Diego Minetto

Ecotoxicity of engineered TiO2 nanoparticles to saltwater organisms: An overview

The innovative properties of nanomaterials make them suitable for various applications in many fields. In particular, TiO2 nanoparticles (nTiO2) are widely used in paints, in cosmetics and in sunscreens that are products accessible to the mass market. Despite the great increase in the use of such nanomaterials, there is a paucity of general information about their potential effects to the aquatic species, especially to saltwater ones. Moreover, the difficulties of determining the effective exposure scenario make the acquired information low comparable. In this work, questions about the complexity of the real exposure scenario determination are discussed. The state of the art, concerning the experimental activities with nTiO2 toward the saltwater organisms is firstly illustrated, providing statistical information about the different matrices, organisms and nanoparticles employed. A comparison of the nTiO2 ecotoxicity effects, grouped by taxonomic classes, is provided illustrating their relative experimental conditions. Findings show the need to develop specific protocols for toxicity tests with ENPs to control the variability of experimental conditions. Some advices are finally proposed for the future experimental activities.

Effects of alginate on stability and ecotoxicity of nano-TiO2 in artificial seawater

The large-scale use of titanium dioxide nanoparticles (nano-TiO₂) in consumer and industrial applications raised environmental health and safety concerns. Potentially impacted ecosystems include estuarine and coastal organisms. Results from ecotoxicological studies with nano-TiO₂ dispersed in salt exposure media are difficult to interpret due to fast flocculation and sedimentation phenomena affecting the dispersion stability. The goal of this study was to investigate the stabilisation effect of alginate on uncoated nano-Ti₂2 in artificial seawater dispersions used in ecotoxicity bioassays. The most effective stabilisation was obtained at alginate concentration of 0.45 g/L after sonicating dispersions for 20 min (100 W). The size distribution remained constant after re-suspension, indicating that no agglomeration occurred after deposition. Ecotoxicity tests on Artemia franciscana and Phaeodactylum tricornutum did not show any adverse effects related to the presence of alginate in the exposure media, and provided evidence on possible reduced bioavailability of nano-TiO₂. The suitable concentration of alginate is recommended to occur on a case-by-case basis.

Potential effects of TiO2 nanoparticles and TiCl4 in saltwater to Phaeodactylum tricornutum and Artemia franciscana.

Nanosized titanium dioxide (nTiO2) is widespread in many commercial products and several authors investigated its ecotoxicity effects focusing mainly on freshwater environments. Data on saltwater species are still lacking or present contradicting results. We compared for the first time the toxicity of TiCl4 and nTiO2 considering standard toxicity tests with microalgae Phaeodactylum tricornutum (growth inhibition test, 1.8-90mg/L) and crustacean Artemia franciscana (mortality test, 0.5-64mg/L). For A. franciscana, two alternative scenarios were considered beside standard protocol: i) darkness; and ii) starvation. About microalgae, results evidenced that effects of TiCl4 (EC50=63mg/L) were greater than nTiO2 (no EC50), but IC10 and IC20 were significantly lower suggesting that nTiO2 is more harmful than TiCl4 at lower concentrations. The effects of TiCl4 to crustaceans larvae in all exposure scenarios were lower compared to nTiO2 (EC50(96h)=15mg/L - standard protocol). During toxicity testing, the absence of light generally lowered nTiO2 effects while starvation increased the toxicity of both TiCl4 and nTiO2.

In situ remediation of contaminated marinesediment: an overview

Sediment tends to accumulate inorganic and persistent hydrophobic organic contaminants representing one of the main sinks and sources of pollution. Generally, contaminated sediment poses medium- and long-term risks to humans and ecosystem health; dredging activities or natural resuspension phenomena (i.e., strongly adverse weather conditions) can remobilize pollution releasing it into the water column. Thus, ex situ traditional remediation activities (i.e., dredging) can be hazardous compared to in situ techniques that try to keep to a minimum sediment mobilization, unless dredging is compulsory to reach a desired bathymetric level. We reviewed in situ physico-chemical (i.e., active mixing and thin capping, solidification/stabilization, chemical oxidation, dechlorination, electrokinetic separation, and sediment flushing) and bio-assisted treatments, including hybrid solutions (i.e., nanocomposite reactive capping, bioreactive capping, microbial electrochemical technologies). We found that significant gaps still remain into the knowledge about the application of in situ contaminated sediment remediation techniques from the technical and the practical viewpoint. Only activated carbon-based technologies are well developed and currently applied with several available case studies. The environmental implication of in situ remediation technologies was only shortly investigated on a long-term basis after its application, so it is not clear how they can really perform.

