The potential of TiO2 nanoparticles as carriers for cadmium uptake in Lumbriculus variegatus and Daphnia magna

Bioavailability of cadmium and biochemical responses on the freshwater bivalve Corbicula fluminea--the role of TiO₂ nanoparticles

The increasing and widespread applications of TiO2 engineered nanoparticles (nTiO2) led to the release of these materials into aquatic environments and consequently a change on the assessment of the environmental risk of trace metals. In this work, the role of two commercial nTiO2 with distinct crystalline phases and sizes (nTiO2-P25: 80% anatase+20% rutile, d=20nm; nTiO2-NA: 100% anatase, d=5 nm; 0.1 and 1.0 mg L(-1)) on Cd (112 μg L(-1)) speciation, biouptake and toxicity for the freshwater bivalve Corbicula fluminea was evaluated. The electroanalytical technique 'absence of gradients and Nernstian equilibrium stripping (AGNES)' was used to quantify the free Cd concentrations in the exposure medium in presence of both particles. Despite ca. 30-40% decrease of free Cd in the medium in presence of nTiO2, Cd uptake by C. fluminea was similar in the absence and presence of either of the particles. Superoxide dismutase and glutathione-S-transferase activities remained unchanged for Cd in absence and presence of nTiO2, whereas a significant increase of the catalase activity was obtained at the third day for Cd in presence of both nTiO2. Despite lipid peroxidation data shows that the presence of both nTiO2 seems to exert cells damage, a more quantitative description is not possible with the obtained data. The lack of clear-cut responses by the studied biomarkers, even when only in presence of Cd, do not allow insights into the effect of the presence of nTiO2 on the Cd toxicity to the bivalves. Notwithstanding, morphological changes in the digestive gland were clearly obtained in the presence of Cd, nTiO2 and Cd+nTiO2 indicating an inflammatory response.

Co-exposure to n-TiO2 and Cd2+ results in interactive effects on biomarker responses but not in increased toxicity in the marine bivalve M. galloprovincialis

The increasing production of nanoparticles (NPs) will lead to their release into the aquatic environment, where they could modify the bioavailability/bioconcentration and consequent biological impact of other contaminants. Interactive effects of n-TiO2, one of the most widespread NP type, and Cd(2+), a common heavy metal pollutant, have been described in freshwater species, whereas no information is available in marine organisms. In this work, the effects of co-exposure to n-TiO2 and Cd(2+) were investigated in the marine bivalve Mytilus galloprovincialis. Experimental conditions (100 μg/L, 96 h), were chosen in order to induce early but measurable stress responses (biomarkers) without toxicity. Several biomarkers, from molecular to tissue level, were measured in hemolymph and digestive gland; the effects on embryo development were also evaluated. In hemolymph, Cd(2+) abolished the increase in immune parameters induced by n-TiO2 (NO production and lysozyme activity). In the digestive gland, distinct interactive effects of n-TiO2 and Cd(2+) were observed on different lysosomal biomarkers (lysosomal membrane stability, lipid accumulation and lysosome/cytoplasm volume ratio) and transcription of the immune genes lysozyme and toll-like receptor (TLR). However, n-TiO2 did not affect specific metal-induced responses (metallothionein induction) and tissue metal accumulation. Cd(2+) alone, but not in combination with n-TiO2, affected embryo development. The interactive effects observed on different biomarkers were not apparently due to differences in bioavailability/bioaccumulation of Cd(2+) in the presence of n-TiO2 agglomerates; these effects may result from interactions of either contaminant with both common and distinct targets/mechanisms of action at different levels of biological organization. Overall, the results indicate that co-exposure to n-TiO2 and Cd(2+) did not result in increased adverse effects in M. galloprovincialis. These data underline the need for further knowledge on the potential interactions of NPs with existing contaminants in marine organisms.

