Microcosm Tests Research Articles

Response of a nematode community to the fungicide fludioxonil in sediments of outdoor freshwater microcosms compared to a single species toxicity test

When entering aquatic ecosystems, hydrophobic organic chemicals like the fungicide fludioxonil partition to the sediment compartment where they pose potential risks to benthic invertebrates. To assess the ecological risk for sediment-dwelling invertebrates, nematodes are a suitable organism group, as they are abundantly present and possess key positions in the benthic food web. Therefore, the toxicity of the fungicide fludioxonil to nematodes was assessed in a standardized sediment toxicity test with Caenorhabditis elegans (ISO 10872), as well as in an outdoor sediment-spiked microcosm test system. In the microcosms, effects on the nematode species composition were studied, while exposure concentrations of fludioxonil were monitored in total sediment and pore water. Toxic effects on nematodes were better predicted using concentrations in pore water than total sediment concentrations. In laboratory single species tests, fludioxonil showed considerably lower toxicity in spiked field-collected sediment, compared to artificial ISO-sediments. Applying an assessment factor of 10 to the C. elegans 96-h EC10, a Tier-1 RACNematode of 7.99 mg kg−1 dry artificial sediment (corresponding to 69 μg l−1 in pore water) appeared to be protective for nematode communities in microcosms that showed no response in total abundance and species composition up to 39.9 mg fludioxonil kg−1 dry sediment (corresponding to 392 μg l−1 in pore water).

Effect of temperature on methane oxidation and community composition in landfill cover soil.

Municipal solid waste (MSW) landfills are the third largest anthropogenic source of methane (CH4) emissions in the United States. The majority of CH4 generated in landfills is converted to carbon dioxide (CO2) by CH4-oxidizing bacteria (MOB) present in the landfill cover soil, whose activity is controlled by various environmental factors including temperature. As landfill temperature can fluctuate substantially seasonally, rates of CH4 oxidation can also vary, and this could lead to incomplete oxidation. This study aims at analyzing the effect of temperature on CH4 oxidation potential and microbial community structure of methanotrophs in laboratory-based studies of landfill cover soil and cultivated consortia. Soil and enrichment cultures were incubated at temperatures ranging from 6 to 70°C, and rates of CH4 oxidation were measured, and the microbial community structure was analyzed using 16S rRNA gene amplicon sequencing and shotgun metagenome sequencing. CH4 oxidation occurred at temperatures from 6 to 50°C in soil microcosm tests, and 6-40°C in enrichment culture batch tests; maximum rates of oxidation were obtained at 30°C. A corresponding shift in the soil microbiota was observed, with a transition from putative psychrophilic to thermophilic methanotrophs with increasing incubation temperature. A strong shift in methanotrophic community structure was observed above 30°C. At temperatures up to 30°C, methanotrophs from the genus Methylobacter were dominant in soils and enrichment cultures; at a temperature of 40°C, putative thermophilic methanotrophs from the genus Methylocaldum become dominant. Maximum rate measurements of nearly 195μg CH4g-1day-1 were observed in soil incubations, while observed maximum rates in enrichments were significantly lower, likely as a result of diffusion limitations. This study demonstrates that temperature is a critical factor affecting rates of landfill soil CH4 oxidation in vitro and that changing rates of CH4 oxidation are in part driven by changes in methylotroph community structure.

Transport and release of electron donors and alkalinity during reductive dechlorination by combined emulsified vegetable oil and colloidal Mg(OH)2: Laboratory sand column and microcosm tests

