Nanosized titanium dioxide (nTiO2) is widely used in products, warranting its discharge from various sources into surface water bodies. However, nTiO2 co-occurs in surface waters with other contaminants, such as metals. Studies with nTiO2 and metals have indicated that the presence of natural organic matter (NOM) can mitigate their toxicity to aquatic organisms. In addition, "aging" of nTiO2 can affect toxicity. However, it is a research challenge, particularly when addressing sublethal responses from dietary exposure over multiple generations. We, therefore exposed the alga Desmodesmus subspicatus to nTiO2 (at concentrations of 0.0, 0.6 and 3.0 mg nTiO2/L) in nutrient medium aged for 0 or 3 days with copper (Cu) at concentrations of 0 and 116 µg Cu/L and with NOM at concentrations equivalent to 0 and 8 mg total organic carbon (TOC) per litre. Subsequently, the exposed alga was fed to Daphnia magna for 23 days over two generations and survival, reproduction and body length were assessed as endpoints of toxicity. In parallel, Cu accumulation and depuration from D. magna were measured. The results indicate that the reproduction of D. magna was the most sensitive parameter in this study, being reduced by 30% (at both parental (F0) and filial (F1) generations) and 50% (at F0 but not F1) due to the dietary Cu exposure in combination with nTiO2 for 0 and 3 days aging, respectively. There was no relationship between the effects observed on reproduction and Cu body burden in D. magna. Moreover, D. magna from the F1 generation showed an adaptive response to Cu in the treatment with 3.0 mg nTiO2/L aged for 3 days, potentially due to epigenetic inheritance. Unexpectedly, the presence of NOM hardly changed the observed effects, pointing towards the function of algal exopolymeric substances or intracellular organic matter, rendering the NOM irrelevant. Ultimately, the results indicate that the transferability of the impacts observed during the F0 to the responses in the F1 generation is challenging due to opposite effect directions. Additional mechanistic studies are needed to unravel this inconsistency in the responses between generations and to support the development of reliable effect models.

The major mechanisms controlling the fate of citrate-coated silver nanoparticles in the aquatic-terrestrial transition zone determined in a mesocosm study are aggregation, sedimentation, and enrichment in/on biota.

Besides their economic value, engineered inorganic nanoparticles (EINPs) may pose a risk for the integrity of ecosystems. Among EINPs, titanium dioxide (nTiO(2)) is frequently used and released into surface waters in the mu g range. There, nTiO(2) interacts with environmental factors, influencing its potential to cause adverse effects on aquatic life. Although factors like ultra violet (UV) light and natural organic matter (NOM) are considered as ubiquitous, their joint impact on nTiO(2)-induced toxicity is poorly understood. This study addressed the acute toxicity of nTiO(2) (P25; 0.00-64.00 mg/L; similar to 60 nm) at ambient UV light (0.00-5.20 WUVA/m(2)) and NOM levels (seaweed extract; 0.00-4.00 mg TOC/L), using the immobility of Daphnia magna as response variable. Confirming previous studies, effects caused by nTiO(2) were elevated with increasing UV radiation (up to similar to 280 fold) and mitigated by higher NOM levels (up to similar to 12 fold), possibly due to reduced reactive oxygen species (ROS; measured as (OH)-O-center dot radicals) formation at lower UV intensities. However, contradicting to former studies, nTiO(2)-mediated ROS formation was not proportional to increasing NOM levels: lower concentrations (0.04-0.40 mg TOC/L) slightly diminished, whereas a higher concentration (4.00 mg TOC/L) promoted the ROS quantity, irrespective of UV intensity. Measured ROS levels do not fully explain the observed nTiO(2)-induced toxicity, whereas increasing acetylcholinesterase and glutathione-S-transferase activities in daphnids (in presence of 8.00 mg/L nTiO(2) and elevated UV intensity) point towards neurotoxic and oxidative stress as a driver for the observed effects. Hence, despite higher (OH)-O-center dot levels in the treatments where 4.00 mg TOC/L were present, NOM was still capable of reducing nTiO(2)-induced stress and ultimately adverse effects in aquatic life. (C) 2019 Elsevier B.V. All rights reserved.

