Multiphase flow and transport simulations were conducted to investigate the impact of soil heterogeneity and non-aqueous phase liquid (NAPL) presence on the distribution of stable carbon isotope signatures during contaminant transport with biodegradation. At a later time during the simulation of a homogeneous case with dense NAPL presence, significant carbon isotope signature (δ¹³C) values could only be observed in a narrow area at the bottom of the aquifer where NAPL accumulated. After this, the δ¹³C distribution remained relatively stable for a long time until all NAPL was dissolved into the groundwater and removed via biodegradation and groundwater flushing. These characteristics of δ¹³C distribution may only be captured when considering NAPL migration and dissolution. The simulation results demonstrated that δ¹³C values and their distribution significantly differed between the heterogeneous case and the homogeneous case, with respect to the maximum δ¹³C value and the shape of δ¹³C contours. When reaction rate constant varied for each soil type (each grid block) by relating it to soil permeability, the δ¹³C distribution demonstrated different patterns. In addition to geological heterogeneity, this indicates that the distribution of δ¹³C highly depends on the biological heterogeneity in the field. Therefore, this study suggests that, to avoid misinterpretation of isotope signature changes, geological and biological soil heterogeneities should be investigated. If a NAPL is present in the system, the NAPL phase transport and dissolution should be considered in addition to dissolved phase transport.

This study compares the effect of heavy metals (Hg²⁺, Cu²⁺, and Pb²⁺) on the Rhodotorula mucilaginosa and Saccharomyces boulardii biofilm and planktonic cells. A MBECᵀᴹ-HTP assay was used to test the levels of tolerance to heavy metals. The minimum inhibitory concentration (MICp) and minimum lethal concentration (MLCp) of the R. mucilaginosa and S. boulardii planktonic cells were determined, as well as minimum biofilm eradication concentration (MBEC). Metal removal efficiency was determined by batch biosorption assay. Previous studies had focused on heavy metal tolerance and removal efficiency of planktonic cells from Rhodotorula species only. Hence, our study presents and compares results for metal tolerance and removal efficiency of the R. mucilaginosa planktonic cells and biofilm. Biofilm tolerance was higher than the planktonic cells. The R. mucilaginosa planktonic cells showed the tolerance in the presence of Hg²⁺ (MICp 0.08 mM), Cu²⁺ (MICp 6.40 mM), and Pb²⁺ (MICp 3.51 mM), while the S. boulardii planktonic cells only tolerated Pb²⁺ (MICp 0.43 mM). The R. mucilaginosa biofilm showed the highest tolerance in the presence of Hg²⁺ (MBEC >0.31 mM), Cu²⁺(MBEC >12.81 mM), Pb²⁺ (MBEC >7.12 mM), and obtained results were confirmed by fluorescence microscopy. S. boulardii did not show potential in biofilm formation. The R. mucilaginosa biofilm exhibited better efficiency in removal of all tested metals than the planktonic cells. Metal removal efficiency was in the range from 4.79–10.25% for planktonic cells and 91.71–95.39% for biofilm.

In Aguascalientes, Mexico, there is a special concern about pesticides because of their intensive use on guava production areas, which are located in the vicinity of water reservoirs; thus, non-target organisms could be exposed. Thereafter, the aim of this work was to assess the effect of cypermethrin, Faena® (glyphosate), and malathion, which are the most used pesticides in Aguascalientes’ guava production, on the indigenous freshwater species Alona guttata (cladoceran) and Lecane papuana (rotifer). Acute 48-h toxicity tests were carried out, and LC₅₀ values were calculated. Then, five sublethal concentrations (1/80, 1/40, 1/20, 1/10, and 1/5 of the respective LC₅₀) were selected for the chronic assays: (a) intrinsic growth rate analysis in the rotifer and (b) partial life table analysis in the cladoceran. The results of the acute toxicity tests showed that A. guttata was more sensitive to malathion (LC₅₀ = 5.26 × 10⁻³ mg/L) at concentrations found in natural environments with continuous application on guava fields, whereas L. papuana was more sensitive to Faena® (LC₅₀ = 19.89 mg/L). The somatic growth of A. guttata was inhibited for the chronic exposure to cypermethrin. In addition, cypermethrin and Faena® seemed to exert endocrine disruptive effects on A. guttata. Moreover, malathion chronic exposure significantly decreased the survival of A. guttata. Moreover, L. papuana was affected chronically for the three pesticides.

