Biochar dispersion in a tropical soil and its effects on native soil organic carbon.

Although biochar application to soils has been found to increase soil quality and crop yield, the biochar dispersion extent and its impacts on native soil organic carbon (SOC) has received relatively little attention. Here, the vertical and lateral migration of fine, intermediate and coarse-sized biochar (<0.5, 0.5-1 and 1-5 mm, respectively), applied at low and high doses (1.5-2 and 3-4% w/w, respectively), was tracked using stable isotope methods, along with its impact on native SOC stocks. Biochar was homogeneously mixed into the surface layer (0-7 cm depth) of a loamy sandy Acrisol in Zambia. After 4.5 y, 38-75% of the biochar carbon (BC) was lost from the applied layer and 4-25% was detected in lower soil layers (7-30 cm). Estimating BC mineralization to be no more than 8%, 25-60% was likely transported laterally out of the experimental plots. This conclusion was supported by observations of BC in the control plot and in soils up to 2 m outside of the experimental plots. These processes were likely progressive as recovery of BC in similar plots 1 year after application was greater in both surface and lower soil layers than after 4.5 y. Fine and intermediate-sized BC displayed the greatest downward migration (25.3 and 17.9%, respectively), particularly when applied at lower doses, suggesting its movement through soil inter-particle spaces. At higher dosages, fine and intermediate-sized particles may have clogged pore, so coarse biochar displayed the greatest downward migration when biochar was applied at higher doses. In the BC treatment plot soil profiles, native SOC stocks were reduced by 2.8 to 24.5% (18.4% on average), i.e. positive priming. However, some evidence suggested that the soils may switch to negative priming over time. The dispersion of biochar in soil should be considered when evaluating biochar's agronomic benefits and environmental effects.

Using the benzenepolycarboxylic acid (BPCA) method to assess activated biochars and their PFAS sorption abilities.

Activated carbon (AC) has important industrial and environmental applications as it has excellent abilities to sorb contaminants such as per- and polyfluoroalkyl substances (PFAS). Current research aims to develop activated biochars (AB) from renewable biomass to replace AC that is produced from fossil feedstock. Both AC and AB are primarily comprised of condensed aromatic carbon (ConAC), the component that is the focus of this study. ConAC is characterized to determine its relationship with biochar activation conditions and PFAS sorption, which are understudied at present. Benzenepolycarboxylic acid (BPCA) markers for ConAC were quantified in steam-activated biochars (AB-Steam) and carbon dioxide-activated biochars (AB-CO2) prepared from waste timber at different temperatures (800, 850, 900 °C) and molar ratios of feedstock-carbon:steam (0.50 - 1.25). A non-activated biochar was also included as a reference. ConAC relative to total organic carbon content was higher in AB-Steam than in AB-CO2 (92 ± 2 % vs. 81 ± 11%). The ratio of benzenehexa- (B6CA) to benzenepentacarboxylic (B5CA) acids revealed that AB-Steam also had larger ConAC clusters than AB-CO2. These findings provide novel evidence that steam activation is more effective than CO2 activation in creating ConAC. To assess how ConAC impacts AB sorption abilities, AB-Steam were used to remediate PFAS from contaminated soils. The observed strong correlations between ConAC content and sorption of long-chain PFAS suggest the importance of hydrophobic interactions between PFAS tails and ConAC. Poor correlations for short-chain PFAS, on the other hand, indicated the existence of electrostatic repulsion interactions between PFAS head groups and ConAC. Collectively, these results explain the great ability of AB-Steam to sorb PFAS from contaminated soils (up to 100% remediation). More broadly, this work demonstrates that the BPCA method can be a valuable tool to assess the quality of biochars and other carbonaceous sorbents in relation to their production conditions or contaminant sorption abilities.

Stabilization of PFAS-contaminated soil with sewage sludge- and wood-based biochar sorbents.

