Ecotoxicological evaluation of sewage sludge contaminated with zinc oxide nanoparticles

Enhancing zinc biofortification and mitigating cadmium toxicity in soil-earthworm-spinach systems using different zinc sources

Cadmium (Cd) pollution poses significant threats to soil organisms and human health by contaminating the food chain. This study aimed to assess the impact of various concentrations (50, 250, and 500 mg·kg-1) of zinc oxide nanoparticles (ZnO NPs), bulk ZnO, and ZnSO4 on morphological changes and toxic effects of Cd in the presence of earthworms and spinach. The results showed that Zn application markedly improved spinach growth parameters (such as fresh weight, plant height, root length, and root-specific surface area) and root morphology while significantly reducing Cd concentration and Cd bioconcentration factors (BCF-Cd) in spinach and earthworms, with ZnO NPs exhibiting the most pronounced effects. Earthworm, spinach root, and shoot Cd concentration decreased by 82.3 %, 77.0 %, and 75.6 %, respectively, compared to CK. Sequential-step extraction (BCR) analysis revealed a shift in soil Cd from stable to available forms, consistent with the available Cd (DTPA-Cd) results. All Zn treatments significantly reduced Cd accumulation, alleviated Cd-induced stress, and promoted spinach growth, with ZnO NPs demonstrating the highest Cd reduction and Zn bioaugmentation efficiencies compared to bulk ZnO and ZnSO4 at equivalent concentrations. Therefore, ZnO NPs offer a safer and more effective option for agricultural production and soil heavy metal pollution management than other Zn fertilizers.

Terrestrial bioassays for assessing the biochemical and toxicological impact of biosolids application derived from wastewater treatment plants

Wastewater treatment plants (WWTP) are facilities where municipal wastewater undergoes treatment so that its organic load and its pathogenic potential are minimized. Sewage sludge is a by-product of this process and when properly treated is preferentially called "biosolids". These treatments may include some or most of the following: thickening, dewatering, drying, digestion, composting, liming. Nowadays it is almost impossible to landfill biosolids, which however can well be used as crop fertilizers. Continuous or superfluous biosolids fertilization may negatively affect non-target organisms such as soil macro-organisms or even plants. These effects can be depicted through bioassays on terrestrial animals and plants. It has been shown that earthworms have been affected to various degrees on the following endpoints: pollutants' bioaccumulation, viability, reproduction, avoidance behavior, burrowing behavior. Collembola have been affected on viability, reproduction, avoidance behavior. Other terrestrial organisms such as nematodes and diplopods have also shown adverse health effects. Phytotoxicity have been caused by some biosolids regimes as measured through the following endpoints: seed germination, root length, shoot length, shoot biomass, root biomass, chlorophyll content, antioxidant enzyme activity. Very limited statistical correlations between pollutant concentrations and toxicity endpoints have been established such as between juvenile mortality (earthworms) and As or Ba concentration in the biosolids, between juvenile mortality (collembola) and Cd or S concentration in the biosolids, or between phytotoxicity and some extractable metals in leachates or aquatic extracts from the biosolids; more correlations between physicochemical characteristics and toxicity endpoints have been found such as between phytotoxicity and ammonium N in biosolids or their liquid extracts, or between phytotoxicity and salinity. An inverse correlation between earthworm/collembola mortality and stable organic matter has also been found. Basing the appropriateness of biosolids only on chemical analyses for pollutants is not cost-effective. To enable risk characterization and subsequent risk mitigation it is important to apply a battery of bioassays on soil macro-organisms and on plants, utilizing a combination of endpoints and established protocols. Through combined analytical quantification and toxicity testing, safe use of biosolids in agriculture can be achieved.