Despite its isolation and scarce occupation, Antarctica is not exempt from the input of contaminants related to present and past human activities. Several deleterious compounds, such as the persistent organic pollutants (POPs) may reach Antarctic ecosystems, mostly via atmospheric long-range transport and further deposition. In this context, snow and its seasonal melting water represent a sink to these pollutants and also the last compartment before they reach marine primary producers. In order to assess the concentration of a selection of organic contaminants, a PDMS headspace extraction method was chosen due to its improvement in fieldwork sampling. Samples were collected in King George Island, during the austral summers from 2007 to 2010. PBDEs and PAHs remained under the method detection limits in all of the cases, restricting data interpretation to organochlorine compounds: average Σ HCHₛ ranged from 1.46 to 4.17, HCBs from 1.36 to 3.77, Σ Dᵣᵢₙₛ from <0.35 to 4.29, Σ Cₕₗₒᵣdₐₙₑₛ from 5.72 to 13.3, Σ DDTₛ from 4.32 to 24.4, and PCBs from 132 to 156 (always in pg kg⁻¹). Results were, in general, in agreement with previous literature. Nevertheless, due to the fact that samples were collected progressively later into the austral summer, one trend can be noticed: the sum of the concentrations in both matrixes seems to decrease, with a proportional increase in snow. Some exceptions can be remarked, hypothetically linked to the passage of South American frontal systems. Finally, results for these two compartments are compatible with the exposure expected for lower trophic-level organisms from such ecosystem.

A set of chitosan-g-poly(acrylic acid)/rice husk ash hydrogel composites was successfully employed as methylene blue (MB) adsorbent. Maximum MB adsorption capacity of 1952 mg/g of dried hydrogel was obtained with the composite at 5 wt% of rice husk ash (RHA) at pH ≥ 5. The adsorption capacity varied from 1450 to 1950 mg/g with increasing the initial MB concentration from 1500 to 2500 mg/L. The MB removal efficiency was higher than 90% for all samples. At pH ≥ 5, negatively charged groups (–COO⁻) in the adsorbent were generated, which could strongly interact with the positive charges from MB, favoring adsorption. Adsorption kinetics followed the pseudo-second-order model, which is based on the chemisorption phenomenon, reaching saturation as fast as 1 h of experiments due to the formation of an adsorbed MB monolayer, as suggested by the Langmuir isotherm model (type I). Desorption experiments showed that 75% of loaded MB can be removed from the adsorbent by immersing it in a pH 1 solution. CHT-g-PAAc/RHA5% composite was submitted to five cycles of adsorption/desorption, maintaining its MB removal efficiency at 91%. Therefore, chitosan-g-poly(acrylic acid)/RHA hydrogel composites present outstanding capacity to be employed in the remediation of MB-contaminated wastewaters.

Excessive algae growth has generated conflicts on the use of water supplies; therefore, the focus on new technologies to remove algae from water bodies is demanding. The aim of the present study was to assess the effect of hydrodynamic cavitation on the inactivation of microalgae belonging to genus Scenedesmus. A laboratory-scale experimental apparatus was built in order to accomplish this goal; it consisted of a Venturi device designed to generate the cavitation phenomenon. Suspended microalgae samples were treated for 60 minutes under different cavitation intensities (cavitation number—Cv—ranging from 0.17 to 0.27). Results evidenced that microalgae decay over time can be modeled through first-order kinetics. The maximum removal efficiency (85%) was recorded at the highest cavitation intensity (Cv = 0.17). The removal efficiency decreased as the cavitation number increased. Hydrodynamic cavitation was effective in inactivating Scenedesmus; it produced irreversible damages to cell morphology such as flotation spines removal, cell wall lesions, cytoplasm extravasation, and cavity formation. Assumingly, hydrodynamic cavitation has great potential to treat eutrophic water bodies. Furthermore, it represents a sustainable removal technique, since it does not produce secondary pollution.