Sustainable and effective remediation technologies for the treatment of soil contaminated with per- and polyfluoroalkyl substances (PFAS) are greatly needed. This study investigated the effects of waste-based biochars on the leaching of PFAS from a sandy soil with a low total organic carbon content (TOC) of 0.57 ± 0.04 % impacted by PFAS from aqueous film forming foam (AFFF) dispersed at a former fire-fighting facility. Six different biochars (pyrolyzed at 700-900 °C) were tested, made from clean wood chips (CWC), waste timber (WT), activated waste timber (aWT), two digested sewage sludges (DSS-1 and DSS-2) and de-watered raw sewage sludge (DWSS). Up-flow column percolation tests (15 days and 16 pore volume replacements) with 1 % biochar indicated that the dominant congener in the soil, perfluorooctane sulphonic acid (PFOS) was retained best by the aWT biochar with a 99.9 % reduction in the leachate concentration, followed by sludge-based DWSS (98.9 %) and DSS-2 and DSS-1 (97.8 % and 91.6 %, respectively). The non-activated wood-based biochars (CWC and WT) on the other hand, reduced leaching by <42.4 %. Extrapolating this to field conditions, 90 % leaching of PFOS would occur after 15 y for unamended soil, and after 1200 y and 12,000 y, respectively, for soil amended with 1 % DWSS-amended and aWT biochar. The high effectiveness of aWT and the three sludge-based biochars in reducing PFAS leaching from the soil was attributed largely to high porosity in a pore size range (>1.5 nm) that can accommodate the large PFAS molecules (>1.02-2.20 nm) combined with a high affinity to the biochar matrix. Other factors like anionic exchange capacity could play a contributing role. Sorbent effectiveness was better for long-chain than for short-chain PFAS, due to weaker, apolar interactions between the biochar and the latter's shorter hydrophobic CF2-tails. The findings were the first to demonstrate that locally sourced activated wood-waste biochars and non-activated sewage sludge biochars could be suitable sorbents for the ex situ stabilization and in situ remediation of PFAS-contaminated soil, bringing this technology one step closer to full-scale field testing.

Exposure assessment of plastics, phthalate plasticizers and their transformation products in diverse bio-based fertilizers.

Bio-based fertilizers (BBFs) produced from organic waste have the potential to reduce societal dependence on limited and energy-intensive mineral fertilizers. BBFs, thereby, contribute to a circular economy for fertilizers. However, BBFs can contain plastic fragments and hazardous additives such as phthalate plasticizers, which could constitute a risk for agricultural soils and the environment. This study assessed the exposure associated with plastic and phthalates in BBFs from three types of organic wastes: agricultural and food industry waste (AgriFoodInduWaste), sewage sludge (SewSludge), and biowaste (i.e., garden, park, food and kitchen waste). The wastes were associated with various treatments like drying, anaerobic digestion, and vermicomposting. The number of microplastics (0.045-5 mm) increased from AgriFoodInduWaste-BBFs (15-258 particles g-1), to SewSludge-BBFs (59-1456 particles g-1) and then to Biowaste-BBFs (828-2912 particles g-1). Biowaste-BBFs mostly contained packaging plastics (e.g., polyethylene terephthalate), with the mass of plastic (>10 g kg-1) exceeding the EU threshold (3 g kg-1, plastics >2 mm). Other BBFs mostly contained small (< 1 mm) non-packaging plastics in amounts below the EU limit. The calculated numbers of microplastics entering agricultural soils via BBF application was high (107-1010 microplastics ha-1y-1), but the mass of plastic released from AgriFoodInduWaste-BBFs and SewSludge-BBFs was limited (< 1 and <7 kg ha-1y-1) compared to Biowaste-BBFs (95-156 kg ha-1y-1). The concentrations of di(2-ethylhexyl)phthalate (DEHP; < 2.5 mg kg-1) and phthalate transformation products (< 8 mg kg-1) were low (< benchmark of 50 mg kg-1 for DEHP), attributable to both the current phase-out of DEHP as well as phthalate degradation during waste treatment. The Biowaste-BBF exposed to vermicomposting indicated that worms accumulated phthalate transformation products (4 mg kg-1). These results are overall positive for the implementation of the studied AgriFoodInduWaste-BBFs and SewSludge-BBFs. However, the safe use of the studied Biowaste-BBFs requires reducing plastic use and improving sorting methods to minimize plastic contamination, in order to protect agricultural soils and reduce the environmental impact of Biowaste-BBFs.