Evaluation of the effects of zinc oxide (ZnO NPs) nanoparticles synthesized by green synthesis on Caenorhabditis elegans

In recent years, the rapid development of nanotechnology has caused the products obtained with this technology to be used more daily. Information on the effects of these products, which provide great advantages in every respect, on human health and the environment is insufficient. It has been suggested that these nanoparticles may have toxic effects on living things, mostly in animal experiments and cell cultures. In this paper, the organism Caenorhabditis elegans (C. elegans), which contains a genome and biochemical ways highly similar to humans, is used to understand and reveal the metabolism of Zinc oxide nanoparticles (ZnO NPs) toxicological effects. The toxicological effects of ZnO NPs on C. elegans organisms were investigated and the results were evaluated in terms of environment and human health. C. elegans was exposed to commercial ZnO NPs and green synthesized ZnO NPs from Olea europaea (olive tree, OLE). LC50 values were determined by probit analysis (green synthesized ZnO NP LC5024h = 84.97 mg/L, LC5072h = 33.27 mg/L, commercial ZnO NPs LC5024h = 5.75 mg/L, LC5072h = 1.91 mg/L). When the survival times of C. elegans were evaluated by the Kaplan-Meier method, it was seen that commercial ZnO NPs were more toxic than green synthesized ZnO NPs. In MTT tests, it was clearly seen that commercial ZnO NPs and green synthesized ZnO NPs entered the cell and caused different cytotoxicity. While there was a difference between control and 0.5, 2.5, 5, 10, 25, and 50 mg/L doses in commercial ZnO NP applications, there were significant differences between control and 25, 50 mg/L concentrations in green synthesized ZnO NP applications.

New insights into vermiremediation of sewage sludge: The effect of earthworms on micropollutants and vice versa

Vermicomposting represents an environmentally friendly method for the treatment of various types of biowastes, including sewage sludge (SS), as documented in numerous studies. However, there are few papers providing insights into the mechanisms and toxicity effects involved in SS vermicomposting to present a comprehensive overview of the process. In this work, the vermiremediation of SS containing various micropollutants, including pharmaceuticals, personal care products, endocrine disruptors, and per/polyfluoroalkyl substances, was studied. Two SSs originating from different wastewater treatment plants (WWTP1 and WWTP2) were mixed with a bulking agent, moistened straw, at ratios of 0, 25, 50, and 75% SS. Eisenia andrei earthworms were introduced into the mixtures, and after six weeks, the resulting materials were subjected to various types of chemical and toxicological analyses, including conventional assays (mortality, weight) as well as tissue- and cell-level assays, such as malondialdehyde production, cytotoxicity tests and gene expression assays. Through the vermiremediation process significant removal of diclofenac (90%), metoprolol (88%), telmisartan (62%), and triclosan (81%) was achieved. Although the concentrations of micropollutants were substantially different in the original SS samples, the micropollutants vermiaccumulated to a similar extent over the incubation period. The earthworms substantially eliminated the present bacterial populations, especially in the 75% SS treatments, in which the average declines were 90 and 79% for WWTP1 and WWTP2, respectively. To the best of our knowledge, this is the first study to investigate the vermiremediation of such a large group of micropollutants in real SS samples and provide a thorough evaluation of the effect of SS on earthworms at tissue and cellular level.

Composting and vermicomposting of sewage sludge at various C/N ratios: Technological feasibility and end-product quality

Even though sewage sludge (SS) contains a high level of pollutants, it is rich in essential plant nutrients and has the potential to enhance soil fertility. However, the SS must be further treated through pre-composting plus vermicomposting to make it safe for use on food crops. More research and data are needed to determine how different carbon-to-nitrogen ratios (C/N) affect the feasibility and quality of composting vs vermicomposting of SS. Therefore, in this study we comprehensively evaluated the feasibility and end-product quality of compost and vermicompost produced from SS under different C/N ratios. SS was mixed with pelletized wheat straw (PWS) at various proportions to produce C/N ratios of 6:1, 18:1, 28:1, and 38:1, then pre-composted for 14 days followed by vermicomposting using the earthworm Eisenia andrei for 120 days. Agrochemical properties were measured at 0, 30, 60, 90, and 120 days. Results revealed significantly higher levels of agrochemicals in vermicompost compared to compost, including total potassium (37-88%) and magnesium (4.3-12%), nitrate nitrogen (71-98%), available potassium (53-88%), available phosphorus (79%), available magnesium (54-453%), available boron (48-303%), and available copper (2.5-82%). However, lower levels of ammonium nitrogen by (59-85%), available iron (2.3-51.3%), available manganese (29.7-52.2%), available zinc (10.5-29.8%), total carbon (0.75-4.5%), and total nitrogen (1.6-22.2%) were measured. Comparison of the various C/N ratios, showed that vermicompost with an 18:1 C/N ratio outperformed compost and demonstrated the highest earthworm population (165 pieces/kg). Thus, vermicomposting SS at an 18:1 C/N ratio is strongly recommended as a sustainable technology for producing high-quality vermicompost from SS.

