On the use of hydroxyl radical kinetics to assess the number-average molecular weight of dissolved organic matter.

Dissolved organic matter (DOM) is involved in numerous environmental processes, and its molecular size is important in many of these processes, such as DOM bioavailability, DOM sorptive capacity, and the formation of disinfection byproducts during water treatment. The size and size distribution of the molecules composing DOM remains an open question. In this contribution, an indirect method to assess the average size of DOM is described, which is based on the reaction of hydroxyl radical (HO(•)) quenching by DOM. HO(•) is often assumed to be relatively unselective, reacting with nearly all organic molecules with similar rate constants. Literature values for HO(•) reaction with organic molecules were surveyed to assess the unselectivity of DOM and to determine a representative quenching rate constant (k(rep) = 5.6 × 10(9) M(-1) s(-1)). This value was used to assess the average molecular weight of various humic and fulvic acid isolates as model DOM, using literature HO(•) quenching constants, kC,DOM. The results obtained by this method were compared with previous estimates of average molecular weight. The average molecular weight (Mn) values obtained with this approach are lower than the Mn measured by other techniques such as size exclusion chromatography (SEC), vapor pressure osmometry (VPO), and flow field fractionation (FFF). This suggests that DOM is an especially good quencher for HO(•), reacting at rates close to the diffusion-control limit. It was further observed that humic acids generally react faster than fulvic acids. The high reactivity of humic acids toward HO(•) is in line with the antioxidant properties of DOM. The benefit of this method is that it provides a firm upper bound on the average molecular weight of DOM, based on the kinetic limits of the HO(•) reaction. The results indicate low average molecular weight values, which is most consistent with the recent understanding of DOM. A possible DOM size distribution is discussed to reconcile the small nature of DOM with the large-molecule behavior observed in other studies.

Photooxidation-induced changes in optical, electrochemical, and photochemical properties of humic substances.

Two aquatic fulvic acids and one soil humic acid were irradiated to examine the resulting changes in the redox and photochemical properties of the humic substances (HS), the relationship between these changes, and their relationship to changes in the optical properties. For all HS, irradiation caused photooxidation, as shown by decreasing electron donating capacities. Photooxidation was accompanied by decreases in specific UV absorbance and increases in the E2/E3 ratio (254 nm absorbance divided by that at 365 nm). In contrast, photooxidation had little effect on the samples' electron accepting capacities. The coupled changes in optical and redox properties for the different HS suggest that phenols are an important determinant of aquatic HS optical properties and that quinones may play a more important role in soil HS. Apparent quantum yields of H2O2, ·OH, and triplet HS decreased with photooxidation, thus demonstrating selective destruction of HS photosensitizing chromophores. In contrast, singlet oxygen ((1)O2) quantum yields increased, which is ascribed to either decreased (1)O2 quenching within the HS microenvironment or the presence of a pool of photostable sensitizers. The photochemical properties show clear trends with SUVA and E2/E3, but the trends differ substantially between aquatic and soil HS. Importantly, photooxidation produces a relationship between the (1)O2 quantum yield and E2/E3 that differs distinctly from that observed with untreated HS. This finding suggests that there may be watershed-specific correlations between HS chemical and optical properties that reflect the dominant processes controlling the HS character.

Dark formation of hydroxyl radical in Arctic soil and surface waters.

Hydroxyl radical (•OH) is a highly reactive and unselective oxidant in atmospheric and aquatic systems. Current understanding limits the role of DOM-produced •OH as an oxidant in carbon cycling mainly to sunlit environments where •OH is produced photochemically, but a recent laboratory study proposed a sunlight-independent pathway in which •OH forms during oxidation of reduced aquatic dissolved organic matter (DOM) and iron. Here we demonstrate this non-photochemical pathway for •OH formation in natural aquatic environments. Across a gradient from dry upland to wet lowland habitats, •OH formation rates increase with increasing concentrations of DOM and reduced iron, with highest •OH formation predicted at oxic-anoxic boundaries in soil and surface waters. Comparison of measured vs expected electron release from reduced moieties suggests that both DOM and iron contribute to •OH formation. At landscape scales, abiotic DOM oxidation by this dark •OH pathway may be as important to carbon cycling as bacterial oxidation of DOM in arctic surface waters.

Chiropractic management of a U.S. Veteran with myofascial pain and concurrent distal bimelic amyotrophy (Hirayama disease): a case report.

