Catching up with tetrazines: coordination of Re(I) to 1,2,4-triazine facilitates an inverse electron demand Diels-Alder reaction with strained alkynes to a greater extent than in corresponding 1,2,4,5-tetrazines.

Inverse electron demand Diels Alder (IEDDA) reactions of 1,2,4-triazines are of interest to biorthogonal chemistry but suffer from slow kinetics. It is shown here that coordination of Re(I) to a 1,2,4-triazine ring speeds up the IEDDA reaction with bicyclooctyne (BCN) by a factor of 55. Comparative analysis with corresponding 1,2,4,5-tetrazine analogues reveals that the origin of the increased reactivity is markedly different and more profound than in tetrazine analogues. DFT calculations and subsequent analysis indicated the greater increase for the triazine than the tetrazines on coordination could be attributed to the triazine's lower distortion energy and more favourable interaction energy for the triazine, the latter attributable to lower Pauli repulsion than the tetrazines rather than to favourable frontier orbital energies.

Boric acid catalysed hydrolysis of peroxyacids.

This study shows for the first time that boric acid catalyses the hydrolysis of peroxyacids, resulting in an approximately 12-fold increase in hydrolysis rate for both peracetic acid (PAA) and 3-chloroperbenzoic acid (MCPBA) when 0.1 M boric acid is present. The maximum rate of hydrolysis occurs at pH 9 and pH 8.4 for PAA and MCPBA respectively. In contrast, carbonate buffer does not enhance the rate of PAA hydrolysis. The reaction was followed by measuring the initial rate of hydrogen peroxide formation using a specific Ti(iv) complexation method. The study of the hydrolysis reaction requires the presence of 2 × 10-5 M each of ethylenediaminetetraacetic acid (EDTA) and ethylenediamine tetramethylene phosphonic acid (EDTMP) in all solutions in order to chelate metal ions across the full pH range (3 to 13) that would otherwise contribute to peroxyacid decomposition. Catalysis of peroxyacid hydrolysis is most likely effected by the triganol boric acid acting as a Lewis acid catalyst, associating with the peroxide leaving group in the transition state to reduce the leaving group basicity. The products of the reaction are the well characterised monoperoxoborate species and the parent carboxylic acid. Analysis of the pH and borate dependence data reveals that in addition to a catalytic pathway involving a single boric acid molecule, there is a significant pathway involving either (a) two boric acid molecules or (b) the polyborate species, B3O3(OH)4 -. Knowledge about catalytic mechanisms for the loss of peroxyacids through hydrolysis is important because they are widely used in reagents in a range of oxidation, bleaching and disinfection applications.

Characterising the ground level concentrations of harmful organic and inorganic substances released during major industrial fires, and implications for human health.

We report on the concentration ranges and combustion source-related emission profiles of organic and inorganic species released during 34 major industrial fires in the UK. These episodic events tend to be acute in nature and demand a rapid public health risk assessment to indicate the likely impact on exposed populations. The objective of this paper is to improve our understanding of the nature, composition and potential health impacts of emissions from major incident fires and so support the risk assessment process. Real world monitoring data was obtained from portable Fourier Transform Infrared (FTIR) monitoring (Gasmet DX-4030/40) carried out as part of the UK's Air Quality in Major Incidents service. The measured substances include carbon monoxide, sulphur dioxide, nitrogen dioxide, ammonia, hydrogen chloride, hydrogen bromide, hydrogen fluoride, hydrogen cyanide, formaldehyde, 1,3-butadiene, benzene, toluene, xylenes, ethyl benzene, acrolein, phosgene, arsine, phosphine and methyl isocyanate. We evaluate the reported concentrations against Acute Exposure Guideline Values (AEGLs) and Emergency Response Planning Guidelines (ERPGs), as well as against UK, EU and WHO short-term ambient guideline values. Most exceedances of AEGL or ERPG guideline values were at levels likely only to cause discomfort to exposed populations (hydrogen cyanide, hydrogen chloride, hydrogen fluoride and formaldehyde), though for several substances the exceedances could have potentially given rise to more serious health effects (acrolein, phosphine, phosgene and methyl isocyanate). In the latter cases, the observed high concentrations are likely to be due to cross-interference from other substances that absorb in the mid-range of the infrared spectrum, particularly when the ground level plume is very concentrated.