Sanitary effect of FE-DBD cold plasma in ambient air on sewage biosolids

Sewage sludge is treated by means of cold plasma and stabilization in terms of biological load deactivation is achieved. The plasma is produced by floating electrode dielectric barrier discharge operating with air under atmospheric pressure conditions. The process is presented in detail and the discharge is characterized electrically. Additionally, simulation of the thermal flow inside the process chamber is implemented, using computational fluid dynamics. Deactivation of the serotypes S. Paratyphi B., S. Livingstone, S. Mbandaka and S. Typhimurium, and Escherichia coli and Coliforms, is hereby claimed. The process involves mean electrical power in the range of tens of watts, treatment time in the scale of minutes, and maximum instantaneous temperature <400 K. The present work is a preliminary contribution towards the promotion of advanced methods for the pro-ecological management of biosolids, according to European Regulations.

Study of Zn availability, uptake, and effects on earthworms of zinc oxide nanoparticle versus bulk applied to two agricultural soils: Acidic and calcareous

The increasing use of zinc oxide nanoparticles (ZnO NPs) in agriculture renders it necessary to evaluate their impact on soil non-target organisms. This work studies Zn availability to earthworms from the ZnO (NP and bulk) applied to two agricultural soils with a different pH at 20, 225, 500, and 1000 mg Zn kg^-1. Zn uptakes and the effects on Eisenia andrei, grown under controlled conditions, were determined. Effects were assessed at three levels: organisms, mortality, growth and reproduction; biochemical, catalase and glutathione S-transferase activities, malondialdehyde (MDA), and protein content; cellular in coelomocytes, reactive oxygen species (ROS) generation, lysosomal membrane alterations (RN) and mitochondrial dysfunction (MTT). Available Zn was 100-fold higher in acidic than in calcareous soil and did not differ among ZnO (NP or bulk). Zn in worms was auto-regulated regardless of the soil Zn concentration, pH and ZnO size. Effects on mortality and weight were observed only in the acidic soil at the highest concentration, ZnO NPs reduced survival and body weight, while ZnO bulk reduced body weight. Reproduction parameters in acidic soil were: EC50 (fecundity) 277 and 256 mg Zn kg-1 and EC50 (fertility) 177 and 179 mg Zn kg-1 for ZnO NPs and bulk, respectively, with no found NP-specific effects. No responses of enzymatic activities, MDA and MTT were detected. ROS and RN were altered in the coelomocyte cells of earthworms in the two soils, but effects depended on ZnO size suggesting nanospecific effects. Soil pH governs toxicity more than ZnO size regardless of body Zn concentration.

Joint effects of zinc oxide nanoparticles and chlorpyrifos on the reproduction and cellular stress responses of the earthworm Eisenia andrei

The co-exposure of soil organisms to ZnO nanoparticles (ZnO NPs) and pesticides is likely to take place in agricultural soils. However, the impacts of co-exposure on terrestrial ecosystems are virtually unknown. In this paper, Eisenia andrei was exposed for a 28-day period to serial concentrations of ZnO NPs and/or the organophosphate insecticide chlorpyrifos (CPF) in natural soil, and was evaluated for single and joint effects. Zn and CPF accumulation in earthworm tissue was also determined. In the single assay, ZnO NPs and CPF caused statistical significant effects on survival and growth, but mainly on reproduction. Significant reductions in fecundity and fertility were detected with EC50 values of 278 and 179 mg Zn/kg for ZnO NPs, and of 50.75 and 38.24 mg/kg for CPF, respectively. The most notable effect on biomarkers was the reduction in acetylcholinesterase (AChE) activity caused by CPF, which reflected the neurotoxicity of this compound. The results of the combined assay indicated that co-exposure to ZnO NPs and CPF increased adverse effects in E. andrei. According to the independent action model, the binary mixtures showed a synergism (a stronger effect than expected from single exposures) on earthworm reproduction, which became up to 84% higher than the theoretically predicted values. Zn, and especially CPF accumulation, were influenced by the co-exposure. These results underpin the need to consider the effects of mixtures of NPs and organic chemicals on soil to adequately make ecological risk assessments of NPs.

