Role Of Black Carbon Research Articles

Role of black carbon in modulating aerosol direct effects driven by air pollution controls during 2013–2017 in China

Aerosol direct effects (ADEs) can modulate shortwave radiation as well as atmospheric dynamics and air quality. As the key absorbing component of aerosol, the black carbon (BC) largely determines the aerosol optical properties. Therefore, it is expected that BC emission controls might gain co-benefits from the simultaneous reduction of ADEs. To demonstrate such synergy, here we quantified the ADEs changes and the role of BC controls in China during 2013–2017 using a regional two-way coupled meteorology chemistry transport model. Simulated results suggest that the control action effectively reduced the wintertime PM2.5 concentration (−26.0 μg m−3) and associated ADEs. In January, the influence of ADEs on surface shortwave radiation, 2-meter temperature, and planetary boundary layer height was weakened from −16.7 W m−2, −0.20 °C, and −15.4 m in 2013 to −11.3 W m−2, −0.06 °C, and −10.7 m in 2017, respectively. The enhancement of SO2, NO2, and PM2.5 concentrations due to ADEs was reduced from +3.1%, +5.2%, and +5.4% in 2013 to +2.6%, +4.5%, and +3.3% in 2017, respectively, demonstrating the extra benefit of air pollution controls for improving air quality by reducing ADEs. Meanwhile, the BC emission reduced by 12.5% simultaneously along with the effective controls on SO2 and NO2 emissions during 2013–2017, mainly from domestic combustion (−11.7%), resulting in 30.3% (−0.9 μg m−3) reduction of BC concentration. Such BC controls contributed 15.6–60.2% of such changes in the ADEs influence on meteorological variables, and 32.6–41.1% on air pollutants. More specially, the effectiveness of collaborative reduction of BC further reduced surface shortwave radiation in China by 3.6 W m−2 in January and 1.0 W m−2 in July, leading to a more weakened ADEs that bring extra benefits in reducing PM2.5 concentrations by 1.8 μg m−3 in January and 0.3 μg m−3 in July. Apparently, BC played an important role in modulating the ADEs and associated influences on meteorology and air quality, suggesting a wise control strategy by targeting absorbing component of PM2.5 reduction to address both air pollution and climate change in the future.

Role of Black Carbon in Modulating Aerosol Direct Effects Driven by Air Pollution Controls During 2013-2017 in China

Role of Black Carbon in Modulating Aerosol Direct Effects Driven by Air Pollution Controls During 2013-2017 in China

The Climatology of Lower Tropospheric Temperature Inversions in China from Radiosonde Measurements: Roles of Black Carbon, Local Meteorology, and Large-Scale Subsidence

AbstractThe variability of the lower tropospheric temperature inversion (TI) across China remains poorly understood. Using seven years’ worth of high-resolution radiosonde measurements at 120 sites, we compile the climatology of lower tropospheric TI in terms of frequency, intensity, and depth during the period from 2011 to 2017. The TI generally exhibits strong seasonal and geographic dependencies. Particularly, the TI frequency is found to be high in winter and low in summer, likely due to the strong aerosol radiative effect in winter. The frequency of the surface-based inversion (SBI) exhibits a “west low, east high” pattern at 0800 Beijing time (BJT), which then switches to “west high, east low” at 2000 BJT. Both the summertime SBI and elevated inversion (EI) reach a peak at 0800 BJT and a trough at 1400 BJT. Interestingly, the maximum wintertime EI frequency occurs over Southeast China (SEC) rather than over the North China Plain (NCP), likely attributable to the combination of the heating effect of black carbon (BC) originating from the NCP, along with the strong subsidence and trade inversion in SEC. Correlation analyses between local meteorology and TI indicate that larger lower tropospheric stability (LTS) favors more frequent and stronger TIs, whereas the stronger EI under smaller LTS conditions (unstable atmosphere) is more associated with subsidence rather than BC. Overall, the spatial pattern of the lower tropospheric TI and its variability in China are mainly controlled by three factors: local meteorology, large-scale subsidence, and BC-induced heating. These findings help shed some light on the magnitude, spatial distribution, and underlying mechanisms of the lower tropospheric TI variation in China.

