Biological Surface Coating and Molting Inhibition as Mechanisms of TiO2 Nanoparticle Toxicity in Daphnia magna

The production and use of nanoparticles (NP) has steadily increased within the last decade; however, knowledge about risks of NP to human health and ecosystems is still scarce. Common knowledge concerning NP effects on freshwater organisms is largely limited to standard short-term (≤48 h) toxicity tests, which lack both NP fate characterization and an understanding of the mechanisms underlying toxicity. Employing slightly longer exposure times (72 to 96 h), we found that suspensions of nanosized (∼100 nm initial mean diameter) titanium dioxide (nTiO2) led to toxicity in Daphnia magna at nominal concentrations of 3.8 (72-h EC50) and 0.73 mg/L (96-h EC50). However, nTiO2 disappeared quickly from the ISO-medium water phase, resulting in toxicity levels as low as 0.24 mg/L (96-h EC50) based on measured concentrations. Moreover, we showed that nTiO2 (∼100 nm) is significantly more toxic than non-nanosized TiO2 (∼200 nm) prepared from the same stock suspension. Most importantly, we hypothesized a mechanistic chain of events for nTiO2 toxicity in D. magna that involves the coating of the organism surface with nTiO2 combined with a molting disruption. Neonate D. magna (≤6 h) exposed to 2 mg/L nTiO2 exhibited a “biological surface coating” that disappeared within 36 h, during which the first molting was successfully managed by 100% of the exposed organisms. Continued exposure up to 96 h led to a renewed formation of the surface coating and significantly reduced the molting rate to 10%, resulting in 90% mortality. Because coating of aquatic organisms by manmade NP might be ubiquitous in nature, this form of physical NP toxicity might result in widespread negative impacts on environmental health

Design, operation, and motion characteristics of a precise piezoelectric linear motor

Due to copyright restrictions, the access to the full text of this article is only available via subscription.This paper presents the design, operation, and motion characteristics of a precise piezoelectric motor for linear translation. The motor is compact, thermally stable, ultra-high vacuum compatible, and suitable for applications requiring fine resolution over millimeter-long travel ranges. Inside the motor, a translating alumina prism is symmetrically constrained within a stationary structure by a compliant suspension that preloads six shear-mode piezoelectric actuators against flat surfaces on the prism. A single step is achieved by sequentially sliding each piezoelectric actuator backward along the prism’s surfaces and then simultaneously moving all actuators forward. Many steps are repeated at 60 Hz for longer translations. Experiments indicate that: the step size is adjustable between 5 nm and 225 nm, the motor can reach speeds of 13.5 View the MathML sourcem/s, the step size is highly uniform with a standard deviation of about 1.2 nm, error motion in the direction orthogonal to the translation is about 800 nm peak-to-valley, and the thermal stability is better than 40 nm/ °C.NS

Three-Dimensional Analysis of the Swimming Behavior of <i>Daphnia magna</i> Exposed to Nanosized Titanium Dioxide

<div><p>Due to their surface characteristics, nanosized titanium dioxide particles (nTiO₂) tend to adhere to biological surfaces and we thus hypothesize that they may alter the swimming performance and behavior of motile aquatic organisms. However, no suitable approaches to address these impairments in swimming behavior as a result of nanoparticle exposure are available. Water fleas <i>Daphnia magna</i> exposed to 5 and 20 mg/L nTiO₂ (61 nm; polydispersity index: 0.157 in 17.46 mg/L stock suspension) for 96 h showed a significantly (<i>p</i><0.05) reduced growth rate compared to a 1-mg/L treatment and the control. Using three-dimensional video observations of swimming trajectories, we observed a treatment-dependent swarming of <i>D. magna</i> in the center of the test vessels during the initial phase of the exposure period. Ensemble mean swimming velocities increased with increasing body length of <i>D. magna</i>, but were significantly reduced in comparison to the control in all treatments after 96 h of exposure. Spectral analysis of swimming velocities revealed that high-frequency variance, which we consider as a measure of swimming activity, was significantly reduced in the 5- and 20-mg/L treatments. The results highlight the potential of detailed swimming analysis of <i>D. magna</i> for the evaluation of sub-lethal mechanical stress mechanisms resulting from biological surface coating and thus for evaluating the effects of nanoparticles in the aquatic environment.</p></div

Exemplary swimming trajectories.

<p>Simultaneously moving daphnids during measurements of (A) <i>C</i>, (B) <i>T</i>₁, (C) <i>T</i>₅ and (D) <i>T</i>₂₀ at <i>t</i>₀, i.e., directly after application and E group-wise averaged minimal distance to a solid boundary at <i>t</i>₀ (circles and solid line connecting the distances of the treatment measurements, error bars denote standard deviations). (F) Swimming trajectories of <i>T</i>₂₀ at <i>t</i>₂₄. Values in the upper right corners of subplots (A-D) and (F) denote the percentage of residence in vicinity (≤ 5 mm) to the boundaries of the experimental tank.</p

Variance preserving power spectral density.

<p>Presentation of <i>PSD ^. f</i> of the vertical swimming velocity component of (A) <i>C</i> and (B) <i>T</i>₅ at <i>t</i>₉₆. Grey error bars show the standard deviation of individual velocity spectra.</p

Ensemble mean swimming velocities.

<p> of <i>Daphnia magna</i> (A) at times after application and (B) in relation to corresponding body lengths. Error bars are omitted for the sake of clarity. Please refer to <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0080960#pone.0080960.s004" target="_blank">Table S2</a> for standard deviations. Velocities significantly different (<i>p</i><0.05) from the control are surrounded by circles. Please note that only velocities of similar body lengths (1.22 mm for <i>C</i>, 1.44 mm for <i>T</i>₅ and 1.23 mm for <i>T</i>₂₀) had been tested with respect to significant differences. Linear regression for <i>C</i> with d<i>v</i>/d<i>L</i> = 4.4 1/s (black line, <i>r</i>² = 0.87) and for <i>T</i>₁ with d<i>v</i>/d<i>L</i> = 1.2 1/s (grey line, <i>r</i>² = 0.3).</p

The Second Young Environmental Scientist (YES) meeting 2011 at RWTH Aachen University - environmental challenges in a changing world

This article reports on the second Young Environmental Scientists Meeting that was hosted from 28 February to 2 March 2011 by the Institute for Environmental Research at RWTH Aachen University, Germany. This extraordinary meeting was again initiated and organized by the Student Advisory Council under the umbrella of Society of Environmental Toxicology and Chemistry Europe. A movie about the meeting and the abstracts of poster and platform presentations are freely available as supplemental material of this article

Mean body length and mean sinking velocity of <i>Daphnia magna.</i>

<p>(A) Body length in control group (<i>C</i>), treatment with 1 mg/L nTiO₂ (<i>T</i>₁), treatment with 5 mg/L nTiO₂ (<i>T</i>₅) and treatment with 20 mg/L nTiO₂ (<i>T</i>₂₀). Please note that ‘Time’ denotes the time of exposure and <i>C</i> (first record) and a second control <i>C*</i> (last record) cover each record period (approx. 3 h). Circles around the symbols denote significant differences (<i>p</i><0.05) to <i>C</i>. Error bars are omitted for the sake of clarity. Please refer to <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0080960#pone.0080960.s003" target="_blank">Table S1</a> for standard deviations. (B) Mean sinking velocity vs. mean <i>Daphnia</i> body length and sinking veloicties estimated using Stokes’ law using organisms densities of 1.007 g/cm³ (black line) and 1.003 g/cm³ (grey line), respectively.</p