A novel approach to the development of 1-hour threshold concentrations for exposure to particulate matter during episodic air pollution events.

Episodic air pollution events that occur because of wildfires, dust storms and industrial incidents can expose populations to particulate matter (PM) concentrations in the thousands of µg m-3. Such events have increased in frequency and duration over recent years, with this trend predicted to continue in the short to medium term because of climate warming. The human health cost of episodic PM events can be significant, and inflammatory responses are measurable even after only a few hours of exposure. Consequently, advice for the protection of public health should be available as quickly as possible, yet the shortest averaging period for which PM exposure guideline values (GVs) are available is 24-h. To address this problem, we have developed a novel approach, based on Receiver Operating Characteristic (ROC) statistical analysis, that derives 1-h threshold concentrations that have a probabilistic relationship with 24-h GVs. The ROC analysis was carried out on PM10 and PM2.5 monitoring data from across the US for the period 2014-2019. Validation of the model against US Air Quality Index (AQI) 24-h breakpoint concentrations for PM showed that the maximum-observed 1-h PM concentration in any rolling 24-h averaging period is an excellent predictor of exceedances of 24-h GVs.

Quantifying organic carbon storage in temperate pond sediments.

Ponds may hold significant stocks of organic carbon in their sediments and pond creation may offer a practical application for land managers to increase carbon storage. However, ponds are overlooked in global carbon budgets. Their potential significance is suggested by the abundance of ponds throughout terrestrial biomes and their high carbon burial rates, but we lack measures of sediment carbon stocks from typical ponds. We sampled sediment from lowland temperate ponds in north east England comparing carbon stocks from ponds categorised by surrounding land use, or dominant vegetation, or drying regime, along with measures of variation within ponds. Sediment carbon varied considerably between ponds. This variation was more important than any systematic variation between pond types grouped by land use, vegetation or drying, or any variation within an individual pond. Our estimates of pond sediment organic carbon give measures that are higher than from soils in widespread habitats such as temperate grassland and woodland, suggesting that ponds are significant for carbon budgets in their own right. Ponds are relatively easy to create, are ubiquitous throughout temperate biomes and can be fitted in amongst other land uses; our results show that pond creation would be a useful and practical application to boost carbon sequestration in temperate landscapes.

Iridium(iii) complexes of 1,2,4-triazines as potential bioorthogonal reagents: metal coordination facilitates luminogenic reaction with strained cyclooctynes.

In this paper we describe unprecedented Ir(iii) complexes of 5-(2-pyridyl)-1,2,4-triazine and their reactivity towards the strained cyclooctyne BCN. The coordination of a 1,2,4-triazine ring to an iridium(iii) ion drastically increases the speed of the reaction, showing the second order rate constant of 8 M-1 s-1, the record value to date for a triazine-BCN reaction.

An apple a day? Assessing gardeners' lead exposure in urban agriculture sites to improve the derivation of soil assessment criteria.

Globally, many of our urban agriculture sites (UAS) contain high levels of lead (Pb), a contaminant of toxicological concern to humans. To improve the derivation of soil assessment criteria at UAS, and avoid inappropriate closure of these valuable community spaces, we sampled nearly 280 paired soil and crop samples across 31 UAS gardens. This sampling was coupled with an exposure and food frequency questionnaire and participants blood Pb levels (BLL), (43 gardeners and 29 non-gardening neighbours). In 98% of the sampled soils, Pb concentrations were above the current UK soil guideline for UAS (80 mg/kg), however despite the high soil Pb (geometric mean: 324 mg/kg), and high soil bioaccessible Pb (geometric mean: 58.7%), all participants BLL were <4.1 µg/dL (range: 0.6-4.1 µg/dL). Indeed, there was no statistically significant difference between the BLL of the UAS gardeners and those of their non-gardening neighbours (p = 0.569). Pb uptake, however, varied with crop type and our study highlights the suitability of certain crops for growing at UAS with elevated Pb (e.g. tubers, shrub and tree fruit), whilst limiting the consumption of others (selected root vegetables, such as rhubarb, beetroot, parsnips and carrots, with observed Pb concentrations > 0.1 mg/kg FW). The importance of defining the exposure scenario of a specific sub-population (i.e. UAS gardeners) is highlighted. Our preferred models predict site specific assessment criteria (SSAC) of 722-1634 mg/kg. We found fruit and vegetable consumption rates by all participants, and not just the UAS gardeners, to be considerably higher than those currently used to derive the UK's category 4 screening levels (C4SLs). Furthermore, the soil to plant concentration factors (SPCFs) used to derive the UAS C4SL significantly over predict Pb uptake. Our study indicates it may be appropriate to develop a distinct exposure dataset for UAS. In particular we recommend the derivation of SPCFs that are reflective of urban soils, both in terms of the range of soil Pb concentrations typically observed, but also the sources (and hence human oral bioaccessibility and plant-availability) of this Pb.

