Effects of particle size on chemical speciation and bioavailability of copper to earthworms (Eisenia fetida) exposed to copper nanoparticles

To investigate the role of particle size on the oxidation, bioavailability, and adverse effects of manufactured Cu nanoparticles (NPs) in soils, we exposed the earthworm Eisenia ferida to a series of concentrations of commercially produced NPs labeled as 20- to 40-nm or < 100-nm Cu in artificial soil media. Effects on growth, mortality, reproduction, and expression of a variety of genes associated with metal homeostasis, general stress, and oxidative stress were measured. We also used X-ray absorption spectroscopy and scanning X-ray fluorescence microscopy to characterize changes in chemical speciation and spatial distribution of the NPs in soil media and earthworm tissues. Exposure concentrations of Cu NPs up to 65 mg kg(-1) caused no adverse effects on ecologically relevant endpoints. Increases in metallothionein expression occurred at concentrations exceeding 20 mg kg(-1) of Cu NPs and concentrations exceeding 10 mg kg(-1) of CuSO4. Based on the relationship of Cu tissue concentration to metallothionein expression level and the spatial distribution and chemical speciation of Cu in the tissues, we conclude that Cu ions and oxidized Cu NPs were taken up by the earthworms. This study suggests that oxidized Cu NPs may enter food chains from soil but that adverse effects in earthworms are likely to occur only at relatively high concentrations (> 65 mg Cu kg(-1) soil).     

An ecological perspective on nanomaterial impacts in the environment

Growing concerns over the potential for unintended, adverse consequences of engineered nanoparticles (ENPs) in the environment have generated new research initiatives focused on understanding the ecological effects of ENPs. Almost nothing is currently known about the fate and transport of ENPs in environmental waters, soils, and sediments or about the biological impacts of ENPs in natural environments, and the bulk of modern nanotoxicogical research is focused on highly controlled laboratory studies with single species in simple media. In this paper, we provide an ecological perspective on the current state of knowledge regarding the likely environmental impacts of nanomaterials and propose a strategy for making rapid progress in new research in ecological nanoscience.     

Quantifying nitrogen process rates in a constructed wetland using natural abundance stable isotope signatures and stable isotope amendment experiments

This study describes the spatial variability in nitrogen (N) transformation within a constructed wetland (CW) treating domestic effluent. Nitrogen cycling within the CW was driven by settlement and mineralization of particulate organic nitrogen and uptake of NO3-. The concentration of NO3- was found to decrease, as the delta15N-NO3- signature increased, as water flowed through the CW, allowing denitrification rates to be estimated on the basis of the degree of fractionation of delta15N-NO3-. Estimates of denitrification hinged on the determination of a net isotope effect (eta), which was influenced byprocesses that enrich or deplete 15NO3- (e.g., nitrification), as well as the rate constants associated with the different processes involved in denitrification (i.e., diffusion and enzyme activity). The influence of nitrification on eta was quantified; however, it remained unclear how eta varied due to variability in denitrification rate constants. A series of stable isotope amendment experiments was used to further constrain the value of eta and calculate rates of denitrification, and nitrification, within the wetland. The maximum calculated rate of denitrification was 956 +/- 187 micromol N m(-2) h(-1), and the maximum rate of nitrification was 182 +/- 28.9 micromol N m(-2) h(-1). Uptake of NO3- was quantitatively more important than denitrification throughoutthe wetland. Rates of N cycling varied spatially within thewetland, with denitrification dominating in the downstream deoxygenated region of the wetland. Studies that use fractionation of N to derive rate estimates must exercise caution when interpreting the net isotope effect. We suggest a sampling procedure for future natural abundance studies that may help improve the accuracy of N cycling rate estimates.     

