Microcosm Tests Research Articles

Evaluation of the importance of sediment organic matter composition for CH4 production by microcosm tests with and without addition of natural sources (cyanobacterial biomass and riparian pasture) in two subtropical, eutrophic reservoirs.

The biochemical composition of sediments, which depends on the origin of the organic matter (OM), is decisive in methane (CH4) production. This study aimed to determine the CH4 produced under anaerobic conditions from different substrates: native reservoir sediments and sediments with the addition of complex OM from Microcystis spp. blooms and terrestrial plants (pasture), alongside the biochemical characterization of the substrates used. The biochemical composition of the sediments explained the differences in CH4 production rate (µmol/g OM/day). Positive correlations were found between CH4 production rate and proteins (PRT) (r = 0.695), lipids (LIP) (r = 0.582), TN (r = 0.605), and biopolymeric carbon (BPC) (r = 0.784). Principal component analysis showed an association of CH4 production rate with PRT, LIP, TN, and BPC concentrations, sharing the same direction of the vectors. The addition of Microcystis bloom and pasture to the sediments significantly increased the rate and production of CH4 compared to native sediments, with higher values for bloom addition. In the studied reservoirs, cyanobacteria biomass is a very important source of organic matter to the sediments and a support for methanogenesis. Nonetheless, OM from surrounding vegetation, mainly pastures, could also play a significant role during events that increase reservoir levels, generating important CH4 emission "hot spots" at the periphery of the reservoirs.

Biodegradation of poly(butylene adipate terephthalate) and poly(vinyl alcohol) within aquatic pathway

Understanding the environmental fate of biodegradable plastics in aquatic systems is crucial, given the alarming amount of plastic waste and microplastic particles transported through aquatic pathways. In particular, there is a need to analyze the biodegradation of commercialized biodegradable plastics upon release from wastewater treatment plants into natural aquatic systems. This study investigates the biodegradation behaviors of poly(butylene adipate terephthalate) (PBAT) and poly(vinyl alcohol) (PVA) in wastewater, freshwater, and seawater. Biodegradation of PBAT and PVA assessed through biochemical oxygen demand (BOD) experiments and microcosm tests revealed that the type of aquatic system governs the biodegradation behaviors of each plastic, with the highest biodegradation rate achieved in wastewater for both PBAT and PVA (25.6 and 32.2 % in 30 d, respectively). Plastic release pathway from wastewater into other aquatic systems simulated by sequential incubation in different microcosms suggested that PBAT exposed to wastewater and freshwater before reaching seawater was more prone to degradation than when directly exposed to seawater. On the other hand, PVA displayed comparable biodegradation rate regardless of whether it was directly exposed to seawater or had passed through other environments beforehand. Metagenome amplicon sequencing of 16S rRNA genes revealed distinct community shifts dependent on the type of plastics in changing environments along the simulated aquatic pathway. Several bacterial species putatively implicated in the biodegradation of PBAT and PVA are discussed. Our findings underscore the significant influence of pollution routes on the biodegradation of PBAT and PVA, highlighting the potential for wastewater treatment to facilitate rapid degradation compared to direct exposure to pristine aquatic environments.

Research on aquatic microcosm: Bibliometric analysis, toxicity comparison and model prediction

Recently, aquatic microcosms have attracted considerable attention because they can be used to simulate natural aquatic ecosystems. First, to evaluate the development of trends, hotspots, and national cooperation networks in the field, bibliometric analysis was performed based on 1841 articles on aquatic microcosm (1962–2022). The results of the bibliometric analysis can be categorized as follows: (1) Aquatic microcosm research can be summarized in two sections, with the first part focusing on the ecological processes and services of aquatic ecosystems, and the second focusing on the toxicity and degradation of pollutants. (2) The United States (number of publications: 541, proportion: 29.5%) and China (248, 13.5%) are the two most active countries. Second, to determine whether there is a difference between single-species and microcosm tests, that is, to perform different-tier assessments, the recommended aquatic safety thresholds in risk assessment [i.e., the community-level no effect concentration (NOECcommunity), hazardous concentrations for 5% of species (HC5) and predicted no effect concentration (PNEC)] were compared based on these tests. There was a significant difference between the NOECcommunity and HC5 (P < 0.05). Moreover, regression models predicting microcosm toxicity values were constructed to provide a reference for ecological systemic risk assessments based on aquatic microcosms.