Use of the Single Particle Soot Photometer (SP2) as a pre-filter for ice nucleation measurements: effect of particle mixing state and determination of SP2 conditions to fully vaporize refractory black carbon

Abstract. Ice nucleation is a fundamental atmospheric process that impacts precipitation, cloud lifetimes, and climate. Challenges remain to identify and quantify the compositions and sources of ice-nucleating particles (INPs). Assessment of the role of black carbon (BC) as an INP is particularly important due to its anthropogenic sources and abundance at upper-tropospheric cloud levels. The role of BC as an INP, however, is unclear. This is, in part, driven by a lack of techniques that directly determine the contribution of refractory BC (rBC) to INP concentrations. One previously developed technique to measure this contribution uses the Single Particle Soot Photometer (SP2) as a pre-filter to an online ice-nucleating particle counter. In this technique, rBC particles are selectively heated to their vaporization temperature in the SP2 cavity by a 1064 nm laser. From previous work, however, it is unclear under what SP2 conditions, if any, the original rBC particles were fully vaporized. Furthermore, previous work also left questions about the effect of the SP2 laser on the ice-nucleating properties of several INP proxies and their mixtures with rBC. To answer these questions, we sampled the exhaust of an SP2 with a Scanning Mobility Particle Sizer and a Continuous Flow Diffusion Chamber. Using Aquadag® as an rBC proxy, the effect of several SP2 instrument parameters on the size distribution and physical properties of particles in rBC SP2 exhaust were explored. We found that a high SP2 laser power (930 nW∕(220 nm PSL)) is required to fully vaporize a ∼ 0.76 fg rBC particle. We also found that the exhaust particle size distribution is minimally affected by the SP2 sheath-to-sample ratio; the size of the original rBC particle, however, greatly influences the size distribution of the SP2 exhaust. The effect of the SP2 laser on the ice nucleation efficiency of Snomax®, NX-illite, and Suwannee River Fulvic Acid was studied; these particles acted as proxies for biological, illite-rich mineral dust, and brown carbon INPs, respectively. The original size distribution and ice nucleation efficiency of all non-rBC proxies were unaffected by the SP2 laser. Furthermore, the ice nucleation efficiencies of all proxies were not affected when externally mixed with rBC. These proxies, however, always show a reduction in ice-nucleating ability when internally mixed with rBC. We end this work with recommendations for users who wish to use the SP2 as a pre-filter to remove large rBC particles from an aerosol stream.

Role of black carbon in soil distribution of organochlorines in Lesser Himalayan Region of Pakistan.

Black carbon and total organic carbon (TOC) along with organochlorines (OCs) were analyzed in soils from four sampling zones of Lesser Himalayan Region based on source proximity/anthropogenic influences along the altitude. CTO-375 method was used for BC analysis while OCs were analyzed by GC-MS/MS system. BC and TOC ranged between 0.16-1.77 and 6.8-41.3mgg-1 while those of OCPs and PCBs ranged between 0.69 and 5.77 and 0.12-2.55ngg-1, respectively. ∑DDTs were the dominant (87.9%) among OCPs while tri- and tetra- (65.5%) homologue groups among PCBs. Hexa-PCBs, however also showed higher contribution (20.4%) in the region. Source diagnostic ratios of DDE+DDD/DDT (0.1-1.53) indicated both fresh and old input while α-HCH/γ-HCH (0.19-2.49) showed presence of lindane in the region. Higher concentration of OCs were observed in Zone C at altitudinal range of 737-975 masl that are close to the human influences and potential sources of POPs. The results of linear regression analysis revealed potential input of BC in soil distribution of OC concentrations in the region.

