Humic Acid Solution Research Articles

Influence of backwashing on the pore size of hollow fiber ultrafiltration membranes

Backwashing is a common method for fouling mitigation. However, its impact on the pore-size distribution (PSD) of hollow fiber (HF) membranes has not been studied to date. This study quantitatively assessed the effects of filtration and backwashing cycles on the PSDs of polyacrylonitrile (PAN) and polyvinylidene difluoride (PVDF) HF membranes by evapoporometry (EP) characterization. The membranes were characterized before and after repeated cycles of filtration and backwashing in the absence of any foulants, and for a feed solution of bentonite and humic acid that caused fouling both on and within the membrane pores. Firstly, in the absence of any foulants, backwashing caused the appearance of larger pores, the effect of which was greater for the rubbery PVDF membrane than for the glassy PAN membrane. Secondly, backwashing was more effective in removing the fouling within the larger pores, but could not remove all the deposits within the smaller pores, which provides a mechanistic explanation for the progressive increase in the transmembrane pressure (TMP) with each backwashing cycle. Thirdly, the membranes that did not undergo the 10th backwashing at the end of 10 cycles of filtration and backwashing displayed a marked shift of the PSD towards smaller pores due to the deposition of foulants on and within the largest pores, whereas those that underwent the 10 complete backwashing cycles achieved nearly complete recovery of the larger pores accompanied by an irreversible increase in the diameter of the largest pores. Fourthly, a higher backwashing flux led to similar average pore diameters of the fouled and virgin membranes due to the increased effectiveness in restoring the smallest pores, but the corresponding higher filtration flux negated the benefits due to a greater fouling extent particularly for the larger pores. Finally, in order to achieve the desired permeation and rejection properties, possible enlargement of the pores needs to be taken into consideration when choosing a ultrafiltration (UF) membrane and when specifying the backwashing intensity and protocol.

Photochemical aqueous mercury removal: effects of DOM and DO

Photochemical reactions between mercury (Hg) and dissolved organic matter were studied to understand what conditions would promote mercury volatilisation from solution. Prepared solutions of mercury (II) nitrate and humic acid (HA) (at different ratios) were exposed to 254-nm ultraviolet irradiation and a continuous purge with nitrogen, air or oxygen gas to create three different dissolved oxygen (DO) concentrations. As HA was introduced into the system with a nitrogen purge, the overall quantity of dissolved gaseous mercury after 60 min, and subsequent mercury removal, decreased. An analysis of variance indicated that there is only a 61% confidence level that the 1:10 and the 1:100 mercury–HA ratios are statistically different, suggesting that the decrease in mercury removal as HA concentration increased cannot be solely attributed to mercury binding with sulfur or other functional groups on the HA. Experiments indicated a positive correlation of HA oxidation as DO increased with an air and oxygen purge.

Uptake of nitrogen dioxide (NO2) on acidic aqueous humic acid (HA) solutions as a missing daytime nitrous acid (HONO) surface source

Uptake of nitrogen dioxide (NO2) on acidic aqueous humic acid (HA) solutions as a missing daytime nitrous acid (HONO) surface source

Investigation of UV/H2O2 pretreatment effects on humic acid fouling on polysulfone/titanium dioxide—And polysulfone/multiwall carbon nanotube—Nanocomposite ultrafiltration membranes

Membrane fouling is an important concern for membrane separation technology. Preparation of the feed before entering into the membrane and physicochemical modifications of membrane are both important approaches toward enhancing the permeability and separation in membrane processes. The present report combines both approaches. In terms of membrane characterization, scanning electron microscopy (SEM) images showed that the addition of titanium dioxide (TiO2) nanoparticles and multiwall carbon nanotube (MWCNT) resulted in increased pore numbers at the top surface and more interconnected pores in the porous membrane structure. The surface hydrophilicity and porosity of the PSF/TiO2 and PSF/MWCNT increased compared with pure PSF membranes. PSF/TiO2 nanocomposites showed just 10% flux decline and improved 95% flux recovery ratio (FRR%). UV/H2O2 pretreatment changed the physicochemical properties of humic acid (HA) aggregates by reducing the super‐micrometer size range (>1 μm) aggregates to a bimodal distribution of two submicrometer size ranges <1 μm (10–100 nm and 100–1000 nm) and increased the zeta potential of HA solution due to the production of new functional groups. The oxidation pretreatment alone improved flux decline at 120 min from 21% to 80% and increased the FRR from 58% to 80% for the pure PSF. The oxidative pretreatment also improved purification for the PSF/TiO2 nanocomposite membranes. The flux decline improved from 81% to 95% with only a slight improvement on the 94% FRR increasing to about 99% FRR. The FRR in the case of PSF/MWCNT actually declined with the pretreatment. The hybrid process of UV/H2O2 pretreatment and PSF/TiO2 nanocomposite membranes exhibited optimal permeability and antifouling properties. © 2016 American Institute of Chemical Engineers Environ Prog, 36: 27–37, 2017