Flame curtain kilns produce biochar from dry biomass with minimal methane emissions.

Flame curtain kilns have emerged as the preferred biochar technology for smallholders but reported methane emissions (30 g kg-1 biochar) have impeded carbon certification. Here, for flame curtain kilns we show almost no methane (0-3.6 g kg-1 biochar) emissions for dry (<15 % moisture) feedstock consisting of twigs and leaves. Wet feedstock (>40 % moisture) however generated significant methane (>500 g kg-1 biochar), underscoring that feedstock preparation is decisive for the carbon balance. Even for dry feedstock, both aerosol and CO emissions were significant (21-82 and 40-118 g kg-1 biochar, respectively). The data demonstrate that certification of low-tech biochar made from dry twigs and leaves should not be objected to on the grounds of methane. Careful selection of feedstock and potential after-combustion of the syn-gases are probably needed to avoid CO and aerosol emissions. More data are needed on methane emissions of other dry feedstocks.

The decomposition and emission factors of a wide range of PFAS in diverse, contaminated organic waste fractions undergoing dry pyrolysis.

Current treatment options for organic waste contaminated with per- and polyfluoroalkyl substances (PFAS) are generally limited to incineration, composting or landfilling, all resulting in emissions. Dry pyrolysis is a promising emerging alternative to these practices, but there is uncertainty related to the fate of PFAS during this process. The present work first developed a robust method for the determination of PFAS in complex matrices, such as sewage sludge and biochar. Then, a mass balance was established for 56 different PFAS during full-scale pyrolysis (2-10 kg biochar hr-1, 500-800 °C) of sewage sludges, food waste reject, garden waste and waste timber. PFAS were found in all wastes (56-3651 ng g-1), but pyrolysis resulted in a ≥ 96.9% removal. Residual PFAS (0.1-3.4 ng g-1) were detected in biochars obtained at temperatures up to 750 °C and were dominated by long chain PFAS. Emitted PFAS loads ranged from 0.01 to 3.1 mg tonne-1 of biochar produced and were dominated by short chain PFAS. Emissions made up < 3% of total PFAS-mass in the wastes. Remaining uncertainties are mainly related to the presence of thermal degradation products in flue gas and condensation oils.

Sewage sludge biochars as effective PFAS-sorbents.

The use of sewage sludge to produce biochar-based sorbents for per- and polyfluoroalkyl substances (PFAS) removal from water and soil may be an economically and environmentally sustainable waste management option. This study compared the sorption of six perfluorinated carboxylic acids (PFCAs) by two sewage sludge biochars (SSBCs) and one wood chip biochar (WCBC), dry pyrolyzed at 700 °C. Batch sorption tests were conducted by adding individual PFCAs and a PFCA-mixture to pure biochars and mixtures of biochar and a sandy soil (1.3% TOC). PFAS-sorption to the SSBCs exhibited log-linear biochar-water distribution coefficients (log Kd), comparable to those previously reported for commercial activated carbons (e.g., 5.73 ± 0.02 for perfluorooctanoic acid at 1 µg/L). The strong sorption of PFCAs was attributed to the SSBCs relatively high pore volumes in the pore size range that can accommodate these compounds. Sorption was attenuated by the presence of soil (by factors 3-10), by the presence of a mixture of PFCAs (by factors of 6-532) and by both together (by factors of 8-6581), indicating strongly competitive sorption between PFCA-congeners, and less severe sorption attenuation by soil organic matter. These findings could enable sustainable value chains for SSBs in soil remediation and water filtration solutions.

Industrial byproducts for the soil stabilization of trace elements and per- and polyfluorinated alkyl substances (PFASs).

