Effects of carbonaceous materials and particle size on oral and inhalation bioaccessibility of PAHs and OPEs in airborne particles

Bioavailability of environmental contaminants is attracting considerable scientific attention due to growing awareness of its importance for risk assessment. In this study, size-segregated airborne particles were collected from six point-source sites, an urban residential site, and a sub-urban site. Potential factors governing bioaccessibility of the particle-bound polycyclic aromatic hydrocarbons (PAHs) and organophosphorus esters (OPEs) in stimulated gastrointestinal and respiratory tracts were elucidated. Particle concentrations of PAHs and OPEs at the eight sites were 2.4-32.3 ng/m³ and 1.6-19.9 ng/m³, respectively. In fine particles (with aerodynamic diameter less than 2.5 μm), 4- to 6-ring PAHs were more strongly correlated with organic carbon (OC) than elemental carbon (EC); while 3- and 4-ring PAHs in coarse particles (2.5-10 μm) tended to associate with EC. OPEs mostly showed significant correlations with EC in both fine and coarse particles. OC and EC exerted a significantly restraining effect on the oral and inhalation bioaccessibility of most hydrophobic organic contaminants (HOCs) in fine particles due to sorption of HOC molecules to these components. Furthermore, the effects varied, which could depend either on the emission sources (for oral bioaccessibility of PAHs) or the physicochemical properties of HOCs (for bioaccessibility of OPEs and inhalation bioaccessibility of PAHs). Linear regression between OC/EC contents and HOC bioaccessibility indicated that EC should play a more important role in the inhalation bioaccessibility than the oral bioaccessibility. Particle size of airborne particles is a relatively less significant factor determining the bioaccessibility.

Characterization of carbonaceous fractions in PM2.5 and PM10 over a typical industrial city in central China

Aerosol samples of PM_2.5 and PM₁₀ were collected every 6 days from March 2012 to February 2013 in Huangshi, a typical industrial city in central China, to investigate the characteristics, relationships, and sources of carbonaceous species. The PM_2.5 and PM₁₀ samples were analyzed for organic carbon (OC), elemental carbon (EC), char, and soot using the thermal/optical reflectance (TOR) method following the IMPROVE_A protocol. PM_2.5 and PM₁₀ concentrations ranged from 29.37 to 501.43 μg m^-3 and from 50.42 to 330.07 μg m^-3, with average levels of 104.90 and 151.23 μg m^-3, respectively. The 24-h average level of PM_2.5 was about three times the US EPA standard of 35 μg m^-3, and significantly exceeds the Class II National Air Quality Standard of China of 75 μg m^-3. The seasonal cycles of PM mass and OC concentrations were higher during winter than in summer. EC and char concentrations were generally highest during winter but lowest in spring, while higher soot concentrations occurred in summer. This seasonal variation could be attributed to different seasonal meteorological conditions and changes in source contributions. Strong correlations between OC and EC were found for both PM_2.5 and PM₁₀ in winter and fall, while char and soot showed a moderate correlation in summer and winter. The average OC/EC ratios were 5.11 and 4.46 for PM_2.5 and PM₁₀, respectively, with individual OC/EC ratios nearly always exceeding 2.0. Higher char/soot ratios during the four seasons indicated that coal combustion and biomass burning were the major sources for carbonaceous aerosol in Huangshi. Contrary to expectations, secondary organic carbon (SOC) which is estimated using the EC tracer method exhibited spring maximum and summer minimum, suggesting that photochemical activity is not a leading factor in the formation of secondary organic aerosols in the study area. The contribution of SOC to OC concentration for PM_2.5 and PM₁₀ were 47.33 and 45.38%, respectively, implying that SOC was an important component of OC mass. The serious air pollution in haze-fog episode was strongly correlated with the emissions of pollutants from biomass burning and the meteorological conditions.