Background: Distal bimelic amyotrophy (DBMA) also known as Hirayama disease, is a rare, self-limiting motor neuron disease manifesting as atrophy of C7-T1 innervated muscles. We present a case report describing the chiropractic management of neck and thoracic pain in a patient with known DBMA. Case presentation: A 30 year-old black male U.S. veteran with DBMA presented with myofascial pain of the neck, shoulder, and back. A trial of chiropractic care was undertaken involving spinal manipulation of the thoracic spine and cervicothoracic region, manual and instrument-assisted soft tissue mobilization, and home exercise prescription. The patient reported modest improvement in pain intensity and did not experience any adverse events. Summary: This case presents the first documentation of chiropractic services in musculoskeletal pain management of a patient with concurrent DBMA. At this time there is no guidance in the existing body of literature for the safety and effectiveness of manual therapy in this population.

Contexte: La myélopathie cervicale basse, également connue sous le nom de maladie d'Hirayama, est une maladie rare et spontanément résolutive du motoneurone qui se manifeste par une atrophie des muscles innervés C7-T1. Nous présentons un rapport de cas décrivant la prise en charge chiropratique de douleurs cervicales et thoraciques chez un patient atteint d'une maladie d'Hirayama connue. Présentation du cas: Un vétéran américain noir de 30 ans, atteint de myélopathie cervicale basse, s'est présenté avec des douleurs myofasciales au cou, aux épaules et au dos. Un essai de soins chiropratiques a été entrepris comprenant des manipulations vertébrales de la colonne thoracique et de la région cervicothoracique, des mobilisations manuelles et instrumentales des tissus mous, et la prescription d'exercices à domicile. Le patient a fait état d'une amélioration modeste de l'intensité de la douleur et n'a pas ressenti d'effets indésirables. Résumé: Ce cas présente la première documentation des services chiropratiques dans la gestion de la douleur musculo-squelettique d'un patient souffrant d'une myélopathie cervicale basse. À l'heure actuelle, il n'existe pas d'orientation dans la littérature existante sur la sécurité et l'efficacité de la thérapie manuelle dans cette population.

Hydroxyl radical formation upon oxidation of reduced humic acids by oxygen in the dark.

Humic acids (HAs) accept and donate electrons in many biogeochemical redox reactions at oxic/anoxic interfaces. The products of oxidation of reduced HAs by O(2) are unknown but are expected to yield reactive oxygen species, potentially including hydroxyl radical (·OH). To quantify the formation of ·OH upon oxidation of reduced HAs by O(2), three HAs were reduced electrochemically to well-defined redox states and were subsequently oxidized by O(2) in the presence of the ·OH probe terephthalate. The formation of ·OH upon oxidation increased with increasing extent of HA reduction. The yield of ·OH ranged from 42 to 160 mmol per mole of electrons donated by the reduced HA. The intermediacy of hydrogen peroxide (H(2)O(2)) in the formation of ·OH was supported by enhancement of ·OH formation upon addition of exogenous H(2)O(2) sources and by the suppression of ·OH formation upon addition of catalase as a quencher of endogenous H(2)O(2). The formation of ·OH in the dark during oxidation of reduced HA represents a previously unknown source of ·OH formation at oxic/anoxic interfaces and may affect the biogeochemical and pollutant redox dynamics at these interfaces.

Psychological distress and positive gain in mothers of children with autism, with or without other children with neurodevelopmental disorders.

Although a wealth of literature has focused on the parenting experiences of mothers of children with autism spectrum disorder (ASD), there is a lack of research about mothers who are parenting a child with ASD, and who have other children with neurodevelopmental disorders. In this matched-comparison study, 10 mothers of a child with ASD and other typically developing children (ASD-TD) were compared to 10 mothers of a child with ASD who also had other children with neurodevelopmental disorders (ASD-NDD). Mothers completed self-report measures of mental health and positive gain. Results indicated no significant between-group differences for mental health, although mothers in the ASD-NDD group reported increased positive gain compared to mothers in the ASD-TD group. Further research is needed to understand practical support needs and theory development.

Assessing the contribution of free hydroxyl radical in organic matter-sensitized photohydroxylation reactions.

