Disturbance by aquatic plant management in streams: Effects on benthic invertebrates

The effect of aquatic plant removal on benthic invertebrates and their habitat was studied in two macrophyte-rich streams of the Swiss Plateau. In each stream, habitat conditions (macrophyte biomass, current velocity, water depth) and invertebrate densities were monitored in a control reach and in a reach where plants were removed by cutting. Biological samples were taken and physical parameters measured on three dates before and six dates after plant removal in both reaches. Responses to plant removal were similar in both streams; macrophyte cutting initially decreased mean plant biomass (ca. 85%) and total number of invertebrates (ca. 65%). Variation between replicates was, however, higher in one of the streams, causing fewer effects on plants and invertebrates to be statistically significant. Plant cutting affected mainly taxa that used macrophytes as habitat (e.g. Simuliidae, Chironomidae), whereas highly mobile taxa (e.g. Ephemeroptera) and taxa living on or within the bed sediments (e.g. Trichoptera, Bivalvia) were less affected. Taxa that decreased after plant removal recovered within 4–6 months, although recovery of macrophytes was quite different in both streams. Invertebrate recovery also seemed to be seasonally dependent, with cutting having a less severe impact during summer than spring. Our results suggest that macrophytes in streams should be removed only in summer, preferably leaving some plant beds to act as refugia for phytophilous invertebrates. © 1998 John Wiley & Sons, Ltd.     

Polymerization of cyclic monomers. VII. Synthesis and radical polymerization of 1,3‐bis[(1‐alkoxycarbonyl‐2‐vinylcyclopropane‐1‐yl)carboxy]benzenes

1,3‐Bis[(1‐alkoxycarbonyl‐2‐vinylcyclopropane‐1‐yl)carboxy]benzenes 1 [RO: CH₃O (a), C₂H₅O (b)] were synthesized by the esterification of the corresponding 1‐alkoxycarbonyl‐2‐vinylcyclopropane‐1‐carboxylic acids with resorcinol. The structure of the new vinylcyclopropanes was confirmed by elemental analysis and infrared (IR), ¹H nuclear magnetic resonance (¹H‐NMR), and ¹³C nuclear magnetic resonance (¹³C‐NMR) spectroscopy. The radical polymerization of difunctional 2‐vinyl‐cyclopropanes in bulk with 2,2′‐azoisobutyronitrile (AIBN) results in hard, transparent, crosslinked polymers. During the bulk polymerization of the crystalline bis[(1‐methoxycarbonyl‐2‐vinylcyclopropane‐1‐yl)carboxy]benzene 1a, an expansion in volume of about 1% took place. The radical solution polymerization of 1a resulted in a soluble polymer with pendant 2‐vinylcyclopropane groups. © 1999 John Wiley & Sons, Inc. J Appl Polym Sci 72: 1775–1782, 1999     

Oxidation of antibacterial molecules by aqueous ozone: moiety-specific reaction kinetics and application to ozone-based wastewater treatment

Ozone and hydroxyl radical (*OH) reaction kinetics were measured for 14 antibacterial compounds from nine structural families, to determine whether municipal wastewater ozonation is likely to result in selective oxidation of these compounds' biochemically essential moieties. Each substrate is oxidized by ozone with an apparent second-order rate constant, k'(O3,app) > 1 x 10(3) M(-1) s(-1), at pH 7, with the exception of N(4)-acetylsulfamethoxazole (K'(O3,app) is 2.5 x 102 M(-1) s(-1)). k'(O3,app) values (pH 7) for macrolides, sulfamethoxazole, trimethoprim, tetracycline, vancomycin, and amikacin appear to correspond directly to oxidation of biochemically essential moieties. Initial reactions of ozone with N(4)-acetylsulfamethoxazole, fluoroquinolones, lincomycin, and beta-lactams do not lead to appreciable oxidation of biochemically essential moieties. However, ozone oxidizes these moieties within fluoroquinolones and lincomycin via slower reactions. Measured k'(O3,app) values and second-order *OH rate constants, k'(*OH,app) were utilized to characterize pollutant losses during ozonation of secondary municipal wastewater effluent. These losses were dependent on k'(O3,app), but independent of k'(*OH,app). Ozone doses > or =3 mg/L yielded > or =99% depletion of fast-reacting substrates (K'(O3,app) > 5 x 10(4) M(-1) s(-1)) at pH 7.7. Ten substrates reacted predominantly with ozone; only four were oxidized predominantly by .OH. These results indicate that many antibacterial compounds will be oxidized in wastewater via moiety-specific reactions with ozone.     