A trade-off in activated biochar capping of complex sediment contamination: reduced PAH transport at the cost of potential As mobilisation

PurposeThe effect of thin-layer capping with activated biochar on sediment-to-water flux was investigated. For the first time, the diffusion of both polycyclic aromatic hydrocarbons (PAHs) and arsenic (As) were studied simultaneously. The fate of As was investigated, under successive dysoxic and oxic conditions, in order to assess and discuss potential trade-off effects when using biochar as an active sorbent for capping of multi-contaminated sediments.MethodsSediments from the Bureå bay (Sweden), contaminated with PAH and metal elements including As and Hg, were capped with activated biochar and/or bentonite in simple microcosm test systems in the laboratory. The contaminant transport from sediment through the capping to water body was studied by sampling metals in the water phase above the cap over time, or PAH in a heptane layer over water, at regular time intervals.ResultsConsistently with the limited previous studies, reductions were observed (e.g., 60–65% for 15-PAH, 100% for chrysene) in sediment-to-water PAH fluxes upon biochar-based thin-layer capping. However, the most important novel finding revealed ambiguous effects of biochar capping on redox-sensitive elements, in particular As. Under the microcosm conditions of the experiment, where pH was affected by the capping material, biochar treatments favoured As mobility under oxic conditions, directly and/or via effects on Fe speciation. While capping limited the diffusion of As under dysoxic conditions, this also favoured greater As mobility under oxic water conditions compared to no capping.ConclusionDesign and monitoring of capping of PAH contaminated sediments should account for potential negative effects on co-occurring contaminants.

Combined Use of a Bacterial Consortium and Early-Colonizing Plants as a Treatment for Soil Recovery after Fire: A Model Based on Los Guájares (Granada, Spain) Wildfire.

During 2022, intense heat waves, together with particularly extreme dry conditions, created a propitious scenario for wildfires, resulting in the area of vegetation consumed in Europe doubling. Mediterranean countries have been particularly affected, reaching 293,155 hectares in Spain, the worst data in the last 15 years. The effects on the vegetation and the soil are devastating, so knowing the recovery factors is essential for after-fire management. Resilient microorganisms play a fundamental role in rapid nutrient recycling, soil structure, and plant colonization in fire-affected soils. In this present work, we have studied emergent microbial communities in the case of the Los Guájares (Granada, Spain) fire, one of the most extensive of the year, to evaluate their role in the recovery of soil and vegetation cover. We aim to discern which are the main actors in order to formulate a new treatment that helps in the ecosystem recovery. Thus, we have found the relevant loss in phosphorous and potassium solubilizers, as well as siderophores or biofilm producers. Here, we decided to use the strains Pseudomonas koreensis AC, Peribacillus frigoritolerans CB, Pseudomonas fluorescens DC, Paenibacillus lautus C, Bacillus toyonensis CD, and Paenarthrobacter nitroguajacolicus AI as a consortium, as they showed most of the capacities required in a regenerative treatment. On the other hand, the microcosm test showed an enhanced pattern of germination of the emerging model plant, Bituminaria bituminosa, as well as a more aggregated structure for soil. This new approach can create a relevant approach in order to recover fire-affected soils in the future.

Assessment on the effect of erythromycin on the microbiome of a bioslurry pilot plant for contaminated sediment bioprocessing

Bioslurry is a microbial-based technology that uses a bioreactor to treat sediments. The role of microbial metabolic capabilities is crucial for the removal performance of this technology and those factors that can affect microbial community. Particularly, antibiotics are among the environmental emergent contaminants. In this work, the effect of erythromycin was evaluated on the removal efficiencies of total petroleum hydrocarbons (TPHs), present in real sediments. On the basis of preliminary microcosm tests, an optimal erythromycin concentration (0.5 μg mL−1) was applied to a bioslurry pilot plant, using as control condition a parallel reactor without erythromycin addition. During experimentation the removal efficiency increased in both reactors, especially in the antibiotic-containing reactor where performance removal reached 81.5 %. A metataxonomic approach, based on a Next Generation Sequencing analysis of amplicons obtained from 16S rRNA encoding gene and ITS regions, showed that the presence of erythromycin affects the dynamic changes of both eukaryotic and prokaryotic communities in the reactor, selecting bacteria capable of degrading aromatic compounds, performing dehalogenation and methane oxidation as inferred by bioinformatic analysis.