The increasing production of engineered inorganic nanoparticles (EINPs) elevates their release into aquatic ecosystems raising concerns about associated environmental risks. Numerous investigations indicate sediments as the final sink, facilitating the exposure of benthic species to EINPs. Although reports of sub-lethal EINP effects on benthic species are increasing, the importance of exposure pathways (either waterborne or dietary) is poorly understood. This study investigates the influence of two EINPs, namely titanium dioxide (nTiO(2)) and silver (nAg), on the benthic model organism Gammarus fossarum specifically addressing the relative relevance of these pathways. For each type of EINP an individual 30-day long bioassay was conducted, applying a two-factorial test design. The factors include the presence or absence of the EINPs (nTiO(2): similar to 80 nm, 4 mg/L or nAg: similar to 30 nm, 0.125 mg/L; n = 30) in the water phase (waterborne), combined with a preceding 6-day long aging of their diet (black alder leaves) also in presence or absence of the EINPs (dietary). Response variables were mortality, food consumption, feces production and energy assimilation. Additionally, the physiological fitness was examined using lipid content and dry weight of the organisms as measures. Results revealed a significantly reduced energy assimilation (up to similar to 30%) in G. fossarum induced by waterborne exposure towards nTiO(2). In contrast, the dietary exposure towards nAg significantly increased the organisms' energy assimilation (up to similar to 50%). Hence, exposure pathway dependent effects of EINPs cannot be generalized and remain particle specific resting upon their intrinsic properties affecting their potential to interact with the surrounding environment. As a result of the different properties of the EINPs used in this study, we clearly demonstrated variations in type and direction of observed effects in G. fossarum. The results of the present study are thus supporting current approaches for nanospecific grouping that might enable an enhanced accuracy in predicting EINP effects facilitating their environmental risk assessment.

Nanoparticle contaminants enter aquatic ecosystems and are transported along the stream network. Here, we demonstrate a novel pathway for the return of nanoparticles from aquatic to terrestrial ecosystems via cross-boundary subsidies. During their emergence, trichopteran caddisflies carried titanium dioxide and gold nanoparticles into their terrestrial life stages. Moreover, their emergence was delayed by ≤30 days, and their energy reserves were depleted by ≤25%. Based on worst case estimates, it is suggested that terrestrial predators, such as bats feeding on aquatic prey, may ingest up to three orders of magnitude higher gold levels than anticipated for humans. Additionally, terrestrial predator species may suffer from alterations in the temporal availability and nutritional quality of their prey. Considering the substantial transfer of insect biomass to terrestrial ecosystems, nanoparticles may decouple aquatic and terrestrial food webs with important (meta-)ecosystem level consequences.

Assessment of reaction pathways, kinetics and water toxicity during the photocatalytic degradation of glyphosate and myclobutanil pesticides has been performed in different aqueous matrices of increasing complexity, from the single pesticides to the mix of their commercial formulations. Using Aeroxide® TiO2-P25 as reference UV-A (Ultraviolet A) light photocatalyst, the ability of photocatalysis to degrade glyphosate and myclobutanil pesticides in water was evidenced independently of the aqueous matrix complexity, complete mineralization into CO2, phosphate and chloride ions being achieved. Further, an unusual volcano-like TOC evolution profile resulting from the proposed glyphosate degradation pathway was observed whatever the aqueous matrix. Increasing the water matrix complexity from single pesticides to the commercial formulation mix reduced the degradation kinetics and consequently extended the time necessary for complete mineralization but, did not influence the overall pesticide fate profiles. This behavior was associated to the competitive adsorption of the organic matter onto the catalyst and to the presence of ions and inorganic matter. The co-presence of glyphosate and to lesser extent of Roundup® formulation additives strongly impacted the myclobutanil fate profile, due to preferential adsorption/degradation of glyphosate. By contrast, despite the impact in the degradation pathway, the inorganic additives of the Systhane® formulation influenced less both the myclobutanil removal duration and the TOC removal than the glyphosate pesticide and its organic additives from Roundup® do. The treatment allowed for most of the cases a strong reduction of acute toxicity to aquatic invertebrate test organisms (D. magna) whatever the water matrix complexity, while the ecotoxicity was reduced by half for the complex formulation mix.