Nucleophilic substitution reactions of chlorpyrifos-methyl with sulfur species

Chlorpyrifos-methyl is widely used in the control of insects on certain stored grain, including wheat, barley, oats, rice, and sorghum. The reactions of chlorpyrifos-methyl with hydrogensulfide/bisulfide (H2S/HS-), polysulfides (Sn(2-)), thiophenolate (PhS-), and thiosulfate (S2O3(2-)) were examined in well-defined aqueous solutions over a pH range from 5 to 9. The rates are first-order in the concentration of the different reduced sulfur species. The resulting data indicate that chlorpyrifos-methyl undergoes a S(N)2 reaction with the reduced sulfur species. The transformation products indicate that the nucleophilic substitution of reduced sulfur species occurs at the carbon atom of a methoxy group to form the desmethyl chlorpyrifos-methyl. The formation of trichloropyridinol, a minor degradation product, could be attributed entirelyto hydrolysis. The reaction of chlorpyrifos-methyl with thiophenolate leads to the formation of the corresponding methylated sulfur compound. The resulting pseudo-first-order rate constant for chlorpyrifos-methyl with bisulfide yielded a second-order rate constant of 2.2 (+/- 0.1) x 10(-3) M(-1) s(-1). The determined second-order rate constants show that the reaction of chlorpyrifos-methyl with HS- is of the same order of magnitude as the reaction of chlorpyrifos-methyl with S2O3(2-) with a second-order rate constant of 1.0 (+/- 0.1) x 10(-3) M(-1) s(-1). The second-order rate constant for chlorpyrifos-methyl with polysulfides (3.1 (+/- 0.3) x 10(-2) M(-1) s(-1)) is of the same order of magnitude as the one with thiophenolate (2.1 (+/- 0.2) x 10(-2) M(-1) s(-1)). The second-order rate constant for the reaction of polysulfides is approximately 1 order of magnitude greater than that for the reaction with HS-. When the determined second-order rate constants are multiplied by the concentration of HS-, polysulfides and thiosulfate reported in salt marshes and porewaters, predicted half-lives show that the inorganic reduced sulfur species present at environmentally relevant concentrations may represent an important sink for phosphorothionate triesters in coastal marine environments.     

Controlling nanowear in a polymer by confining segmental relaxation

Molecular relaxation of a copolymer designed for nano-electromechanical systems was chemically confined by varying the spacing between cross-links, delta(c). A critical cross-link spacing of 1-3 nm marks a transition in the nano-mechanical properties evaluated by atomic force microscopy. The transition reveals an interplay between the cross-link spacing and the length scale for backbone relaxation, xi(alpha), in cooperatively rearranging regions. For delta(c) > xi(alpha), the natural backbone relaxation process is relatively unaffected by the cross-links and a ductile, low hardness behavior results. For delta(c) < xi(alpha), the cross-links directly interfere with backbone relaxation and confine segmental mobility, leading to a brittle, high hardness response.     

Kinetics and mechanistic aspects of As(III) oxidation by aqueous chlorine, chloramines, and ozone: relevance to drinking water treatment

