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

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

Arsenic efflux from Microcystis aeruginosa under different phosphate regimes.

Phytoplankton plays an important role in arsenic speciation, distribution, and cycling in freshwater environments. Little information, however, is available on arsenic efflux from the cyanobacteria Microcystis aeruginosa under different phosphate regimes. This study investigated M. aeruginosa arsenic efflux and speciation by pre-exposing it to 10 µM arsenate or arsenite for 24 h during limited (12 h) and extended (13 d) depuration periods under phosphate enriched (+P) and phosphate depleted (-P) treatments. Arsenate was the predominant species detected in algal cells throughout the depuration period while arsenite only accounted for no greater than 45% of intracellular arsenic. During the limited depuration period, arsenic efflux occurred rapidly and only arsenate was detected in solutions. During the extended depuration period, however, arsenate and dimethylarsinic acid (DMA) were found to be the two predominant arsenic species detected in solutions under -P treatments, but arsenate was the only species detected under +P treatments. Experimental results also suggest that phosphorus has a significant effect in accelerating arsenic efflux and promoting arsenite bio-oxidation in M. aeruginosa. Furthermore, phosphorus depletion can reduce arsenic efflux from algal cells as well as accelerate arsenic reduction and methylation. These findings can contribute to our understanding of arsenic biogeochemistry in aquatic environments and its potential environmental risks under different phosphorus levels

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

Insights into Distribution of Soil Available Heavy Metals in Karst Area and Its Influencing Factors in Guilin, Southwest China

The bioavailable contents of heavy metals in karstic soils are a subject of increasing concern since the uptake of heavy metals by plants can pose a severe threat to food safety and public health. However, the bioavailable contents of heavy metals and their effective factors are poorly understood in karst regions. Calcareous soil and red soil developed from carbonate and clastic rocks, respectively, were chosen from a typical karst region (Guilin) of southwestern China, and the total (CT) and available (CA) contents of 11 heavy metals, as well as their influencing factors in soil profiles, were investigated. The results showed that calcareous soil has greater soil organic carbon, total nitrogen, available nitrogen, available potassium, and calcium (Ca) contents than red soil, but lower available phosphorus and C:N. Acid-soluble Ca (Aca) was the dominant fraction in both types of soil. Heavy metals were highly accumulated in calcareous soil, mainly controlled by secondary enrichment in the processing of carbonate rock weathering. For the majority of metals, calcareous soil had higher CT and lower CA than red soil. According to a redundancy analysis (RDA) and Pearson correlation coefficient, the high pH and Ca content in calcareous soils were primary factors influencing both the CT and CA of the metals, especially residual Ca to CT and Aca to CA. Additionally, higher soil cation exchange capacity and clay minerals also probably improved the immobility of heavy metals

Impact of water composition on association of Ag and CeO2 nanoparticles with aquatic macrophyte Elodea canadensis

In this study, the potential association of (citrate-stabilized) Ag (14.1 +/- 1.0 nm) and CeO2 (6.7 +/- 1.2 nm) engineered nanoparticles (ENPs), or their ionic counterparts, with the submerged aquatic plant Elodea canadensis, was examined and, in particular, parameters affecting the distribution of the nanoparticles (or metal ions) between plant biomass and the water phase were assessed using five distinct aqueous matrices (i.e. tap water, 10 % Hoagland's solution and three natural surface water samples). Individual plants were exposed to varying concentrations of Ag and CeO2 ENPs or Ag+ and Ce3+ ions during 72-h-lasting batch experiments. A dose-dependent increase of silver or cerium in plant biomass was observed for both the nanoparticles and the ions, whereby exposure to the latter systematically resulted in significantly higher biomass concentrations. Furthermore, the apparent plant uptake of CeO2 ENPs appeared to be higher than that for Ag ENPs when comparing similar exposure concentrations. These findings suggest that association with E. canadensis might be affected by particle characteristics such as size, composition, surface charge or surface coating. Moreover, the stability of the ENPs or ions in suspension/solution may be another important aspect affecting plant exposure and uptake. The association of the nanoparticles or ions with E. canadensis was affected by the physicochemical characteristics of the water sample. The silver biomass concentration was found to correlate significantly with the electrical conductivity (EC), dry residue (DR) and Cl-, K, Na and Mg content in the case of Ag ENPs or with the EC, inorganic carbon (IC) and Cl-, NO3 (-), Na and Mg content in the case of Ag+ ions, whereas significant relationships between the cerium biomass concentration and the EC, DR, IC and Ca content or the pH, EC, DR, IC and Cl-, Ca and Mg content were obtained for CeO2 ENPs or Ce3+ ions, respectively. Results also indicated that the Ag ENPs and Ag+ ions might potentially be toxic towards E. canadensis whereas no evidence of phytotoxicity was noted in the case of CeO2 ENPs or Ce3+ ions

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