The impact of titanium dioxide nanoparticles (nano-TiO2) on the bioavailability of metals in aquatic filter-feeding organisms has rarely been investigated, especially in the presence of algae as a food source. In this study, we quantified the accumulation and subcellular distribution of arsenate (As (V)) in Daphnia magna in the presence of nano-TiO2 and a green alga (Scenedesmus obliquus) food source. Results showed that S. obliquus significantly increased the accumulation of total arsenic (As) and titanium (Ti) in D. magna. The presence of this food source increased As in metal-sensitive fractions (MSF) and as biologically detoxified metals (BDM), while it decreased Ti levels in MSF but increased levels as BDM. The difference in the subcellular distribution of As and Ti demonstrates the dissociation of As from nano-TiO2 during digestion at subcellular partitioning irrespective of food availability. In turn, the presence of algae was shown to increase metal-based toxicity in D. magna due to the transfer of As from BMD to MSF. Furthermore, S. obliquus significantly increased the concentration of As and Ti in soluble fractions, indicating that As and nano-TiO2 ingested by D. magna could be transferred more readily to their predators in the presence of S. obliquus. Our study shows the potential of algae to increase the toxicity and biomagnification of As (V) . Furthermore, it highlights food as an important factor in the toxicity assessment of nanomaterials and co-existing pollutants.

Only little information is available on combined effects of abiotic environmental factors on algal arsenate (As-v) metabolic biokinetics. Herein, we demonstrated the methods of using the Taguchi statistical method to investigate four environmental factors including As-v, nitrate (N), orthophosphate (P) and pH for their combined effects on algal growth and arsenic (As) uptake but also extracellular adsorption of Micro cystis aeruginosa, as well as As release from dead algal cells. Results showed that an increase of N facilitated M. aeruginosa growth and thus was the principal factor for the algal maximum specific growth rate (mu(max)). P was vital to As-v bioconcentration factor (BCF) and As partition coefficients (LogK(d)) released from deal algal cells. As-v impacted the extracellular As adsorption onto the algal cells, which thereby increased with increasing initial As-v level. The initial pH had an imperative effect on the As-v uptake (k(u)) and release rate (K-e) from the dead cells. Collectively, the condition of low P, high N and alkaline pH level was favorable toAs accumulation rate of living cells and restrictive to As release rate from dead cells of M. aeruginosa. The obtained information can pave a road for extensive understanding on efficient utilization of As bioremediation of algae in practical environment. Principal factors were identified on As-v metabolic biokinetics by Taguchi method. High N and pH but low P fasten As-v uptake and reduce As efflux from dead cells. As-v only as the main factor impacted As extracellular adsorption on algal cells. (C) 2018 The Author(s). Published by Elsevier B.V.

The production volume of engineered inorganic nanoparticles (EINP) successively increased over the last years. Once released into the natural environment, these particles may change their size and surface properties in interaction with other substances. This is expected to control their mobility and their impact on biochemical processes. However, the underlying processes are not fully understood yet. Transformation processes and long-term fate of citrate-coated silver nanoparticles (Ag NP) were investigated in an innovative floodplain mesocosm, which was run with river Rhine water and natural soil from an adjacent floodplain for 33 weeks. Flooding events were simulated every three weeks. The Ag NP with a concentration of 5 mg L-1 were continuously introduced into the water for three weeks followed by a three-week period without spiking. Every third week the ecotoxicological impact of Ag NP was determined by means of Gammarus mortality and feeding assays. At the end of the experiment, the total Ag concentrations were measured in profiles of the floodplain soil and the sediment as well as in algae that developed in the mesocosm. The total Ag concentration in the aquatic phase in the main zone as well as in the floodplain fluctuated according to the periodic Ag NP pulse. Further, significant amounts of Ag accumulated in algae (up to 4.7 mg g-1) and exposed leaves (up to 170 μg g-1). However, for the applied experimental conditions we did neither observed mortality nor sublethal effects on Gammarus feeding activity. More than 40 % of the Ag remained in the sediment of the main zone and 7 % were transported during flooding into the floodplain soil. Furthermore, 0.5 % of the Ag was still in the water phase. Most of the particles were immobilized in the top layer of the sediments and soil. Only very little transport in deeper soil layers was observed in the soil columns and sediment. Accumulation in algae, sediment, and soil is alarming for long-term environmental impact assessments and the long lifetime in the aqueous phase suggests long-range transport of Ag NP in rivers.