Polysulfone/sulfonated polysulfone alloy membranes with an improved performance in processing mariculture wastewater

In this study, hydrophilic sulfonated polysulfone (SPSf) was synthesized via direct sulfonation of polysulfone (PSf) and efficiently implemented as a hydrophilic additive to prepare the polysulfone/sulfonated polysulfone alloy membranes. On a basis of a high compatibility of PSf and SPSf, the effect of SPSf content in the casting solution on the structure and separation performance of the membranes was investigated. It was demonstrated that the SPSf incorporation could significantly change the hydrophilicity, porosity, morphology and the charge characteristic of the resulting membranes. Compared the pure PSf membrane, the membrane with SPSf 15% yielded an improved hydrophilicity (contact angle was lowered by 23%), more porous structure and more negatively charged surface. It exhibited a high pure water permeability of 2521.6L/m2hMPa, excellent steady-state flux of 118.0L/m2h and HA rejection of 86.8% when filtrating 10mg/L humic acid (HA) solution in dead-end mode under an operating pressure of 0.08MPa. In a real treatment of mariculture wastewater for 8h, this membrane exhibited a significant improved steady-state permeation flux of 175.7L/m2h, which was increased by 144% and 26% compared to those of the homemade and commercial PSf membranes, without any deterioration of the permeate quality. The current investigation indicated that the PSf/SPSf alloy membranes held a promise for the real application.

The assessment of the suitability of synthetic humic acids in the production of cellular concrete

Investigated the suitability of the synthetic humic acids as foaming agent in the production of aerated non-autoclaved concrete. It is shown that in aqueous-alkaline solutions of humic acids tend to form hardened pins and can be recommended as surface-active substances in the production of aerated concrete.

Ultrafiltration membranes with ultrafast water transport tuned via different substrates

A series of self-supporting and substrate-supporting polysulfone (PSf) ultrafiltration (UF) membranes was fabricated using various substrates including glass plates, polypropylene random plates (PPR) and three kinds of non-woven fabrics (NWFs) via a typical phase inversion technique. Effects of the substrate hydrophilicity and structure on the membrane characteristics, morphology, separation and anti-fouling performance were systematically investigated. For self-supporting membranes, compared to glass plates, PPR facilitated more porous membranes and higher pure water permeability (Lp), permeation flux as well as anti-fouling property. NWFs density played an important role in the separation performance of the NWFs-supporting membranes. The resulting membrane with loosest NWFs exhibited an ultrahigh Lp of approximate 13,572L/m2h per MPa without any sacrifice of rejection, which significantly outperformed almost all the PSf membranes with Lp of 1000–7000L/m2h per MPa in literature. In addition, fouling filtration tests were performed in dead-end mode using humic acids solution followed by physical washing. More reversible rather than irreversible fouling was found in the NWFs-supporting membranes, especially for the membrane with loosest NWFs, indicating an improved anti-fouling property. This work endows the conventional PSf membranes with the outstanding properties such as ultrafast water transport and high flux recovery in an efficient and facile way.

Removal of Humic Acid in Water by Rice Hull Magnetic Activated Carbon and Magnetic Separation

We have newly developed a rice hull magnetic activated carbon (RH-MAC) and studied its adsorption property for humic acid from water and high-gradient magnetic separation (HGMS) characteristics. Rice hull was impregnated with an iron nitrate solution and heat-treated in both nitrogen and carbon dioxide atmosphere. In these processes, the rice hull changed to activated carbon that had a lot of mesopores and nanosize magnetite inside. Magnetization of RH-MAC increased with an increase in iron nitrate concentration during the process and reached 20.8 Am <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> /kg at 0.5 T. In the adsorption examination, it was able to adsorb humic acid effectively, and the removal ratio achieved 97.6% from a humic acid solution of 50 mg/L. In HGMS studies, we used the magnetic wire filter rounded on a magnet drum with 0.5-T permanent magnet and the slurry of RH-MAC concentration of 100 mg/L. Consequently, 99.4% of RH-MAC in the slurry of 2 L was captured in the magnetic filter at flow rates of 230 mL/min. These results show that this water purification system has higher removal ratio of humic acid than that for current advanced water treatments.