Toxicity assessment within the application of in situ contaminated sediment remediation technologies: A review

Polluted sediment represents a great problem for aquantic environments with potential direct acute and chronic effects for the biota and can be tackled with both in situ and ex situ treatments. Once dredging activities are not compulsory, sediment can be kept in place and managed with techniques involving the use of amendment and/or capping. Before their application, the assessment of their potential impact to the target environment cannot ignore the safe-by-design approach. The role of toxicity in in situ sediment remediation was reviewed discussing about how it can be used for the selection of amendments and the monitoring of treatment technologies. Results evidenced that capping technology coupled to activated carbon (AC) is the most frequently applied approach with effects varying according to the rate of contamination in treated sediment, the amount of AC used (% v/v), and target biological models considered. Little data are available for zerovalent iron as well as other minor amending agents such as hematite, natural zeolite, biopolymers and organoclays. Current (eco-)toxicological information for in situ sediment remediation technologies is fragmentary and incomplete or entirely missing, making also the interpretation of existing data quite challenging. In situ sediment remediation represents an interesting potentially effective approach for polluted sediment recovering. As its application in some lab-based and field studies reported to induce negative effects for target organisms, amendments and capping agents must be attentively evaluated for short- and long-term environmental effects, also in the perspective of the remediated site monitoring and maintenance.

Monitored natural recovery of contaminated marine sediments. Proposal of a monitoring plan for in situ continuous testing and sensing

The aim of this study was to identify the pillars for the realization of a proposal of monitoring plan based on the application of Monitored Natural Recovery processes. The proposal has been realized considering the Mar Piccolo case study in Taranto (Southern Italy) that has been included into the list of polluted Sites of National Interest (SIN) by the Italian Law n. 426/98. In fact, submarine sediments contain high concentrations of heavy metals (Hg, Pb, Cd, Cu and Zn) and organic pollutants (PCBs, PAHs and dioxins). In order to achieve the goal, the ISRAP methodology (Interactive Sediment Remedy Assessment Portal) was applied. The main outlooks have been the identification (i) of the principal pollutants as well as the main natural recovery processes, (ii) the definition of the remediation objectives and (iii) the proposal of monitoring activates identifying, also, the principal tools to be adopted. Furthermore, the role of in situ testing and sensing has been discussed.

Nano-scale zero valent iron (nzvi) treatment of marine sediments slightly polluted by heavy metals

Zero valent iron (ZVI) is an electron donor that is used to reduce or indirectly oxidize several contaminants in soil and groundwater (e.g. halogenated species). The development of stable nano-scale ZVI (nZVI) products has gained a growing interest in environmental remediation with numerous applications all over the world. Several studies addressed both treatment efficiency and ecotoxicological effects of nano-based products for site remediation. However only a few information related to nZVI use for the treatment of marine sediments slightly polluted by heavy metals are available. The present study was aimed at evaluating the effectiveness of nZVI treatment for the decontamination of marine sediments polluted by heavy metals, using the commercial product Nanofer 25s. Two kinds of experiments labelled as (i) sediment at low dosage (2, 3 and 4 g nZVI per kg of SS) and (ii) sediment at high dosage (5, 10 and 20 g nZVI for every kg SS) were performed on sieved sediment with a size < 5 mm. The optimal amount of nZVI to be potentially used for sediment reclamation was identified. According to results, nZVI is more suitable to be used for specific elements removal rather than to be applied for a generalised contamination, meaning that a mix of techniques can be suggested for whole sediment remediation.