A study of particulate emissions during 23 major industrial fires: Implications for human health.

Public exposure to significantly elevated levels of particulate matter (PM) as a result of major fires at industrial sites is a worldwide problem. Our paper describes how the United Kingdom developed its Air Quality in Major Incidents (AQinMI) service to provide fire emission plume concentration data for use by managers at the time of the incident and to allow an informed public health response. It is one of the first civilian services of its type anywhere in the world. Based on the involvement of several of the authors in the AQinMI service, we describe the service's function, detail the nature of fires covered by the service, and report for the first time on the concentration ranges of PM to which populations may be exposed in major incident fires. We also consider the human health impacts of short-term exposure to significantly elevated PM concentrations and reflect on the appropriateness of current short-term guideline values in providing public health advice. We have analysed monitoring data for airborne PM (≤10µm, PM10;≤2.5µm, PM2.5 and ≤1.0µm, PM1) collected by AQinMI teams using an Osiris laser light scattering monitor, the UK Environment Agency's 'indicative standard' equipment, during deployment to 23 major incident industrial fires. In this context, 'indicative' is applied to monitoring equipment that provides confirmation of the presence of particulates and indicates a measured mass concentration value. Incident-averaged concentrations ranged from 38 to 1450µgm-3 for PM10 and 7 to 258µgm-3 for PM2.5. Of concern was that, for several incidents, 15-min averaged concentrations reached >6500µgm-3 for PM10 and 650µgm-3 for PM2.5, though such excursions tended to be of relatively short duration. In the absence of accepted very short-term (15-min to 1-h) guideline values for PM10 and PM2.5, we have analysed the relationship between the 1-h and 24-h threshold values and whether the former can be used as a predictor of longer-term exposure. Based on this analysis, for PM10, our tentative 1-h threshold value for use in deciding whether to close public buildings or to evacuate areas is 510µgm-3. For PM2.5, 1-h concentrations exceeding 350µgm-3 might indicate longer-term exposure problems. We conclude that whilst services such as AQinMI are a positive development, there is a need to consider further the accuracy of the data provided and for the development of very short-term guideline values (i.e. minutes to hours) that responders can use to determine the appropriate public health response.

Practicalities of mapping PM10 and PM2.5 concentrations on city-wide scales using a portable particulate monitor.

Fine particulate matter is considered to be the most significant ambient air pollutant in terms of potential health impacts. Therefore, it is important that regulators are able to accurately assess the exposure of populations to PM10 and PM2.5 across municipal areas. We report on the practicalities of using a laser light scattering portable particulate monitor (Turnkey Instruments DustMate), in combination with a GPS, to map PM10 and PM2.5 concentrations on city-wide scales in Newcastle upon Tyne/Gateshead (UK), during a series of walking surveys. A heated inlet is necessary to remove moisture droplets from the sampled air prior to analysis by the instrument, though this also results in the loss of volatile particulate components, particularly from the PM2.5 fraction. A co-location calibration study was carried out with a reference urban background Tapered Element Oscillating Micro-Balance/Filter Dynamics Measuring System (TEOM-FDMS) system in Newcastle that is part of the UK's Automatic Urban and Rural Network (AURN) of air quality monitoring stations. For PM10, orthogonal regression of the DustMate against TEOM-FDMS data gave a slope and intercept of 1.02 ± 0.06 and -3.7 ± 1.2, respectively (R2 = 0.73), whereas for PM2.5, the respective values were 0.78 ± 0.06 and -0.63 ± 0.55 (R2 = 0.79). These parameters are comparable to literature calibration studies using this technology. There was good agreement between simultaneous samples taken using two DustMate instruments: for PM10, a slope and intercept of 1.05 ± 0.03 and 0.36 ± 0.5, respectively (R2 = 0.73), were obtained, whereas for the PM2.5, the respective values were 0.79 ± 0.01 and 0.19 ± 0.06 (R2 = 0.86). Correction factors based on the slope and intercepts obtained from the calibration exercise were applied to raw data collected from the DustMate. An annually-normalised correction procedure was then used to account for different background particulate concentrations on different sampling days. These corrected PM10 and PM2.5 concentrations and corresponding GPS coordinates were displayed on a base map using Google Fusion Tables and Google Earth Professional. Almost all areas surveyed in Newcastle/Gateshead were well below the EU Air Quality Standards for PM10 and PM2.5.