Revisiting nitrous acid (HONO) emission from on-road vehicles: A tunnel study with a mixed fleet

ABSTRACTNitrous acid (HONO) is an important precursor of OH radicals in the atmosphere. In urban areas, emissions from vehicles are the main source of air pollutants, including reactive nitrogen. Previously reported emission ratios of HONO (HONO/NOx) from vehicles were measured in the late 1990s and need to be updated due to the significant changes in emission control technologies. We measured the emission ratio of a fleet of vehicles (38% diesel on average) from March 11 to 21, 2015, in a road tunnel in Hong Kong. The emission ratio of 1.24% (±0.35%) obtained is greater than the commonly adopted 0.8% or 0.3%. The elevated emission ratio is found to be related to the presence of vehicles equipped with diesel particle filters (DPFs). Positive correlation between HONO and black carbon (BC) shows that HONO and BC were emitted together, while the lack of correlation or even anticorrelation between HONO/NOx and BC indicates that the BC-mediated conversion of NO2 to HONO in the dark was insignificant in the immediate vicinity of the emission sources.Implications: Vehicular emission is a key source for HONO in the urban atmosphere. However, the most commonly used emission ratio HONO/NOx in modeling studies was measured more than 15 years ago. Our tunnel study suggests that a mixed fleet nowadays has a higher emission ratio, possibly because of the diesel particle filter (DPF) retrofit program and the growing share of Euro IV or more advanced diesel vehicles. Our study also provides new insight into the role of black carbon in HONO formation from vehicles.

Active Mobility and Blood Pressure: Roles of Black Carbon and Physical Activity

Background Active mobility (ie walking and cycling) has been associated with health benefits like increasing levels of physical activity and reduction of cardiovascular risk in the general population. However, increased inhalation rate during physical activity may result in increased inhaled dose of traffic-related air pollutants. short-term exposure to traffic-related air pollutants has been associated with adverse cardiovascular outcomes like increasing blood pressure. The current study evaluates the association between active mobility patterns and blood pressure, and also if the exposure to black carbon and levels of physical activity are mediators of this association. Methods A panel study was performed in three European cities (Antwerp, Barcelona, and London) with 119 healthy adults (approximately 40 participants/city) who completed three 7-day measurement periods in winter, summer, and mid-season. Between February 2015 and March 2016 they wore sensors to measure the exposure to black carbon (i.e. a marker of traffic-related air pollutants) and to monitor their physical activity levels. blood pressure was measured three times during each measurement period: at the beginning (day 0), middle (day 4), and end (day 7). On these days, participants also completed a questionnaire about their personal characteristics and lifestyle behaviours. Multilevel regression models will be used to evaluate the association between active mobility and blood pressure, and Baron and Kenny's framework will be followed to establish the mediation roles. All models will be adjusted for potential confounders. Results The analyses for this study are ongoing. The current sample had a fairly equal distribution of sexes (55% females) and the mean age was 35 ± 10 years. The majority of participants were Caucasian (94%) and had high education degrees (89%). The sample was fairly active with a median (Inter-quartile range) moderate-to-vigorous physical activity of 71 (49-111) min/day measured by an accelerometer. Mean black carbon exposure over all sample in coinciding time periods was 1636 ± 673 ng/m³. The mean black carbon exposure increased with higher levels of physical activity. We expect to find an association between active mobility patterns and lower BP. We also expect to find indications for mediation of this association by black carbon exposure and physical activity levels. Conclusions The increased levels of physical activity through active mobility could attenuate the effects of black carbon exposure in blood pressure.