Photochemical formation of reactive oxygen species from dissolved organic matter (DOM) is incompletely understood, especially in the case of hydroxyl radical (•OH) production. Many studies have used various probes to detect photochemically produced •OH from DOM, but the fundamental reactions of these probes are not necessarily specific for free •OH and may also detect lower-energy hydroxylation agents. In this study, two tests were applied that have previously been used as a diagnostic for the presence of free •OH: methane quenching of •OH and hydroxybenzoic acid (hBZA) product yields. Upon application of these two tests to a set of five DOM isolates, it was found that methane quenching and the hBZA ratio results were not necessarily consistent. Overall, the results provide compelling evidence that all isolates studied photochemically produce free •OH. The hydroxylating acitivity of Elliot Soil Humic Acid and Pony Lake Fulvic Acid, however, also had a significant contribution from a photochemically generated hydroxylating agent that is lower in energy than free •OH. Catalase quenching experiments were conducted to assess whether hydrogen peroxide was the immediate precursor to hydroxyl in these systems. In all cases, catalase addition slowed photohydroxylation of terephthalate, but the contribution of hydrogen peroxide photolysis was determined to be less than 50%.

Terephthalate as a probe for photochemically generated hydroxyl radical.

Hydroxyl radical ( OH) production in sunlit natural waters is known to be an important factor in pollutant degradation and nutrient cycling, and various probes have been developed to study this species in aquatic systems. Many of these probes have limitations in sensitivity and/or selectivity for OH, leaving room for improvement. Terephthalate (TPA) is a known probe for OH that produces a fluorescent product, hydroxyterephthalate (hTPA), upon hydroxylation, but its suitability for studying photochemical OH production has not been fully tested. To that end, the photochemical behavior of TPA and hTPA was characterized. TPA and hTPA react with OH with rate constants of (4.4 +/- 0.1) x 10(9) M(-1) s(-1) and (6.3 +/- 0.1) x 10(9) M(-1) s(-1), respectively. They were found to react with singlet oxygen ((1)O(2)) with significantly lower rate constants of <<10(4) M(-1) s(-1) and (5.0 +/- 0.1) x 10(4) M(-1) s(-1), respectively, indicating that TPA is selective for OH versus(1)O(2). TPA did not undergo direct photolysis, while hTPA was shown to undergo direct photochemical degradation with a Phi(direct,365nm) of (6.3 +/- 0.1) x 10(-3). TPA was applied to monitoring photochemical OH production by nitrate, nitrite and dissolved organic matter (DOM), and OH quenching rate constants measured for DOM were similar to results from previous studies. TPA provides a stable and sensitive probe for OH under significantly shorter photo-exposure times than similarly structured probe molecules, such as benzoate. However, the photoinstability of the analyte, hTPA, makes TPA an unsuitable probe for the study of photochemical systems under ultraviolet irradiation with wavelengths shorter than 360 nm.

Evidence for dissolved organic matter as the primary source and sink of photochemically produced hydroxyl radical in arctic surface waters.

Hydroxyl radical (˙OH) is an indiscriminate oxidant that reacts at near-diffusion-controlled rates with organic carbon. Thus, while ˙OH is expected to be an important oxidant of dissolved organic matter (DOM) and other recalcitrant compounds, the role of ˙OH in the oxidation of these compounds in aquatic ecosystems is not well known due to the poorly constrained sources and sinks of ˙OH, especially in pristine (unpolluted) natural waters. We measured the rates of ˙OH formation and quenching across a range of surface waters in the Arctic varying in concentrations of expected sources and sinks of ˙OH. Photochemical formation of ˙OH was observed in all waters tested, with rates of formation ranging from 2.6 ± 0.6 to 900 ± 100 × 10(-12) M s(-1). Steady-state concentrations ranged from 2 ± 1 to 290 ± 60 × 10(-17) M, and overlapped with previously reported values in surface waters. While iron-mediated photo-Fenton reactions likely contributed to the observed ˙OH production, several lines of evidence suggest that DOM was the primary source and sink of photochemically produced ˙OH in pristine arctic surface waters. DOM from first-order or headwater streams was more efficient in producing ˙OH than what has previously been reported for DOM, and ˙OH formation decreased with increasing residence time of DOM in sunlit surface waters. Despite the ubiquitous formation of ˙OH in arctic surface waters observed in this study, photochemical ˙OH formation was estimated to contribute ≤4% to the observed photo-oxidation of DOM; however, key uncertainties in this estimate must be addressed before ruling out the role of ˙OH in the oxidation of DOM in these waters.

Sensitive and selective time-gated luminescence detection of hydroxyl radical in water.

A terbium probe for the selective time-gated detection of hydroxyl radical is presented. This probe demonstrates high sensitivity with an 11.0-fold increase in time-gated luminescence intensity for an hour-long exposure to hydroxyl radical concentration in the femtomolar range, and high selectivity for HO* over other reactive oxygen species.