Development of a novel kinetic model for the analysis of PAH biodegradation in the presence of lead and cadmium co-contaminants.

We report on the results of a 40 week study in which the biodegradation of 16 US EPA polycyclic aromatic hydrocarbons (PAHs) was followed in microcosms containing soil of high organic carbon content (11%) in the presence and absence of lead and cadmium co-contaminants. The total spiked PAH concentration was 2166mg/kg. Mercury amendment was also made to give an abiotic control. A novel kinetic model has been developed to explain the observed biphasic nature of PAH degradation. The model assumes that PAHs are distributed across soil phases of varying degrees of bioaccessibility. The results of the analysis suggest that overall percentage PAH loss is dependent on the respective rates at which the PAHs (a) are biodegraded by soil microorganisms in pore water and bioaccessible soil phases and (b) migrate from bioaccessible to non-bioaccessible soil phases. In addition, migration of PAHs to non-bioaccessible and non-Soxhlet-extractable soil phases associated with the humin pores gives rise to an apparent removal process. The presence of metal co-contaminants shows a concentration dependent inhibition of the biological degradation processes that results in a reduction in overall degradation. Lead appears to have a marginally greater inhibitory effect than cadmium.

Use of 24 kHz ultrasound to improve sulfate precipitation from wastewater.

Elevated sulfate concentrations in industrial effluent can lead to a number of significant problems, the most serious of which is the corrosion of concrete sewers as a result of hydrogen sulfide induced biogenic sulfuric acid attack; hydrogen sulfide can also create odor nuisance problems. The most common treatment process for sulfate removal from wastewaters is to precipitate it as gypsum using lime addition. Nevertheless, meeting discharge consent limits for sulfate can often present practical challenges due to the solubility of gypsum and so there is a need to investigate technological solutions that might provide for more consistent sulfate removal. This paper reports on the application of ultrasound during the sulfate precipitation process. We show that with as little as 10 s sonication at 24 kHz, significant increases in the rate of sulfate precipitation are observed. Particle size analysis, pH profiles and SEM micrographs, suggest that the likely mode of action is disaggregation of the calcium hydroxide particles, giving a greater solid-liquid interface, thus resulting in a faster dissolution rate and more readily available calcium ions. A range of experimental variables are studied, including the duration and power of sonication, as well as initial sulfate concentration and the effect of changing the time at which sonication is applied. For both sonicated and non-sonicated samples, precipitation commences almost immediately that the lime is added and so induction time is not an issue in this system.

Development and application of an inhalation bioaccessibility method (IBM) for lead in the PM10 size fraction of soil.