Uptake and depuration of gold nanoparticles in Daphnia magna

This study presents a series of short-term studies (total duration 48 h) of uptake and depuration of engineered nanoparticles (ENP) in neonate Daphnia magna. Gold nanoparticles (Au NP) were used to study the influence of size, stabilizing agent and feeding on uptake and depuration kinetics and animal body burdens. 10 and 30 nm Au NP with different stabilizing agents [citrate (CIT) and mercaptoundecanoic acid (MUDA)] were tested in concentrations around 0.5 mg Au/L. Fast initial uptake was observed for all studied Au NP, with CIT stabilized Au NP showing similar rates independent of size and MUDA showing increased uptake for the smaller Au NP (MUDA 10 nm > CIT 10 nm, 30 nm > MUDA 30 nm). However, upon transfer to clean media no clear trend on depuration rates was found in terms of stabilizing agent or size. Independent of stabilizing agent, 10 nm Au NP resulted in higher residual whole-animal body burdens after 24 h depuration than 30 nm Au NP with residual body burdens about one order of magnitude higher of animals exposed to 10 nm Au NP. The presence of food (P. subcapitata) did not significantly affect the body burden after 24 h of exposure, but depuration was increased. While food addition is not necessary to ensure D. magna survival in the presented short-term test design, the influence of food on uptake and depuration kinetics is essential to consider in long term studies of ENP where food addition is necessary. This study demonstrates the feasibility of a short-term test design to assess the uptake and depuration of ENP in D. magna. The findings underlines that the assumptions behind the traditional way of quantifying bioconcentration are not fulfilled when ENPs are studied.

Interactive effects of n-TiO2 and 2,3,7,8-TCDD on the marine bivalve Mytilus galloprovincialis

Despite the growing concern over the potential biological impact of nanoparticles (NPs) in the aquatic environment, little is known about their interactions with other pollutants. The bivalve Mytilus sp, largely utilized as a sentinel for marine contamination, has been shown to represent a significant target for different types of NP, including n-TiO2, one of the most widespread in use. In this work, the possible interactive effects of n-TiO2 and 2,3,7,8-TCDD, chosen as models of NP and organic contaminant, respectively, were investigated in Mytilus galloprovincialis. In vitro experiments with n-TiO2 and TCDD, alone and in combination, were carried out in different conditions (concentrations and times of exposure), depending on the target (hemocytes, gill cells and biopsies) and the endpoint measured. Mussels were also exposed in vivo to n-TiO2 (100 μg L(-1)) or to TCDD (0.25 μg L(-1)), alone and in combination, for 96 h. A wide range of biomarkers, from molecular to tissue level, were measured: lysosomal membrane stability and phagocytosis in hemocytes, ATP-binding cassette efflux transporters in gills (gene transcription and efflux activity), several biomarkers of genotoxicity in gill and digestive cells (DNA damage, random amplified polymorphic DNA-RAPD changes), lysosomal biomarkers and transcription of selected genes in the digestive gland. The results demonstrate that n-TiO2 and TCDD can exert synergistic or antagonistic effects, depending on experimental condition, cell/tissue and type of measured response. Some of these interactions may result from a significant increase in TCDD accumulation in whole mussel organisms in the presence of n-TiO2, indicating a Trojan horse effect. The results represent the most extensive data obtained so far on the sub-lethal effects of NPs and organic contaminants in aquatic organisms. Moreover, these data extend the knowledge on the molecular and cellular targets of NPs in bivalves.

Modification of metal bioaccumulation and toxicity in Daphnia magna by titanium dioxide nanoparticles

Titanium dioxide (TiO2) nanoparticles are widely used in water treatments, yet their influences on other contaminants in the water are not well studied. In this study, the aqueous uptake, assimilation efficiency, and toxicity of two ionic metals (cadmium-Cd, and zinc-Zn) in a freshwater zooplankton, Daphnia magna, were investigated following 2 days pre-exposure to nano-TiO2. Pre-exposure to 1 mg/L nano-TiO2 resulted in a significant increase in Cd and Zn uptake from the dissolved phase. After the nano-TiO2 in the guts were cleared, the uptake rates immediately recovered to the normal levels. Concurrent measurements of reactive oxygen species (ROS) and metallothioneins (MTs) suggested that the increased metal uptake was mainly due to the increased number of binding sites provided by nano-TiO2 presented in the guts. Consistently, pre-exposure to nano-TiO2 increased the toxicity of aqueous Cd and Zn due to enhanced uptake. Our study provides the evidence that nano-TiO2 in the guts of animals could increase the uptake and toxicity of other contaminants.

The combined effect of dissolved organic carbon and salinity on the bioaccumulation of copper in marine mussel larvae

Larvae of Mytilus spp. are among the most Cu sensitive marine species. In this study we assessed the combined effect of salinity and dissolved organic carbon (DOC) on Cu accumulation on mussel larvae. Larvae were exposed for 48 h to three Cu concentrations in each of nine salinity/DOC treatments. Synchrotron radiation X-ray fluorescence was used to determine the Cu concentration in 36 individual larvae with a spatial resolution of 10 × 10 μm. Cu body burden concentrations varied between 1.1 and 27.6 μg/g DW larvae across all treatments and Cu was homogeneously distributed at this spatial resolution level. Our results indicate decreasing Cu accumulation with increasing DOC concentrations which can be explained by an increase in Cu complexation. In contrast, salinity had a nonlinear effect on Cu. This cannot be explained by copper speciation or competition processes and suggests a salinity-induced alteration in physiology.