Effects of radical scavengers on humic acid removal by electron beam irradiation

Despite many efforts to remove humic acid (HA) in water resources, this problem is not overcome, especially in underdeveloped countries. The aim of this study is to evaluate the effects of inorganic anions (Cl−, HCO3-, SO42-, and NO3-) as radical scavenger on the efficacy of electron beam (EB) irradiation for the removal of HA from aqueous solutions. In this study, stock HA solution was prepared in alkaline condition; furthermore, different concentrations of anions were added to all HA samples. Here, the effect of different electron beam absorbed doses (1, 3, 6, 9, and 15 kGy) on the removal of HA is studied. HA concentration was measured using UV–vis spectrophotometer at 254 nm. The results showed that by increasing absorbed dose from 1 to 15 kGy, HA removal efficiency increased from 28.2 to 77.7%, respectively. While, by increasing different inorganic anion concentrations from 25 to 100 mg/L, the removal efficiency decreased. According to the results, nitrate has more inhibitory effect on the hydroxyl free radicals and HA removal efficiency in the presence of EB irradiation compared with chloride, bicarbonate, and sulfate anions. Furthermore, the kinetic model fitted the pseudo-second-order kinetics well.

Study on PVDF-TiO2 mixed-matrix membrane behaviour towards humic acid adsorption

Despite the expansion and successful application of membrane systems in water industry, membrane fouling which predominantly caused by the irreversible adsorption is still a critical problem. The objective of this work is to study the adsorptive behaviour of membrane for the removal of humic acid (HA). Apart of neat membrane that has very often been used in adsorption study, PVDF-TiO2 mixed-matrix membranes (MMMs) with varied titanium dioxide (TiO2) concentration (0.001g/L, 0.01g/L, and 0.1g/L) were explored in the present work. A dynamic stirring cell with continuous stirring for 24h at 250rpm was applied in this study. Different operating parameters such as initial HA solution concentration, calcium chloride (CaCl2) concentration, and HA solution pH were performed in this study. HA adsorption ratio in each single batch of experiment was determined by measuring the HA adsorbance as a function of time. The results, interpreted in terms of adsorption ratio (A/A0) yield severe HA adsorption at low pH and high initial HA solution concentration. In addition, it was found that, increased CaCl2 concentration reduces the electrostatic repulsion between HA aggregates and membrane surface, consequently appears to be more adapted to HA adsorption.

Release of 14C-labelled carbon nanotubes from polycarbonate composites

Waste disposal of carbon nanotube (CNT) containing products is expected to be the most important pathway for release of CNTs into the environment. In the present work, the use of radiolabelled CNTs (14C-CNT) for polycarbonate polymer nanocomposites with 1 wt% 14C-CNT content allowed for the first time to quantify and differentiate the CNT release according to the type of impact along the materials' ageing history. After an initial exposure of the nanocomposite by solar-like irradiation, further environmental impacts were applied to composite material. They aimed at mimicking disposal site conditions that may induce further ageing effects and CNT release. This study included shaking in water, rapid temperature changes, soaking in humic acid solution as well as waste water effluent, and, finally, gentle mechanical abrasion. All ageing impacts were applied sequentially, both on pristine (control) and on solar-irradiated nanocomposites. All experiments were accompanied by absolute quantification of radioactive release as well as chemical and morphological analyses of the nanocomposite surfaces using infra-red (IR) spectroscopy, X-ray photoelectron spectroscopy (XPS) and scanning electron microscopy (SEM). The morphological analysis showed that spectral irradiation can uncover CNT networks on the outer nanocomposite surface layers by polymer degradation. After having subjected the solar-irradiated nanocomposite to all studied disposal site effect, the total radioactive release was quantified to amount to 64 mg CNT/m2, whereas only 0.8 mg CNT/m2 were found for the un-irradiated control sample. Solar degradation of polymers was thus found to significantly increase the propensity of the studied polymer nanocomposites to release CNTs during ageing effects at the product's end-of-life typical for disposal sites.

The impact of natural and anthropogenic Dissolved Organic Carbon (DOC), and pH on the toxicity of triclosan to the crustacean Gammarus pulex (L.)

