Effects of wastewater-spiked nanoparticles of silver and titanium dioxide on survival, growth, reproduction and biochemical markers of Daphnia magna.

Silver (Ag) and titanium dioxide (TiO2) nanoparticles (NPs) are released into aquatic environments through wastewater treatment plants (WWTPs). Even though these NPs are mostly retained in WWTPs, a small fraction can be found in released effluents and may exert toxic effects on aquatic biota. Currently, the available information about the sublethal effects of wastewater-borne NPs on aquatic organisms is inconclusive and the importance of exposure media remains poorly understood. Previously, we demonstrated that rainbow trout juveniles chronically exposed to wastewater-borne AgNPs or TiO2NPs caused no effects on growth, but antioxidative stress mechanisms were triggered in fish organs. Accordingly, this study aimed to: (i) assess the chronic (21-d) effects of wastewater-borne AgNPs (0.3-23.5 µg L-1 Ag) and TiO2NPs (2.7-3.9 µg L-1 Ti) on survival, growth and reproduction of Daphnia magna; (ii) determine the short-term (96-h) effects of wastewater-borne AgNPs (30.3 µg L-1 Ag) and TiO2NPs (6.3 µg L-1 Ti) at the subcellular level (biochemical markers of neurotoxicity, anaerobic metabolism and oxidative stress); and (iii) compare the effects obtained in (i) and (ii) with the corresponding ones induced by effluent-supplemented and water-dispersed NPs. Total Ag and Ti levels were analytically quantified in all treatments. It was demonstrated that both wastewater-borne NPs are considered non-toxic to daphnids at tested concentrations, considering the endpoints at the individual (survival, growth, reproduction) and subcellular (biochemical markers) levels. Contrarily, when pristine forms of NPs were supplemented to effluents or water, concentration-dependent effects were noticed, particularly on cumulative offspring of daphnids. The significant effects on anaerobic metabolism and detoxification pathways caused by the effluent indicate background toxicity. Bearing in mind the achievement of a suitable risk assessment of NPs in aquatic environments, this combined approach looking at both the individual and subcellular levels responses come up with relevant information about the ecotoxicological harmlessness of wastewater-borne NPs in complex environmental matrices like WWTP effluents.

Chronic effects of wastewater-borne silver and titanium dioxide nanoparticles on the rainbow trout (Oncorhynchus mykiss).

Even though nanoparticles (NPs) are mostly removed by wastewater treatment plants, wastewater-borne NPs may show an altered toxicity to aquatic organisms. The main objectives of this work were: i) to assess the chronic (28 days) effects of wastewater-borne NPs of silver (AgNPs, 1.4-36.2 µg L-1) and titanium dioxide (TiO2NPs, 3.1-50.2 µg L-1) at the individual (growth) and biochemical (biomarkers of neurotoxicity, oxidative stress and energy metabolism) levels in rainbow trout Oncorhynchus mykiss; and ii) to compare them with their effluent-supplemented and water-dispersed counterparts. The total Ag and Ti levels were determined in several fish organs. The growth of O. mykiss was not affected by the NPs in any treatment, except a 29% increase at 5.5 µg L-1 of total Ag supplemented to effluents. The Ag level in organs of O. mykiss was significantly higher after exposure to water-dispersed AgNPs than their wastewater-borne or effluent-supplemented counterparts. No significant Ti uptake could be observed. Effluent-supplemented TiO2NPs (50.1 µg L-1 Ti) potentially induced neurotoxic effects, indicated by a 24% increase in acetylcholinesterase activity comparatively to controls. Energy reserves were unaffected by TiO2 treatments, while nearly all AgNP-containing treatments caused a depletion of total lipids, proteins and carbohydrates in the muscle, suggesting an increased energy demand for detoxification processes to cope with AgNPs. Besides NPs, the effluent matrix and dispersing agent (for AgNPs) induced significant effects on energetic reserves and oxidative stress, indicating background toxicity of both treatments at the biochemical level. Our study is the first to assess chronic effects of wastewater-borne NPs on rainbow trout. While no effects were found at the individual level, several biochemical markers were changed by the NPs exposure. Our results highlight the importance of using complex matrices for a reliable risk assessment of NPs in the aquatic environment.

Bioavailability of silver from wastewater and planktonic food borne silver nanoparticles in the rainbow trout Oncorhynchus mykiss.