Role of black carbon in the Arctic’s new normal

Role of black carbon in the Arctic’s new normal

Role of black carbon in the Arctic’s new normal

Role of black carbon in the Arctic’s new normal

Persistence, variance and toxic levels of organochlorine pesticides in fluvial sediments and the role of black carbon in their retention

The present study assesses the persistence and variation of organochlorine pesticides (OCPs) and their regulation by total organic carbon (TOC) and black carbon (BC) in freshwater sediment. Sediment samples from the Yamuna River, a major tributary of the Ganges (one of the most populated and intensively used rivers in Asia), had high levels of Σ20OCPs (21.41 to 139.95 ng g(-1)). β-Hexachlorocyclohexane (β-HCH) was the most predominant component. ΣHCH and Σdichloro-diphenyl-trichloroethane (DDT) constituted ~86% of Σ20OCPs. Isomer ratios indicated fresh usage of lindane, DDT and technical-grade HCH. Toxicological comparison with freshwater sediment quality guidelines showed γ-HCH and DDT at high levels of concern. β-HCH, α-HCH, endrin, heptachlor epoxide, dichloro-diphenyl-dichloroethane (DDD), dichloro-diphenyl-dichloroethylene and chlordane were above some of the guideline levels. TOC and BC had mean concentrations of 1.37 ± 0.51% and 0.46 ± 0.23 mg g(-1), respectively. BC constituted 1.25 to 10.56% of TOC. We observed low to moderate correlations of BC with isomers of HCH, p,p'-DDT and methoxychlor while of TOC with Σ20OCPs, γ-HCH, endosulfan sulfate and methoxychlor. Principal component analysis enabled correlating and clustering of various OCPs, BC and TOC. OCP distribution was related with pH, electrical conductivity, soil moisture and finer fractions of sediment. OCPs with similarity in properties that determine their interactions with carbonaceous components of sediment clustered together. A number of factors may, thus, be involved in the regulation of interactive forces between BC and OCPs. BC in this study may be more important than TOC in the retention of some OCPs into fluvial sediments, thereby reducing their bioavailability. The finding is probably the first of its kind to report and emphasises the role of BC in the persistence of OCPs in fluvial sediments.

Modernizing Artisanal Brick Kilns: A Global Need

The city of Cusco in southeastern Peru is a World Heritage Site and a tourist attraction for those drawn by the Inca ruins nearby. But anyone who lives in or visits Cusco has to contend with its heavily polluted air. Trucks and buses belch clouds of diesel exhaust, and on the outskirts of town hundreds of family-run artisanal brick kilns send plumes of oily black smoke into the sky. Brick makers near Cusco fire their traditional kilns mainly with coal, but they also have a long history of burning plastic trash, used motor oil, and discarded tires. “They produce huge air quality problems,” says Jon Bickel, a Swiss development expert based in Lima. Most of the bricks that are made in Peru and other low-income countries are fired in artisanal kilns that pump greenhouse gases and other pollutants into the atmosphere, posing a health threat to brick workers, their surrounding communities, and even farther afield. And since brick production keeps pace with population growth, its environmental health impacts are likely growing throughout the developing world, says Jie Li, an energy and environmental specialist with the World Bank’s South Asia Region in Washington, DC. Workers cut firewood to light a brick kiln in Kabul, Afghanistan. The few health studies that have been conducted on kiln workers typically reveal musculoskeletal effects and health effects similar to those seen in other smoky, dusty occupations. A number of both small-scale and multinational development groups coordinated by the World Bank, the United Nations, and other organizations are now turning their attention to this important but poorly characterized industrial sector. Leading the charge in Latin America, Bickel directs a Swiss-funded group known by its Spanish acronym, EELA (for Eficiencia Energetica en Ladrilleras Artesanales) that aims to modernize artisanal brick making in Peru, Argentina, Brazil, Bolivia, Ecuador, Colombia, Nicaragua, Honduras, and Mexico. Bickel says EELA’s long-term goal is to reduce kiln emissions by 30–50%. But achieving that goal won’t be easy. Throughout Latin America and other countries in the developing world, artisanal kiln operators comprise an informal industry; they rarely pay taxes or obtain operating permits, and because of that, they often lack access to the financial credit and capital needed to purchase cleaner technology. Many also lack electricity (required for newer types of mechanized production) and access to roads and other infrastructure that could help in the modernization effort. Some are unwilling to change age-old manufacturing processes. Pakistani families prepare bricks at a fixed-chimney Bull’s trench kiln on the outskirts of Islamabad. Under debt bondage, an entrenched custom in South Asia, families can work at kilns for years paying off loans from the owners. Still, the associated benefits of modernization justify the effort, Li says. In addition to the environmental health impacts associated with artisanal brick kilns, these operations employ “the poorest of the poor, including, in many instances, women and children,” Li says. “So by promoting more efficient kilns and manufacturing, we can also address related development problems, such as poverty, child labor, and women’s issues.”

