Showing papers by "Michael R. Hoffmann published in 2009"

Treatment technologies for aqueous perfluorooctanesulfonate (PFOS) and perfluorooctanoate (PFOA)

Abstract: Fluorochemicals (FCs) are oxidatively recalcitrant, environmentally persistent, and resistant to most conventional treatment technologies. FCs have unique physiochemical properties derived from fluorine which is the most electronegative element. Perfluorooctanesulfonate (PFOS), and perfluorooctanoate (PFOA) have been detected globally in the hydrosphere, atmosphere and biosphere. Reducing treatment technologies such as reverses osmosis, nano-filtration and activated carbon can remove FCs from water. However, incineration of the concentrated waste is required for complete FC destruction. Recently, a number of alternative technologies for FC decomposition have been reported. The FC degradation technologies span a wide range of chemical processes including direct photolysis, photocatalytic oxidation, photochemical oxidation, photochemical reduction, thermally-induced reduction, and sonochemical pyrolysis. This paper reviews these FC degradation technologies in terms of kinetics, mechanism, energetic cost, and applicability. The optimal PFOS/PFOA treatment method is strongly dependent upon the FC concentration, background organic and metal concentration, and available degradation time.

Warfare in Biodiversity Hotspots

Abstract: Conservation efforts are only as sustainable as the social and political context within which they take place. The weakening or collapse of sociopolitical frameworks during wartime can lead to habitat destruction and the erosion of conservation policies, but in some cases, may also confer ecological benefits through altered settlement patterns and reduced resource exploitation. Over 90% of the major armed conflicts between 1950 and 2000 occurred within countries containing biodiversity hotspots, and more than 80% took place directly within hotspot areas. Less than one-third of the 34 recognized hotspots escaped significant conflict during this period, and most suffered repeated episodes of violence. This pattern was remarkably consistent over these 5 decades. Evidence from the war-torn Eastern Afromontane hotspot suggests that biodiversity conservation is improved when international nongovernmental organizations support local protected area staff and remain engaged throughout the conflict. With biodiversity hotspots concentrated in politically volatile regions, the conservation community must maintain continuous involvement during periods of war, and biodiversity conservation should be incorporated into military, reconstruction, and humanitarian programs in the world's conflict zones.

Electrochemical Water Splitting Coupled with Organic Compound Oxidation: The Role of Active Chlorine Species

Abstract: The need for alternative energy sources with minimal to no carbon footprint is growing. A solar-powered electrochemical system that produces hydrogen via water splitting using organic pollutants as sacrificial electron donors is a possible solution. The hybridization of a BiO_x−TiO_2/Ti anode with a stainless steel cathode powered by a photovoltaic (PV) array has been shown to achieve this process. The electrochemical degradation kinetics of a variety of organic substrates is investigated as a function of a background electrolyte, NaCl versus Na_2SO_4. The observed substrate (S) degradation kinetics (k_(obs)^S) are found to correlate well with the cell current (I_(cell)) and the H_2 production energy efficiency (EE) in the presence of NaCl as the background electrolyte. In the case of Na_2SO_4, no correlation is observed and the degradation rates are greatly reduced in comparison to NaCl. This suggests that the primary chemical oxidant is electrolyte-dependent. The k_(obs)^S’s are found to be proportional to the bimolecular rate constants of Cl_2^(•−) with the substrate (k_(Cl_2^(•−) + S)) and to substrate-induced ΔEEs (EE with substrate − EE without substrate) in the presence of NaCl. The ΔEE correlation arises from the active chlorine species acting as an electron shuttle, which compete with H_2 production for cathodic electrons. In the presence of the organic substrates, the active chlorine species are quenched, increasing the fraction of electrons utilized for the H_2 production.