Arsenate microbial reducing behavior regulated by the temperature fields in landfills

Attention should be paid to the As(V) reducing behavior in landfills under different temperature fields. In this study, microcosm tests were conducted using enrichment culture from a landfill. The results revealed that the reduction rate of As(V) was significantly affected by the temperature field, with the highest reduction rate observed at 50 °C, followed by 35 °C, 25 °C, and 10 °C. Different As cycling pathways were observed under various temperature fields. At room and medium temperatures, As4S4 was detected, indicating that both biomineralization and methylation processes occurred after As(V) reduction. However, only biogenic methylation was observed under high or low temperatures, indicating that the viability and adaptability of microorganisms varied depending on the temperature field and As contents. Pseudomonas was found to be the primary genus and dominant As(V) reduction bacteria (ARB) in all reactors. The study revealed that Pseudomonas accounted for a significant proportion of arsC genes, ranging from 87.29% to 97.59%, while arsCs genes were predominantly found in Bacillales and Closestridiales, with a contribution ranging from 89.17% to 96.59%. Interestingly, Bacillus and Clostridium were found to possess arsA genes in their metagenome-ssembled genome, resulting in a higher As(V) reducing rate under medium and high temperatures. These findings underscore the importance of temperature in modulating As(V) reducing behavior and As cycling, and could have implications for managing As pollution in landfill sites.

Microcosm test for pesticide fate assessment in planted water filters: 13C,15N-labeled glyphosate as an example

Planted filters are often used to remove pesticides from runoff water. However, the detailed fate of pesticides in the planted filters still remains elusive. This hampers an accurate assessment of environmental risks of the pesticides related to their fate and thereby development of proper mitigation strategies. In addition, a test system for the chemical fate analysis including plants and in particular for planted filters is not well established yet. Therefore, we developed a microcosm test to simulate the fate of pesticide in planted filters, and applied 2-13C,15N-glyphosate as a model pesticide. The fate of 2-13C,15N-glyphosate in the planted microcosms over 31 day-incubation period was balanced and compared with that in the unplanted microcosms. The mass balance of 2-13C,15N-glyphosate turnover included 13C mineralization, degradation products, and the 13C and 15N incorporation into the rhizosphere microbial biomass and plants. We observed high removal of glyphosate (> 88%) from the water mainly due to adsorption on gravel in both microcosms. More glyphosate was degraded in the planted microcosms with 4.1% of 13C being mineralized, 1.5% of 13C and 3.8% of 15N being incorporated into microbial biomass. In the unplanted microcosms, 1.1% of 13C from 2-13C,15N-glyphosate was mineralized, and only 0.2% of 13C and 0.1% of 15N were assimilated into microbial biomass. The total recovery of 13C and 15N was 81% and 85% in planted microcosms, and 91% and 93% in unplanted counterparts, respectively. The microcosm test was thus proven to be feasible for mass balance assessments of the fate of non-volatile chemicals in planted filters. The results of such studies could help better manage and design planted filters for pesticide removal.

Effect of Ginkgo biloba leaves on the removal efficiency of Cr(VI) in soil and its underlying mechanism

Cr(VI) is a toxic, teratogenic, and carcinogenic heavy metal element in soil that poses major ecological and human health risks. In this study, microcosm tests combined with X-ray absorption near-edge spectra (XANES) and 16Sr DNA amplification techniques were used to explore the effect of Ginkgo biloba leaves on the removal efficiency of Cr(VI) in soil and its underlying mechanism. Ginkgo biloba leaves had a favorable remediation effect on soil varying in Cr(VI) contamination levels, and the optimal effect was observed when 5% Ginkgo biloba leaves were added. The occurrence state of Cr(VI) in soil before and after the addition of Ginkgo biloba leaves was analyzed by XANES, which revealed that Cr(VI) was fully converted to the more biologically innocuous Cr(III), and the hydroxyl-containing quercetin in Ginkgo biloba leaves was one of the primary components mediating this reduction reaction. The Cr(VI) content was significantly lower in non-sterilized soil than in sterilized soil, suggesting that soil microorganisms play a key role in the remediation process. The addition of Ginkgo biloba leaves decreased the α-diversity and altered the β-diversity of the soil bacterial community. Actinobacteria was the dominant phylum in the soil remediated by Ginkgo biloba leaves; four genera of Cr(VI)-reducing bacteria were also enriched, including Agrococcus, Klebsiella, Streptomyces, and Microbacterium. Functional gene abundances predicted by PICRUST indicated that the expression of glutathione synthesis genes was substantially up-regulated, which might be the main metabolic pathway underlying the mitigation of Cr(VI) toxicity in soil by Cr(VI)-reducing bacteria. In sum, Ginkgo biloba leaves can effectively remove soil Cr(VI) and reduce Cr(VI) to Cr(III) via quercetin in soil, which also functions as a carbon source to drive the production of glutathione via Cr(VI)-reducing bacteria and mitigate Cr(VI) toxicity. The findings of this study elucidate the chemical and microbial mechanisms of Cr(VI) removal in soil by Ginkgo biloba leaves and provide insights that could be used to enhance the remediation of Cr(VI)-contaminated soil.