Satellite observations of desert dust‐induced Himalayan snow darkening

AbstractThe optically thick aerosol layer along the southern edge of the Himalaya has been subject of several recent investigations relating to its radiative impacts on the South Asian summer monsoon and regional climate forcing. Prior to the onset of summer monsoon, mineral dust from southwest Asian deserts is transported over the Himalayan foothills on an annual basis. Episodic dust plumes are also advected over the Himalaya, visible as dust‐laden snow surface in satellite imagery, particularly in western Himalaya. We examined spectral surface reflectance retrieved from spaceborne MODIS observations that show characteristic reduction in the visible wavelengths (0.47 µm) over western Himalaya, associated with dust‐induced solar absorption. Case studies as well as seasonal variations of reflectance indicate a significant gradient across the visible (0.47 µm) to near‐infrared (0.86 µm) spectrum (VIS‐NIR), during premonsoon period. Enhanced absorption at shorter visible wavelengths and the resulting VIS‐NIR gradient is consistent with model calculations of snow reflectance with dust impurity. While the role of black carbon in snow cannot be ruled out, our satellite‐based analysis suggests the observed spectral reflectance gradient dominated by dust‐induced solar absorption during premonsoon season. From an observational viewpoint, this study underscores the importance of mineral dust deposition toward darkening of the western Himalayan snow cover, with potential implications to accelerated seasonal snowmelt and regional snow albedo feedbacks.

Effect of Black Carbon in Soil and Sediment on Organic Chemical Sorption and Carbon Sequestration

Environmental black carbon (BC) in soils and sediments has received increasing attention due to the sorption for organic chemicals and the potentials for carbon sequestration. In this work, pyrene sorption to humic acid and BC fractions in sediment was investigated by using extracted humic acid and preheated sediment, respectively. Thermally labile organic matter was removed during preheating and the remaining fraction of organic carbon (OC) is recognized as BC. The comparison results highlighted the important role of BC in pyrene sorption, especially at low concentrations. In addition, the micro-porosity of pristine and preheated sediments was analyzed by CO2 sorption. The blocking effect of associated humic substances on the micro-pores of BC for CO2 sorption was not observed. On the contrary, the probed micro-pore volume was higher in the case of pristine sediment, which implies the sorption of CO2 molecules by humic substances.

The role of black carbon as a catalyst for environmental redox transformation

Black carbon (BC) is an important class of geosorbents that control the fate and transport of organic pollutants in soil and sediment. We previously demonstrated a new role of BC as an electron transfer mediator in the abiotic reduction of nitroaromatic and nitramine compounds by Oh and Chiu (Environ Sci Technol 43:6983-6988, 2009). We proposed that BC can catalyze the reduction of nitro compounds because it contains microscopic graphitic (graphene) domains, which facilitate both sorption and electron transfer. In this study, we assessed the ability of different types of BC--graphite, activated carbon, and diesel soot--to mediate the reduction of 2,4-dinitrotoluene (DNT) and 2,4-dibromophenol (DBP) by H(2)S. All three types of BC enhanced DNT and DBP reduction. H(2)S supported BC-mediated reduction, as was observed previously with a thiol reductant. The results suggest that BC may influence the fate of organic pollutants in reducing subsurface environments through redox transformation in addition to sorption.

