Gerard Cornelissen

Comparison of quantification methods to measure fire‐derived (black/elemental) carbon in soils and sediments using reference materials from soil, water, sediment and the atmosphere

Black carbon (BC), the product of incomplete combustion of fossil fuels and biomass (called elemental carbon (EC) in atmospheric sciences), was quantified in 12 different materials by 17 laboratories from different disciplines, using seven different methods. The materials were divided into three classes: (1) potentially interfering materials, (2) laboratory-produced BC-rich materials, and (3) BC-containing environmental matrices (from soil, water, sediment, and atmosphere). This is the first comprehensive intercomparison of this type (multimethod, multilab, and multisample), focusing mainly on methods used for soil and sediment BC studies. Results for the potentially interfering materials (which by definition contained no fire-derived organic carbon) highlighted situations where individual methods may overestimate BC concentrations. Results for the BC-rich materials (one soot and two chars) showed that some of the methods identified most of the carbon in all three materials as BC, whereas other methods identified only soot carbon as BC. The different methods also gave widely different BC contents for the environmental matrices. However, these variations could be understood in the light of the findings for the other two groups of materials, i.e., that some methods incorrectly identify non-BC carbon as BC, and that the detection efficiency of each technique varies across the BC continuum. We found that atmospheric BC quantification methods are not ideal for soil and sediment studies as in their methodology these incorporate the definition of BC as light-absorbing material irrespective of its origin, leading to biases when applied to terrestrial and sedimentary materials. This study shows that any attempt to merge data generated via different methods must consider the different, operationally defined analytical windows of the BC continuum detected by each technique, as well as the limitations and potential biases of each technique. A major goal of this ring trial was to provide a basis on which to choose between the different BC quantification methods in soil and sediment studies. In this paper we summarize the advantages and disadvantages of each method. In future studies, we strongly recommend the evaluation of all methods analyzing for BC in soils and sediments against the set of BC reference materials analyzed here.

Effects of chemical, biological, and physical aging as well as soil addition on the sorption of pyrene to activated carbon and biochar.

In this study, the suitability of biochar and activated carbon (AC) for contaminated soil remediation is investigated by determining the sorption of pyrene to both materials in the presence and absence of soil and before as well as after aging. Biochar and AC were aged either alone or mixed with soil via exposure to (a) nutrients and microorganisms (biological), (b) 60 and 110 °C (chemical), and (c) freeze-thaw cycles (physical). Before and after aging, the pH, elemental composition, cation exchange capacity (CEC), microporous SA, and sorption isotherms of pyrene were quantified. Aging at 110 °C altered the physicochemical properties of all materials to the greatest extent (for example, pH increased by up to three units and CEC by up to 50% for biochar). Logarithmic K(Fr) values ranged from 7.80 to 8.21 (ng kg(-1))(ng L(-1))(-nF) for AC and 5.22 to 6.21 (ng kg(-1))(ng L(-1))(-nF) for biochar after the various aging regimes. Grinding biochar to a smaller particle size did not significantly affect the sorption of d(10) pyrene, implying that sorption processes operate on the subparticle scale. Chemical aging decreased the sorption of pyrene to the greatest extent (up to 1.8 log unit for the biochar+soil). The sorption to AC was affected more by the presence of soil than the sorption to biochar was. Our results suggest that AC and biochar have a high sorption capacity for pyrene that is maintained both in the presence of soil and during harsh aging. Both materials could therefore be considered in contaminated land remediation.

The sorption and desorption of phosphate-P, ammonium-N and nitrate-N in cacao shell and corn cob biochars.

The sorption of PO4-P, NH4-N and NO3-N to cacao shell and corn cob biochars produced at 300-350°C was quantified. The biochars were used; (i) as received (unwashed), (ii) after rinsing with Millipore water and (iii) following leaching with Millipore water. In addition to sorption, desorption of PO4-P from the unwashed biochars was quantified. There was no sorption of PO4-P to either washed or rinsed biochars, but following leaching, both biochars adsorbed PO4-P and distribution coefficients (Kd L kg(-1)) were very similar for both materials (10(1.1±0.5) for cacao shell biochar and 10(1.0±0.2) for corn cob biochar). The BET surface area and micropore volume increased 80% and 60% for the cacao shell and corn cob biochars following leaching. After 60 d, 1483±45 mg kg(-1) and 172±1 mg kg(-1) PO4-P was released from the cacao shell and corn cob biochars. NH4-N was sorbed by both unwashed biochars, albeit weakly with Kd values around 10(2) L kg(-1). We speculate that NH4-N could bind via an electrostatic exchange with other cationic species on the surface of the biochar. There was no significant release or sorption of NO3-N from or to either of the biochars.