Despite recent regulations, atmospheric ammonia (NH₃) emissions have not changed much over the last decades and excessive nitrogen remains as one of the major drivers for biodiversity changes. To prevent deleterious effects on species and ecosystems, it is very important to establish safety thresholds, such as those defined by the Critical Level (CLE) concept, “the concentration above which direct adverse effects on receptors may occur, based on present knowledge.” Empirical critical levels of atmospheric NH₃ have mainly been reported for temperate forests and there is a lack of information for Mediterranean forests. Here, we provide a case study on NH₃ CLEs for a typical Mediterranean ecosystem, the holm-oak (Quercus ilex) forest. To derive the CLE value, we measured NH₃ concentrations for 1 year at a distance gradient in the forest surrounding a point source (cattle farm) and used diversity changes of lichen functional groups to indicate the onset of adverse effects. We estimate a NH₃ CLE threshold of 2.6 μg m⁻³, a value that is higher than that reported in other Mediterranean ecosystems and suggests that the site has been already impacted by NH₃ pollution in the past. In a more general context, this study confirms the validity of lichen functional groups to derive CLEs in Mediterranean forests and woodlands and contribute to the body of knowledge regarding the impacts of NH₃ on ecosystems.

Five common fungal strains, Cladosporium cladosporioides, Aspergillus clavatus, Penicillium citrinum, Fusarium oxysporum, and Alternaria alternata, were cultivated in presence of iodide and iodate to evaluate their efficiency in iodine biovolatilization and bioaccumulation. Our results suggest that iodide and iodate bioaccumulation by microscopic filamentous fungi is similar although the biological transformation into volatile iodine compounds is driven by various pathways resulting in higher volatilization efficiency of iodate. Thus, the mobilization of iodate by filamentous fungi is superior to iodide mobilization. Our paper is also the first to compare the iodide and iodate volatilization efficiency by microorganisms. Our results highlight the significant role of filamentous fungi in biogeochemistry of iodine, especially in formation of environmentally reactive volatile forms that may contribute to ozone layer destruction.

A simple and green preconcentration method of hydrophobic to hydrophilic switchable liquid-solid dispersive microextraction (HSL-SDM) has been first time introduced as separation method for arsenic ion in real water samples. Multiwall carbon nanotube (MWCNT) was immobilized with diethylenetriamine (DETA) and then used as solid phase adsorbent for the determination of trace level of arsenic ion by HSL-SDM method prior to analysis by hydride generation atomic absorption spectrometry. Reversibly hydrophobic-hydrophilic switchable of functionalized MWCNT can occur due to the exposing of carbon dioxide (CO₂) as anti-solvent trigger. The reversibly hydrophobic-hydrophilic switchable phenomena of immobilized MWCNT in the liquid-solid dispersive microextraction were checked by using FT-IR and SEM. The optimized analytical condition for arsenic ion analysis such as enrichment factor and limits of detection were obtained 83 and 3.05 ng L⁻¹, respectively. Accuracy of the developed HSL-SDM method was confirmed by the analysis of certified reference materials. Our developed HSL-SDM method was successfully applicable for measurements of arsenic ions in real water samples.

Endosulfan, an organochlorine pesticide, has been applied ubiquitously worldwide. However, endosulfan has been identified as a type of persistent organic pollutants (POPs), and its ecotoxicity has drawn attentions from scientists. The present study was implemented to examine the effects of endosulfan on the diversity and structure of soil microorganism communities. A control treatment and three concentrations (0.1, 1.0, and 10.0 mg/kg) were set up in laboratory experiments and sampled on days 7, 14, 21, and 28. The results revealed that the populations of bacteria and actinomycetes decreased significantly after 1.0 and 10.0 mg/kg treatments and that the soil microbial biomass carbon (MBC) was increased by endosulfan compared with the control. Terminal restriction fragment length polymorphism (T-RFLP) results revealed that the soil bacterial diversity was decreased by endosulfan and that the soil microbial community structure became unstable after endosulfan application. Moreover, the results of a 16S rRNA clone library revealed that the phyla Proteobacteria, Actinobacteria, Bacteroidetes, Spirochaetes, and Firmicutes showed an obvious advantage and closely relative. In conclusion, the results of the present study indicated that 0.1–10.0 mg/kg endosulfan showed obvious influences on the diversity and structure of the soil microbial community.