Regulatory ecotoxicology testing rarely accounts for the influence of natural water chemistry on the bioavailability and toxicity of a chemical. Therefore, this study identifies whether key omissions in relation to Dissolved Organic Carbon (DOC) and pH have an impact on measured effect concentrations (EC). Laboratory ecotoxicology tests were undertaken for the widely used antimicrobial compound triclosan, using adult Gammarus pulex (L.), a wild-type amphipod using synthetic fresh water, humic acid solutions and wastewater treatment works effluent. The toxicity of triclosan was tested at two different pHs of 7.3 and 8.4, with and without the addition of DOC and 24 and 48hour EC values with calculated 95% confidence intervals calculated. Toxicity tests undertaken at a pH above triclosan's pKa and in the presents of humic acid and effluent, containing 11 and 16mgL−1 mean DOC concentrations respectively, resulted in significantly decreased triclosan toxicity. This was most likely a result of varying triclosan speciation and complexation due to triclosan's pKa and high hydrophobicity controlling its bioavailability. The mean 48hour EC50 values varied between 0.75±0.45 and 1.93±0.12mgL−1 depending on conditions. These results suggest that standard ecotoxicology tests can cause inaccurate estimations of triclosan's bioavailability and subsequent toxicity in natural aquatic environments. These results highlight the need for further consideration regarding the role that water chemistry has on the toxicity of organic contaminants and how ambient environmental conditions are incorporated into the standard setting and consenting processes in the future.

Comparative study on the removal of humic acids from drinking water by anodic oxidation and electro-Fenton processes: Mineralization efficiency and modelling

The management of natural organic matter in drinking water treatment plants is an important matter of concern. It can generate toxic disinfection by-products as well as decrease the efficiency of membrane filtration and oxidation processes. This is the first study that investigates the use of anodic oxidation (AO) and electro-Fenton (EF) for the removal of humic acids (HAs) from aqueous solutions. Both sorption and catalytic oxidation of HAs are assessed and discussed. These electrochemical advanced oxidation processes are based on the in situ production of hydroxyl radicals, a highly oxidizing agent. The EF process involves the use of carbon-based porous materials (carbon sponge) as cathode, leading to the fast adsorption of hydrophobic HAs. It has been observed that adsorbed HAs can react with hydroxyl radical produced in the bulk from Fenton’s reaction. Then, the release in the solution of more hydrophilic by-products from the oxidation of HAs leads to a rebound effect of the organic matter concentration. Therefore, the AO process using non-carbonaceous cathode materials appears to be more suitable for HAs removal. Using boron-doped diamond anode and stainless steel cathode, the mineralization efficiency of a HAs solution (TOC0=16.2mgL−1) reached more than 99% after 7h of AO treatment with a current intensity of 1000mA. By considering both sorption and oxidation processes, this study proposed a new modelling approach to monitor TOC evolution during AO and EF processes.

Transformation of 17β-estradiol in humic acid solution by ε-MnO2 nanorods as probed by high-resolution mass spectrometry combined with 13C labeling

Steroidal estrogens (SEs), widespread in aquatic systems, have a potential to disrupt the endocrine system of wildlife species and humans. In our experiments, the performance of ε-MnO2 nanorods in transforming 17β-estradiol (E2) was investigated, and the effect of humic acid (HA) on the reaction behaviors was systematically characterized. Reconfiguration of humic molecules was also investigated by high-performance size exclusion chromatography (HPSEC). Results indicated that ε-MnO2 nanomaterials ensured efficient removal of E2 from the aqueous solution. The presence of HA hindered the transformation of E2, while enhanced the cross-coupling between E2 and humic molecules. In particular, we used a mixture of un-labeled E2 and 13C3-labeled E2 at a 1: 1 set ratio (w/w) to probe the reaction products via high-resolution mass spectrometry (HRMS). The combination of HRMS and 13C3-labeling revealed the intermediate products including estrone (E1), and hydroxylated, quinone-like, and ring-opened species, as well as E2 dimer and trimer. More importantly, possible cross-coupling products between E2 and HA were also identified. A reaction mechanism including two-electron oxidation and single-electron oxidation was proposed. The applied analytical approach using HRMS along with 13C3-labeling for reaction-product identification is crucial to understanding the role of HA in the transformation of SEs.

