Jeffrey D. Weidenhamer

In Situ silicone tube microextraction: A new method for undisturbed sampling of root-exuded thiophenes from marigold (Tagetes erecta L.) in soil

Brian K. Mohney et al. — Mon, 30 May 2011 15:25:52 PDT

The difficulties of monitoring allelochemical concentrations in soil and their dynamics over time have been a major barrier to testing hypotheses of allelopathic effects. Here, we evaluate three diffusive sampling strategies that employ polydimethylsiloxane (PDMS) sorbents to map the spatial distribution and temporal dynamics of root-exuded thiophenes from the African marigold, Tagetes erecta. Solid phase root zone extraction (SPRE) probes constructed by inserting stainless steel wire into PDMS tubing were used to monitor thiophene concentrations at various depths beneath marigolds growing in PVC pipes. PDMS sheets were used to map the distribution of thiophenes beneath marigolds grown in thin glass boxes. Concentrations of the two major marigold thiophenes measured by these two methods were extremely variable in both space and time. Dissection and analysis of roots indicated that distribution of thiophenes in marigold roots also was quite variable. A third approach used 1 m lengths of PDMS microtubing placed in marigold soil for repeated sampling of soil without disturbance of the roots. The two ends of the tubing remained out of the soil so that solvent could be washed through the tubing to collect samples for HPLC analysis. Unlike the other two methods, initial experiments with this approach show more uniformity of response, and suggest that soil concentrations of marigold thiophenes are affected greatly even by minimal disturbance of the soil. Silicone tube microextraction gave a linear response for α-terthienyl when maintained in soils spiked with 0–10 ppm of this thiophene. This method, which is experimentally simple and uses inexpensive materials, should be broadly applicable to the measurement of non-polar root exudates, and thus provides a means to test hypotheses about the role of root exudates in plant-plant and other interactions.

Bioavailability of Cadmium in inexpensive jewelry

Jeffrey D. Weidenhamer et al. — Sun, 20 Mar 2011 18:14:10 PDT

BACKGROUND: High cadmium (Cd) concentrations have recently been found in some inexpensive jewelry. In response, the US Consumer Product Safety Commission (CPSC) has issued five recalls of children’s jewelry products for Cd contamination. However, there is no formal standard for Cd in jewelry and few data exist regarding potential exposures.

OBJECTIVES: We evaluated the bioavailability of Cd in 86 components of 57 jewelry items found to contain high levels of Cd (>10,000 ppm) by X-ray fluorescence (XRF), using extractions which simulate mouthing or swallowing of jewelry items.

METHODS: Jewelry was screened for Cd content by XRF. Bioavailability was measured in two ways. Items were placed in saline solution at 37oC for six hr to simulate exposures from mouthing of jewelry items. Items were placed in dilute HCl at 37°C for 6-96 hr, simulating the worst case scenario of a child swallowing a jewelry item. Damaged pieces of selected samples were also extracted by both methods to determine the effect of breaching the outer plating on bioavailability. Total Cd content of all items was determined by atomic absorption (AA).

RESULTS: The six hr saline extraction yielded as much as 2200 µg Cd, and 24 hr dilute HCl extraction yielded a maximum of more than 20,000 µg Cd. Leaching of Cd in dilute HCl increased linearly over 6-96 hr, indicating potential for increasing harm the longer an item remains in the stomach. Damage to jewelry by breaching the outer plating generally but not always increased Cd release. Bioavailability did not correlate directly with Cd content.

CONCLUSIONS: These results indicate the potential for dangerous Cd exposures to children who wear, mouth, or accidentally swallow high-Cd jewelry items.

Constituents of Calamintha ashei: effects on Florida sandhill species

M. A. Menelaou et al. — Thu, 25 Nov 2010 18:39:45 PST

Chemical constituents of the perennial shrub Calamintha ashei have been characterized as part of our investigation of the allelopathic properties of this plant. Besides the known monoterpenes, (+)-evodone, (-)-calaminthone and (+)-desacetylcalaminthone, fresh aerial parts of C. ashei provided six new menthofurans, two new germacrane sesquiterpenes, and the six, known flavonoids: 5-desmethoxynobiletin, 5-hydroxy-6,7,8,4'-tetramethoxyflavone, 5,4'-dihydroxy-6,7,8,3'-tetramethoxyflavone, thymonin, 5,4'-dihydroxy-6,7-dimethoxyflavone and 6-hydroxy-7,3'-dimethoxyluteolin. The structures of the new compounds were elucidated by spectroscopic methods and comparison of their H-1 NMR spectra with those of structurally related compounds. The molecular structures of (+)-evodone, 5-desmethoxynobiletin (5-hydroxy-6,7,8,3',4'-pentamethoxyflavone) and the triacetate of thymonin (7,8,3'-trimethoxy-5,6,4'-triacetoxyflavone), were determined by single crystal X-ray diffraction. Saturated aqueous solutions of menthofuran, (+)-evodone, (-)-calaminthone, (+)-esacetylcalaminthone, 4 alpha,5 beta-diacetoxymenthofuran, as well as mixtures of (+)-evodone and (+)-desacetylcalaminthone inhibited the germination and root growth of Schizachyrium scoparium and Leptochloa dubia, two native Florida sandhill grasses, as well as Lactuca saliva. (+)-Evodone and (+)-desacetylcalaminthone were the most active. 5-Hydroxy-6,7,8,3',4'-pentamethoxyflavone and 5,4'-dihydroxy-6,7,8,3'-tetramethoxyflavone and mixtures of the two flavonoids in aqueous as well as in saturated aqueous solutions of ursolic acid were tested on the same species, but showed no significant activity.

