A new test system for unraveling the effects of soil components on the uptake and toxicity of silver nanoparticles (NM-300K) in simulated pore water

The effect of sulfidation and soil type on the uptake of silver nanoparticles in annelid Enchytraeus crypticus

Hazard assessment of silver nanoparticles is crucial as their presence in agricultural land is increasing through sewage sludge application. This study compared the uptake and elimination kinetics in the annelid Enchytraeus crypticus of AgNPs with different core sizes and coatings in Lufa 2.2 soil, and of Ag₂S NPs (simulating aged AgNPs) in three different soils. For both experiments, AgNO₃ was used as ionic control. E. crypticus was exposed to soil spiked at 10 μg Ag g^-1 dry soil for 14 days and then transferred to clean soil for a 14-day elimination phase. The uptake rate constants were similar for 3-8 nm and 60 nm AgNPs and AgNO₃, but significantly different between 3 and 8 nm and 50 nm AgNPs. The uptake kinetics of Ag from Ag₂S NPs did not significantly differ compared to pristine AgNPs. Therefore, Ag bioavailability was influenced by AgNP form and characteristics. Uptake and elimination rate constants of both Ag forms (AgNO₃ and Ag₂S NPs) significantly differed between different test soils (Lufa 2.2, Dorset, and Woburn). For AgNO₃, significantly higher uptake and elimination rate constants were found in the Dorset soil compared to the other soils, while for Ag₂S NPs this soil showed the lowest uptake and elimination rate constants. Therefore, not only the form and characteristics but also soil properties affect the bioavailability and uptake of Ag nanoparticles.

Potential of the Red Alga Dixoniella grisea for the Production of Additives for Lubricants

There is an increasing interest in algae-based raw materials for medical, cosmetic or nutraceutical applications. Additionally, the high diversity of physicochemical properties of the different algal metabolites proposes these substances from microalgae as possible additives in the chemical industry. Among the wide range of natural products from red microalgae, research has mainly focused on extracellular polymers for additive use, while this study also considers the cellular components. The aim of the present study is to analytically characterize the extra- and intracellular molecular composition from the red microalga Dixoniella grisea and to evaluate its potential for being used in the tribological industry. D. grisea samples, fractionated into extracellular polymers (EPS), cells and medium, were examined for their molecular composition. This alga produces a highly viscous polymer, mainly composed of polysaccharides and proteins, being secreted into the culture medium. The EPS and biomass significantly differed in their molecular composition, indicating that they might be used for different bio-additive products. We also show that polysaccharides and proteins were the major chemical compounds in EPS, whereas the content of lipids depended on the separation protocol and the resulting product. Still, they did not represent a major group and were thus classified as a potential valuable side-product. Lyophilized algal fractions obtained from D. grisea were found to be not toxic when EPS were not included. Upon implementation of EPS as a commercial product, further assessment on the environmental toxicity to enchytraeids and other soil organisms is required. Our results provide a possible direction for developing a process to gain an environmentally friendly bio-additive for application in the tribological industry based on a biorefinery approach.

Ion compositions in artificial media control the impact of humic acid on colloidal behaviour, dissolution and speciation of CuO-NP

The toxicity of copper oxide nanoparticles (CuO-NP) strongly depends on their interactions with the surrounding environment, impacting their dissolution and colloidal stability. This behaviour is studied quite extensively for simplified electrolytes, but information on the behaviour of CuO-NP in more complex artificial media are lacking. In our study, we analysed the colloidal behaviour and considered the speciation of CuO-NP in pure water and three artificial media of different complexity which are used in ecotoxicology. Measurements were done over 7 days in the absence and presence of humic acid (HA) as a model organic molecule. In pure water, the addition of HA lowered the zeta potential from +11 to -41 mV, while in all artificial media, it stayed constantly at about -20 mV. The hydrodynamic diameter of CuO-NP remained unaffected by HA in pure water and seawater, while in porewater and especially in freshwater, HA suppressed strong agglomeration. In pure water, HA strongly increased dissolution to the highest observed value (3% of total Cu), while HA reduced dissolution in all artificial media. Speciation calculations revealed that cations from the media competed with Cu from the NP surface for complexing sites of the HA. This competition may have caused the reduced dissolution in the presence of ions. Furthermore, speciation calculations also suggest that ion composition drove agglomeration behaviour rather than ion concentration: agglomeration was high when divalent cations where the major interaction partner and dominant in relative terms. HA may have reduced the relative dominance and thus altered the agglomeration, aligning it in all media. Summarizing, ion composition and the presence of HA strongly drive the dissolution and agglomeration of CuO-NP in artificial media, consequently, analysing complexation can help to predict environmental behaviour and toxicity.