Practical application of PAC sludge-valorized biochars to the mitigation of methyl arsenic in wetlands

This study aims to mitigate As pollution in wetlands by using biochar composites, which are a byproduct of valorizing drinking water treatment sludge (i.e., polyaluminum chloride (PAC) sludge). Biochar composites were fabricated under N2 and CO2 environments, systematically characterized by X-ray diffraction, thermogravimetric, and Brunauer–Emmett–Teller/Barrett–Joyner–Halenda analyses, and tested for the adsorption of As species. Both biochar composites exhibited excellent adsorption performance for both inorganic As (As(III) and As(V)) and organic As (dimethylarsinic acid, DMA). A detailed study of the adsorption behavior of DMA revealed that the adsorption reaction complies with the pseudo-second-order kinetics and Freundlich isotherm models. A laboratory-scale microcosm test showed that ∼ 30 % of spiked DMA was removed by biochar and that the total As fixed in the sediment decreased by ∼ 20 %. In addition, the As speciation results for the sediment and biochar revealed demethylation of the DMA and reduction of As(V) to As(III) by microorganisms, which was confirmed by a microbial growth batch test. Finally, a large-scale field experiment carried out in an artificial ecological wetland ensured that the addition of biochar could reduce the total amount of As to be immobilized in wetland sediment by 19 %. In addition, the presence of biochar could alter the migration trend of As species in plants by reducing the amount of organic As to be fixed in the sediment. The aforementioned results demonstrate the practical feasibility of using PAC sludge-derived biochar as an adsorbent for As species.

Biological effect of phosphate on the dissimilatory arsenate-respiring bacteria-catalyzed reductive mobilization of arsenic from contaminated soils

Dissimilatory arsenate-respiring prokaryotes (DARPs) are considered to be the major drive of the reductive mobilization of arsenic from solid phases. However, it is not fully understood how phosphate, a structural analog of arsenate, affects the DARPs-mediated arsenic mobilization. This work aimed to address this issue. As-contaminated soils were collected from a Shimen Realgar Mine-affected area. We identified a unique diversity of DARPs from the soils, which possess high As(V)-respiring activities using one of multiple small organic acids as the electron donor. After elimination of the desorption effect of phosphate on the As mobilization, the supplement of additional 10 mM phosphate to the active slurries markedly increased the microbial community-mediated reductive mobilization of arsenic as revealed by microcosm tests; this observation was associated to the fact that phosphate significantly increased the As(V)-respiratory reductase (Arr) gene abundances in the slurries. To confirm this finding, we further obtained a new DARP strain, Priestia sp. F01, from the samples. We found that after elimination of the chemical effect of phosphate, the supplement of 10 mM phosphate to the active slurries resulted in an 82.2% increase of the released As(III) in the solutions, which could be contributed to that excessive phosphate greatly increased the Arr gene abundance, and enhanced the transcriptional level of arrA gene and the bacterial As(V)-respiring activity of F01 cells. Considering that phosphate commonly coexists with As in the environment, and is a frequently-used fertilizer, these findings are helpful for deeply understanding why As concentrations in contaminated groundwater are dynamically fluctuated, and also provided new knowledge on the interactions between the biogeochemical processes of P and As.

Assessing Microbial Corrosion Risk on Offshore Crude Oil Production Topsides under Conditions of Nitrate and Nitrite Treatment for Souring.