Decontamination of water polluted by heavy metals with Taro (Colocasia esculenta) cultured in a hydroponic NFT system

The toxicity and bioaccumulation of two heavy metals—lead (Pb) and cadmium (Cd)—in a semi-aquatic plant, Colocasia esculenta (L. Schott), from a synthetic heavy metal solution were studied. Young plants of equal size were grown hydroponically in shallow raceways containing Hoagland medium amended with 20, 40, and 60 mg l^?1 of Pb and 2, 4, and 6 mg l^?1 of Cd. The medium containing heavy metals was allowed to flow through the raceways with a change in influent heavy metal solution on every 5th day. The experiment was continued for 20 days. A set of control raceways—one comprised of nutrient medium with heavy metal supplements, devoid of plants, and another with the plants and nutrient medium having no metal supplement—was also simultaneously run. Chlorosis in the leaves was the prominent toxicity symptom observed due to Pb and Cd on the test plants. A significant decrease in the relative growth, biomass productivity, and total chlorophyll content were noticed in the plants with an increase in concentration of metal supplement in the solution and exposure time. Both metals accumulated to higher concentrations in the roots than in shoots, suggesting that the metals were bound to the root cells and their translocation to the leaves was limited. The results of the 20-day-long experiments indicate that from a phytoremediation perspective, C. esculenta is a promising plant species for remediation of wastewater polluted with lower concentrations of Pb and Cd.     

High efficiencies in the electrochemical oxidation of an anthraquinonic dye with conductive-diamond anodes

Oxidation of anthraquinonic dye Acid Blue 62 by electrolysis with conductive-diamond electrodes is studied in this work. COD, TOC, and color have been selected to monitor the degradation of the molecule as a function of several operating inputs (current density, pH, temperature, and NaCl concentration). Results show that the electrochemical oxidation of this model of large molecules follows a first order kinetics in all the conditions assessed, and it does not depend on the pH and temperature. The occurrence of chloride ions in wastewaters increases the rate of color and COD removal as a consequence of the mediated oxidation promoted by the chlorinated oxidizing species. However, chloride occurrence does not have an influence on the mineralization rate. First-order kinetic-constants for color depletion (attack to chromophores groups), oxidation (COD removal), and mineralization (TOC removal) were found to depend on the current density and to increase significantly with its value. A single model was proposed to explain these changes in terms of the mediated oxidation processes. Rate of mineralization remained very close to that expected for a purely mass transfer-controlled process. This was explained assuming that mediated oxidation does not have a significant influence on the mineralization in spite it has some effect on intermediate oxidation stages. The efficiency of the oxidation was found to depend mainly on the concentration of COD being negligible the effect of the other inputs assessed except for the occurrence of chloride ions. Opposite, the efficiency of mineralization depends on concentration of TOC and current density and it did not depend on the chloride occurrence. This observation was found to have an important influence on the power required to remove a given percentage of the initial TOC or COD. To decrease COD efficiently, the occurrence of chloride in the solution is very important, while to remove TOC efficiently, it is more important to work at low current densities and chloride effect is negligible. Energy consumption could be decreased by folds using the proper conditions.     

Frequency of micronuclei and of other nuclear abnormalities in erythrocytes of the grey mullet from the Mondego,Douro and Ave estuaries—Portugal

Fish are bioindicators of water pollution, and an increased rate of their erythrocyte nuclear morphological abnormalities (ENMAs)—and particularly of erythrocyte micronuclei (EMN)—is used as a genotoxicity biomarker. Despite the potential value of ENMAs and MN, there is scarce information about fish captured in Iberian estuaries. This is the case of the Portuguese estuaries of the Mondego, Douro and Ave, suffering from different levels of environmental stress and where chemical surveys have been disclosing significant amounts of certain pollutants. So, the aim of this study was to evaluate genotoxicants impacts and infer about the exposure at those ecosystems, using the grey mullet (Mugil cephalus) as bioindicator and considering the type and frequency of nuclear abnormalities of erythrocytes as proxies of genotoxicity. Sampling of mullets was done throughout the year in the important Mondego, Douro and Ave River estuaries (centre and north-western Portugal). The fish (total n?=?242) were caught in campaigns made in spring–summer and autumn–winter, using nets or fishing rods. The sampled mullets were comparable between locations in terms of the basic biometric parameters. Blood smears were stained with Diff-Quik to assess the frequencies of six types of ENMAs and MN (given per 1,000 erythrocytes). Some basic water physicochemical parameters were recorded to search for fluctuations matching the ENMAs. Overall, the most frequent nucleus abnormality was the polymorphic type, sequentially followed by the blebbed/lobed/notched, segmented, kidney shaped, vacuolated, MN and binucleated. The total average frequency of the ENMAs ranged from 73?‰ in the Mondego to 108?‰ in the Ave. The polymorphic type was typically ≥50 % of the total ENMAs, averaging about 51?‰, when considering all three estuaries. The most serious lesion—the MN—in fish from Mondego and Douro had a similar frequency (≈0.38?‰), which was significantly lower than that in the Ave (0.75?‰). No significant seasonal differences existed as to the MN rates and seasonal differences existed almost only in the Douro, with the higher values in AW. In general, the pattern of ENMAs frequencies was unrelated with the water physicochemical parameters. Considering the data for both the total ENMAs and for each specific abnormality, and bearing in mind that values of MN in fish erythrocytes >0.3?‰ usually reflect pollution by genotoxicants, it is suggested that mullets were likely being chronically exposed to such compounds, even in the allegedly less polluted ecosystem (Mondego). Moreover, data supported the following pollution exposure gradient: Mondego?<?Douro?<?Ave. The scenario and inferences nicely agree with the published data from chemical monitoring.     