The present work was the first exploration of the use of industrial byproducts from iron and titanium processing as sorbents for the stabilization of soil contamination. The main aim was to test slag waste and iron-rich charred fossil coal ("Fe-char"), as sorbents for per- and polyfluorinated alkyl substances (PFASs), as well as lead (Pb) and antimony (Sb), in four soils from a firefighting training area (PFASs) and a shooting range (Pb and Sb). Adding slag (10-20%) to shooting range soils decreased the leaching of Pb and Sb up to 50-90%. Fe-char amendment to these soils resulted in a moderate reduction in Sb leaching (20-70%) and a slightly stronger effect on Pb (40-50%). The sorption is most likely explained by the presence of Fe oxyhydroxides. These are present in the highest concentrations in the slag, probably resulting in more effective metal binding to the slag than to the Fe-char. Fe-char but not slag proved to be a strong sorbent for PFASs (reducing PFAS leaching from the soil by up to 99.7%) in soil containing low total organic carbon (TOC; 1.2%) but not in high-TOC soil (34%). The sorption coefficient KD for Fe-char was high, in the range of 104.3 to 106.5 L/kg at 1 ng/L in the low-TOC soil. The KD value increased with increasing perfluorocarbon chain length, exceeding PFAS sorption to biochar in the low ng/L concentration range. This result indicates that the mechanism behind the strong PFAS sorption to Fe-char was mainly van der Waals dispersive interactions between the hydrophobic PFAS-chain and the aromatic π-electron systems on nanopore walls within the Fe-char matrix. Overall, this study indicates that industrial byproducts can provide sustainable and cost-effective materials for soil remediation. However, the sorbent needs to be tailored to the type of soil and type of contamination.

Stabilization of PFAS-contaminated soil with activated biochar.

Biochars are considered potential sustainable sorbents to reduce the leaching of per- and polyfluoroalkyl substances (PFAS) from contaminated soils. However, biochar characteristics must probably be optimized to achieve useful sorption capacity. In the present work, eight waste timber biochars were produced, including biochars activated to different degrees, at different temperatures, and using both steam and CO2. In laboratory batch experiments, the eight biochars were amended to soil samples from two different horizons, with low and high total organic carbon (TOC, 1.6% and 34.2%, respectively), of a heavily PFAS-contaminated soil (1200-3800 µg kg-1 PFAStot), at varying doses (0, 0.1, 0.5, 1.0 and 5.0%). With a 5% amendment to the low-TOC soil, all eight biochars resulted in strongly reduced leachate PFAS concentrations (by 98-100%). At the same amendment dose in the high-TOC soil, leachate concentration reductions were more modest (23-100%). This was likely due to a strong PFAS-sorption to the high-TOC soil itself, as well as biochar pore clogging in the presence of abundant organic matter, resulting in fewer sorption sites available to PFAS. Reduction in PFAS leaching was proportional to the degree of activation and activation temperature. Thus, lower amendment doses of activated biochars were needed to reduce PFAS leaching to the same level as with the non-activated biochar. Activation however, came at a tradeoff with biochar yield. Furthermore, the adsorption ability of these biochars increased proportionally with PFAS-fluorocarbon chain length, demonstrating the role of hydrophobic interactions in reduction of PFAS leaching. Development of internal surface area and porosity was proposed as the main factor causing the improved performance of activated biochars. This study shows that woody residues such as waste timber can be used to produce effective sorbents for the remediation of PFAS-contaminated soil. It also highlights the desirability of sorbate and matrix-specific optimization of biochar production.

Environmental and economic impacts of biochar production and agricultural use in six developing and middle-income countries.

The feasibility of using biowaste for the production of biochar and its use in agriculture depends on its environmental and economic performance. This paper quantifies environmental and economic life cycle impacts of biochar production and agricultural use in six developing and middle-income countries (Ethiopia, Indonesia, Kenya, Peru, Vietnam, and China). Two types of production technologies typical for rural and urban areas were investigated (flame curtain kiln and gasifier, respectively), and comparisons were made with composting (either home composting or windrow composting) as alternative biowaste management systems. The results showed that both pyrolysis systems performed better than composting and both were expected to bring environmental benefits. The largest environmental benefits were observed for the gasifier systems, mainly due to the substitution of electricity production from the grid. Damage to ecosystems and human health ranged from -1 × 10-7 to -2 × 10-8 species×yr and from -1 × 10-5 to -5 × 10-6 DALY per kg of biowaste treated, respectively (negative scores indicating environmental benefits). However, net economic benefits were only achieved when low-cost simple kilns were used in countries with low labor cost, like Ethiopia, Kenya and Vietnam (net profit from 0.01 to 0.08 USD per kg of biowaste treated). Further, high investment and operating costs and relatively small electricity revenue from substituting the grid electricity resulted in gasifier scenarios being economically unsustainable (net loss from 0.29 to 1.58 USD per kg of biowaste treated). Thus, there are trade-offs between positive environmental impacts for society and net market loss for the individual decision-maker (company or individual farmer) that should be considered when making decisions regarding the implementation of biochar technology in developing and middle-income countries. The use of simple kilns in countries with relatively low labor costs appears to be favorable.