Emulsified vegetable oil combined with colloidal Mg(OH)2 (EVO-CM) can slowly release electron donors and OH– into groundwater and is therefore regarded as a promising amendment for enhanced in situ treatment of chlorinated solvents, such as tetrachloroethene (PCE) and trichloroethene (TCE). However, its migration ability in different porous media and the simultaneous release of electron donor and pH buffer during enhanced reductive dechlorination (ERD) have never been evaluated in detail. In this study, EVO-CM with uniform drop size and desirable stability was prepared. Laboratory-scale column tests were conducted to investigate the transport and spatial distribution of the EVO-CM in different porous media. Batch microcosm experiments were carried out to study the dechlorination efficiency under different EVO:Mg(OH)2 ratios. Experimental results indicate that prepared EVO-CM emulsions can be transported effectively through different porous media with grain size ranging from 0.1–1.0 mm. The emulsified vegetable oil (EVO) and colloidal Mg(OH)2 showed synchronous movement through the porous media column systems, providing both electron donor and alkalinity at the same location. The retention degree of EVO-CM is greater in the finer grained media and decreases with increasing distance from the inlet. The injection of EVO-CM lead to a significant mobilization of TCE in the column. The reductive dechlorination of TCE in the microcosms was remarkably enhanced in the presence of EVO-CM. The coaddition of sufficient colloidal Mg(OH)2 effectively limits the deleterious pH decline caused by acid release. The microcosm achieves an optimum dechlorination efficiency when the EVO:Mg(OH)2 ratio is 1:1.

Duckweed as an Agricultural Amendment: Nitrogen Mineralization, Leaching, and Sorghum Uptake.

Excessive N and P in surface waters can promote eutrophication (algae-dominated, low-O waters), which decreases water quality and aquatic life. Duckweed (Lemnaceae), a floating aquatic plant, rapidly absorbs N and P from water and its composition shows strong potential as a soil amendment. Therefore, it may be used to transfer N and P from eutrophic water bodies to agricultural fields. In this work, dried duckweed was incorporated into agricultural soil in microcosm, column, and field tests to evaluate biological N cycling, nutrient retention, and crop yield compared with compost, diammonium phosphate (DAP), and an amendment-free control. In microcosm tests, 25 ± 13% of duckweed N was mineralized, providing on average less mineral N than DAP (107 ± 21%), but more than compost (11 ± 12%). In columns, duckweed treatments leached only 2% of the N added, significantly less than DAP, which leached 60% of its N. Compared with the control, DAP leached significantly more phosphate (78%), whereas duckweed and compost treatments leached less (56 and 27%, respectively). Crop yield, as well as runoff N and P, were measured in field tests growing forage sorghum [ (L.) Moench.]. Although less total N was applied to duckweed plots than to DAP plots (75 vs. 130 kg ha, respectively), duckweed was found to retain 30% more total mineral N in a tilled agricultural field than DAP, while supporting a comparable yield. These tests indicate that duckweed may provide a sustainable source of N and P for agriculture.

ANÁLISIS ECOTOXICOLÓGICO DEL FUNGICIDA FOSFITO DE SODIO SOBRE UNA COMUNIDAD PLANCTÓNICA

Agriculture is a strategic activity for the society, capable of causing impacts on the environment. Most of the impacts are related to the overuse of synthetic products for pest control and/or chemical fertilization. Sodium phosphite used as a fungicide presents low toxicity under standard laboratory conditions and type test organisms. However, no ecotoxicological tests have been performed to assist in the environmental risk assessment of this substance within a holistic framework. The present study shows the effect of the long-term exposure (60 days) of the fungicide sodium phosphite on the planktonic community, through outdoor microcosm tests. To determine the convenient concentrations to be used in the microcosms, a preliminary monospecific test was carried out with Daphnia magna in the laboratory. Considering its results, the levels of exposure to the microcosms were 5 and 10 mg/L. The results have shown no effect on the zooplankton community structure (taxonomic composition or abundance) associated with treatments. In addition, the community of primary producers, phytoplankton and periphyton, also showed negative response (abundance) under the exposure conditions. Present results indicate that the use of sodium phosphite at these concentrations does not represent a risk for the zooplankton community, however the lack of information about the effects on the phytoplankton structure should make the precautionary principle prevail in the use of this substance.

