Persistence of dissolved organic matter explained by molecular changes during its passage through soil

Dissolved organic matter affects fundamental biogeochemical processes in the soil such as nutrient cycling and organic matter storage. The current paradigm is that processing of dissolved organic matter converges to recalcitrant molecules (those that resist degradation) of low molecular mass and high molecular diversity through biotic and abiotic processes. Here we demonstrate that the molecular composition and properties of dissolved organic matter continuously change during soil passage and propose that this reflects a continual shifting of its sources. Using ultrahigh-resolution mass spectrometry and nuclear magnetic resonance spectroscopy, we studied the molecular changes of dissolved organic matter from the soil surface to 60 cm depth in 20 temperate grassland communities in soil type Eutric Fluvisol. Applying a semi-quantitative approach, we observed that plant-derived molecules were first broken down into molecules containing a large proportion of low-molecular-mass compounds. These low-molecular-mass compounds became less abundant during soil passage, whereas larger molecules, depleted in plant-related ligno-cellulosic structures, became more abundant. These findings indicate that the small plant-derived molecules were preferentially consumed by microorganisms and transformed into larger microbial-derived molecules. This suggests that dissolved organic matter is not intrinsically recalcitrant but instead persists in soil as a result of simultaneous consumption, transformation and formation

Chemical (C, N, S, black carbon, soot and char) and stable carbon isotope composition of street dusts from a major West African metropolis: Implications for source apportionment and exposure

Street dust is a major source of pollution and exposure of residents of West Africa to toxic chemicals. There is however, limited knowledge about the chemical composition and sources of street dust in urban areas of sub-Saharan Africa. The total carbon (TC), nitrogen (TN), sulfur (TS) and the stable carbon isotope ratios (delta C-13) contents of street dust sampled from 25 sites distributed across Kumasi (a metropolis in Ghana with a population of ca.2 million) were determined. In addition, black carbon (BC) and their subunits (soot and char) in these samples were also determined. The concentrations of TC, TN and TS in the dusts were 5-71 mg g(-1), 0.3-4.3 mg g(-1) and 0.2-1.4 mg g(-1), respectively. The concentrations of TC, TN and TS were higher than at the background site of the metropolis by a factor of 5.1 (range: 1.7-12), 3.9 (1.1-13) and 2.8 (0.7-5), respectively. The BC, char and soot concentrations in these samples averaged 1.6 mg g(-1) (0.13-4.4), 1.2 mg g(-1) (0.08-3.7) and 0.36 mg g(-1) (0.05-1.5), respectively. The concentrations of BC, char and soot in the street dust were higher than in the background location by factors of 5 (range: 0.8-13), 6 (0.7-17) and 3 (0.5-12), respectively. The TC, TN, TS, BC, soot and char concentrations were positively correlated with each other and with polycyclic aromatic compounds (PAHs, oxygenated PAHs and azaarenes from a previous study), indicating their common origin and fate. The delta C-13 values ranged from -27 to -24 [parts per thousand], with more polluted sites being more depleted in C-13. Based on the chemical composition of the street dusts, the 25 sites could be clustered into four groups by hierarchical cluster analysis which reflect areas of varying anthropogenic influence and, accordingly, exposure to hazardous chemicals

Characterization of chemical components and bioreactivity of fine particulate matter (PM2.5) during incense burning

202308 bcchAccepted ManuscriptRGCPublishe

The chemical composition and toxicological effects of fine particulate matter (PM2.5) emitted from different cooking styles

202203 bcfcNot applicableRGCPublished24 month

PM2.5-bound oxygenated PAHs, nitro-PAHs and parent-PAHs from the atmosphere of a Chinese megacity: Seasonal variation, sources and cancer risk assessment

Polycyclic aromatic compounds (PACs) in air particulate matter contribute considerably to the health risk of air pollution. The objectives of this study were to assess the occurrence and variation in concentrations and sources of PM2.5-bound PACs [Oxygenated PAHs (OPAHs), nitro-PAHs and parent-PAHs] sampled from the atmosphere of a typical Chinese megacity (Xi&#39;an), to study the influence of meteorological conditions on PACs and to estimate the lifetime excess cancer risk to the residents of Xi&#39;an (from inhalation of PM2.5-bound PACs). To achieve these objectives, we sampled 24-h PM2.5 aerosols (once in every 6 days, from 5 July 2008 to 8 August 2009) from the atmosphere of Xi&#39;an and measured the concentrations of PACs in them. The PM2.5-bound concentrations of &Sigma;carbonyl-OPAHs, &sum;hydroxyl +carboxyl-OPAHs, &Sigma;nitro-PAHs and &Sigma;alkyl + parent-PAHs ranged between 5&ndash;22, 0.2&ndash;13, 0.3&ndash;7, and 7&ndash;387 ng m&minus;3, respectively, being markedly higher than in most western cities. This represented a range of 0.01&ndash;0.4% and 0.002&ndash;0.06% of the mass of organic C in PM2.5 and the total mass of PM2.5, respectively. The sums of the concentrations of each compound group had winter-to-summer ratios ranging from 3 to 8 and most individual OPAHs and nitro-PAHs had higher concentrations in winter than in summer,suggesting a dominant influence of emissions from household heating and winter meteorological conditions. Ambient temperature, air pressure, and wind speed explained a large part of the temporal variation in PACs concentrations. The lifetime excess cancer risk from inhalation (attributable to selected PAHs and nitro-PAHs) was six fold higher in winter (averaging 1450 persons per million residents of Xi&#39;an) than in summer. Our results call for the development of emission control measures.</p