The effect of biochar, lime and ash on maize yield in a long-term field trial in a Ultisol in the humid tropics.

A multi-season field trial was carried out to investigate the effect of the amendment of biochar, lime, ash and washed biochar on the growth of maize. A degraded, strongly acidic Ultisol (pHKCl 3.60), with a relatively high exchangeable aluminium content (2.4 cmolc/kg) and a low exchangeable calcium content (0.99 cmolc/kg), was used. Soil was treated once at the beginning of the field trial and crop growth was monitored over seven planting seasons (PS). All treatments increased maize yield. The average increases were; seven times for biochar, five times for lime, five times for washed biochar and eight times for ash treatment, when compared to the control across all PS. The effect of biochar, lime and ash treatments on maize yield were sustained over the seven PS. Soil pHKCl was significantly increased (p < 0.05 level) following the addition of all of the amendment materials. All treatments significantly reduced the concentration of Al3+ when compared to the control (p < 0.05), with the lowest concentrations for the lime and ash treatments. The ash treatment also increased the concentration of macronutrients (K, P and Mg) to the greatest extent. Results showed that there was a clear liming effect at play. The better performance of biochar compared to lime, despite lime having the highest pH and the lowest Al3+ concentration, can be explained by the additional K, Mg and P the biochar adds to the soil. Results also showed a clear nutrient addition effect where ash added the most nutrients. Overall, this work supports the fact that small scale farmers in Indonesia should produce biochar from their waste agricultural materials. Doing so not only provides an increase in crop productivity, but also sequesters carbon resulting in the best overall environmental benefit.

Waste timber pyrolysis in a medium-scale unit: Emission budgets and biochar quality.

Pyrolysis of organic waste or woody materials yields a stable carbonaceous product that can be mixed into soil and is often termed "biochar". During pyrolysis carbon-containing gases are emitted, mainly volatile organic carbon species, carbon monoxide and aerosols. In modern pyrolysis units, gases are after-combusted, which reduces emissions substantially. However, emission data for medium- to large-scale pyrolysis units are scant, both regarding gases, aerosols, heavy metals and polycyclic aromatic hydrocarbons (PAH). Making biochar from lightly contaminated waste timber (WT) is a promising waste handling option as it results in the potential valorization of such residues into e.g. sorbents for contaminant stabilization. For this process to be environmentally sustainable, emissions during the process need to be low and the resulting biochar of sufficient quality. To investigate both issues, we pyrolyzed three batches of WT and one reference batch of clean wood/leaves in a representative medium-scale pyrolysis unit (Pyreg-500, 750 t/year) with after-combustion of the pyrolysis gases, and measured the gas, aerosol, metal and PAH emissions, as well as the characteristics and contamination levels of the resulting biochar, including contaminant leaching. Mean emission factors for the WT were (g/kg biochar); CO = 7 ±â€¯2, non-methane volatile organic compounds (NMVOC) = 0.86 ±â€¯0.14, CH4 = 0, aerosols (PM10) = 0.6 ±â€¯0.3, total products of incomplete combustion (PIC) = 9 ±â€¯3, PAH-16 = (2.0 ±â€¯0.2) ·â€¯10-5, As (most abundant metal) = (2.3 ±â€¯1.9) ·â€¯10-3 and NOX = 0.65 ±â€¯0.10. There were no significant differences in emission factors between the pyrolysis of WT and the reference respectively, except for PM10, NMVOC, and PAH-16, which were significantly lower for WT than for the clean wood/leaves. The WT biochar did not satisfy premium or basic European Biochar Certificate criteria due to high levels of zinc and PAH. However, leachable metal contents were <0.1% of total contents. Still, use of the WT-biochar without further improvement or investigation would be limited to ex situ use, not improving soil fertility or in situ remediation.

