Growth inhibition in Raphidocelis subcapita - Evidence of nanospecific toxicity of silver nanoparticles.

Silver, known for its antibacterial properties and for its toxicity to aquatic organisms, is one of the most frequently used nanomaterials and silver nanoparticles can be found in a range of consumer products as well as medical applications. The present study investigated the toxicity of three different silver nanomaterials (Mesosilver (M-Ag), NM300K and NM302) and AgNO3, in the algae Raphidocelis subcapitata. Exposures in the low µg L-1 range were combined with characterization of exposure media to determine whether differences in toxicity could be linked to changes in Ag speciation and/or any nanospecific mechanisms. All tested Ag compounds, except the NM302, reduced growth in the following order AgNO3 ≥ M-Ag > NM300K > NM302 with 50% effect concentrations of 7.09 (3.83-10.52), 9.7 (range not calculated) and 24.18 (15.66-98.16) µg L-1, for AgNO3, Mesosilver and NM300K, respectively. Characterization of exposure media showed that both concentration and time influenced the speciation and stability of Ag in algal test media, regardless of Ag source, and also affected the toxicity to R. subcapitata. In both AgNO3 and Mesosilver exposure the toxicity was correlated with the presence of dissolved Ag species (<10 kDa), however levels of dissolved Ag were too low to account for the observed Mesosilver effects, indicating a nanospecific contribution. Nanospecific toxicity was also observed for NM300K after 24 h of exposure, however the algal population recovered over time, probably due to changes in exposure caused by aggregation of the nanoparticles.

Route of exposure has a major impact on uptake of silver nanoparticles in Atlantic salmon (Salmo salar).

The potential impact of silver nanoparticles (Ag NPs) on aquatic organisms is to a large extent determined by their bioavailability through different routes of exposure. In the present study juvenile Atlantic salmon (Salmo salar) were exposed to different sources of radiolabeled Ag (radiolabeled 110m Ag NPs and 110m AgNO3 ). After 48 h of waterborne exposure to 3 µg/L citrate stabilized 110m Ag NPs or 110m AgNO3 , or a dietary exposure to 0.6 mg Ag/kg fish (given as citrate stabilized or uncoated 110m Ag NPs, or 110m AgNO3 ), Ag had been taken up in fish regardless of route of exposure or source of Ag (Ag NPs or AgNO3 ). Waterborne exposure led to high Ag concentrations on the gills, and dietary exposure led to high concentrations in the gastrointestinal tract. Silver distribution to the target organs was similar for both dietary and waterborne exposure, with the liver as the main target organ. The accumulation level of Ag was 2 to 3 times higher for AgNO3 than for Ag NPs when exposure was through water, whereas no significant differences were seen after dietary exposure. The transfer (Bq/g liver/g food or water) from exposure through water was 4 orders of magnitude higher than from feed using the smallest, citrate-stabilized Ag NPs (4 nm). The smallest NPs had a 5 times higher bioavailability in food compared with the larger and uncoated Ag NPs (20 nm). Despite the relatively low transfer of Ag from diet to fish, the short lifetime of Ag NPs in water and their transfer to sediment, feed, or sediment-dwelling food sources such as larvae and worms could make diet a significant long-term exposure route. Environ Toxicol Chem 2018;37:2895-2903. © 2018 SETAC.

Characterizing the behavior, uptake, and toxicity of NM300K silver nanoparticles in Caenorhabditis elegans.