Data relating to carbonaceous components in Songkhla Lake sediments, Thailand

The focus of this research was to present a data article associated with organic carbon (OC) and elemental carbon (EC) preserved in lake sediments. Descriptive statistics were applied in this dataset. Sediment cores were sliced immediately at the following layers: 0-20; 20-40; 40-60; 60-80; 80-100; 100-120; 120-140; 140-160; 160-180; 180-200; 200-220; 220-240; 240-260; 260-280; 280-300; 300-320; 320-340; 340-360; 360-380; 380-400; 440-460; 460-480; 480-500; 500-520; 520-540; 540-560 and 560-580 mm of depth. Chemical analysis of OC (i.e. OC1, OC2, OC3, OC4), EC (i.e. EC1, EC2, EC3), and the pyrolyzed organic carbon (OP) (i.e. OP1, OP2, OP3, OP4, OP5, OP6, Char, Soot) contents was conducted by using a DRI Model 2001 Thermal/Optical Carbon Analyzer. The chemical characterization coupled with statistical analysis reveal that vehicle exhausts are the most prominent factor governing OC/EC data detected in core sediments. These data underline some noticeable concerns associated with ecotoxicology and environmental safety of residents surrounding the Songkhla Lake.

Batch soil adsorption and column transport studies of 2,4-dinitroanisole (DNAN) in soils

The explosive 2,4,6-trinitrotoluene (TNT) is currently a main ingredient in munitions; however the compound has failed to meet the new sensitivity requirements. The replacement compound being tested is 2,4-dinitroanisole (DNAN). DNAN is less sensitive to shock, high temperatures, and has good detonation characteristics. However, DNAN is more soluble than TNT, which can influence transport and fate behavior and thus bioavailability and human exposure potential. The objective of this study was to investigate the environmental fate and transport of DNAN in soil, with specific focus on sorption processes. Batch and column experiments were conducted using soils collected from military installations located across the United States. The soils were characterized for pH, electrical conductivity, specific surface area, cation exchange capacity, and organic carbon content. In the batch rate studies, change in DNAN concentration with time was evaluated using the first order equation, while adsorption isotherms were fitted using linear and Freundlich equations. Solution mass-loss rate coefficients ranged between 0.0002h^-1 and 0.0068h^-1. DNAN was strongly adsorbed by soils with linear adsorption coefficients ranging between 0.6 and 6.3Lg^-1, and Freundlich coefficients between 1.3 and 34mg^1-nLⁿkg^-1. Both linear and Freundlich adsorption coefficients were positively correlated with the amount of organic carbon and cation exchange capacity of the soil, indicating that similar to TNT, organic matter and clay minerals may influence adsorption of DNAN. The results of the miscible-displacement column experiments confirmed the impact of sorption on retardation of DNAN during transport. It was also shown that under flow conditions DNAN transforms readily with formation of amino transformation products, 2-ANAN and 4-ANAN. The magnitudes of retardation and transformation observed in this study result in significant attenuation potential for DNAN, which would be anticipated to contribute to a reduced risk for contamination of ground water from soil residues.

Size distribution characteristics of carbonaceous aerosol in Xishuangbanna, southwest China: a sign for biomass burning in Asia

In 2012, size-segregated aerosol samples were collected in Xishuangbanna, a forest station in southwest China. The concentrations of organic and elemental carbon (OC and EC for short) were quantified with thermal/optical carbon analyzer in the filter samples. OC and EC exhibited similar seasonal patterns, with the highest concentrations in spring, possibly due to the influence of biomass burning in south and southeast Asia. The mass size distributions of OC and EC were bimodal in all the sampling seasons, each with a dominant peak in the fine mode of 0.4-0.7 μm and a coarse peak in the size range of 2.1-4.7 μm. In fine mode, OC and EC showed smaller geometric mean diameters (GMDs) during winter. OC and EC were prone to be more concentrated in fine particles in spring and winter than in summer and autumn. Furthermore, EC was more abundant in fine particles than OC. Good correlations (R(2) = 0.75-0.82) between OC and EC indicated that they had common dominant sources of combustion such as biomass burning and fossil fuel combustion emissions. The daily average OC/EC ratios ranged from 2.1 to 9.1, more elevated OC/EC ratios being found in the winter.