Effect of conservation farming and biochar addition on soil organic carbon quality, nitrogen mineralization, and crop productivity in a light textured Acrisol in the sub-humid tropics.

Conservation farming (CF), involving basin tillage, residue retention and crop rotation, combined with biochar may help to mitigate negative impacts of conventional agriculture. In this study, the effects of CF on the amount and quality of soil organic matter (SOM) and potential nitrogen (N) mineralization were investigated in a maize-soya-maize rotation in an Acrisol in Zambia. A large field was run under CF for 7 years and in the subsequent three growing seasons (2015-2018), four management practices were introduced to study effects on soil characteristics and crop yield. We tested i) a continuation of regular CF (CF-NORM) ii) CF without residue retention (CF-NO-RES); iii) Conventional (CONV), with full tillage and removal of residues; and iv) CF with 4 ton ha-1 pigeon pea biochar inside basins and residue retention (CF-BC). The experiment involved the addition of fertilizer only to maize, while soya received none. Soya yield was significantly higher in CF systems than in CONV. Maize yields were not affected by the different management practices probably due to the ample fertilizer addition. CF-NORM had a higher stock of soil organic carbon (SOC), higher N mineralization rates, more hot-water extractable carbon (HWEC; labile SOC) and particulate organic matter (POM) inside basins compared to the surrounding soil (outside basins). Our results suggest that the input of roots inside basins are more effective increasing SOM and N mineralization, than the crop residues that are placed outside basins. CONV reduced both quality and quantity of SOM and N mineralization as compared to CF inside basins. CF-BC increased the amount of SOC as compared with CF-NORM, whereas N mineralization rate and HWEC remained unaffected. The results suggest benefits on yield of CF and none of biochar; larger impact of root biomass on the build-up of SOM than crop residues; and high stability of biochar in soil.

Can biochar and designer biochar be used to remediate per- and polyfluorinated alkyl substances (PFAS) and lead and antimony contaminated soils?

Designer biochars can be used to remediate organic and inorganic contaminant polluted soils. Here, a waste timber biochar (BC), a coconut shell activated biochar (aBC) and a wood shrub iron enriched designer biochar (Fe-BC) were investigated. Per- and polyfluorinated alkyl substances (PFAS) contaminated soils with different total organic carbon (TOC) contents (1.6 and 34.2%) were amended with six doses of BC and aBC. Two shooting range soils (TOC 5.2 and 10.2%) contaminated with heavy metals (mainly Pb and Sb) were amended with four doses of BC and Fe-BC. An amendment of 20% BC reduced the PFOS leachate concentration by 86% for the low TOC soil but was not effective for the high TOC soil. An amendment of 1% aBC reduced PFOS leachate concentrations by over >96% for both soils. For the low TOC shooting range soil, a 20% amendment of BC reduced Pb and Sb leaching by 61% and 12%, respectively. An amendment of 20% Fe-BC to soil with low TOC reduced Pb and Sb leaching by 99% and 40%, respectively. The need for "designer" biochars using processes such as iron enrichment or activation should be considered depending on the TOC of the soil, the type of contaminants and remediation goals.

Biochar amendment improves degraded pasturelands in Brazil: environmental and cost-benefit analysis.

Most deforested lands in Brazil are occupied by low-productivity cattle ranching. Brazil is the second biggest meat producer worldwide and is projected to increase its agricultural output more than any other country. Biochar has been shown to improve soil properties and agricultural productivity when added to degraded soils, but these effects are context-dependent. The impact of biochar, fertilizer and inoculant on the productivity of forage grasses in Brazil (Brachiaria spp. and Panicum spp.) was investigated from environmental and socio-economic perspectives. We showed a 27% average increase in Brachiaria production over two years but no significant effects of amendment on Panicum yield. Biochar addition also increased the contents of macronutrients, soil pH and CEC. Each hectare amended with biochar saved 91 tonnes of CO2eq through land sparing effect, 13 tonnes of CO2eq sequestered in the soil, equating to U$455 in carbon payments. The costs of biochar production for smallholder farmers, mostly because of labour cost, outweighed the potential benefits of its use. Biochar is 617% more expensive than common fertilizers. Biochar could improve productivity of degraded pasturelands in Brazil if investments in efficient biochar production techniques are used and biochar is subsidized by low emission incentive schemes.