Perfluorinated Surfactant Chain-Length Effects on Sonochemical Kinetics

Abstract: The sonochemical degradation kinetics of the aqueous perfluorochemicals (PFCs) perfluorobutanoate (PFBA), perfluorobutanesulfonate (PFBS), perfluorohexanoate (PFHA), and perfluorohexanesulfonate (PFHS) have been investigated Surface tension measurements were used to evaluate chain-length effects on equilibrium air−water interface partitioning The PFC air−water interface partitioning coefficients, KeqPF, and maximum surface concentrations, ΓmaxPF, were determined from the surface pressure equation of state for PFBA, PFBS, PFHA, and PFHS Relative KeqPF values were dependent upon chain length KeqPFHS ≅ 21KeqPFHA ≅ 39KeqPFBS ≅ 50KeqPFBA, whereas relative ΓmaxPF values had minimal chain length dependence ΓmaxPFHS ≅ ΓmaxPFHA ≅ ΓmaxPFBS ≅ 22ΓmaxPFBA The rates of sonolytic degradation were determined over a range of frequencies from 202 to 1060 kHz at dilute (<1 μM) initial PFC concentrations and are compared to previously reported results for their C8 analogs: perfluorooctanesulfonate (PFOS) and perfluor

Optical absorptivity versus molecular composition of model organic aerosol matter.

Abstract: Aerosol particles affect the Earth’s energy balance by absorbing and scattering radiation according to their chemical composition, size, and shape. It is generally believed that their optical properties could be deduced from the molecular composition of the complex organic matter contained in these particles, a goal pursued by many groups via high-resolution mass spectrometry, although: (1) absorptivity is associated with structural chromophores rather than with molecular formulas, (2) compositional space is a small projection of structural space, and (3) mixtures of polar polyfunctional species usually exhibit supramolecular interactions. Here we report a suite of experiments showing that the photolysis of aqueous pyruvic acid (a proxy for aerosol α-dicarbonyls absorbing at λ > 300 nm) generates mixtures of identifiable aliphatic polyfunctional oligomers that develop absorptions in the visible upon standing in the dark. These absorptions and their induced fluorescence emissions can be repeatedly bleached...

Acid dissociation versus molecular association of perfluoroalkyl oxoacids: environmental implications

Abstract: Perfluorooctanoate (PFO) and perfluorooctanesulfonate (PFOS) surfactant anions, once released, may rapidly reach remote regions. This phenomenon is puzzling because the water-bound anions of strong F-alkyl acids should be largely transported by slow oceanic currents. Herein, we investigate whether these hydrophobic F-alkyl oxoanions would behave anomalously under environmental conditions, as suggested elsewhere. Negative electrospray ionization mass spectra of micromolar aqueous PFO or PFOS solutions from pH 1.0 to 6.0 show (1) m/z = 499 (PFOS) signals that are independent of pH and (2) m/z = 413 (PFO) and 369 (PFO − CO2) signals, plus m/z = 213 (C3F7CO2−) and 169 (C3F7−) signals at higher collision energies, and, below pH ∼ 4, m/z = 827 signals from a remarkably stable (PFO)2H− cluster that increase with decreasing pH. Since the sum of the m/z = 369, 413, and 827 signal intensities is independent of pH, that is, effectively encompasses all major species, we infer that pKa(PFOSA) < 1.0 and pKa(PFOA) < 1.0...

Anion-Catalyzed Dissolution of NO2 on Aqueous Microdroplets

Abstract: Fifty-seven years after NOx (NO + NO2) were identified as essential components of photochemical smog, atmospheric chemical models fail to correctly predict •OH/HO2• concentrations under NOx-rich conditions. This deficiency is due, in part, to the uncertain rates and mechanism for the reactive dissolution of NO2(g) (2NO2 + H2O = NO3− + H+ + HONO) in fog and aerosol droplets. Thus, state-of-the-art models parametrize the uptake of NO2 by atmospheric aerosol from data obtained on “deactivated tunnel wall residue”. Here, we report experiments in which NO3− production on the surface of microdroplets exposed to NO2(g) for ∼1 ms is monitored by online thermospray mass spectrometry. NO2 does not dissolve in deionized water (NO3− signals below the detection limit) but readily produces NO3− on aqueous NaX (X = Cl, Br, I) microdroplets with NO2 uptake coefficients γ that vary nonmonotonically with electrolyte concentration and peak at γmax ∼ 10−4 for [NaX] ∼ 1 mM, which is >103 larger than that in neat water. Since ...

Simultaneous detection of cysteine sulfenate, sulfinate, and sulfonate during cysteine interfacial ozonolysis.

