Stability and aggregation of silver and titanium dioxide nanoparticles in seawater: role of salinity and dissolved organic carbon

Toxicity of silver and gold nanoparticles on marine microalgae

The increased use of nanomaterials in several novel industrial applications during the last decade has led to a rise in concerns about the potential toxic effects of released engineered nanoparticles (NPs) into the environment, as their potential toxicity to aquatic organisms is just beginning to be recognised. Toxicity of metallic nanoparticles to aquatic organisms, including microalgae, seems to be related to their physical and chemical properties, as well as their behaviour in the aquatic media where processes of dissolution, aggregation and agglomeration can occur. Although the production of these particles has increased considerably in recent years, data on their toxicity on microalgae, especially those belonging to marine or estuarine environments remain scarce and scattered. The literature shows a wide variation of results on toxicity, mainly due to the different methodology used in bioassays involving microalgae. These can range for up to EC50 data, in the case of AgNPs, representing five orders of magnitude. The importance of initial cellular density is also addressed in the text, as well as the need for keeping test conditions as close as possible to environmental conditions, in order to increase their environmental relevance. This review focuses on the fate and toxicity of silver, gold, and gold-silver alloy nanoparticles on microalgae, as key organisms in aquatic ecosystems. It is prompted by their increased production and use, and taking into account that oceans and estuaries are the final sink for those NPs. The design of bioassays and further research in the field of microalgae nanoecotoxicology is discussed, with a brief survey on newly developed technology of green (algae mediated) production of Ag, Au and Ag-Au bimetallic NPs, as well as some final considerations about future research on this field.

Accumulation and effects of sediment-associated silver nanoparticles to sediment-dwelling invertebrates

Sediment is increasingly recognized as the major sink for contaminants including nanoparticles (NPs). Thus, sediment-living organisms are especially susceptible to NP exposure. Studies of the fate and effects of NPs in the sediment matrix are still in their infancy, and data from such studies are in high demand. Here, we examine the effects of exposure to sediment mixed with either aqueous Ag (administered as AgNO3) or Ag NPs (13nm, citrate-capped) at a nominal exposure concentration of 100μg Ag/g dry weight sediment on four benthic invertebrates: two clones of the gastropod Potamopyrgus antipodarum (clones A and B) and two polychaete species (Capitella teleta, Capitella sp. S). Our results show that both species sensitivity and Ag form (aqueous Ag, Ag NPs) play a role in bioaccumulation and effects. Following two weeks of exposure, both clones of P. antipodarum were found to be insensitive towards both Ag forms (generally low Ag accumulation, no toxicity). In contrast, the two Capitella species varied widely with respect to Ag uptake and observed toxicity. Capitella sp. S was adversely affected by both aqueous Ag (mortality) and Ag NPs (growth), whereas C. teleta was not affected by either Ag form. For neither polychaete species was the observed toxicity directly related to bioaccumulation. Therefore, future nano-ecotoxicological research should focus on understanding differences in uptake and handling mechanisms among species and the relationship between bioaccumulation and toxicity.

Interaction of TiO2 nanoparticles with the marine microalga Nitzschia closterium: growth inhibition, oxidative stress and internalization

The toxicity of TiO2 engineered nanoparticles (NPs) to the marine microalga Nitzschia closterium was investigated by examining growth inhibition, oxidative stress and uptake. The results indicated that the toxicity of TiO2 particles to algal cells significantly increased with decreasing nominal particle size, which was evidenced by the 96 EC50 values of 88.78, 118.80 and 179.05 mg/L for 21 nm, 60 nm and 400 nm TiO2 particles, respectively. The growth rate was significantly inhibited when the alga was exposed to 5mg/L TiO2 NPs (21 nm). Measurements of antioxidant enzyme activities showed that superoxide dismutase (SOD), catalase (CAT) and peroxidase (POD) activities were first induced and subsequently inhibited following exposure to 5mg/L TiO2 NPs. The depletion of antioxidant enzymes with a concomitant increase in malondialdehyde (MDA) levels and reactive oxygen species (ROS) posed a hazard to membrane integrity. A combination of flow cytometry analysis, transmission electron microscopy and Ti content measurement indicated that TiO2 NPs were internalized in N. closterium cells. The level of extracellular ROS, which was induced by TiO2 NPs under visible light, was negligible when compared with the intracellular ROS level (accounting for less than 6.0% of the total ROS level). These findings suggest that elevated TiO2 nanotoxicity in marine environments is related to increased ROS levels caused by internalization of TiO2 NPs.

Toxicity, bioaccumulation, and biotransformation of silver nanoparticles in marine organisms

The toxicity, bioaccumulation, and biotransformation of citrate and polyvinylpyrrolidone (PVP) coated silver nanoparticles (NPs) (AgNP-citrate and AgNP-PVP) in marine organisms via marine sediment exposure was investigated. Results from 7-d sediment toxicity tests indicate that AgNP-citrate and AgNP-PVP did not exhibit toxicity to the amphipod (Ampelisca abdita) and mysid (Americamysis bahia) at ≤75 mg/kg dry wt. A 28-d bioaccumulation study showed that Ag was significantly accumulated in the marine polychaete Nereis virens (N. virens) in the AgNP-citrate, AgNP-PVP and a conventional salt (AgNO3) treatments. Synchrotron X-ray absorption spectroscopy (XAS) results showed the distribution of Ag species in marine sediments amended with AgNP-citrate, AgNP-PVP, and AgNO3 was AgCl (50–65%) > Ag2S (32–42%) > Ag metal (Ag0) (3–11%). In N virens, AgCl (25–59%) and Ag2S (10–31%) generally decreased and, Ag metal (32–44%) increased, relative to the sediments. The patterns of speciation in the worm were different depending upon the coating of the AgNP and both types of AgNPs were different than the AgNO3 salt. These results show that the AgNP surface capping agents influenced Ag uptake, biotransformation, and/or excretion. To our knowledge, this is the first demonstration of the bioaccumulation and speciation of AgNPs in a marine organism (N. virens).