Using Caenorhabditis elegans as a model organism, we addressed the potential linkage among toxicity of NM300K Ag nanoparticles (AgNPs), their particle size distribution, and the presence of dissolved Ag in the test media. Of the 3 endpoints assessed (growth, fertility, and reproduction), reproduction was the most sensitive, with the 50% effect concentration (EC50) ranging from 0.26 to 0.84 mg Ag L-1 and 0.08 to 0.11 mg Ag L-1 for NM300K and AgNO3 , respectively. Silver uptake by C. elegans was similar for both forms of Ag, whereas bioaccumulation was higher in AgNO3 exposure. The observed differences in toxicity between NM300K and AgNO3 did not correlate with bioaccumulated Ag, which suggests that toxicity is a function of the type of exposing agent (AgNPs vs AgNO3 ) and its mode of action. Before addition of the food source (Escherichia coli), size fractionation revealed that dissolved Ag comprised 13 to 90% and 4 to 8% of total Ag in the AgNO3 and NM300K treatments, respectively. No dissolved Ag was detectable in the actual test media due to immediate Ag adsorption to bacteria. The results of the present study indicate that information on behavior and characterization of exposure conditions is essential for nanotoxicity studies. Environ Toxicol Chem 2018;37:1799-1810. © 2018 SETAC.

Transcriptional changes in Atlantic salmon (Salmo salar) after embryonic exposure to road salt.

Road salt is extensively used as a deicing chemical in road maintenance during winter and has in certain areas of the world led to density stratifications in lakes and ponds, and adversely impacted aquatic organisms in the recipients of the road run-off. Aquatic vertebrates such as fish have been particularly sensitive during fertilisation, as the fertilisation of eggs involves rapid uptake of the surrounding water, reduction in egg swelling and in ovo exposure to high road salt concentrations. The present study aimed to identify the persistent molecular changes occurring in Atlantic salmon (Salmo salar) eggs after 24h exposure to high concentrations (5000 mg/L) of road salt at fertilisation. The global transcriptional changes were monitored by a 60k salmonid microarray at the eyed egg stage (cleavage stage, 255 degree days after fertilisation) and identified a high number of transcripts being differentially regulated. Functional enrichment, pathway and gene-gene interaction analysis identified that the differentially expressed genes (DEGs) were mainly associated with toxiciologically relevant processes involved in osmoregulation, ionregulation, oxidative stress, metabolism (energy turnover), renal function and developmental in the embryos. Quantitative rtPCR analysis of selected biomarkers, identified by global transcriptomics, were monitored in the eggs for an extended range of road salt concentrations (0, 50, 100, 500 and 5000 mg/L) and revealed a positive concentration-dependent increase in cypa14, a gene involved in lipid turnover and renal function, and nav1, a gene involved in neuraxonal development. Biomarkers for osmoregulatory responses such as atp1a2, the gene encoding the main sodium/potassium ATP-fueled transporter for chloride ions, and txdc9, a gene involved in regulation of cell redox homeostasis (oxidative stress), displayed apparent concentration-dependency with exposure, although large variance in the control group precluded robust statistical discrimination between the groups. A No Transcriptional Effect Level (NOTEL) of 50mg/L road salt was found to be several orders of magnitude lower than the adverse effects documented in developing fish embryos elsewhere, albeit at concentrations realistic in lotic systems receiving run-off from road salt. It remains to be determined whether these transcriptional changes may cause adverse effects in fish at ecologically relevant exposure concentrations of road salt.

Toxicity of road deicing salt (NaCl) and copper (Cu) to fertilization and early developmental stages of Atlantic salmon (Salmo salar).

In many countries, salting of ice or snow covered roads may affect aquatic organisms in the catchment directly or indirectly by mobilization of toxic metals. We studied the toxicity of road deicing salt and copper (Cu) on the vulnerable early life stages of Atlantic salmon (Salmo salar), from fertilization till hatching. Controlled episodic exposure to road salt (≥ 5,000 mg/L) during fertilization resulted in reduced swelling and less percent egg survival. Exposure to Cu both during and post fertilization caused delayed hatching. Larval deformities were, however found as an additional effect, when eggs were exposed to high salt concentration (≥ 5,000 mg/L) mixed with Cu (10 µg Cu/L) during fertilization. Thus, it appears that the sensitivity of early developmental stages of Atlantic salmon increased when exposed to these stressors, and road salt application during spawning can pose threat to Atlantic salmon in water bodies receiving road runoff. The study gives insight on assessment and management of risks on Atlantic salmon population posed by road related hazardous chemicals.