Abstract: Sulfenic acids (RSOH) are reactive intermediates in the oxidation of protein cysteines. Among cysteine oxoforms, RSOH represent redox-reversible species that can thus participate in regulation and signaling mechanisms and play key roles in enzyme catalysis and antioxidant activity. How the cysteine (CyS) thiol groups of the human surfactant protein that lines the lung epithelium react with inhaled ozone is deemed critical in preserving structural integrity and immune functions. Here we report the simultaneous detection, by online thermospray ionization mass spectrometry, of cysteine sulfenate (CySO^−) and the overoxidized cysteine sulfinate (CySO_2^−) and cysteine sulfonate (CySO_3^−) species on the surface of aqueous CyS microdroplets exposed to O_3(g) for <1 ms. These species are produced by rapid, sequential O-atom additions whose relative rates are herein quantified for the first time. From the pH-dependence of ozonation rates, we derive pK_a(CySOH) = 7.6 ± 0.3 < pKa(CyS) = 8.3.

Enrichment Factors of Perfluoroalkyl Oxoanions at the Air/Water Interface

Abstract: The refractory, water-bound perfluoro-n-alkyl carboxylate F(CF2)nCO2− and sulfonate F(CF2)nSO3− surfactant anions reach remote locations by mechanisms that are not well understood. Here we report experiments in which the relative concentrations of these anions on the surface of microdroplets produced by nebulizing their aqueous solutions are measured via electrospray ionization mass spectrometry. Enrichment factors f (relative to Br−: f(Br−) ≡ 1) increase with n, asymptotically reaching f[F(CF2)nSO3−] ∼ 2 f[F(CF2)nCO2−] ∼ 200 f(Br−) values above n ∼ 8. The larger f values for F(CF2)nSO3− over their F(CF2)nCO2− congeners are consistent with a closer approach of the bulkier, less hydrated −SO3− headgroup to the air/water interface. A hyperbolic, rather than the predicted linear log f[F(CF2)nCO2−] vs n dependence suggests the onset of conformational restrictions to interfacial enrichment above n ∼ 4. Marine aerosols produced from contaminated ocean surface waters are therefore expected to be highly enriched ...

How Phenol and α-Tocopherol React with Ambient Ozone at Gas/Liquid Interfaces

Abstract: The exceptional ability of alpha-tocopherol (alpha-TOH) for scavenging free radicals is believed to also underlie its protective functions in respiratory epithelia. Phenols, however, can scavenge other reactive species. Herein, we report that alpha-TOH/alpha-TO(-) reacts with closed-shell O(3)(g) on the surface of inert solvent microdroplets in or = 2)(-) homologues are unreactive toward O(3)(g) and split CO(2) instead. On this basis, alpha-TO-O(-) is assigned to a chroman-6-ol (4a, 8a)-ene oxide, alpha-TO-O(2)(-) to an endoperoxide, and alpha-TO-O(3)(-) to a secondary ozonide. The atmospheric degradation of the substituted phenols detected in combustion emissions is therefore expected to produce related oxidants on the aerosol particles present in the air we breathe.

Absorption of Inhaled NO2

Abstract: Nitrogen dioxide (NO_2), a sparingly water-soluble π-radical gas, is a criteria air pollutant that induces adverse health effects. How is inhaled NO_2(g) incorporated into the fluid microfilms lining respiratory airways remains an open issue because its exceedingly small uptake coefficient (γ 10^(−7)−10^(−8)) limits physical dissolution on neat water. Here, we investigate whether the biological antioxidants present in these fluids enhance NO_2(g) dissolution by monitoring the surface of aqueous ascorbate, urate, and glutathione microdroplets exposed to NO_2(g) for 1 ms via online thermospray ionization mass spectrometry. We found that antioxidants catalyze the hydrolytic disproportionation of NO_2(g), 2NO_2(g) + H_2O(l) = NO_3^−(aq) + H^+(aq) + HONO, but are not consumed in the process. Because this function will be largely performed by chloride, the major anion in airway lining fluids, we infer that inhaled NO_2(g) delivers H^+, HONO, and NO_3^− as primary transducers of toxic action without antioxidant participation.