Sorption of native polyaromatic hydrocarbons (PAH) to black carbon and amended activated carbon in soil

Organic pollutants (e.g. polyaromatic hydrocarbons (PAH)) strongly sorb to carbonaceous sorbents such as black carbon and activated carbon (BC and AC, respectively). For a creosote-contaminated soil (Sigma15PAH 5500 mg kg(dry weight(dw))(-1)) and an urban soil with moderate PAH content (Sigma15PAH 38 mg kg(dw)(-1)), total organic carbon-water distribution coefficients (K(TOC)) were up to a factor of 100 above values for amorphous (humic) organic carbon obtained by a frequently used Linear-Free-Energy Relationship. This increase could be explained by inclusion of BC (urban soil) or oil (creosote-contaminated soil) into the sorption model. AC is a manufactured sorbent for organic pollutants with similar strong sorption properties as the combustion by-product BC. AC has the potential to be used for in situ remediation of contaminated soils and sediments. The addition of small amounts of powdered AC (2%) to the moderately contaminated urban soil reduced the freely dissolved aqueous concentration of native PAH in soil/water suspensions up to 99%. For granulated AC amended to the urban soil, the reduction in freely dissolved concentrations was not as strong (median 64%), especially for the heavier PAH. This is probably due to blockage of the pore system of granulated AC resulting in AC deactivation by soil components. For powdered and granulated AC amended to the heavily contaminated creosote soil, median reductions were 63% and 4%, respectively, probably due to saturation of AC sorption sites by the high PAH concentrations and/or blockage of sorption sites and pores by oil.

Effect of temperature on sorption equilibrium and sorption kinetics of organic micropollutants - a review

Abstract Temperature is an important parameter that can influence the equilibria and rates of environmental processes. In the present paper, a review of the influence of temperature on sorption equilibrium and sorption kinetics for organic micropollutants is presented. A fast and a slow process can be distinguished for sorption. For most compounds, equilibrium sorption decreases with increasing temperature. Some examples of increasing equilibrium sorption with increasing temperature and of no effect of temperature on sorption equilibrium were also found. The rate of fast desorption increased with increasing temperature. Calculated activation energies for desorption were in the range of 10–50 kJ/mol. Also, examples of no influence of temperature on the rates of fast adsorption and desorption were reported. In the present paper, the slow desorption step is assumed to be a diffusion process. Literature on the effect of temperature on the diffusion of organic compounds in polymeric structures is summarized. Activation energies for diffusion in polymers average 60 kJ/mol. The reported values for the activation energy of slow desorption are comparable to those found for diffusion of organic micropollutants through organic polymers. This is an indication that diffusion causes nonequilibrium sorption effects.

Field testing of equilibrium passive samplers to determine freely dissolved native polycyclic aromatic hydrocarbon concentrations

Equilibrium passive samplers are promising tools to determine freely dissolved aqueous concentrations (C(W,free)) of hydrophobic organic compounds. Their use in the field, however, remains a challenge. In the present study on native polycyclic aromatic hydrocarbons (PAHs) in Oslo Harbor, Norway, two different passive sampler materials, polyoxymethylene (POM; thickness, 55 microm [POM-55] and 500 microm [POM-500]) and polydimethylsiloxane (PDMS; thickness, 200 microm), were used to determine in the laboratory C(W,free) in sediment pore water (C(PW,free)), and the suitability of five passive samplers for determination of C(W,free) in overlying surface water was tested under field conditions. For laboratory determinations of C(PW,free), both POM-55 and PDMS turned out to be suitable. In the field, the shortest equilibrium times (approximately one month) were observed for POM-55 and PDMS (thickness, 28 microm) coatings on solid-phase microextraction fibers, with PDMS tubing as a good alternative. Low-density polyethylene (thickness, 100 microm) and POM-500 did not reach equilibrium within 119 d in the field. Realistic values were obtained for dissolved organic carbon-water partition coefficients in the field (approximately one log unit under log K(OW)), which strengthened the conclusion that equilibrium was established in field-exposed passive samplers. At all four stations, chemical activity ratios between pore water and overlying water were greater than one for all PAHs, indicating that the sediment was a PAH diffusion source and that sediment remediation may be an appropriate treatment for PAH contamination in Oslo Harbor.