Kinetics and mechanisms of As(III) oxidation by free available chlorine (FAC-the sum of HOCl and OCl-), ozone (O3), and monochloramine (NH2Cl) were investigated in buffered reagent solutions. Each reaction was found to be first order in oxidant and in As(III), with 1:1 stoichiometry. FAC-As(III) and O3-As(III) reactions were extremely fast, with pH-dependent, apparent second-order rate constants, k'app, of 2.6 (+/- 0.1) x 10(5) M(-1) s(-1) and 1.5 (+/- 0.1) x 10(6) M(-1) s(-1) at pH 7, whereas the NH2Cl-As(III) reaction was relatively slow (k'app = 4.3 (+/- 1.7) x 10(-1) M(-1) s(-1) at pH 7). Experiments conducted in real water samples spiked with 50 microg/L As(III) (6.7 x 10(-7) M) showed that a 0.1 mg/L Cl2 (1.4 x 10-6 M) dose as FAC was sufficient to achieve depletion of As(III) to <1 microg/L As(III) within 10 s of oxidant addition to waters containing negligible NH3 concentrations and DOC concentrations <2 mg-C/L. Even in a water containing 1 mg-N/L (7.1 x 10(-5) M) as NH3, >75% As(III) oxidation could be achieved within 10 s of dosing 1-2 mg/L Cl2 (1.4-2.8 x 10(-5) M) as FAC. As(III) residuals remaining in NH3-containing waters 10 s after dosing FAC were slowly oxidized (t1/2 > or = 4 h) in the presence of NH2Cl formed by the FAC-NH3 reaction. Ozonation was sufficient to yield >99% depletion of 50 microg/L As(III) within 10 s of dosing 0.25 mg/L O3 (5.2 x 10(-6) M) to real waters containing <2 mg-C/L of DOC, while 0.8 mg/L O3 (1.7 x 10(-5) M) was sufficientfor a water containing 5.4 mg-C/L of DOC. NH3 had negligible effect on the efficiency of As(III) oxidation by O3, due to the slow kinetics of the O3-NH3 reaction at circumneutral pH. Time-resolved measurements of As(III) loss during chlorination and ozonation of real waters were accurately modeled using the rate constants determined in this investigation.     

Biodegradation and product identification of [14C]hexabromocyclododecane in wastewater sludge and freshwater aquatic sediment

In a previous study the biodegradation of hexabromocyclododecane (HBCD) was reported to occur under realistic environmental concentrations in soils and freshwater aquatic sediments with biotransformation half-lives ranging from approximately 2 days to 2 months. In this study we extend our knowledge as to the environmental behavior of HBCD with respect to the fate of the three major diastereomers of HBCD (alpha, beta, and gamma) as well as to the identification of major intermediate metabolites formed during degradation. Substantial biological transformation of the alpha-, beta-, and gamma-[14C]HBCD diastereomers was observed in wastewater (i.e., digester) sludge and in freshwater aquatic sediment microcosms prepared under aerobic and anaerobic conditions. Concomitant with the loss of [14C]HBCD in these matrixes there was a concurrent production of three [14C]products. Using a combination of high performance liquid chromatography atmospheric pressure photoionization mass spectrometry and gas chromatography electron impact ionization mass spectrometry these metabolites were identified as tetrabromocyclododecene, dibromocyclododecadiene, and cyclododecatriene. We propose that HBCD is sequentially debrominated via dihaloelimination where at each step there is the loss of two bromines from vicinal carbons with the subsequent formation of a double bond between the adjacent carbon atoms. These results demonstrate that microorganisms naturally occurring in aquatic sediments and anaerobic digester sludge mediate complete debromination of HBCD.     

Ethanol and CO electro-oxidation with amorphous alloys as electrodes

In recent years the interest in the use of ethanol as fuel in direct ethanol fuel cells (DEFCs) has increased. Ethanol is less toxic than methanol and the bigger size of the molecule reduces the permeability through the electrolytic membrane. But, the use of this fuel with platinum catalysts leads to the acetaldehyde and acetic acid formation as main reaction products, so the electrical efficiency decreases. Furthermore, platinum shows an important susceptibility to CO poisoning which is formed during the ethanol electro-oxidation.The aim of this work is the study of the electro-catalytic behaviour of ethanol and CO electro-oxidation reaction with amorphous alloys, obtained by mechanical alloying technique. Ni₅₉Nb₄₀Pt_0.6Pd_0.4, Ni₅₉Nb₄₀Pt_0.6Rh_0.4 and Ni₅₉Nb₄₀Pt_0.6Rh_0.2Ru_0.2 compositions were studied. The bi-catalytic alloys show a similar behaviour for the ethanol electro-oxidation. In comparison to these, the current density towards ethanol oxidation decreases with the presence of Ru, although the tri-catalytic electrode shows the best tolerance to CO, with a lower surface coverage compared to other studied.