A synthesis of African and western Indian Ocean Island mammal taxa (class: Mammalia) described between 1988 and 2008: An update to Allen (1939) and Ansell (1989)

Abstract: We provide a synthesis of all mammal taxa described from the African mainland, Madagascar and all surrounding islands in the 20 years since 1988, thereby supplementing the earlier works of G.M. Allen (1939) and W.F.H. Ansell (1989), and bringing the list of African mammals described over the last 250 years current to December 2008. We list 175 new extant taxa, including five new genera, one new subgenus, 138 new species and 31 new subspecies, including remarks, where relevant, on the current systematic position of each taxon. Names of seven species of primates are emended, according to the requirements of the ICZN. The taxonomic group in which the largest number of new taxa has been described is the Primates, with two new genera, 47 new species and 11 new subspecies, while geographically the biggest increase in new species descriptions has been on the island of Madagascar, accounting for roughly half (67) of all new species described in the past 20 years. Nearly half of all new species listed currently are assessed as Data Deficient on the IUCN Red List of Threatened Species (49 of 101 listed species) suggesting further research is urgently needed to help clarify the status of those recently described species.

A. J. Colussi*: Acid Dissociation versus Molecular Association of Perfluoroalkyl Oxoacids: Environmental Implications

Abstract: Perfluorooctanoate (PFO) and perfluorooctanesulfonate (PFOS) surfactant anions, once released, may rapidly reach remote regions. This phenomenon is puzzling because the water-bound anions of strong F-alkyl acids should be largely transported by slow oceanic currents. Herein, we investigate whether these hydrophobic F-alkyl oxoanions would behave anomalously under environmental conditions, as suggested elsewhere. Negative electrospray ionization mass spectra of micromolar aqueous PFO or PFOS solutions from pH 1.0 to 6.0 show (1) m/z = 499 (PFOS) signals that are independent of pH and (2) m/z = 413 (PFO) and 369 (PFO-CO(2)) signals, plus m/z = 213 (C(3)F(7)CO(2)(-)) and 169 (C(3)F(7)(-)) signals at higher collision energies, and, below pH approximately 4, m/z = 827 signals from a remarkably stable (PFO)(2)H(-) cluster that increase with decreasing pH. Since the sum of the m/z = 369, 413, and 827 signal intensities is independent of pH, that is, effectively encompasses all major species, we infer that pK(a)(PFOSA) < 1.0 and pK(a)(PFOA) < 1.0. We also derive K(2) < or = 4 x 10(7) M(-2) for the clustering equilibrium 2PFO + H(+) <==> (PFO)(2)H. Thus, although (PFO)(2)H is held together by an exceptionally strong homonuclear covalent hydrogen bond, neither PFOS nor PFO will associate or protonate significantly at environmentally relevant subnanomolar concentrations above pH approximately 1.

Additions/Corrections to Enrichment Factors of Perfluoroalkyl Oxoanions at the Air/Water Interface

Abstract: The original paper (DOI: 10.1021/jp902795m) for this Correction appears in the same issue. • Introduction, first paragraph: (pKa ∼ 0) should be replaced by (pKa < 1). • Experimental Section, first paragraph: Milli-Q water resistivity (18 MΩ cm) should read Milli-Q water (resistivity 18 MΩ cm). • Results and Discussion: Caption to Figure 3 should quote “Goss, K. U.; Bronner, G. J. Phys. Chem. A 2006, 110, 9518, 14054.” rather than Goss et al.5 • Equation 3 should read

Photochemical formation of large molecular weight oligomers from low-molecular weight keto-carbonyls in haze aerosol

Abstract: The optical properties of the atmospheric aerosol play a fundamental role in the Earth's radiative balance. Since ~60% of the aerosol mass consists of complex natural and anthropogenic organic matter that absorbs in the ultraviolet and, particularly, in the visible regions of the solar spectrum, it is important to establish the chemical identity of the organic chromophores and the mechanism by which they contribute to aerosol color. Here we report studies on the chemical composition versus chromism of photolyzed (λ > 305 nm) solutions of PA, under a variety of experimental conditions that include substrate concentration, temperature and the presence of relevant spectator solutes, such ammonium sulfate. We use high resolution mass and ^1H, ^(13)C NMR spectrometries to track chemical speciation in photolyzed solutions as they go through thermochromic and photobleaching cycles. The chemical identity of the components of these mixtures does not change in these cycles, in which photobleached solutions gradually recover their yellow color in the dark with non-conventional kinetics typical of aggregation processes, we infer that visible absorptions involve the intermolecular coupling of carbonyl chromophores in supramolecular assemblies.