The way forward in biochar research: targeting trade-offs between the potential wins

Biochar application to soil is currently widely advocated for a variety of reasons related to sustainability. Typically, soil amelioration with biochar is presented as a multiple‐‘win’ strategy, although it is also associated with potential risks such as environmental contamination. The most often claimed benefits of biochar (i.e. the ‘wins’) include (i) carbon sequestration; (ii) soil fertility enhancement; (iii) biofuel/bioenergy production; (iv) pollutant immobilization; and (v) waste disposal. However, the vast majority of studies ignore possible trade‐offs between them. For example, there is an obvious trade‐off between maximizing biofuel production and maximizing biochar production. Also, relatively little attention has been paid to mechanisms, as opposed to systems impacts, behind observed biochar effects, often leaving open the question as to whether they reflect truly unique properties of biochar as opposed to being simply the short‐term consequences of a fertilization or liming effect. Here, we provide an outline for the future of soil biochar research. We first identify possible trade‐offs between the potential benefits. Second, to be able to better understand and quantify these trade‐offs, we propose guidelines for robust experimental design and selection of appropriate controls that allow both mechanistic and systems assessment of biochar effects and trade‐offs between the wins. Third, we offer a conceptual framework to guide future experiments and suggest guidelines for the standardized reporting of biochar experiments to allow effective between‐site comparisons to quantify trade‐offs. Such a mechanistic and systems framework is required to allow effective comparisons between experiments, across scales and locations, to guide policy and recommendations concerning biochar application to soil.

Distinct oxidative stabilities of char versus soot black carbon: Implications for quantification and environmental recalcitrance

Distinct oxidative stabilities of char versus soot black carbon : Implications for quantification and environmental recalcitrance

Activated carbon and biochar amendments decrease pore-water concentrations of polycyclic aromatic hydrocarbons (PAHs) in sewage sludge

The aim of the research was to determine the influence of biochar and activated carbon (AC) on the freely dissolved concentration of polycyclic aromatic hydrocarbons (PAHs) in sewage sludge. Two different biochars (MSB and PMW) and two ACs (CP1 and BP2) were used in the present experiment. Addition of AC/biochar to sewage sludge caused significant decrease of freely dissolved PAHs concentration. Depending on the dose, the reduction of freely dissolved PAHs ranged from 56% to 95% (ACs) and from 0% to 57% (biochars). Only for the biochars was there a significant difference between short 7-d and long 30/60-d mixing time. It is concluded that both AC and biochar are effective at reducing PAH pore-water concentrations, the more expensive and non-carbon negative AC having the greatest effect.

Remediation of Contaminated Marine Sediment Using Thin-Layer Capping with Activated Carbon—A Field Experiment in Trondheim Harbor, Norway

In situ amendment of contaminated sediments using activated carbon (AC) is a recent remediation technique, where the strong sorption of contaminants to added AC reduces their release from sediments and uptake into organisms. The current study describes a marine underwater field pilot study in Trondheim harbor, Norway, in which powdered AC alone or in combination with sand or clay was tested as a thin-layer capping material for polycyclic aromatic hydrocarbon (PAH)-contaminated sediment. Several novel elements were included, such as measuring PAH fluxes, no active mixing of AC into the sediment, and the testing of new manners of placing a thin AC cap on sediment, such as AC+clay and AC+sand combinations. Innovative chemical and biological monitoring methods were deployed to test capping effectiveness. In situ sediment-to-water PAH fluxes were measured using recently developed benthic flux chambers. Compared to the reference field, AC capping reduced fluxes by a factor of 2-10. Pore water PAH concentration profiles were measured in situ using a new passive sampler technique, and yielded a reduction factor of 2-3 compared to the reference field. The benthic macrofauna composition and biodiversity were affected by the AC amendments, AC + clay having a lower impact on the benthic taxa than AC-only or AC + sand. In addition, AC + clay gave the highest AC recoveries (60% vs 30% for AC-only and AC + sand) and strongest reductions in sediment-to-water PAH fluxes and porewater concentrations. Thus, application of an AC-clay mixture is recommended as the optimal choice of the currently tested thin-layer capping methods for PAHs, and more research on optimizing its implementation is needed.