Oilfield souring is a detrimental effect caused by sulfate-reducing microorganisms that reduce sulfate to sulfide during their respiration process. Nitrate or nitrite can be used to mitigate souring, but may also impart a corrosion risk. Produced fluids sampled from the topside infrastructure of two floating, production, storage, and offloading (FPSO) vessels (Platform A and Platform B) were assessed for microbial corrosion under nitrate and nitrite breakthrough conditions using microcosm tests incubated at 54 °C. Microbial community compositions on each individual FPSO were similar, while those between the two FPSO vessels differed. Platform B microbial communities responded as expected to nitrate breakthrough conditions, where nitrate-reducing activity was enhanced and sulfate reduction was inhibited. In contrast, nitrate treatments of Platform A microbial communities were not as effective in preventing sulfide production. Nitrite breakthrough conditions had the strongest sulfate reduction inhibition in samples from both platforms, but exhibited the highest pitting density. Live experimental replicates with no nitrate or nitrite additive yielded the highest general corrosion rates in the study (up to 0.48 mm/year), while nitrate- or nitrite-treated fluids revealed general corrosion rates that are considered low or moderate (<0.12 mm/year). Overall, the results of this study provide a description of nitrogen- and sulfur-based microbial activities under thermophilic conditions, and their risk for MIC that can occur along fluid processing lines on FPSO topsides that process fluids during offshore oil production operations.

Strategic Development of Microcosm Test Method for Environmental Impact Risk Assessment

Strategic Development of Microcosm Test Method for Environmental Impact Risk Assessment

Bioremediation of trichloroethylene-polluted groundwater using emulsified castor oil for slow carbon release and acidification control.

In this study, the emulsified castor oil (ECO) substrate was developed for a long-term supplement of biodegradable carbon with pH buffering capacity to anaerobically bioremediate trichloroethylene (TCE)-polluted groundwater. The ECO was produced by mixing castor oil, surfactants (sapindales and soya lecithin [SL]), vitamin complex, and a citrate/sodium phosphate dibasic buffer system together for slow carbon release. Results of the emulsification experiments and microcosm tests indicate that ECO emulsion had uniform small droplets (diameter = 539 nm) with stable oil-in-water characteristics. ECO had a long-lasting, dispersive, negative zeta potential (-13 mv), and biodegradable properties (viscosity = 357 cp). Approximately 97% of TCE could be removed with ECO supplement after a 95-day operational period without the accumulation of TCE dechlorination byproducts (dichloroethylene and vinyl chloride). The buffer system could neutralize acidified groundwater, and citrate could be served as a primary substrate. ECO addition caused an abrupt TCE adsorption at the initial stage and the subsequent removal of adsorbed TCE. Results from the next generation sequences and real-time polymerase chain reaction (PCR) indicate that the increased microbial communities and TCE-degrading bacterial consortia were observed after ECO addition. ECO could be used as a pH-control and carbon substrate to enhance anaerobic TCE biodegradation effectively. PRACTITIONER POINTS: Emulsified castor oil (ECO) contains castor oil, surfactants, and buffer for a slow carbon release and pH control. ECO can be a long-term carbon source for trichloroethylene (TCE) dechlorination without causing acidification. TCE removal after ECO addition is due to adsorption and reductive dechlorination mechanisms.

Effects of sewer biofilm on the degradation of drugs in sewage: A microcosm study

A thorough understanding of the in-sewer stability of chemical biomarkers is critical in applying wastewater-based surveillance of community drug use. In this study, we examined the effects of sewer biofilm on the degradation of commonly abused drugs, namely, morphine, fentanyl, cocaine, and amphetamine, in wastewater using 48-h batch degradation tests. The experiments were designed to distinguish among abiotic, biochemical, and physical degradation processes, and used mature biofilm obtained from an actual sewer line. Parallel microcosm tests were conducted using wastewater with and without suspended biofilm. Results indicate that first order kinetics describe the degradation of the drugs in both wastewater and wastewater-biofilm microcosms. Amphetamine was most stable in all microcosms, with a maximum removal of only 34% after 48 h. Abiotic chemical transformation played a major role in the degradation of morphine (kab = 0.018 h-1), fentanyl (kab = 0.022 h-1) and cocaine (kab = 0.049 h-1) in wastewater. Fentanyl removal from wastewater was also influenced by the presence of biofilm (kf = 0.015 h-1). This study is the first to report on the effect of sewer biofilm on fentanyl degradation, and highlights the need to account for in-sewer drug stability in wastewater-based drug use estimation, particularly for chemicals with high affinity for organics.