Correlations between PAH bioavailability,degrading bacteria,and soil characteristics during PAH biodegradation in five diffusely contaminated dissimilar soils

The natural biodegradation of seven polycyclic aromatic hydrocarbons (PAHs) by native microorganisms was studied in five soils from Normandy (France) from diffusely polluted areas, which can also pose a problem in terms of surfaces and amounts of contaminated soils. Bioavailability tests using cyclodextrin-based extractions were performed. The natural degradation of low molecular weight (LMW) PAHs was not strongly correlated to their bioavailability due to their sorption to geosorbents. Conversely, the very low degradation of high molecular weight (HMW) PAHs was partly correlated to their poor availability, due to their sorption on complexes of organic matter and kaolinites or smectites. A principal component analysis allowed us to distinguish between the respective degradation behaviors of LMW and HMW PAHs. LMW PAHs were degraded in less than 2–3 months and were strongly influenced by the relative percentage of phenanthrene-degrading bacteria over total bacteria in soils. HMW PAHs were not significantly degraded, not only because they were less bioavailable but also because of a lack of degrading microorganisms. Benzo[a]pyrene stood apart since it was partly degraded in acidic soils, probably because of a catabolic cooperation between bacteria and fungi.     

Identification and source apportionment of polycyclic aromatic hydrocarbons in ambient air particulate matter of Riyadh, Saudi Arabia

In an effort to assess the occurrence and sources of polycyclic aromatic hydrocarbons (PAHs) in the ambient air of Riyadh, Saudi Arabia, PM₁₀ samples were collected during December 2010. Diagnostic PAH concentration ratios were used as a tool to identify and characterize the PAH sources. The results reflect high PM₁₀ and PAH concentrations (particulate matter (PM)?=?270–1,270 μg/m³). The corresponding average PAH concentrations were in the range of 18?±?8 to 1,003?±?597 ng/m³ and the total concentrations (total PAHs (TPAHs) of 17 compounds) varied from 1,383 to 13,470 ng/m³ with an average of 5,871?±?2,830 ng/m³. The detection and quantification limits were 1–3 and 1–10 ng/ml, respectively, with a recovery range of 42–80 %. The ratio of the sum of the concentrations of the nine major non-alkylated compounds to the total (CPAHs/TPAHs) was 0.87?±?0.10, and other ratios were determined to apportion the PM sources. The PAHs found are characteristic for emissions from traffic with diesel being a predominant source.     

Forest Die-Back Modified Plankton Recovery from Acidic Stress

We examined long-term data on water chemistry of Lake Rachelsee (Germany) following the changes in acidic depositions in central Europe since 1980s. Despite gradual chemical recovery of Rachelsee, its biological recovery was delayed. In 1999, lake recovery was abruptly reversed by a coincident forest die-back, which resulted in elevated terrestrial export of nitrate and ionic aluminum lasting ~5 years. This re-acidification episode provided unique opportunity to study plankton recovery in the rapidly recovering lake water after the abrupt decline in nitrate leaching from the catchment. There were sudden changes both in lake water chemistry and in plankton biomass structure, such as decreased bacterial filaments, increased phytoplankton biomass, and rotifer abundance. The shift from dominance of heterotrophic to autotrophic organisms suggested their substantial release from severe phosphorus stress. Such a rapid change in plankton structure in a lake recovering from acidity has, to the best of our knowledge, not been previously documented.