in this limited sampling implies that many more lead-painted items are being sold. These results suggest that the potential hazards of seasonal and holiday products deserve the attention of government agencies seeking to limit the exposure of children to lead. Jeffrey D. Weidenhamer Lead Contamination http://works.bepress.com/jeffrey_weidenhamer/10 http://works.bepress.com/jeffrey_weidenhamer/10 Tue, 17 Mar 2009 09:39:35 PDT Jeffrey D. Weidenhamer Allelopathy -- Research Methods http://works.bepress.com/jeffrey_weidenhamer/9 http://works.bepress.com/jeffrey_weidenhamer/9 Tue, 17 Mar 2009 06:26:32 PDT Jeffrey D. Weidenhamer Lead Contamination http://works.bepress.com/jeffrey_weidenhamer/8 http://works.bepress.com/jeffrey_weidenhamer/8 Tue, 17 Mar 2009 06:15:55 PDT The neurological hazards of lead to children are well-known. As a result of recent documented cases of lead poisoning, regulatory attention in the United States has focused on the lead content of children's metal jewelry. By contrast, little is known about the possible hazards of plastic jewelry items. The objective of this study was to determine whether inexpensive plastic jewelry is a possible source of toxic lead for children. Samples of more than 100 inexpensive plastic jewelry items were analyzed for lead content. Beads were screened by soaking in 1 M nitric acid. Nine items found to release more than 30 µg of lead per bead were further tested for accessible lead, and scrapings of the bead coatings were analyzed for total lead content. The maximum accessible lead found was 49 µg per bead, which is below the current US Consumer Product Safety Commission limit of 175 µg. However, when the number of beads in each item was taken into account, six of the nine leaded samples contained more than 175 µg accessible lead per item. The lead in these items appears to be associated with lead-based paints used to produce glossy coatings on imitation pearls and similar items. Coatings obtained by scraping individual beads contained 3.5-23% lead, which far exceeds the US regulatory limit of 0.06% lead in paints on items intended for children. Our results demonstrate that plastic jewelry items merit the attention of public health and consumer protection agencies seeking to limit the exposure of children to lead. Jamie L. Yost Lead Contamination http://works.bepress.com/jeffrey_weidenhamer/7 http://works.bepress.com/jeffrey_weidenhamer/7 Tue, 17 Mar 2009 05:40:21 PDT Highly leaded jewelry, often imported from China, remains widely available in the United States. Leaded electronic waste is exported from the United States to several Asian countries where solder is recovered and circuit boards are stripped of parts in small workshops. To assess whether electronic waste is being recycled into the jewelry, lead, tin and copper content of highly leaded jewelry samples were determined by atomic absorption spectrometry. Sixteen jewelry items previously determined to contain 20-80% lead by weight were analyzed. Samples were digested in nitric acid for analysis of lead and copper, and in aqua regia for analysis of tin. Six samples contained significant amounts of tin, from 20.8% to 29.9% by weight. In addition, copper was a significant minor component of five of these samples (up to 4% by weight). Copper (present at 10-40% by weight in circuit boards) was shown to rapidly move into heated lead-tin solder. The combined lead-tin-copper content of these six items ranges from 93.5% to 100%, suggestive of a solder-based source material. These results are consistent with the hypothesis that recycled circuit board solders are being used to produce some of the heavily leaded imported jewelry sold in the United States. Should this hypothesis be substantiated, it suggests that environmental policies to protect children's health must address both proper recycling of source materials as well as restrictions of the lead content in consumer goods. Jeffrey D. Weidenhamer Lead Contamination http://works.bepress.com/jeffrey_weidenhamer/6 http://works.bepress.com/jeffrey_weidenhamer/6 Mon, 16 Mar 2009 17:53:50 PDT Recent recalls of lead-contaminated jewelry and the death of a Minnesota child by lead poisoning after swallowing a jewelry charm have highlighted the hazards of leaded jewelry to children. We sought to determine the extent of lead contamination in inexpensive, imported jewelry available in United States retail stores. A total of 139 jewelry items were purchased from ten retail store chains in five different geographic locations. Samples were digested in nitric acid followed by atomic absorption analysis. Accessibility of lead was analyzed by leaching a subset of heavily leaded samples in 0.07M hydrochloric acid. Almost half (42.6%) of the items assayed were heavily leaded, exceeding 80% lead by weight. Average lead content for all items tested was 44.0%, and one or more heavily leaded items were found in samples from each retail store and each geographic location. Six of ten samples tested for leachability of lead exceeded the US Consumer Product Safety Commission guidelines of 175μg accessible lead. Our results show that much inexpensive children's and costume jewelry imported and sold in the US is heavily leaded. Given the high neurotoxicity of lead to young children, inexpensive jewelry items pose a potential yet avoidable threat to children's health. Jeffrey D. Weidenhamer Lead Contamination http://works.bepress.com/jeffrey_weidenhamer/5 http://works.bepress.com/jeffrey_weidenhamer/5 Tue, 10 Mar 2009 11:25:51 PDT Gallic acid and hydroquinone have been identified as the major allelochemicals of the known allelopathic plant Polygonella myriophylla. Both of these compounds occur in the foliage as glycosides. Quercetin and rhamnetin were identified as the major flavonoid constituents, but in much lower concentration. The behavior of gallic acid, hydroquinone, the hydroquinone glycoside arbutin, and benzoquinone in sterile and nonsterile soil from beneath Polygonella was investigated. Sterilization effectively stabilized arbutin, hydroquinone, and gallic acid. Concentrations of benzoquinone rapidly diminished in sterilized soil, and the compound was almost completely gone after 7 days. In nonsterile soils, all four compounds degraded rapidly. The order of persistence was hydroquinone > benzoquinone > gallic acid > arbutin. Persistence was rate-dependent. Arbutin degraded to hydroquinone, and benzoquinone formed as a degradation product of hydroquinone. Hydroquinone was also observed as a degradation product of benzoquinone. Benzoquinone degrades rapidly by nonmicrobial oxidative processes. These results support the hypothesis that microbial and nonmicrobial oxidative transformations of soil allelochemicals are crucial in mediating the allelopathic effects of Polygonella myriophylla. Jeffrey D. Weidenhamer Allelopathic Effects of Florida Scrub Perennials