Using raw and sulfur-impregnated activated carbon as active cap for leaching inhibition of mercury and methylmercury from contaminated sediment

Sulfur-impregnated activated carbon (SAC) has been reported with a high affinity to Hg, but little research has done on understanding its potential as active cap for inhibition of Hg release from contaminated sediments. In this study, high-quality coconut-shell activated carbon (AC) and its derived SAC were examined and shown to have great affinity to both aqueous Hg2+ and methylmercury (MeHg). SAC had greater partitioning coefficients for Hg2+ (KD = 9.42 × 104) and MeHg (KD = 7.661 × 105) as compared to those for AC (KD = 3.69 × 104 and 2.25 × 105, respectively). However, AC appeared to have greater inhibition in total Hg (THg) leaching from sediment (14.2–235.8 mg-Hg/kg-sediment) to porewater phase as compared to SAC. 3 wt% AC amendment in sediment (235.8 mg/kg Hg) was the optimum dosage causing the porewater THg reduction by 99.88%. Moreover, significant inhibition in both THg and MeHg releases within the 83-d trial microcosm tests was demonstrated with active caps composed of SAC + bentonite, SAC + clean sediment, and AC + bentonite. While both AC and SAC successfully reduce the porewater Hg in sediment environment, the smaller inhibition in Hg release by SAC as compared to that by raw AC may suggest that possibly formed HgS nanoparticles could be released into the porewater that elevates the porewater Hg concentration.

Understanding the impact of water distribution system conditions on the biodegradation of haloacetic acids and expression of bacterial dehalogenase genes

The objective of this study is to evaluate the influence of water distribution system conditions (pH, total organic carbon, residual chlorine, and phosphate) on haloacetic acids (HAAs) biodegradation. A series of batch microcosm tests were conducted to determine biodegradation kinetics and collected biomass was used for real time quantitative reverse transcription polymerase chain reaction analyses to monitor how these drinking water distribution system conditions affect the relative expression of bacterial dehalogenase genes. It was observed that tested water distribution system conditions affected HAA biodegradation with different removal efficiencies (0–100%). HAA biodegradation was improved in tested samples with TOC (3 mg/L) and pH 8.5 compared to those of TOC (0 mg/L) and pH 7, respectively. However, slight improvement was observed with the increased PO4 concentration (3.5 mg/L), and the presence of residual chlorine even at low concentration prohibited biodegradation of HAAs. The observed trend in the relative expression of dehII genes was compatible with the HAA biodegradation trend. Overall relative expression ratio of dehII genes was lower at pH 7, phosphate (0.5 mg/L), and TOC (0 mg/L) in comparison with pH 8.5, phosphate (3.5 mg/L), and TOC (3 mg/L) in the same experimental conditions.

Effects of Substitutions on the Biodegradation Potential of Benzotriazole Derivatives

Fourteen benzotriazole derivatives were subjected to microcosm tests to study the influence of substitutions on their biodegradation potential. Methylated, nitrated, carboxylated, and propionated bezotriazoles, a heterocyclic triazole, as well as methylated benzimidazoles, were introduced to activated sludge and soil enrichment cultures as the only carbon source. Some of the enrichment cultures were derived from airport soils that had been previously contaminated with aircraft deicing fluids and subsequently enriched with the commercially significant corrosion inhibitor methylbenzotriazole. The 5-methylbenzotriazole and only the carboxylated derivatives were degraded by soil or activated sludge biomass regardless of acclimation conditions. Radiotracer studies of [U-14C] 5-methylbenzotriazole, and [U-14C] 5-carboxybenzotriazole confirmed that relatively high concentrations (25mg L-1) of these derivatives can be completely mineralized in relatively short time frames by microbial consortia regardless of prior exposure. Observations suggested that the growth yield on these compounds is likely low. Biodegradation patterns suggested that carboxylated benzotriazole derivatives are more readily biodegradable than their more popular methylated counterparts.

Nano-fumed silica as a novel pollutant that inhibits the algicidal effect of p-hydroxybenzoic acid on Microcystis aeruginosa

ABSTRACTNanomaterials and/or contaminants are becoming more common in the developing world, but their effects on interspecific interactions are rarely reported, particularly in aquatic ecosystems. Thus, the present study determined the effects of the novel pollutant nano-fumed silica (NFS) on algal control by a macrophyte via the allelochemical p-hydroxybenzoic acid in a microcosm test. The allelochemical p-hydroxybenzoic acid caused significant decreases in chlorophyll a, but increased the amount of superoxide anion radicals () and the electric conductivity in Microcystis aeruginosa. The 50% inhibitory concentration (IC50) for p-hydroxybenzoic acid was 0.919 mmol/L in microalga during the exponential phase. Interestingly, NFS at 100–1600 mg/L had clear stimulatory effects on M. aeruginosa. When NFS at 800 mg/L was combined with different concentrations of p-hydroxybenzoic acid, the IC50 for p-hydroxybenzoic acid was 1.045 mmol/L. Thus, NFS significantly reduced the algicidal effect exhibited by p-hydroxybenzoic acid on M. aeruginosa. Furthermore, NFS might act as a silicon nutrient and enhance allelopathic resistance in M. aeruginosa to inhibit the algicidal effects of macrophytes via allelopathy. These findings suggest that before algal control is considered using macrophyte allelopathy, it is essential to remove the pollutant NFS from polluted lakes.