Do natural rubber latex condoms pose a risk to aquatic systems?

The presence and potential adverse effects of plastic-polymers in the environment are receiving increasing attention in the popular and scientific press. However, quantifying emissions, exposure and effects of these materials remains a challenge. This paper describes the application of a questionnaire survey to quantify emissions of condom material from the domestic household to the sewage waste stream. Condoms are an important mainstay for birth control and the reduction of sexually transmitted infections. Survey participants were estimated to flush condoms down the toilet 2.96% of the time, and emissions were calculated as 0.99 mg of condom material per person per day. Using information on screening efficiencies at sewage treatment plants, the questionnaire data was combined with a GIS-based water quality model (LF2000-WQX) to predicted environmental concentrations (PEC) in a UK river basin catchment. Annual average PECs of condom material were 0.08-0.2 μg L(-1), under the model scenario used. To put these PECs into context, rubber latex condom material was degraded in outdoor microcosms. This resulted in the formation of a complex mixture of substances including chemical degradation products and particles in the nano range. The direct effects of the degradation mixture were investigated using two freshwater organisms with different life cycle traits, the water column crustacean Daphnia magna and the sediment-dwelling larval of Chironomus riparius. Ecotoxicity tests investigated both acute and chronic endpoints and were shown to exhibit no toxic effects. This precluded the derivation of a genuine no-effect concentration. Hence, the results suggest that limited risk to invertebrates is associated with latex condom degradation products to the organisms tested. Future studies should extend this risk framework to assess risks of condoms to other taxonomic groups as well as the risks of other polymer materials.

Toxic effects of the interaction of titanium dioxide nanoparticles with chemicals or physical factors

Due to their chemical stability and nonallergic, nonirritant, and ultraviolet protective properties, titanium dioxide (TiO2) nanoparticles (NPs) have been widely used in industries such as electronics, optics, and material sciences, as well as architecture, medicine, and pharmacology. However, increasing concerns have been raised in regards to its ecotoxicity and toxicity on the aquatic environment as well as to humans. Although insights have been gained into the effects of TiO2 NPs on susceptible biological systems, there is still much ground to be covered, particularly in respect of our knowledge of the effects of the interaction of TiO2 NPs with other chemicals or physical factors. Studies suggest that interactions of TiO2 NPs with other chemicals or physical factors may result in an increase in toxicity or adverse effects. This review highlights recent progress in the study of the interactive effects of TiO2 NPs with other chemicals or physical factors.

The influence of ZnO and TiO2 nanoparticles on the toxicity of sewage sludges

More and more often sewage sludges become the place of deposition of nanoparticles (NPs), the use of which in consumer products is increasing. In turn, the increasing amount of sewage sludges enforces the need for their utilization (e.g. through the application of sludges to the soil). Therefore, the presence of NPs in sewage sludges may create a new threat to the environment. Thus it becomes important to perform evaluation of the toxicity of sewage sludges in the context of their content of NPs. The objective of the study was to estimate the effect of nanoparticles of ZnO (nano-ZnO) and TiO2 (nano-TiO2) and their bulk counterparts (bZnO and bTiO2) on the toxicity of sewage sludges in relation to selected organisms (plants – Lepidium sativum and Sinapis alba, and microorganisms – Vibrio fischeri and 11 different strains from Microbial Assay for Risk Assessment – MARA). The study also involved the estimation of other factors that may have an effect on the phytotoxicity of NPs in sewage sludge: the size of the particles, the dose of the sewage sludge, the time of NP–sewage sludge contact and light conditions. The effect of both nano-ZnO and nano-TiO2 on the toxicity of the sludges is dependent on the kind of NPs and their concentration. Sludges containing NPs displayed a different level of toxicity from their bulk counterparts. All of the factors estimated (size of particles, dose of sludge, contact time and light conditions) had a significant effect on the phytotoxicity of NPs which was dependent both on the kind of the NPs and on that of the sewage sludge. Estimation of the leachate toxicity indicated a greater sensitivity of plants to the presence of NPs as compared to the sensitivity of microorganisms. Leachates caused a greater reduction of bioluminescence of V. fischeri in the presence of nano-TiO2 than nano-ZnO. Nano-ZnO caused a reduction of the toxicity of the sewage sludge leachates.