An approach for assessing the inhalation bioaccessibility of Pb in the PM10 size fraction is presented, using an in vitro simulated epithelial lung fluid to represent the extracellular environment of the lung. The developed inhalation bioaccessibility method (IBM) is applied to a range of urban surface soils and mining wastes obtained from Mitrovica, Kosovo, a site where impacts upon human health following exposure to Pb have been internationally publicised. All Pb determinations were undertaken by inductively coupled plasma mass spectrometry (ICP-MS). The pseudo-total concentration of Pb (microwave acid digestion using aqua-regia) varied between matrices: smelter (20,900-72,800mgkg(-1)), topsoil (274-13,700mgkg(-1)), and tailings (2990mgkg(-1)-25,300mgkg(-1)). The in vitro inhalation bioaccessibility was typically several orders of magnitude lower: smelter (7.0-965mgkg(-1)), topsoil (9.8-1060mgkg(-1)), and tailings (0.7mgkg(-1)-49.2mgkg(-1)). The % inhalation bioaccessibility ranged from 0.02 to 11.0%, with the higher inhalation bioaccessible Pb concentrations being observed for samples from the Bosniak Mahalla area of Mitrovica (an area proposed for the relocation of internally displaced peoples). The estimated inhalation dose (for adults) calculated from the PM10 pseudo-total Pb concentration ranged from 0.369 to 1.284µgkg(-1)BWday(-1) (smelter), 0.005-0.242µgkg(-1)BWday(-1) (topsoil), and 0.053-0.446µgkg(-1)BWday(-1) (tailings). When daily inhalation doses were calculated using the bioaccessible Pb concentration the modelled exposure doses were much lower: smelter (0.0001-0.0170µgkg(-1)BWday(-1)), topsoil (0.0002-0.0187µgkg(-1)BWday(-1)) and tailings (0.0001-0.0009µgkg(-1)BWday(-1)). Modelled for the neutral pH conditions of the interstitial lung environment, the results indicate a low potential inhalation bioaccessibility for Pb in these samples. Given the already elevated environmental Pb burden experienced by the local population, where significant prolonged dust or particulate generating activities are taking place, or where the inhaled particles are phagocytized, then inhalation exposure has the potential to significantly add to the overall Pb burden. Such data are important for local policy makers to better enable them to assess risk, especially in areas where soils/dusts have elevated levels of contamination.

A kinetic and theoretical study of the borate catalysed reactions of hydrogen peroxide: the role of dioxaborirane as the catalytic intermediate for a wide range of substrates.

Our recent work has provided new insights into the equilibria and species that exist in aqueous solution at different pHs for the boric acid - hydrogen peroxide system, and the role of these species in oxidation reactions. Most recently, (M. C. Durrant, D. M. Davies and M. E. Deary, Org. Biomol. Chem., 2011, 9, 7249-7254), we have produced strong theoretical and experimental evidence for the existence of a previously unreported monocyclic three membered peroxide species, dioxaborirane, that is the likely catalytic species in borate mediated electrophilic reactions of hydrogen peroxide in alkaline solution. In the present paper, we extend our study of the borate-peroxide system to look at a wide range of substrates that include substituted dimethyl anilines, methyl-p-tolyl sulfoxide, halides, hydrogen sulfide anion, thiosulfate, thiocyanate, and hydrazine. The unusual selectivity-reactivity pattern of borate catalysed reactions compared with hydrogen peroxide and inorganic or organic peracids previously observed for the organic sulfides (D. M. Davies, M. E. Deary, K. Quill and R. A. Smith, Chem.-Eur. J., 2005, 11, 3552-3558) is also seen with substituted dimethyl aniline nucleophiles. This provides evidence that the pattern is not due to any latent electrophilic tendency of the organic sulfides and further supports dioxaborirane being the likely reactive intermediate, thus broadening the applicability of this catalytic system. Moreover, density functional theory calculations on our proposed mechanism involving dioxaborirane are consistent with the experimental results for these substrates. Results obtained at high concentrations of both borate and hydrogen peroxide require the inclusion the diperoxodiborate dianion in the kinetic analysis. A scheme detailing our current understanding of the borate-peroxide system is presented.

No effect of 12 weeks' supplementation with 1 g DHA-rich or EPA-rich fish oil on cognitive function or mood in healthy young adults aged 18-35 years.

