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A novel, multiwalled carbon nanotube (MWCNT)-supported micro-solid-phase extraction (mu-SPE) procedure has been developed. A 6-mg sample of MWCNTs was packed inside a (2 cm x 1.5 cm) sheet of porous polypropylene membrane whose edges were heat-sealed to secure the contents. The mu-SPE device, which was wetted with dichloromethane, was then placed in a stirred sewage sludge sample solution to extract organophosporous pesticides, used here as model compounds. Tumbling of the extraction device within the sample solution facilitated extraction, and the porous membrane acted as a filter to exclude the extraction of extraneous materials. After extraction, analytes were desorbed in hexane and analyzed using gas chromatography/mass spectrometry. Since the porous membrane afforded protection of the MWCNTs, no further cleanup of the extract was required. The pi-pi electrostatic interaction with the analytes and the large surface area of MWCNTs facilitated the adsorption of analytes, with good selectivity and reproducibility. Under the optimized extraction conditions, the method showed good linearity in the range of 0.1-50 mug/L, repeatability of the extractions (RSD 2-8%, n = 4), and low limits of detection (1-7 pg/g). No analyte carryover effect was observed, and each mu-SPE device could be used for up to 30 extractions. Comparison was made with hollow fiber protected solid-phase microextraction and headspace solid-phase microextraction; mu-SPE was demonstrated to be a fast, accurate, and cost-effective pretreatment method for sewage sludge samples.

Persistent organic pollutants, such as polychlorinated biphenyls (PCBs), are a global problem. We demonstrate enhanced depletion of PCBs using root-associated microbes, which can use plant secondary metabolites, such as phenylpropanoids. Using a "rhizosphere metabolomics" approach, we show that phenylpropanoids constitute 84% of the secondary metabolites exuded from Arabidopsis roots. Phenylpropanoid-utilizing microbes are more competitive and are able to grow at least 100-fold better than their auxotrophic mutants on roots of plants that are able to synthesize or overproduce phenylpropanoids, such as flavonoids. Better colonization of the phenylpropanoid-utilizing strain in a gnotobiotic system on the roots of flavonoid-producing plants leads to almost 90% removal of PCBs in a 28-d period. Our work complements previous approaches to engineer soil microbial populations based on opines produced by transgenic plants and used by microbes carrying opine metabolism genes. The current approach based on plant natural products can be applied to contaminated soils with pre-existing vegetation. This strategy is also likely to be applicable to improving the competitive abilities of biocontrol and biofertilization strains.The establishment of large numbers of metabolically active populations of beneficial soil microbes is critical for the success of several environmental remediation and agricultural practices (Metting, 1992). These microorganisms are successful in getting established in the soil ecosystem due to their high adaptability in a wide variety of environments, their faster growth rate, and their biochemical versatility to metabolize a variety of natural and xenobiotic chemicals. Majority of the microbial population found in the soil is associated with the plant roots, where their numbers can reach up to 10 9 to 10 12 per gram of soil (Whipps, 1990), leading to a biomass equivalent to 500 kg ha Ϫ1 (Metting, 1992). This abundance in vegetated soils is due to the availability of nutrients via plant root exudation (Brimecombe, 2001), which can stimulate microbial growth in the immediate vicinity of the roots (a region also known as the "rhizosphere"). Hence, the rhizosphere has been promoted as the ideal site to modify microbial populations ("rhizoengineering") to suite various applications in the soil (O'Connell, 1996).Rhizoengineering has been demonstrated successfully by devising strategies that favored the growth of the targeted microbes that possessed the ability to metabolize exotic nutrients exuded by plants . It was thus possible to create a nutritional bias that can be especially successful in identifying microbial populations due to the general nutrient-limiting conditions in the rhizosphere. One of the earliest successes in rhizoengineering was based on favorably partitioning the exotic nutrient, opines, which were produced by the transgenic plants (Oger, 1997;Savka and Farrand, 1997). This led to the improved and competitive growth of the metabolizing strains in comparison with the microbes unable to metab...

Nanotechnology has revolutionized the world through introduction of a unique class of materials and consumer products in many arenas. It has led to production of innovative materials and devices. Despite of their unique advantages and applications in domestic and industrial sectors, use of materials with dimensions in nanometers has raised the issue of safety for workers, consumers, and human environment. Because of their small size and other unique characteristics, nanoparticles have ability to harm human and wildlife by interacting through various mechanisms. We have reviewed the characteristics of nanoparticles which form the basis of their toxicity. This paper also reviews possible routes of exposure of nanoparticles to human body. Dermal contact, inhalation, and ingestion have been discussed in detail. As very limited data is available for long-term human exposures, there is a pressing need to develop the methods which can determine short and long-term effects of nanoparticles on human and environment. We also discuss in brief the strategies which can help to control human exposures to toxic nanoparticles. We have outlined the current status of toxicological studies dealing with nanoparticles, accomplishments, weaknesses, and future challenges.

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