The role of black carbon in the sorption and desorption of phenanthrene on river sediments

Black carbon (BC) is ubiquitous in an aquatic environment. In the present study, the role of BC in the sorption and desorption of phenanthrene on the sediments sampled from the Yangtze River and the Yellow River of China has been studied. The BC content in total organic carbon ranged from 23 to 50% in sediment samples and BC accounted for 52.7–79.1% of the overall sorption, revealing the important role of BC in the sorption of phenanthrene on natural river sediments. The mean value of BC-water distribution coefficient (kBC) was about 50 times that of organic carbon (OC)-water distribution coefficient (kOC) for phenanthrene. The values of logkBC for the CTO375-combusted sediments ranged from 5.66 to 5.95, and the Freundlich exponent ranged from 0.40 to 0.67, suggesting that a difference exists among sorption capacities of BC from different river sediments. Therefore, the sources of BC should be taken into account when assessing its sorption capacity. For the desorption process, approximately 10.5–21.4 and 27.1–49.2% phenanthrene was desorbed from CTO375-combusted and original sediments, respectively. The results revealed that the OC-sorbed phenanthrene could not all desorb, and a fraction of BC-sorbed phenanthrene could desorb, although BC is considered a strong sorbent.

Role of Black Carbon in the Sorption of Polychlorinated Dibenzo-p-dioxins and Dibenzofurans at the Diamond Alkali Superfund Site, Newark Bay, New Jersey

The sorption of polychlorinated dibenzo-p-dioxins and dibenzofurans (PCDD/Fs) to organic carbon (OC) and black carbon (BC) was measured in two sediment cores taken near the Diamond Alkali superfund site (DA) in the Passaic River and Newark Bay, New Jersey (U.S.A.). An OC partitioning model and a BC-inclusive, Freundlich distribution model were used to interpret measurements of freely dissolved PCDD/Fs using passive samplers in sediment incubations, together with measured sedimentary concentrations of OC, BC, and PCDD/Fs. Samples were also analyzed for polycyclic aromatic hydrocarbons (PAHs) as controls on the two distribution models. The OC partitioning model underpredicted the distribution of PAHs and PCDD/Fs by 10-100-fold. The Freundlich model predicted the distribution of PAHs at the DA to within a factor of 2-3 of observations. Black carbon-water partition coefficients (K(iBC)) for PCDD/Fs, derived from literature results of both field and laboratory studies differed up to 1000-fold from values derived from this study. Contrary to expectations, PCDDs displayed stronger sorption than either PCDFs or PAHs relative to their subcooled liquid aqueous solubilities. Even though the presence of BC in the sediments reduced the overall bioavailability of PCDD/Fs by >90%, the sediments at 2 m depth continue to display the highest pore water activities of PCDD/Fs.

Black Carbon: The Dark Horse of Climate Change Drivers

For decades, efforts to slow global warming have mostly aimed to limit heat-trapping emissions of carbon dioxide (CO2). Now scientists are pointing to a different class of warming agents they say also must be targeted to keep global temperatures in check. Dubbed “short-lived climate forcings” (SLCFs), these other emissions—namely, black carbon particles, methane, hydrofluorocarbons, and tropospheric ozone—are even more powerful than CO2 in terms of their warming potential. But they persist in the atmosphere for much shorter durations than CO2, which can linger airborne for hundreds to thousands of years.1 Steve Seidel, vice president for policy analysis at the Pew Center on Global Climate Change, says the recent emphasis on SLCFs represents new policy thinking on climate change. “We thought the Kyoto Protocol and its follow-on agreements would get us to where we need to be, but that’s not working out the way we hoped it would,” he says. “So, we’re broadening the discussion and opening up new pathways for going forward.” Given the enormity of human emissions, many climate scientists believe CO2 will one day become the dominant force behind climate change. But for now, CO2 and the SLCFs are nearly on par in terms of their climate changing effects, according to Veerabhadran Ramanathan, a professor at The Scripps Institute of Oceanography. In a report published in February 2011, the United Nations Environment Programme (UNEP) called attention to SLCFs, claiming their emissions must be cut together with CO2 in order to prevent global temperatures from crossing a dangerous threshold.2 Doing that would offer health benefits too, UNEP stated, because SLFCs are also toxic air pollutants. Particulate emissions from diesel exhaust—a major source of black carbon—have been linked to lung and heart disease as well as cancer.3 But where it would take a transformation of the energy sector (at a cost of trillions of dollars over multiple decades1) to drop CO2 emissions enough to influence the climate, cutting SLCFs to achieve a similar goal could be achieved with current technologies under policy frameworks that are already in place, such as clean air regulations, according to Seidel.