How Important is Bioturbation for Sediment-to-Water Flux of Polycyclic Aromatic Hydrocarbons in the Baltic Sea?

In the present study a recently developed benthic flow-through chamber was used to assess the sediment-to-water flux of polycyclic aromatic hydrocarbons (PAHs) at 4 sites on the Swedish Baltic Sea coast. The flow-through chamber allows for assessment of the potential effect of bioturbation on the sediment-to-water flux of hydrophobic organic contaminants. The sediments at the 4 investigated sites have both varying contamination degree and densities of bioturbating organisms. The flux of individual PAHs measured with the flow-through chamber ranged between 21 and 510, 11 and 370, 3 and 9700, and 62 and 2300 ng m-2 d-1 for the 4 sites. To assess the potential effect of bioturbation on the sediment-to-water flux, 3 flow-through and closed chambers were deployed in parallel at each site. The activity of benthic organisms is attenuated or halted because of depletion of oxygen in closed benthic chambers. Therefore, the discrepancy in flux measured with the 2 different chamber designs was used as an indication of a possible effect of bioturbation. A potential effect of bioturbation on the sediment-to-water flux by a factor of 3 to 55 was observed at sites with a high density of bioturbating organisms (e.g., Marenzelleria spp., Monoporeia affinis, and Macoma balthica of approximately 860-1200 individuals m-2 ) but not at the site with much lower organism density (<200 individuals m-2 ). One site had a high organism density and a low potential effect of bioturbation, which we hypothesize to be caused by the dominance of oligochaetes/polychaetes at this site because worms (Marenzelleria spp.) reach deeper into the sediment than native crustaceans and mollusks. Environ Toxicol Chem 2019;38:1803-1810. © 2019 SETAC.

Can polyethylene passive samplers predict polychlorinated biphenyls (PCBs) uptake by earthworms and turnips in a biochar amended soil?

A pot experiment was carried out in which aged polychlorinated biphenyls (PCBs) contaminated soil was amended with biochar, and three phases: earthworms, turnips and polyethylene (PE) passive samplers, were added simultaneously in order to investigate changes in bioavailability of PCB following biochar amendment. Two biochars were used: one made from rice husk in Indonesia using local techniques and the other made from mixed wood shavings using more advanced technology. The biochars were amended at 1 and 4% doses. The overall accumulation of PCBs to the phases followed the order: earthworm lipid > PE > turnip. The rice husk biochar reduced PCB accumulation to a greater degree than the mixed wood biochar for all phases, however there was no effect of dose for either biochar. Earthworm uptake was reduced between 52% and 91% for rice husk biochar and by 19% to 63% for mix wood biochar. Turnip uptake was not significantly reduced by biochar amendment. Phase to soil accumulation factors (PSAF) were around 0.5 for turnips, approximately 5 for PE and exceeded 100 for earthworms. This study demonstrates that both biochars can be a sustainable alternative for in situ soil remediation and that PE can be used as tool to simulate the uptake in earthworms and thus remediation effectiveness.

Significant build-up of soil organic carbon under climate-smart conservation farming in Sub-Saharan Acrisols.