Chitosan as natural coagulant in hybrid coagulation-nanofiltration membrane process for water treatment

Water treatment industries are exploring the possibility to use environmental friendly chemicals and to discover the potential of advanced treatment technology in order to achieve sustainable development. Hybrid coagulation-membrane process has been introduced and proven to be a reliable water treatment process. In this study, the potential of chitosan as natural coagulant in hybrid coagulation-NF membrane process was studied. Three synthetic humic acid (HA) solutions with different ionic strength and composition will be used; without salt (Set 1), with NaCl only (Set 2), and with NaCl, CaCl2, and NaHCO3 (Set 3). Our findings indicated that gradual flux decline for Set 1 can be related to the continuous accumulation of neutral charged particles (pH 4.2) on the membrane surface. Formation of compact foulant layer due to further charge suppression of the foulants by dissolved ions (Set 2) resulted in severe membrane flux decline. When the pH of Set 1 and Set 2 supernatant solutions were increased to 7, fouling has been resolved due to the presence of strong electrostatic repulsion between the foulants and membrane. During the initial filtration process for Set 3, the flux has remained constant due to the strong repulsion between negatively charged foulants and membrane (pH 7). It was followed by severe flux decline which could be attributed to the effect of concentration polarization. Hence, this study highlighted that the impact of natural coagulant on the membrane process should be systematically studied in order to prevent unnecessary loss due to the incompatibility between both processes.

Development of polyamide forward osmosis membrane for humic acid removal

This paper presents synthesis and performance of polyamide forward osmosis (FO) membrane for humic acid (HA) removal. Three polyamide membranes were synthesized by reaction between m-phenylenediamine and trimesoyl chlorideat different reaction times (10, 30 and 60 s). Five different concentrations of sodium chloride draw solutions and 15 mg/L of HA solution as feed solution were tested in one hour to obtain water flux, reverse salt diffusion and HA removal. Reverse salt diffusion and HA removal were measured using conductivity and a UV–vis spectrometer, respectively. Overall, membranes modified for longer reaction times (30 and 60 s) exhibited good performance in term of moderate flux, higher HA removal and low reverse salt activity. In addition, it was found that higher concentration of draw solution leads to lower HA rejection and higher reverse salt diffusion, which indirectly represented overall membrane performance.

Efficient condensation of organic colloids in deep groundwater using surface-modified nanofiltration membranes under optimized hydrodynamic conditions

Abstract The transport of radionuclides by organic colloids in deep groundwater is one of the important issues for the geological disposal of high-level radioactive waste. Because of their low concentration, it is difficult to directly analyze organic colloids in deep groundwater. Hence, it is useful to utilize porous membranes for the condensation which can increase the concentration of organic colloids in groundwater physically without alteration of their properties, although some part of the components is lost by membrane fouling. In this study, hydrodynamic conditions were optimized, and surfaces of nanofiltration (NF) membranes were modified using a cationic phosphorylcholine polymer, poly(2-methacryloyloxyethyl phosphorylcholine-co-2-aminoethyl methacrylate) (p(MPC-co-AEMA)), for preventing membrane fouling and improving condensation efficiency. Aqueous solutions of humic acid or bovine serum albumin (BSA) were used as models of organic colloids, and they were condensed using a laboratory-scale cross-flow filtration apparatus equipped with a commercial sulfonated polyethersulfone NF membrane. The effects of hydrodynamic conditions, such as the applied transmembrane pressure (TMP) and stirring rate, and membrane surface modification on condensation efficiency were evaluated. A low TMP and high stirring rate effectively improved the recovery yield of humic acids and BSA. The membrane surface coated with p(MPC-co-AEMA) was significantly effective for preventing the decline in permeate flux, caused by fouling with BSA. Deep groundwater, obtained from a depth of 300 m at the Mizunami Underground Research Laboratory in Japan, was condensed. The recovery yield of the organic colloids in the deep groundwater condensation test at 5-fold condensation was improved from 62% to 92% by the optimized hydrodynamic conditions and membrane surface modification for prevention of membrane fouling. The composition of organic colloids in the condensates was analyzed using pyrolysis gas chromatography coupled with mass spectrometry.

An interlaboratory comparison on whole water samples

The European Water Framework Directive 2000/60/EC requires monitoring of organic priority pollutants in so-called whole water samples, i.e. in aqueous non-filtered samples that contain natural colloidal and suspended particulate matter. Colloids and suspended particles in the liquid phase constitute a challenge for sample homogeneity and stability. Within the joint research project ENV08 “Traceable measurements for monitoring critical pollutants under the European Water Framework Directive 2000/60/EC”, whole water test materials were developed by spiking defined amounts of aqueous slurries of ultra-finely milled contaminated soil or sediment and aqueous solutions of humic acid into a natural mineral water matrix. This paper presents the results of an European-wide interlaboratory comparison (ILC) using this type of test materials. Target analytes were tributyltin, polybrominated diphenyl ethers and polycyclic aromatic hydrocarbons in the ng/L concentration range. Results of the ILC indicate that the produced materials are sufficiently homogeneous and stable to serve as samples for, e.g. proficiency testing or method validation. To our knowledge, this is the first time that ready-to-use water materials with a defined amount of suspended particulate and colloidal matter have been applied as test samples in an interlaboratory exercise. These samples meet the requirements of the European Water Framework Directive. Previous proficiency testing schemes mainly employed filtered water samples fortified with a spike of the target analyte in a water-miscible organic solvent.