Modeled Influence of East Asian Black Carbon on Inter-Decadal Shifts in East China Summer Rainfall

AbstractTwo inter-decadal shifts in East China summer rainfall during the last three decades of the 20th century have been identified. One shift occurred in the late 1970s and featured more rainfall in the Yangtze River valley and prolonged drought in North China. The other shift occurred in the early 1990s and featured increased rainfall in South China. The role of black carbon (BC) aerosol in the first shift event is controversial, and it has not been documented for the second event. In this study, the authors used Geophysical Fluid Dynamics Laboratory’s (GFDL’s) atmospheric general circulation model known as Atmosphere and Land Model (AM2.1), which has been shown to capture East Asian climate variability well, to investigate these issues by conducting sensitive experiments with or without historical BC in East Asia. The results suggest that the model reproduces the first shift well, including intensified rainfall in the Yangtze River and weakened monsoonal circulation. However, the model captures only ...

Role of black carbon in the distribution of polychlorinated dibenzo- p-dioxins/dibenzofurans in aged field-contaminated soils

Floodplain soils containing elevated levels of polychlorinated dibenzo- p-dioxins/dibenzofurans (PCDD/Fs) were collected from several locations along the Tittabawassee River (Michigan, USA). The PCDD/F profiles of these soils exhibited distinct congener patterns consistent with byproducts from either chloralkali manufacturing or chlorophenols productions. Black carbon (BC) particles were isolated for the first time from floodplain soil impacted by PCDD/Fs. Petrographic analysis showed that BC particles, including coal, oxidized coal, metallurgical coke, depositional carbon, coal tar/pitch, cenosphere, and charcoal, comprised approximately 30% by volume of the organic fraction with size range of 250 μm–2000 μm from a typical floodplain soil. The BC particles with anthropogenic origin such as pitch and coke associated with the chloralkali production process served as both the source and subsequent transporter for the highly hydrophobic PCDD/Fs. These anthropogenic BC particles were enriched with high levels of PCDFs, containing approximately 1000-fold the concentration found in the bulk soil. The strong association of PCDD/Fs with anthropogenic BC directly impacts the physicochemical and biological availability thus the risk associated with these hydrophobic organochlorines in soils and sediments.

Influence of black carbon and chemical planarity on bioavailability of sediment‐associated contaminants

Black carbon (BC) and chemical properties may play a significant role in defining the bioavailability of hydrophobic organic compounds (HOCs) in sediment. In the current study, bioavailability of four HOCs with differing planarity was determined in sediments amended with two types of BC (soot and charcoal) at different concentrations by matrix solid-phase microextraction (matrix-SPME) and bioaccumulation testing using the freshwater oligochaete Lumbriculus variegatus. Furthermore, the applicability of the matrix-SPME method to bioavailability estimation in BC-amended sediment was tested. The charcoal treatment significantly reduced the bioaccumulation of the planar compounds (3,3',4,4'-tetrachlorobiphenyl and benzo[a]pyrene) in L. variegatus, and the matrix-SPME method showed a similar trend as contaminant bioaccumulation in L. variegatus. Conversely, manipulation of sediment with soot had no effect or slightly increased bioavailability of the planar compounds in both bioaccumulation and matrix-SPME tests. Little if any affect was noted in bioavailability of the nonplanar compounds (2,2',4,4',5,5'-hexachlorobiphenyl and permethrin) with the soot and charcoal amendments. Results showed that the role of BC in defining bioavailability of HOCs depends not only on the type and concentrations of BC present, but also the planarity of the HOCs.