Conservation farming (CF) involving minimum tillage, mulching and crop rotation may offer climate change adaptation and mitigation benefits. However, reported effects of CF, as applied by smallholders, on storage of soil organic carbon (SOC) and soil fertility in Sub-Saharan Africa differ considerably between studies. This is partly due to differences in management practice, soil type and adoption level between individual farmers. Where CF involves planting basins, year-to-year changes in position of basins make SOC stock estimates more uncertain. Here we assess the difference in SOC build-up and soil quality between inside planting basins (receiving inputs of lime and fertilizer; basins opened each year) and outside planting basins (no soil disturbance or inputs other than residues) under hand-hoe tilled CF in an Acrisol at Mkushi, Zambia. Seven years of strict CF husbandry significantly improved soil quality inside planting basins as compared with outside basins. Significant effects were found for SOC concentration (0.74 ±â€¯0.06% vs. 0.57 ±â€¯0.08%), SOC stock (20.1 ±â€¯2.0 vs. 16.4 ±â€¯2.6 t ha-1, 0-20 cm), soil pH (6.3 ±â€¯0.2 vs. 4.95±â€¯0.4) and cation exchange capacity (3.8 ±â€¯0.7 vs. 1.6 ±â€¯0.4 cmolc kg-1). As planting basins only occupy 9.3% of the field, the absolute rate of increase in SOC, compared with outside basins, was 0.05 t C ha-1 yr-1. This corresponds to an overall relative increase of 2.95‰ SOC yr-1 in the upper 20 cm of the soil. Also, hot water extractable carbon (HWEC), a proxy for labile organic matter, and potential nitrification rates were consistently greater inside than outside basins. The significant increase in quantity and quality of SOC may be due to increased inputs of roots, due to favorable conditions for plant growth through input of fertilizer and lime, along with increased rainwater infiltration in the basins.

Sorption of α-, ß-, γ- and δ-hexachlorocyclohexane isomers to three widely different biochars: Sorption mechanisms and application.

Within this study different biochars (BC) with widely varying characteristics have been tested as materials for the adsorption of hexachlorocyclohexane's (HCH) isomers (α, ß, γ and δ) from water. Three BCs produced from digestate (700 °C), greenhouse tomato waste (550 °C) and durian shell (400 °C) were tested. The BCs demonstrated variable physico-chemical characteristics, especially with respect to surface area, with CO2-surface area ranging from 5.4 to 328.6 m2 g-1 and iron content ranging from 0.0733 to 11.17 g kg-1. Isotherm tests were carried out to understand which mechanisms drive HCH uptake to BC, to assess whether stereochemistry affects adsorption and to assess whether competitive sorption occurs. Log KF values ranged from 3.7 to 5.8 (µg kg-1) (µg L-1)-n for the various isomers on the three biochars. No competition (t-test, P < 0.0001) was observed between α-, ß-, γ- and δ-HCH. Freundlich adsorption constants of α-, γ- and δ-HCH followed the order: BC digestate > BC greenhouse tomato waste > BC durian shell, in contrast to ß-HCH which followed the order: BC durian shell > BC greenhouse tomato waste > BC digestate. In addition to stereochemistry, sorption coefficients were affected most strongly by BC surface area and iron content, in addition to specific HCH/BC matrix interactions. In this study the iron content of a carbonaceous material has been investigated, for the first time, as a factor that can affect the sorption of HCHs.

Monitoring wastewater discharge from the oil and gas industry using passive sampling and Danio rerio bioassay as complimentary tools.

Produced water (PW) represents the largest volume waste stream in oil and gas production operations from most offshore platforms. PW is difficult to monitor as releases are rapidly diluted and concentrations can reach trace levels. The use of passive samplers can over come this. Here polyethylene (PE) was calibrated for a diverse range of PW pollutants. Zebrafish were exposed to dilutions of PW and passive sampler extracts in order to investigate the relationship between freely dissolved chemical concentrations and acute toxic effects. The raw PW had an LC50 of 13% (percentage of PW in the standardized zebrafish medium). Observed non-viable deformations to embryos (at 5 hpf) included heart and yolk edema, head, spine and tail deformations. The dose-response relationship of lethal effects showed that if 0.0041 g of PE is exposed to this PW, then extracted, 50% of exposed D. rerio will suffer lethal effects. The sum of tested freely dissolved concentrations that led to 50% lethal effects (mortality and non-viable deformations) was 2.32 × 10-4 mg/L for PW and 7.92 × 10-2 mg/L for PE. This implies that exposure to raw PW was more toxic than exposure to PE extracts. This toxicity was attributed both to the presence of contaminants as well as PW salinity. Passive samplers are able to detect very low freely dissolved pollutant concentrations which is important for assessing the spatial dilution of PW releases. Bioassays provide complimentary information as they account for all toxic compounds including those that are not taken up by passive samplers.