Trichloroethene hydrodechlorination by Pd-Fe bimetallic nanoparticles: Solute-induced catalyst deactivation analyzed by carbon isotope fractionation

Pd-Fe bimetallic nanoparticles (BNPs) have substantially higher reactivity for reductive dehalogenation of chlorinated ethenes (e.g., trichloroethylene, TCE) compared to monometallic zero-valent iron nanoparticles, yet the rapid deactivation of BNPs in groundwater matrices limits their large-scale use in field applications. In spite of this shortcoming, the causes of BNP deactivation have not been clearly delineated. Stable carbon isotope fractionation measurements and product distribution analysis were used in this study to investigate the mechanisms of Pd-Fe deactivation in the presence of common groundwater solutes. Based on the apparent TCE degradation rates and at a constant solute concentration of 5mM (except for humic acid, which was dosed at 20mg/L), Pd-Fe BNPs exposed to SO42−, HPO42−, and humic acid solutions showed moderate declines in TCE dechlorination rates. Aging the bimetallic particles in Cl−, SO32−, HCO3−, and NO3− solutions, however, resulted in excessive or complete loss of TCE dechlorination reactivity. Analyses of the isotope fractionation associated with TCE hydrodechlorination (εTCEHDC) as well as the yield of ethane over other dechlorination products suggest at least four distinctive causes of deactivation: (i) aging the BNPs in deionized water and humic acid induces surface passivation due to buildup of mineral or organic carbon deposits; (ii) SO32− and Cl− ions interact specifically with Pd sites and disable the catalyst functions; (iii) NO3− and HCO3− inhibits iron corrosion, thereby limiting the production of H2 as the precursor of reactive hydrogen species, and (iv) selective deactivation of surface sites involved in ethene hydrogenation was observed for BNPs aged in SO42− and HPO42− solutions. The findings suggest the Pd-on-Fe configuration of the bimetallic particles is susceptible to deactivation in a broader range of groundwater chemistry than previously expected.

Investigating the Uptake and Some Subcellular Effects of Manufactured Goethite Nanoparticles on Lumbriculus variegatus

Investigating the Uptake and Some Subcellular Effects of Manufactured Goethite Nanoparticles on Lumbriculus variegatus The aims of this work were: 1) to investigate whether the freshwater oligochaete Lumbriculus variegatus incorporates manufactured goethite nanoparticles (NPs) after an acute exposure; 2) to evaluate the influence of a solution of humic acids (HA) on the uptake of NPs; 3) to investigate the effects of these NPs on several biomarkers related to the generation of reactive oxygen species (ROS). NPs were analyzed by transmission electron microscopy. To evaluate the uptake, animals were exposed to 10 mg NPs L-1 for 48 h and then depurated for different periods (0;4;16, and 24 h). Iron concentrations were measured by atomic absorption spectrophotometry. Biomarker parameters were determined in oligochaetes exposed to a suspension containing 10 mg NPs L-1 for 48 h without depuration. Oligochaetes depurated for 4 h presented higher levels of Fe in their whole body tissues than control organisms. However, values returned to control levels when the oligochaetes were depurated for periods longer than 16 h, suggesting that organisms may transitorily incorporate the NPs in their digestive tract and/or superficially adsorbed them but they could not absorb the NPs. Exposures for periods longer than 48 h did not increase the Fe body burden. The presence of a 20 mg L-1 of humic acid solution prevented the NPs uptake. Several biomarker parameters related to the generation of reactive oxygen species were assessed. The activity of the enzyme superoxide dismutase and levels of total glutathione were higher in animals exposed to the NPs for 48 h than in controls. However, the catalase activity and the determination of the total scavenger capacity (TOSC assay) were not modified.The release of manufactured nanomaterials to the aquatic environment may elicit some subcellular responses even when the NPs are not absorbed by the organisms.