The n-3 PUFA are a unique class of fatty acids that cannot be manufactured by the body, and must be acquired via dietary sources. In the UK, as well as in other Western nations, these 'essential' fatty acids are consumed in quantities that fall below government guidelines. The present study explored the effects of 12 weeks' dietary supplementation with 1 g/d of two types of fish oil (FO; DHA-rich and EPA-rich) in 159 healthy young adults aged 18-35 years. An assessment of performance on a battery of computerised cognitive tasks and mood measures took place before and following the 12-week treatment regimen. Venous blood samples were also supplied by participants at both time points which were later analysed for serum fatty acid concentrations. Despite good adherence to the study protocol - as reflected in increased concentrations of n-3 serum fatty acids - compared with placebo, the observed effects of both active treatments were minimal. The only finding of note revealed that supplementation with EPA-rich FO may reduce subjective mental fatigue at times of high cognitive demand, although further investigation is required. These findings, taken together with other recent reports of null effects, suggest that dietary supplementation with n-3 PUFA in healthy, normally developing and impairment-free populations is unlikely to result in cognitive enhancement.

Dioxaborirane: a highly reactive peroxide that is the likely intermediate in borate catalysed electrophilic reactions of hydrogen peroxide in alkaline aqueous solution.

This paper reports on a kinetic and theoretical study into the borate mediated reaction of dimethyl sulfide with hydrogen peroxide in both acid and alkaline conditions. At high pH, whilst the kinetic data is consistent with the catalytic species being monoperoxoborate, formed from the rapid equilibrium between hydrogen peroxide and boric acid, DFT calculations show that this species is in fact less reactive than hydrogen peroxide, requiring us to seek an alternative catalytic mechanism. DFT provides an important insight for this, showing that although boric acid and peroxoboric acid are primarily Lewis acids, they can exhibit a small degree of Brønsted acidity, allowing, respectively, the B(O)(OH)(2)(-) and HOOB(OH)(O)(-) anions to exist in small concentrations. Whilst the peroxoborate anion, HOOB(OH)(O)(-), is predicted to have only marginal catalytic activity, its tautomer, dioxaborirane, (HO)(2)BO(2)(-), a three membered cyclic peroxide, has a very low activation barrier of 2.8 kcal/mol. Hence, even though dioxaborirane is likely to be present in very low concentrations, it is still sufficiently reactive for overall rate enhancements to be observed for this system. This is the first literature report of this species. The observed low selectivity observed for borate catalysed reactions of hydrogen peroxide with a range of substituted phenyl methyl sulfides in our previous study (D. M. Davies, M. E. Deary, K. Quill and R. A. Smith, Chem.-Eur. J. 2005, 11, 3552-3558) is further evidence in favour of a highly reactive catalytic species. At low pH, kinetic data shows that borate catalyses the reaction between hydrogen peroxide and dimethyl sulfide; this is supported by DFT calculations that predict peroxoboric acid to be an effective catalytic intermediate, with an energy barrier of 7.4 kcal mol(-1) compared to 10.1 kcal mol(-1) for the uncatalysed system. Nevertheless, the overall contribution of this pathway is small because of the unfavourable equilibrium between hydrogen peroxide and boric acid to form peroxoboric acid.

Borate-catalyzed reactions of hydrogen peroxide: kinetics and mechanism of the oxidation of organic sulfides by peroxoborates.

The kinetics of the oxidation of substituted phenyl methyl sulfides by hydrogen peroxide in borate/boric acid buffers were investigated as a function of pH, total peroxide concentration, and total boron concentration. Second-order rate constants at 25 degrees C for the reaction of methyl 4-nitrophenyl sulfide and H(2)O(2), monoperoxoborate, HOOB(OH)(3) (-), or diperoxoborate, (HOO)(2)B(OH)(2) (-), are 8.29 x 10(-5), 1.51 x 10(-2) and 1.06 x 10(-2) M(-1) s(-1), respectively. Peroxoboric acid, HOOB(OH)(2), is unreactive. The Hammett rho values for the reactions of a range of substituted phenyl methyl sulfides and hydrogen peroxide, monoperoxoborate or diperoxoborate are -1.50 +/- 0.1, -0.65 +/- 0.07 and -0.48 (two points only), respectively. The rho values for the peroxoborates are of significantly lower magnitude than expected from their reactivity compared to other peroxides. Nevertheless the negative rho values indicate positive charge development on the sulfur atom in the transition state consistent with nucleophilic attack by the organic sulfides on the peroxoborates as with the other peroxides. The kinetic parameters, including the lack of reactivity of peroxoboric acid, are discussed in terms of the differences in the transition state of reactions involving peroxoboron species with respect to those of other peroxides.