Leaf litter is a major source of carbon and energy for stream food webs, while both leaf-decomposing microorganisms and macroinvertebrate leaf shredders can be affected by fungicides. Despite the potential for season-long fungicide exposure for these organisms, however, such chronic exposures have not yet been considered. Using an artificial stream facility, effects of a chronic (lasting up to 8 wk) exposure to a mixture of 5 fungicides (sum concentration 20 mu g/L) on leaf-associated microorganisms and the key leaf shredder Gammarus fossarum were therefore assessed. While bacterial density and microorganism-mediated leaf decomposition remained unaltered, fungicide exposure reduced fungal biomass (<= 71%) on leaves from day 28 onward. Gammarids responded to the combined stress from consumption of fungicide-affected leaves and waterborne exposure with a reduced abundance (<= 18%), which triggered reductions in final population biomass (18%) and in the number of precopula pairs (<= 22%) but could not fully explain the decreased leaf consumption (19%), lipid content (<= 43%; going along with an altered composition of fatty acids), and juvenile production (35%). In contrast, fine particulate organic matter production and stream respiration were unaffected. Our results imply that long-term exposure of leaf-associated fungi and shredders toward fungicides may result in detrimental implications in stream food webs and impairments of detrital material fluxes. These findings render it important to understand decomposer communities' long-term adaptational capabilities to ensure that functional integrity is safeguarded. (C) 2017 SETAC.

The study provided a better understanding of arsenate bioavailability and toxicity associated with nano-TiO2 in saltwater environments.

Titanium dioxide nanoparticles (TiO2-NPs) adsorb co-occurring heavy metals in surface waters, modulating their toxicity for freshwater invertebrates. The processes triggering this interaction may be influenced by several environmental parameters; however, their relative importance remains unclear. The present study assessed the implications of aging on the joint acute toxicity of copper (Cu) and TiO2-NPs for Daphnia magna over a duration of up to 72h. The influences of aging duration as well as ionic strength, pH, and presence of different qualities of organic matter during aging were assessed. The results indicated that the presence of TiO2-NPs often reduced the Cu-induced toxicity for daphnids after aging (albeit with varying extent), which was displayed by up to 3-fold higher EC50 (50% effective concentration) values compared to the absence of TiO2-NPs. Moreover, the Cu speciation, influenced by the ionic composition and the pH as well as the presence of organic additives in the medium, strongly modulated the processes during aging, with partly limited implications of the aging duration on the ecotoxicological response of D. magna. Nonetheless, the present study underpins the potential of TiO2-NPs to modify toxicity induced by heavy metals in freshwater ecosystems under various environmental conditions. This pattern, however, needs further verification using heavy metal ions with differing properties in combination with further environmental factors, such as ultraviolet irradiation. Environ Toxicol Chem 2016;35:1766-1774. (c) 2015 SETAC

Nano-sized palladium (nano-Pd) is used in catalytic converters of automobiles, where it can be released into the environment by abrasion. Although these particles may subsequently be transported into surface water bodies, no data estimating their fate and toxicity in aquatic systems exists. This study characterized the particle size development of nano-Pd (advertised size ~12 nm; hydrodynamic size ~70 nm) in media with variable ionic strength (IS). Additionally, the particles’ acute toxicity for daphnids and chironomids was assessed. While nano-Pd agglomerated more quickly with increasing IS, it caused only marginal effects in both test species after 96 h of exposure. After 144 h of exposure, however, an EC50 value of 1.23 mg nano-Pd/L for daphnids was determined indicating effects over the long run. When considering the relatively low environmental concentration of elemental Pd in surface waters (usually ng/L), though, this study suggests only a low aquatic risk in response to nano-Pd.

CeO2 nanoparticles with various characteristics find an increasing number of applications in the electronic, medical, and other industries and are therefore likely released in the environment. This calls for investigations linking the physicochemical properties of these particles with their potential environmental impacts. In this study, CeO2 nanoparticle powders were prepared using three different precursors [Ce(NO3)3, CeCl3, and Ce(CH3COO)3] and annealing temperatures (300, 500, and 700 °C). This procedure resulted in nine different types of nanoparticles with differing size (5–90 nm), morphology, surface Ce3+/Ce4+ ratio, and slightly different crystal structures as characterized using transmission electron microscopy, dynamic light scattering, X-ray photoelectron spectroscopy, and X-ray diffraction measurements with Rietveld refinement. These CeO2 nanoparticles underwent toxicity testing at concentrations up to 64 mg L−1 using Daphnia magna. Toxic effects were observed for three particle types with EC50 values between 5 and 64 mg L−1. No clear correlation was observed between the physicochemical properties (size, shape, oxygen occupancy, Ce3+/Ce4+ ratio) of the nanoparticles and their toxicity. However, toxicity was correlated with the amount of Ce remaining suspended in the test medium after 24 h. This indicated that toxic effects may depend on the colloidal stability of CeO2 nanoparticles during the first day of exposure. Therefore, being readily suspended and remaining stable for several days in the aquatic media increases the likelihood that CeO2 nanoparticles will cause unwanted adverse effects.