TOXICIDAD AGUDA DEL INSECTICIDA CIPERMETRINA (CYPERMON® 20 EC) EN CUATRO ESPECIES DE ANUROS COLOMBIANOS

El insecticida cipermetrina (CY) es usado en la agricultura para el control de plagas; sin embargo, por su acción neurotóxica puede afectar organismos no blanco como los anuros. El objetivo del trabajo fue determinar la toxicidad (concentración letal media: CL50, y algunos efectos subletales: retrasos en el desarrollo, capacidad de natación y longitud total de las larvas) del insecticida CY (Cypermon® 20EC) expuesto durante 96 horas en embriones y renacuajos de cuatro especies de anuros bajo pruebas de laboratorio y microcosmos. Los embriones de Rhinella humboldti fueron los más sensibles en condiciones de laboratorio (CL50= 6,27 mg/L) y Boana xerophylla en microcosmos (CL50= 88,32 mg/ha), mientras que los de Engystomops pustulosus fueron los más resistentes (laboratorio: CL50= 11,80 mg/L; microcosmos: CL50= 112,37 mg/ha). Rhinella marina mostró una sensibilidad intermedia. En los renacuajos no fue posible calcular los valores CL50 debido a la alta mortalidad registrada en las concentraciones experimentales en laboratorio y microcosmos, las cuales fueron 40 y 122 veces menores al valor de aplicación del insecticida (500 mg/L y 1,52 mg/ha, respectivamente). Por otra parte, se encontró una reducción significante en la longitud total y la capacidad de natación de las larvas obtenidas de los embriones expuestos a la CY, pero no en el tiempo de desarrollo. En conclusión, la exposición a la cipermetrina provocó una letalidad alta en los renacuajos y efectos subletales en estadíos tempranos del desarrollo, por lo que a las concentraciones recomendadas de aplicación, este insecticida es tóxico para las especies de estudio.

Growing evidence for facultative biotrophy in saprotrophic fungi: data from microcosm tests with 201 species of wood-decay basidiomycetes.

Ectomycorrhizal (ECM) symbioses have evolved a minimum of 78 times independently from saprotrophic lineages, indicating the potential for functional overlap between ECM and saprotrophic fungi. ECM fungi have the capacity to decompose organic matter, and although there is increasing evidence that some saprotrophic fungi exhibit the capacity to enter into facultative biotrophic relationships with plant roots without causing disease symptoms, this subject is still not well studied. In order to determine the extent of biotrophic capacity in saprotrophic wood-decay fungi and which systems may be useful models, we investigated the colonization of conifer seedling roots invitro using an array of 201 basidiomycete wood-decay fungi. Microtome sectioning, differential staining and fluorescence microscopy were used to visualize patterns of root colonization in microcosm systems containing Picea abies or Pinus sylvestris seedlings and each saprotrophic fungus. Thirty-four (16.9%) of the tested fungal species colonized the roots of at least one tree species. Two fungal species showed formation of a mantle and one showed Hartig net-like structures. These features suggest the possibility of an active functional symbiosis between fungus and plant. The data indicate that the capacity for facultative biotrophic relationships in free-living saprotrophic basidiomycetes may be greater than previously supposed.