Medium-term effects of Ag supplied directly or via sewage sludge to an agricultural soil on Eisenia fetida earthworm and soil microbial communities

The widespread use of silver nanoparticles (AgNPs) in consumer products that release Ag throughout their life cycle has raised potential environmental concerns. AgNPs primarily accumulate in soil through the spreading of sewage sludge (SS). In this study, the effects of direct exposure to AgNPs or indirect exposure via SS contaminated with AgNPs on the earthworm Eisenia fetida and soil microbial communities were compared, through 3 scenarios offering increasing exposure concentrations. The effects of Ag speciation were analyzed by spiking SS with AgNPs or AgNO₃ before application to soil. SS treatment strongly impacted Ag speciation due to the formation of Ag₂S species that remained sulfided after mixing in the soil. The life traits and expression of lysenin, superoxide dismutase, cd-metallothionein genes in earthworms were not impacted by Ag after 5 weeks of exposure, but direct exposure to Ag without SS led to bioaccumulation of Ag, suggesting transfer in the food chain. Ag exposure led to a decrease in potential carbon respiration only when directly added to the soil. The addition of SS had a greater effect on soil microbial diversity than the form of Ag, and the formation of Ag sulfides in SS reduced the impact of AgNPs on E. fetida and soil microorganisms compared with direct addition.

Soil properties can evoke toxicity of copper oxide nanoparticles towards springtails at low concentrations

Copper oxide nanoparticles (CuO-NP) are used as an efficient alternative to conventional Cu in agriculture and might end up in soils. They show a high toxicity towards cells and microorganisms, but only low toxicity towards soil invertebrates. However, most existing soil ecotoxicological studies were conducted in a sandy reference soil and at test concentrations ≥100 mg Cu/kg soil. Therefore, there is a knowledge gap concerning the effect of soil texture on the toxicity of CuO-NP at lower, more realistic test concentrations. In our study, a sandy reference soil and three loamy soils were spiked with CuO-NP at up to four concentrations, ranging from 5 to 158 mg Cu/kg. We investigated 28-day reproduction as well as weight and Cu content after 14-day bioaccumulation and subsequent 14-day elimination for the springtail Folsomia candida. For the first time we analysed the size distribution of CuO-NP in aqueous test soil extracts by single particle-ICP-MS which revealed that the diameter of CuO-NP significantly increased with increasing concentration, but did not vary between test soils. Negative effects on reproduction were only observed in loamy soils, most pronounced in a loamy-acidic soil (-61%), and they were always strongest at the lowest test concentration. The observed effects were much stronger than reported by other studies performed with sandy soils and higher CuO-NP concentrations. In the same soil and concentration, a moderate impact on growth (-28%) was observed, while Cu elimination from springtails was inhibited. Rather than Cu body concentration, the diameter of the CuO-NP taken up, as well as NP-clay interactions might play a crucial role regarding their toxicity. Our study reports for the first time toxic effects of CuO-NP towards a soil invertebrate at a low, realistic concentration range. The results strongly suggest including lower test concentrations and a range of soil types in nanotoxicity testing.

Ecotoxicology of silver nanoparticles and their derivatives introduced in soil with or without sewage sludge: A review of effects on microorganisms, plants and animals

Silver nanoparticles (AgNPs) are widely incorporated in many products, partly due to their antimicrobial properties. The subsequent discharge of this form of silver into wastewater leads to an accumulation of silver species (AgNPs and derivatives resulting from their chemical transformation), in sewage sludge. As a result of the land application of sewage sludge for agricultural or remediation purposes, soils are the primary receiver media of silver contamination. Research on the long-term impact of AgNPs on the environment is ongoing, and this paper is the first review that summarizes the existing state of scientific knowledge on the potential impact of silver species introduced into the soil via sewage sludge, from microorganisms to earthworms and plants. Silver species can easily enter cells through biological membranes and affect the physiology of organisms, resulting in toxic effects. In soils, exposure to AgNPs may change microbial biomass and diversity, decrease plant growth and inhibit soil invertebrate reproduction. Physiological, biochemical and molecular effects have been documented in various soil organisms and microorganisms. Negative effects on organisms of the dominant form of silver in sewage sludge, silver sulfide (Ag₂S), have been observed, although these effects are attenuated compared to the effects of metallic AgNPs. However, silver toxicity is complex to evaluate and much remains unknown about the ecotoxicology of silver species in soils, especially with respect to the possibility of transfer along the trophic chain via accumulation in plant and animal tissues. Critical points related to the hazards associated with the presence of silver species in the environment are described, and important issues concerning the ecotoxicity of sewage sludge applied to soil are discussed to highlight gaps in existing scientific knowledge and essential research directions for improving risk assessment.