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- Cornelissen, G., et al.
(författare)
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Effect of sorbate planarity on environmental black carbon sorption
- 2004
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Ingår i: Environmental Science and Technology. - : American Chemical Society (ACS). - 0013-936X .- 1520-5851. ; 38:13, s. 3574-3580
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Tidskriftsartikel (refereegranskat)abstract
- Soot and charcoal, collectively termed "black carbon" or BC, can exhibit extremely strong sorption of many hydrophobic organic compounds. In order to include BC sorption in fate models, it is important to know BC nanopore surface areas. In addition, it is useful to know for which compounds BC sorption can be expected to be important. By nitrogen adsorption measurements at ultralow pressures on sediment that was strongly enriched in BC by HF treatment and/or chemothermal oxidation at 375 degreesC, we found that environmental BC has nanoporosity in the <4-10 Angstrom size range. The nanopore surface area (<50 Angstrom) of BC in Lake Ketelmeer (The Netherlands) sediment was approximately 58 m(2)/g. We measured sorption isotherms over a wide concentration interval for four compounds with the same K-OW (10(4.6+/-0.1)): planar anthracene (ANT), phenanthrene (PHE), and 4-chlorobiphenyl (4-PCB) along with nonplanar 2,2'-dichlorobiphenyl (2,2'-PCB). The environmental BC sorption coefficients of these iso-K-OW compounds decreased in the order ANT > PHE approximate to 4-PCB much greater than 2,2'-PCB and spanned a factor of 50-200, depending on concentration. Nonplanar 2,2'-PCB showed much more linear BC sorption (n(F) = 0.92) than the planar compounds (n(F) = 0.54-0.70). This shows that steric hindrance strongly attenuates BC-sorbate interactions for a nonplanar PCB. Thus, BC is more important for environmental sorption of planar compounds (>50% sorbed to BC in the nanogram per liter range) than for nonplanar ones (<10-20%). Using the measured BC nanopore surface area, a close agreement between modeled and measured BC sorption data could be found.
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| 3. |
- Knudsen, Jette, 1961-, et al.
(författare)
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Trends in floral scent chemistry in pollination syndromes : floral scent composition in hummingbird-pollinated taxa
- 2004
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Ingår i: Botanical journal of the Linnean Society. - London : Academic Press. - 0024-4074 .- 1095-8339. ; 146:2, s. 191-199
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Tidskriftsartikel (refereegranskat)abstract
- We studied an assemblage of 17 species of bird-pollinated Ecuadorian plants (from 14 angiosperm families), including taxa pollinated by short-billed (trochiline) and sickle-billed (hermit) hummingbirds. Hummingbirds are widely supposed to ignore fragrance while visiting flowers. We collected floral headspace odours in order to test the general prediction that specialist hummingbird-pollinated flowers are scentless. In nine out of 17 of these species we failed to detect any odours using gas chromatography-mass spectrometry (GC-MS), whereas the remaining eight species produced trace levels of volatile compounds. Most of these odour compounds were of terpenoid or lipoxygenase derivation and are commonly emitted by vegetative as well as floral plant tissues. Further studies will be required to determine whether these weak odours attract alternative pollinators, repel enemies or represent vestiges of a scented ancestry.
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