Catalase and Phosphatase Activities During Hydrocarbon Removal from Oil-Contaminated Soil Amended with Agro-Industrial By-products and Macronutrients

Microbiological activities are essential in the bioremediation of polluted soils. The enzymatic activities of microorganisms are usually used as a biological indicator of soil health. The aim of this work was to observe the catalase, acid phosphatase (AcP), and alkaline phosphatase (AlP) activities in soil that was amended with agro-industrial by-products and macronutrients during the process of total petroleum hydrocarbon (TPH) removal. To this end, microcosm tests were performed with soil and agro-industrial by-products ratios of 100:2:2, for soil:sugarcane bagasse pith:filter cake mud (SSF); 100:2, for both soil:sugarcane bagasse pith (SS); and for soil filter cake mud (SF). The macronutrients—carbon, nitrogen, and phosphorus—in the experimental treatments were adjusted to 100:10:1 with a solution of NH4NO3 and K2HPO4. The best TPH removal (51.4%) was obtained with SSF at 15 days. In addition, a significant correlation was observed between TPH removal and AlP as well as AcP (r = 0.74, p < 0.0001; r = 0.70, p < 0.0107, respectively). Fungi growth was also correlated with both AlP (r = 0.97, p < 0.0001) and AcP (r = 0.95, p < 0.0001) activities. Besides, bacterial and fungi growth showed a correlation with TPH (r = 0.86, p < 0.001; r = 0.77, p < 0.0034, respectively). It could be said that the agro-industrial by-products and macronutrients contributed to pollutant removal from the oil-polluted soil at relatively short amount of time. In addition, the enzymatic activities were increased after the treatment; in this study, the high sensitivity enzyme was AlP, and it could be used as an indirect indicator of oil pollutant removal.

Influence of Nonionic Surfactants on Fungal and Bacterial Degradation of Hexane

Batch solubility and microcosm studies were conducted to examine the role of nonionic surfactants (Brij 30, Brij 35, Triton X‐100, and Tween 80) on fungal and bacterial degradation of hexane, a model volatile organic compound with a high Henry's law constant. The apparent solubility of gas phase hexane was not observed as a linear correlation in respect to surfactant concentration due to the insufficient mass transfer at the gas–liquid interface. The hexane partitioning to micellar phase was related to the unique structure of surfactants with different lengths of hydrophobic alkyl or hydrophilic polyoxyethylene chains. Microcosm test results revealed that most tested surfactants below critical micelle concentration (CMC) improved the fungal and bacterial growth, but surfactants at high concentration (5 CMC) adversely affected biodegradation kinetics. The observed low hexane removal was possibly attributed to the toxicity of surfactants at elevated concentration, the preferential utilization of a surfactant as substrate, and the partitioning of hexane into micellar phase. The results from this study suggest that low concentrations of Brij 30 and Tween 80 are favorable to enhance both the solubility and bioavailability of hexane with fungi as working consortium, while Brij 30 and Triton X‐100 below their CMC hold promising potential for bacterial degradation of hexane without having significant biodegradation of the surfactant.

Aerobic Vinyl Chloride Metabolism in Groundwater Microcosms by Methanotrophic and Etheneotrophic Bacteria.

Vinyl chloride (VC) is a carcinogen generated in groundwater by reductive dechlorination of chloroethenes. Under aerobic conditions, etheneotrophs oxidize ethene and VC, while VC-assimilators can use VC as their sole source of carbon and energy. Methanotrophs utilize only methane but can oxidize ethene to epoxyethane and VC to chlorooxirane. Microcosms were constructed with groundwater from the Carver site in MA containing these three native microbial types. Methane, ethene, and VC were added to the microcosms singly or as mixtures. In the absence of VC, ethene degraded faster when methane was also present. We hypothesized that methanotroph oxidation of ethene to epoxyethane competed with their use of methane, and that epoxyethane stimulated the activity of starved etheneotrophs by inducing the enzyme alkene monooxygenase. We then developed separate enrichment cultures of Carver methanotrophs and etheneotrophs, and demonstrated that Carver methanotrophs can oxidize ethene to epoxyethane, and that starved Carver etheneotrophs exhibit significantly reduced lag time for ethene utilization when epoxyethane is added. In our groundwater microcosm tests, when all three substrates were present, the rate of VC removal was faster than with either methane or ethene alone, consistent with the idea that methanotrophs stimulate etheneotroph destruction of VC.

