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

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

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

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

Diastereoisomer- and Enantiomer-Specific Accumulation, Depuration, and Bioisomerization of Hexabromocyclododecanes in Zebrafish (<i>Danio rerio</i>)

In this study, zebrafish (<i>Danio rerio</i>) were exposed to two dietary concentrations of individual HBCD diastereoisomers (α-, β-, and γ-HBCD) for 42 days, followed by clean food for 21 days, to examine bioaccumulation, depuration, and enantiomer fractions (EFs) of HBCD diastereoisomers and to test the bioisomerization of HBCDs in fish. The depuration of α-, β-, and γ-HBCD in zebrafish followed the first-order process. Bioaccumulation parameters of the three diastereoisomers differed between low and high dose, suggesting that the bioaccumulation of them is concentration dependent. Calculated assimilation efficiencies (AEs), biomagnification factors (BMFs), and half-lives (<i>t</i>_1/2) of α-HBCD were the highest among the three diastereoisomers. Furthermore, the study showed that zebrafish could biotransform γ-HBCD to α-HBCD. The highest AE, BMF, and <i>t</i>_1/2 of α-HBCD and bioisomerization of γ-HBCD to α-HBCD could explain why α-HBCD appears to be dominant in biota samples. The EFs for α- and γ-HBCD in zebrafish estimated at different times of bioaccumulation and depuration were all significantly greater than those in corresponding food (<i>P</i> < <i>0.05</i>), indicating selective enrichment of (+) α-enantiomer and (+) γ-enantiomer relative to (−) α-enantiomer and (−) γ-enantiomer, respectively

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