Assessment of leaching potential of highly leaded jewelry

Jeffrey D. Weidenhamer et al. — Wed, 28 Apr 2010 16:31:50 PDT

Lead is a potent neurotoxin particularly toxic to young children, and in response to recent poisonings of children and high levels of lead contamination in children's jewelry, US regulatory standards for lead content in these items have become much more stringent. Parents are often advised to throw out suspect items in the trash. While household wastes are generally exempt from consideration as hazardous waste, the potential for leaching of hazardous quantities of lead from such items is unknown. A modified Toxicity Characteristic Leaching Procedure (TCLP), in which intact jewelry components were subjected to leaching, was used to evaluate the potential for leaching of lead from highly leaded jewelry. Of 62 jewelry components tested, 61 exceeded the US regulatory standard for lead of 5 mg/L, and leachate lead concentrations averaged 1460 mg/L. Twenty-six of the component items tested yielded TCLP lead concentrations exceeding 1000 mg/L. These results demonstrate that highly leaded jewelry items may leach significant amounts of lead, and provide another reason to remove lead from these products. Furthermore, these results suggest that while the volume of such items in the municipal solid waste (MSW) stream is small, they have the potential to contribute significant quantities of lead to MSW leachates. (C) 2010 Elsevier By. All rights reserved.

Direct and indirect effects of invasive plants on soil chemistry and ecosystem function

Jeffrey D. Weidenhamer et al. — Wed, 28 Apr 2010 16:18:45 PDT

Invasive plants have a multitude of impacts on plant communities through their direct and indirect effects on soil chemistry and ecosystem function. For example, plants modify the soil environment through root exudates that affect soil structure, and mobilize and/or chelate nutrients. The long-term impact of litter and root exudates can modify soil nutrient pools, and there is evidence that invasive plant species may alter nutrient cycles differently from native species. The effects of plants on ecosystem biogeochemistry may be caused by differences in leaf tissue nutrient stoichiometry or secondary metabolites, although evidence for the importance of allelochemicals in driving these processes is lacking. Some invasive species may gain a competitive advantage through the release of compounds or combinations of compounds that are unique to the invaded community-the "novel weapons hypothesis." Invasive plants also can exert profound impact on plant communities indirectly through the herbicides used to control them. Glyphosate, the most widely used herbicide in the world, often is used to help control invasive weeds, and generally is considered to have minimal environmental impacts. Most studies show little to no effect of glyphosate and other herbicides on soil microbial communities. However, herbicide applications can reduce or promote rhizobium nodulation and mycorrhiza formation. Herbicide drift can affect the growth of non-target plants, and glyphosate and other herbicides can impact significantly the secondary chemistry of plants at sublethal doses. In summary, the literature indicates that invasive species can alter the biogeochemistry of ecosystems, that secondary metabolites released by invasive species may play important roles in soil chemistry as well as plant-plant and plant-microbe interactions, and that the herbicides used to control invasive species can impact plant chemistry and ecosystems in ways that have yet to be fully explored.

Solid-phase root zone extraction (SPRE): a new methodology for measurement of allelochemical dynamics in soil

Jeffrey D. Weidenhamer et al. — 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.

Evidence of recycling of lead battery waste into highly leaded jewelry

Jeffrey D. Weidenhamer et al. — 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.

Dynamic root exudation of sorgoleone and its in planta mechanism of action.

Franck E. Dayan et al. — 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.

Lead contamination of inexpensive seasonal and holiday products.

Jeffrey D. Weidenhamer — 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.

Bioassays for allelopathy in terrestrial plants

Jeffrey D. Weidenhamer et al. — Tue, 17 Mar 2009 09:39:35 PDT

Lead and civilization: a new general education science course

Jeffrey D. Weidenhamer et al. — Tue, 17 Mar 2009 06:26:32 PDT

Lead contamination of inexpensive plastic jewelry

Jamie L. Yost et al. — 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.

Leaded electronic waste is a possible material for lead-contaminated jewelry

Jeffrey D. Weidenhamer et al. — 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.

Widespread lead contamination of imported low-cost jewelry in the US

Jeffrey D. Weidenhamer et al. — 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.

Allelochemicals of polygonella myriophylla: chemistry and soil degradation

Jeffrey D. Weidenhamer et al. — 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.

Allelochemicals as a mechanism for resisting invasion: the case of polygonella myriophylla

Jeffrey D. Weidenhamer et al. — Tue, 10 Mar 2009 10:57:33 PDT

Distinguished allelopathy from resource competition: the role of density

Jeffrey D. Weidenhamer — Tue, 10 Mar 2009 10:04:17 PDT

Biomimetic measurement of allelochemical dynamics in the rhizoshere

Jeffrey D. Weidenhamer — Tue, 10 Mar 2009 09:59:29 PDT

Density-dependent phytotoxicity: distinguished resource competition and allelopathic interference in plants

Jeffrey D. Weidenhamer — Tue, 10 Mar 2009 09:55:58 PDT