Nanoparticles' fate is amongst other parameters determined by the quantity and quality of natural organic matter (NOM). Consequently, the ecotoxicity of nanoparticles is modified, while only little information is available on the NOM characteristics triggering this interplay. This study systematically examined how NOM quantity and quality influences the acute ecotoxicity of titanium dioxide nanoparticles (nTiO(2)) towards Daphnia magna. Therefore, two nTiO(2) products (A-100 and P25; approximate to 100nm) were investigated in combination with seven NOM types of variable quality at four levels each (up to 4.00mg total organic carbon/L). The results showed that - independent of the applied nTiO(2) product and NOM type - nTiO(2) ecotoxicity decreased up to a factor of>18 with increasing NOM concentration. More importantly, increasing levels of aromaticity and hydrophobicity of the NOM decreased the magnitude of toxic effects caused by nTiO(2), which was again independent of the nTiO(2) product tested. In the light of the ubiquitary presence of NOM, the ecotoxicological risk of nTiO(2) in surface waters with high NOM loads is likely moderate. However, interactions of nTiO(2) and NOM in combination with other natural or chemical stressors are not well-understood but seem to be fundamental for a reliable risk assessment of nanoparticles.

Aggregation status of Ag NPs in ecotoxicological test media is controlled by the Ca2+/Mg2+ ratio, presence of Cl− and Br− and NOM quality.

Although nanoparticles are increasingly investigated, their impact on the availability of food (i.e., algae) at the bottom of food chains remains unclear. It is, however, assumed that algae, which form heteroagglomerates with nanoparticles, sediment quickly limiting the availability of food for primary consumers such as Daphnia magna. As a consequence, it may be hypothesized that this scenario - in case of fundamental importance for the nanoparticles impact on primary consumers - induces a similar pattern in the life history strategy of daphnids relative to situations of food depletion. To test this hypothesis, the present study compared the life-history strategy of D. magna experiencing different degrees of food limitation as a consequence of variable algal density with daphnids fed with heteroagglomerates composed of algae and titanium dioxide nanoparticles (nTiO2). In contrast to the hypothesis, daphnids' body length, weight, and reproduction increased when fed with these heteroagglomerates, while the opposite pattern was observed under food limitation scenarios. Moreover, juvenile body mass, and partly length, was affected negatively irrespective of the scenarios. This suggests that daphnids experienced - besides a limitation in the food availability - additional stress when fed with heteroagglomerates composed of algae and nTiO2. Potential explanations include modifications in the nutritious quality of algae but also an early exposure of juveniles to nTiO2.

Summary Ecotoxicology is often criticised for its simplistic approach, which does not normally consider the complexity of field conditions. Simple laboratory experiments can still be useful, however, especially for assessing effects of emerging stressors such as nanoparticles, which exhibit fates, exposure profiles and modes of action substantially different from those of traditional chemicals. Here we argue that it is important to understand the potential effects of environmental conditions (e.g. UV radiation, dissolved organic matter, chemical stressors) on the fate and ecotoxicological potential of nanoparticles by using simple and well‐controlled experiments, while aiming to mimic realistic environmental conditions as closely as possible. The observation that increasingly complex test systems may yield lower effect thresholds for nanoparticles than standardised tests suggests that current approaches require modification. Specifically, research is encouraged on interactions among trophic levels, community composition and ecosystem and evolutionary processes, so that effects observed in complex environmental settings can be explained mechanistically. We highlight recent discoveries in ecotoxicology and ecology that suggest nanoparticle‐induced consequences on evolutionary and ecosystem processes as well as their potential transfer across ecosystem boundaries. These insights may encourage further research on nanoparticle effects informed by ecological theory.