Silver nanoparticles (AgNPs) are present in a wide field of applications and consumer products and are likely to be released into the environment, mainly via urban and industrial sewage due to their extensive use. Even though AgNPs are mostly retained within the sludge of wastewater treatment plants (WWTPs), a small amount of mainly sulfidized particles still enters the aquatic environment, where they can be taken up by various aquatic organisms and transferred along the food chain. In this study, uptake and bioavailability of Ag from AgNPs following aqueous and dietary exposure were investigated in the rainbow trout Oncorhynchus mykiss. AgNPs in the effluent of model WWTPs and in tap water were used to perform aqueous exposure studies. No significant Ag uptake into the gills and carcass of the analyzed fish could be found for wastewater-borne AgNPs. However, when added to tap water at a concentration of 12.4 µg L-1, a maximum total Ag tissue concentrations of around 100 µg kg-1 and 50 µg kg-1 in gills and carcass were measured, respectively. For the dietary exposure studies, freshwater zooplankton was exposed to AgNPs, and used for the preparation of food pellets with a total Ag concentration of 121.5 µg kg-1. During the feeding study with rainbow trout significant total Ag concentrations up to 34.3 µg kg-1 could be found in the digestive tract. However, only a limited transfer of Ag through the intestinal walls into the carcass could be detected. AgNPs in plankton and WWTP effluent were characterized by transmission electron microscopy (TEM) in combination with energy dispersive X-ray spectroscopy (EDX) and found to be sulfidized. This transformation most presumably has led to their limited bioavailability for fish. The results emphasize the importance of realistic test conditions for the risk assessment of AgNPs by the use of environmental matrices.

Impact of wastewater-borne nanoparticles of silver and titanium dioxide on the swimming behaviour and biochemical markers of Daphnia magna: An integrated approach.

Due to their widespread use, silver (Ag) and titanium dioxide (TiO2) nanoparticles (NPs) are commonly discharged into aquatic environments via wastewater treatment plants. The study was aimed to assess the effects of wastewater-borne AgNPs (NM-300 K; 15.5 ±â€¯2.4 nm; 25-125 µg L-1) and TiO2NPs (NM-105; 23.1 ±â€¯6.2 nm; 12.5-100 µg L-1), from a laboratory-scale wastewater treatment plant, on Daphnia magna, at individual and subcellular level. For effect comparison, animals were also exposed to ASTM-dispersed NPs at the same nominal concentrations. The behaviour of D. magna was evaluated through monitoring of swimming height and allocation time for preferred zones after 0 h and 96 h of exposure. Biochemical markers of neurotransmission, anaerobic metabolism, biotransformation, and oxidative stress were subsequently determined. No 96-h EC50 (immobilization ≤ 4 %) could be obtained with wastewater-borne NPs and ASTM-dispersed TiO2NPs, whereas the ASTM-dispersed AgNPs resulted in an immobilization 96-h EC50 of 113.8 µg L-1. However, both wastewater-borne and ASTM-dispersed TiO2NPs, at 12.5 µg L-1, caused immediate (0 h) alterations on the swimming height. Allocation time analyses showed that animals exposed to ASTM-dispersed AgNPs spent more time on the surface and bottom at 0 h, and in the middle and bottom at 96 h. This pattern was not observed with ASTM-dispersed TiO2NPs nor with wastewater-borne AgNPs and wastewater-borne TiO2NPs. At the biochemical level, the more pronounced effects were observed with wastewater-borne AgNPs (e.g. induction of lactate dehydrogenase and glutathione S-transferase activities, and inhibition of catalase activity). This integrative approach showed that: (i) the behavioural and biochemical response-patterns were distinct in D. magna exposed to environmentally relevant concentrations of wastewater-borne and ASTM-dispersed NPs; (ii) the most pronounced effects on allocation time were induced by ASTM-dispersed AgNPs; and (iii) at the subcellular level, wastewater-borne AgNPs were more toxic than wastewater-borne TiO2NPs. This study highlights the need for the assessment of the effects of wastewater-borne NPs under realistic exposure scenarios, since processes in wastewater treatment plants may influence their toxicity.

Octopamine Underlies the Counter-Regulatory Response to a Glucose Deficit in Honeybees (Apis mellifera).

An animal's internal state is a critical parameter required for adaptation to a given environment. An important aspect of an animal's internal state is the energy state that is adjusted to the needs of an animal by energy homeostasis. Glucose is one essential source of energy, especially for the brain. A shortage of glucose therefore triggers a complex response to restore the animal's glucose supply. This counter-regulatory response to a glucose deficit includes metabolic responses like the mobilization of glucose from internal glucose stores and behavioral responses like increased foraging and a rapid intake of food. In mammals, the catecholamines adrenalin and noradrenalin take part in mediating these counter-regulatory responses to a glucose deficit. One candidate molecule that might play a role in these processes in insects is octopamine (OA). It is an invertebrate biogenic amine and has been suggested to derive from an ancestral pathway shared with adrenalin and noradrenalin. Thus, it could be hypothesized that OA plays a role in the insect's counter-regulatory response to a glucose deficit. Here we tested this hypothesis in the honeybee (Apis mellifera), an insect that, as an adult, mainly feeds on carbohydrates and uses these as its main source of energy. We investigated alterations of the hemolymph glucose concentration, survival, and feeding behavior after starvation and examined the impact of OA on these processes in pharmacological experiments. We demonstrate an involvement of OA in these three processes in honeybees and conclude there is an involvement of OA in regulating a bee's metabolic, physiological, and behavioral response following a phase of prolonged glucose deficit. Thus, OA in honeybees acts similarly to adrenalin and noradrenalin in mammals in regulating an animal's counter-regulatory response.