Cannabis sativa L. and Brassica juncea L. grown on arsenic-contaminated industrial soil: potentiality and limitation for phytoremediation.

Phytoremediation represents a natural method to remove contaminants from soil. The goal of this study was to investigate the potential of phosphate-assisted phytoremediation by two energy crops, Cannabis sativa L. and Brassica juncea L., for the sustainable remediation of heavily arsenic-contaminated industrial soil. The two species were investigated for uptake, translocation, and physiological effects of arsenic and phosphate in a microcosm test. Although C. sativa and B. juncea were symptomless when grown in arsenic-contaminated soil, an important reduction of biomass (50 and 25%, respectively) was observed as a stress marker. Phytotoxicity and cytotoxicity effects promoted by contaminated soils were investigated in both the species and a model plant for ecotoxicity studies, Vicia faba L., which is the most developed model to test genotoxicity effects in terms of chromosomal aberration and micronuclei presence. The higher amount of arsenic was found in C. sativa and B. juncea roots (on average 1473 and 778 mg kg-1, respectively), but both species were able to uptake and translocate arsenic in leaves and stems, up to 47.0 and 189 mg kg-1, respectively. Phosphate treatment had no effect on arsenic uptake in none of the crop, but significantly improved the plant performance. Biomass production resulted similar to that of B. juncea control plants. Antioxidant enzymatic activities and photosynthetic performance responded differently in the two crops. The present investigation provides new insight for a proficient selection of the most suitable crop species for sustainable phytomanagement of a highly polluted As-contaminated site by coupled phytoremediation-bioenergy approach.

Application of Combined In Situ Chemical Reduction and Enhanced Bioremediation to Accelerate TCE Treatment in Groundwater

Groundwater at trichloroethylene (TCE)-contaminated sites lacks electron donors, which prolongs TCE’s natural attenuation process and delays treatment. Although adding electron donors, such as emulsified oil, accelerates TCE degradation, it also causes the accumulation of hazardous metabolites such as dichloroethylene (DCE) and vinyl chloride (VC). This study combined in situ chemical reduction using organo-iron compounds with enhanced in situ bioremediation using emulsified oil to accelerate TCE removal and minimize the accumulation of DCE and VC in groundwater. A self-made soybean oil emulsion (SOE) was used as the electron donor and was added to liquid ferrous lactate (FL), the chemical reductant. The combined in situ chemical reduction and enhanced in situ bioremediation achieved favorable results in a laboratory microcosm test and in an in situ biological field pilot test. Both tests revealed that SOE+FL accelerated TCE degradation and minimized the accumulation of DCE and VC to a greater extent than SOE alone after 160 days of observation. When FL was added in the microcosm test, the pH value decreased from 6.0 to 5.5; however, during the in situ biological pilot test, the on-site groundwater pH value did not exhibit obvious changes. Given the geology of the in situ pilot test site, the SOE+FL solution that was injected underground continued to be released for at least 90 days, suggesting that the solution’s radius of influence was at least 5 m.

On the balance between practical relevance and standardization - Testing the effects of zinc and pyrene on native nematode communities in soil microcosms

Soils are among the most densely inhabited and biodiverse habitats on our planet, and many important soil ecosystem services depend on the health condition of the native soil fauna. Anthropogenic stress such as chemical pollution acting on the native soil fauna might jeopardize these functions. Laboratory microcosm tests are an appropriate tool for assessing the risk of chemicals on the native soil fauna and can be regarded as intermediate tier tests, bridging the gap between single species toxicity tests and field testing. Nematodes are one of the most abundant and divers soil invertebrates, and as such native nematode communities might be suitable for ecotoxicological assessments in laboratory microcosm set ups. In order to test such a small-scale (30 g soil) microcosm system, two different chemicals (zinc and pyrene) were assessed in various soil types for their effects on the respective native nematode communities. Various community parameters such as total nematode density, genus richness and genus composition, as well as trait-related indices (e.g. maturity index) were monitored over a period of 8–10 weeks. The response of the nematode communities strongly varied between soil types, and these differences were more pronounced for Zn than for pyrene. Interestingly, the structure of the respective native nematode communities was shown to play a larger role for explaining the varying toxic effects than soil properties governing the bioavailability of the spiked chemicals. We demonstrated that exposure of natural nematode communities in their original soil matrix to the metal zinc and to pyrene under climatically highly controlled conditions resulted in quantitatively and qualitatively distinct responses. Upon comparison of various community indices, the maturity index was shown to be the most sensitive toxicity endpoint for all tested soils and chemicals.