Benthic Fauna Promote Algicidal Effect of Allelopathic Macrophytes on Microcystis aeruginosa

In the present study, a microcosm test was used to explore the effects of the zoobenthos on macrophyte allelopathy. Four representative zoobenthos showed low algal inhibition ranging within 0.05–0.16 in separate co-culture. When zoobenthos and tested microalgae were mixed completely, the inhibition rate was enhanced by 0.68. The inhibition potential followed the order: Corbicula fluminea > Palaemonetes sinensis > Chironomus plumosus > Limnodrilus hoffmeisteri. Furthermore, the benthic fauna significantly enhanced algal inhibition of the emergent plant Typha angustifolia and the submerged plant Potamogeton crispus by 0.43 and 0.32, respectively. Meanwhile, there was a significant difference in algal inhibition between five growth phases of macrophytes combined with zoobenthos community. In addition, a significant positive relationship occurred between the algal inhibition of allelopathic macrophytes and the mean individual biomass of the zoobenthos. Through the determination of physiological and biochemical traits of macrophytes, it was concluded that the zoobenthos would be a significant disturbance factor and induce strong stress-resistance response in macrophytes. Subsequently, the specific response will facilitate the algal inhibition of allelopathic macrophytes. Therefore, to keep a reasonable biodiversity will fully display strong function of the aquatic ecosystem and efficiently control harmful algal bloom.

Fabrication of biodegradable polylactide foam for algal bloom control

Eutrophication of reservoirs, lakes and rivers is the phenomenon that induces algal blooms by accumulating nutriments in the water system because of the continuous inflow of pollutants such as domestic sewage and industrial wastewater. This phenomenon is a global environmental problem that threatens water systems, coastal ecosystems and even human life. A recent method to solve the problem is the use of scaffolding for releasing algicide. Although this method has the effect of controlling algae, it can cause secondary environmental problems such as toxicity to other species and waste of the used scaffold. In this research, to improve the eco-friendliness and efficiency of the algicide-releasing process, biodegradable polymer foam as a carrier of the algicide was prepared. Polylactide is a biodegradable polymer that can be obtained from natural resources such as cornstarch and tapioca starch. Polylactide foam, which has high porosity and surface area because of its open-cell structure, was produced using the salt-leaching method. The most important property of polylactide foam is controlling the pore size to make it suitable for the size of the algicide. The pore size of polylactide foam is controlled by the size of the used salt particle itself. The pore size and porosity were confirmed by analyzing the morphology of polylactide foam. The algicide was loaded on the polylactide foam using the injection method. A microcosm test of Stephanodiscus was performed to confirm the efficiency of algicide release from the polylactide foam. To investigate the biodegradability of the polylactide foam, an enzymatic degradation test was performed.

겨울철 규조류 대발생 제어를 위한 Naphthoquinone 유도체 Nq 4-6의 적용 가능성

We conducted the algicidal activity screening tests using 10 L microcosm to investigate the possibility of the field application of naphthoquinone derivative Nq 4-6 compound as an algicide. We determined its application range to assess its algicidal effects on the phytoplankton and to evaluate the response of the planktonic community and the water environment to this chemical. From results of the microcosm experiments, Nq 4-6 compound showed high algicidal activity on the centric diatoms such as Stephanodiscus hantzschii and Cyclotella meneghiniana, but it had no effect on other phytoplankton. The abundance of S. hantzschii continuously increased in the control, but its cell density decreased 1 day after the Nq 4-6 treatment. In particular, Nq 4-6 showed algicidal activity of 94.4% against S. hantzschii 7 days after the treatment. The dominance index of phytoplankton community was lower in the treatment than in the control. The diversity index, richness index and evenness index of phytoplankton community was higher in the treatment. Environmental factors and biological factors did not show specific changes after the Nq 4-6 compound treatment. Therefore, the results of this study demonstrates that Nq 4-6 is an effective agent for the control of S. hantzschii blooms, and that the microcosm tests play a crucial role when assessing field application.

