Dispersion and sedimentation of titanium dioxide nanoparticles in freshwater algae and daphnia aquatic culture media in the presence of arsenate

<p>Little information is available on Titanium dioxide nanoparticles (nTiO₂) behavior in different culture media for aquatic organisms. This study aimed to accurately evaluate nTiO₂ dispersion and sedimentation in common freshwater algae (BG-11) and daphnia aquatic (SM7) culture media. We additionally investigated potential mechanisms of nTiO₂ stability under arsenate influence. Results showed that high ionic strength in culture media was probably a key reason for the acute nTiO₂ agglomeration found. Additionally, the hydrodynamic size of nTiO₂ suspension in the presence of arsenate was significantly larger, increasing with arsenate concentration in ultrapure water. Conversely, the hydrodynamic size in BG-11 and SM7 decreased with arsenate concentration. The nTiO₂ sedimentation rate increased significantly with arsenate concentration in ultrapure water but significantly decreased in BG-11 and SM7 culture media. Many nTiO₂ remained suspended after initial rapid sedimentation and the slight sedimentation that occurred in the subsequent 24 h, suggesting that algae and daphnia within the water column will be exposed to small nanoparticle aggregates for a long period of time. Such nTiO₂ behavior, especially in the presence of arsenate, requires more consideration than the different toxicological results reported in literature.</p

Proportional arsenic loss from <i>M. aeruginosa</i> after 24 h arsenate or arsenite exposure under the different phosphate regimes employed.

<p>Each symbol denotes arsenic concentration (from which background concentrations were subtracted) as a percentage of the intracellular concentration at 0 d (means ± SD, n = 3). Arsenic loss over a period of 13 d after a period of 24 h individual exposure to 10 µM arsenate and arsenite under +P or −P treatments is shown in (a) and (b), respectively (arsenic loss over 12 h is shown in the corresponding embedded box).</p

Cellular partitioning in +P or −P media.

<p>Cellular partitioning in +P or −P media.</p

Changes in concentrations of different arsenic species in media during the 13 d depuration period under −P treatments after (a) arsenate or (b) arsenite pre-exposure.

<p>Each point is represented as means ± SD (n = 3).</p

Total arsenic concentrations in solutions for the limited (12 h) and extended (13 d) depuration periods after 24 h individual 10 µM arsenate and arsenite pre-exposures.

<p>(a) and (b) represent +P treatments while (c) and (d) represent −P treatments. Each point is represented as means ± SD (n = 3).</p

Fraction of arsenite in <i>M. aeruginosa</i> over the limited (12 h) and extended (13 d) depuration periods after 24 h of 10 µM individual arsenate and arsenite pre-exposure.

<p>The arsenite fraction under +P treatments is shown in (a) and (b). Correspondingly, the arsenite fraction under −P treatments is shown in (c) and (d). Data are means ± SD (n = 3).</p

Arsenate Accumulation, Distribution, and Toxicity Associated with Titanium Dioxide Nanoparticles in <i>Daphnia magna</i>

Titanium dioxide nanoparticles (nano-TiO₂) are widely used in consumer products. Nano-TiO₂ dispersion could, however, interact with metals and modify their behavior and bioavailability in aquatic environments. In this study, we characterized and examined arsenate (As­(V)) accumulation, distribution, and toxicity in Daphnia magna in the presence of nano-TiO₂. Nano-TiO₂ acts as a positive carrier, significantly facilitating D. magna’s ability to uptake As­(V). As nano-TiO₂ concentrations increased from 2 to 20 mg-Ti/L, total <i>As</i> increased by a factor of 2.3 to 9.8 compared to the uptake from the dissolved phase. This is also supported by significant correlations between arsenic (<i>As</i>) and titanium (<i>Ti</i>) signal intensities at concentrations of 2.0 mg-Ti/L nano-TiO₂ (<i>R</i> = 0.676, <i>P</i> < 0.01) and 20.0 mg-Ti/L nano-TiO₂ (<i>R</i> = 0.776, <i>P</i> < 0.01), as determined by LA-ICP-MS. Even though <i>As</i> accumulation increased with increasing nano-TiO₂ concentrations in D. magna, As­(V) toxicity associated with nano-TiO₂ exhibited a dual effect. Compared to the control, the increased <i>As</i> was mainly distributed in BDM (biologically detoxified metal), but <i>Ti</i> was mainly distributed in MSF (metal-sensitive fractions) with increasing nano-TiO₂ levels. Differences in subcellular distribution demonstrated that adsorbed As­(V) carried by nano-TiO₂ could dissociate itself and be transported separately, which results in increased toxicity at higher nano-TiO₂ concentrations. Decreased As­(V) toxicity associated with lower nano-TiO₂ concentrations results from unaffected <i>As</i> levels in MSFs (when compared to the control), where several <i>As</i> components continued to be adsorbed by nano-TiO₂. Therefore, more attention should be paid to the potential influence of nano-TiO₂ on bioavailability and toxicity of cocontaminants

Impact of urbanization on nutrients and heavy metal pollution of Napahai Wetland, Shangri-La County, China

<div><p>This study investigated the nutrients and heavy metal contents in water body and sediment of the Napahai Wetland during summer through fluorescence spectroscopy and inductively coupled plasma optical emission spectrometer analysis. Results indicated that most of the heavy metal contents in water body are derived from municipal sewage when the stream passes through the town center. The primary organic compounds in the water body of the Nachi River and the Napahai Wetland were hydrophobic acid, fulvic acid, and aromatic protein-like compounds. Cr, Ni, Cd, As, Pb, and V contents in wetland sediments significantly differ from sampling sites and depths, and varied in the following order: V > Cr > Ni > Pb > As > Cd. Principal component analysis showed that the distribution of heavy metals was primarily affected by urbanization and secondarily affected by other abiotic factors.</p></div