Studies into Fungal Decay of Wood In Ground Contact—Part 1: The Influence of Water-Holding Capacity, Moisture Content, and Temperature of Soil Substrates on Fungal Decay of Selected Timbers

This article presents the results from two separate studies investigating the decay of wood in ground contact using adapted versions of laboratory-based terrestrial microcosm (TMC) tests according to CEN/TS 15083-2:2005. The first study (A) sought to isolate the effect of soil water-holding capacity (WHCsoil [%]) and soil moisture content (MCsoil [%WHCsoil]) on the decay of five commercially important wood species; European beech (Fagus sylvatica), English oak heartwood (Quercus robur), Norway spruce (Picea abies), Douglas-fir heartwood (Pseudotsuga menziesii), and Scots pine sapwood (Pinus sylvestris), while keeping soil temperature (Tsoil) constant. Combinations of soil mixtures with WHCsoil of 30%, 60%, and 90%, and MCsoil of 30%, 70%, and 95%WHCsoil were utilized. A general trend showed higher wood decay, measured in oven-dry mass loss (MLwood [%]), for specimens of all species incubated in soils with WHCsoil of 60% and 90% compared to 30%. Furthermore, drier soils (MCsoil of 30 and 70%WHCsoil) showed higher MLwood compared to wetter soils (95%WHCsoil). The second study (B) built on the first’s findings, and sought to isolate the effect of Tsoil and MCsoil on the decay of European beech wood, while keeping WHCsoil constant. The study used constant incubation temperature intervals (Tsoil), 5–40 °C, and alternating intervals of 10/20, 10/30, and 20/30 °C. A general trend showed drier MCsoil (60%WHCsoil), and Tsoil of 20–40 °C, delivered high wood decay (MLwood &gt; 20%). Higher MCsoil (90%WHCsoil) and Tsoil of 5–10 °C, delivered low wood decay (MLwood &lt; 5%). Alternating Tsoil generally delivered less MLwood compared to their mean constant Tsoil counterparts (15, 20, 25 °C). The results suggest that differences in wood species and inoculum potential (WHCsoil) between sites, as well as changes in MCsoil and Tsoil attributed to daily and seasonal weather patterns can influence in-ground wood decay rate.

Evaluation of fly ash, apatite and rice straw derived-biochar in varying combinations for in situ remediation of soils contaminated with multiple heavy metals

ABSTRACT In -situ sorbent amendment is a relatively low-cost, low-impact approach for remediation of soil contaminated with heavy metals (HMs), and thus is considered a way to be favored in developing countries. In this study, materials of non-hazardous, alkaline agronomic and industrial by-products were used as sorbents to explore their capacity of in situ immobilization of multiple HMs in mining-impacted arable soil. These sorbents included fly ash (FA), biochar (BC) and apatite (AP) and they were implemented with varying ratios of combinations. Results of soil microcosm tests showed that after incubation for 90 days, concentrations of Pb, Zn, and Cd in their exchangeable forms determined by a sequential extraction method significantly decreased in amended soils, as opposed to the unamended control. Of the five sets of amendments, the composite of FA, BC, and AP resulted in the maximum reduction (up to 80%) in the mobility of Pb, Zn, and Cd in soils. The mechanisms underlying the immobilization of HMs in amended soils might involve processes of surface precipitation, ion exchange and complexation, in which the physicochemical properties of sorbent materials played an important role. The immobilization efficacy of sorbent amendments on HMs in soil was further supported by pot experiments in which significant inhibition of HM accumulation in the belowground and aboveground tissues of maize was observed after 50-day cultivation in amended soils as compared with control soil. Together, these results suggest that the application of cost-saving and environmentally friendly materials derived from wastes as sorbents to remediate soils contaminated with multiple HMs is promising for developing countries like Vietnam.