A field application feasibility assessment of naphthoquinone derivatives for the mitigation of freshwater diatom Stephanodiscus blooms

Although many algicidal substances have been developed, their field application remains a serious challenge due to their high toxicity in the ecosystem and also due to economic reasons. Therefore, we evaluated the claim that naphthoquinone (NQ) derivatives can be used for the efficient mitigation of natural Stephanodiscus hantzschii blooms in freshwater. We tested a total of 23 algicidal NQ compounds to select the best based on the algicidal activity of S. hantzschii species. Among them, NQ 4–6 showed the highest algicidal activities (96 % at ≥0.2 μM). We conducted an acute toxicity assessment of the new algicide and found that NQ 4–6 had advanced solubility and lower toxicity, as represented by the survival rates of Selenastrum capricornutum, Daphnia magna, and Danio rerio, which are interconnected components of the freshwater ecosystem. None of these organisms seemed to be affected by the highest NQ concentration (2 μM), indicating a lack of significant toxic effects. These results indicate that the NQ 4–6 compound is promising for use as a selective control agent for S. hantzschii that does not cause negative side effects in the freshwater ecosystem. To evaluate the possibility of field application of NQ 4–6, we first performed microcosm tests. In the microcosm tests (60 L), S. hantzschii was completely eliminated 10 days after inoculation with the NQ 4–6 compound (0.2 μM). In the microcosm experiments, the dynamics of the biotic (except the phytoplankton) and abiotic factors showed similar trends in the control and treatment groups. Therefore, the NQ 4–6 compound has potential as an alternative algicidal substance to effectively mitigate natural S. hantzschii blooms.

Ecotoxicological effect of zinc oxide nanoparticles on soil microorganisms

The widespread production and use of zinc oxide nanoparticles (ZnO-NPs) in recent years have posed potential threat to the ecosystem. This study aimed to investigate the ecotoxicological effect of ZnO-NPs on soil microorganisms using laboratory microcosm test. Respiration, ammonification, dehydrogenase (DH) activity, and fluorescent diacetate hydrolase (FDAH) activity were used as ecotoxicological parameters. The results showed that in the neutral soil treated with 1 mg ZnO-NPs per g soil (fresh, neutral), ammonification was significantly inhibited during the study period of three months, but the inhibition rate decreased over increasing time. Inhibition in respiration was observed in the first month of the test. In various ZnO-NPs treatments (1 mg, 5 mg, and 10 mg ZnO-NPs per g soil), DH activity and FDAH activity were inhibited during the study period of one month. For both enzyme activities, there were positive dose–response relationships between the concentration of ZnO-NPs and the inhibition rates, but the curves changed over time due to changes of ZnO-NPs toxicity. Soil type affected the toxicity of ZnONPs in soil. The toxicity was highest in the acid soil, followed by the neutral soil. The toxicity was relatively low in the alkaline soil. The toxicity was not accounted for by the Zn2+ released from the ZnO-NPs. Direct interaction of ZnO-NPs with biologic targets might be one of the reasons. The adverse effect of ZnO-NPs on soil microorganisms in neutral and acid soils is worthy of attention.

Aspects of storage and corrosion characteristics of biodiesel

Process and corrosion engineers have critically addressed compatibility of biodiesel components in petroleum refinery infrastructure because of different processing, storage and dispatching histories of shipments. Concerns were related to aging and corrosion and to accumulation of a bottom layer in the dedicated storage tank. Corrosion tests were executed in a microcosm test environment modified to the recommended practice of ASTM G4-01 procedure. Colloid chemical properties and technology of biodiesel refining operations can plausibly explain different material responses at different temperatures. The sampled bottom layer consisted mainly of glycerides, resembling characteristics of extract byproducts that are separated in trans-esterification in biodiesel synthesis. This bottom layer exerts both beneficial and detrimental effects. The positive side is that it extracts polar components and by this improves quality. The negative side is that it reduces resistance of the oil against aging. There was no risk of detrimental effects in terms of corrosion of storage tank materials. Overall progress of corrosion is controlled by the slightly alkaline bottom layer via neutralizing the oxidation products and exerting protection to metallic surfaces. Microbial degradation can only pose risks if normal and prudent conditions are not observed. Upon extended incubation microorganisms that are present in the bottom layer below the level detection limit, can develop countable colonies, if nutrients are available and conditions are favorable. It can be concluded that there is no risk of significant corrosion in storage and downstream infrastructure if the stored biodiesel meets standard quality specifications and storage conditions are normal.