Toxicokinetics of zinc-oxide nanoparticles and zinc ions in the earthworm Eisenia andrei

The toxicokinetics of zinc in the earthworm Eisenia andrei was investigated following exposure for 21 days to ionic zinc (ZnCl₂) or zinc oxide nanoparticles (ZnO-NPs) in Lufa 2.2 soil, followed by 21 days elimination in clean soil. Two concentrations were tested for both ZnCl₂ (250 and 500μg Zn g^-1) and ZnO-NPs (500 and 1000μg Zn g^-1), corresponding to EC₂₅ and EC₅₀ for effects on reproduction. Based on the measured internal Zn concentrations in the earthworms over time of exposure, the kinetics parameters k_a - assimilation rate constant (g_soil g^-1_{body weight} day^-1) and k_e - elimination rate constant (day^-1) were estimated using a one-compartment model for either total Zn concentrations in the soil or porewater Zn concentrations. In the ZnCl₂ treatments, k_a was higher for total Zn concentrations in soil, whereas in the ZnO-NP treatments, k_a was higher for porewater Zn concentrations. The value of k_e did not differ between the two Zn forms (ZnCl₂ vs ZnO-NPs) for either EC₅₀ or EC₂₅ when related to total Zn concentrations in soil, but for EC₅₀, k_e related to porewater Zn concentrations was significantly higher for ZnCl₂ than for ZnO-NPs. It is concluded that differences in kinetic parameters between treatments were connected with exposure concentrations rather than with the form of Zn. Zinc was efficiently regulated by the earthworms in all treatments: a 2-fold increase in exposure concentration resulted in a less than 2-fold increase in internal concentration, and after transfer to uncontaminated soil the internal Zn concentrations in the earthworms returned to ca 111μgg^-1 dw in all treatments.

Agricultural utilization of biosolids: A review on potential effects on soil and plant grown

Environmental and economic implications linked with the proper ecofriendly disposal of modern day wastes, has made it essential to come up with alternative waste management practices that reduce the environmental pressures resulting from unwise disposal of such wastes. Urban wastes like biosolids are loaded with essential plant nutrients. In this view, agricultural use of biosolids would enable recycling of these nutrients and could be a sustainable approach towards management of this hugely generated waste. Therefore biosolids i.e. sewage sludge can serve as an important resource for agricultural utilization. Biosolids are characterized by the occurrence of beneficial plant nutrients (essential elements and micro and macronutrients) which can make help them to work as an effective soil amendment, thereby minimizing the reliance on chemical fertilizers. However, biosolids might contain toxic heavy metals that may limit its usage in the cropland. Heavy metals at higher concentration than the permissible limits may lead to food chain contamination and have fatal consequences. Biosolids amendment in soil can improve physical and nutrient property of soil depending on the quantity and portion of the mixture. Hence, biosolids can be a promising soil ameliorating supplement to increase plant productivity, reduce bioavailability of heavy metals and also lead to effective waste management.

Sewage sludge toxicity assessment using earthworm Eisenia fetida: can biochemical and histopathological analysis provide fast and accurate insight?

Sewage sludge (SS) is a complex organic by-product of wastewater treatment plants. Deposition of large amounts of SS can increase the risk of soil contamination. Therefore, there is an increasing need for fast and accurate assessment of SS toxic potential. Toxic effects of SS were tested on earthworm Eisenia fetida tissue, at the subcellular and biochemical level. Earthworms were exposed to depot sludge (DS) concentration ratio of 30 or 70 %, to undiluted and to 100 and 10 times diluted active sludge (AS). The exposure to DS lasted for 24/48 h (acute exposure), 96 h (semi-acute exposure) and 7/14/28 days (sub-chronic exposure) and 48 h for AS. Toxic effects were tested by the measurements of multixenobiotic resistance mechanism (MXR) activity and lipid peroxidation levels, as well as the observation of morphological alterations and behavioural changes. Biochemical markers confirmed the presence of MXR inhibitors in the tested AS and DS and highlighted the presence of SS-induced oxidative stress. The MXR inhibition and thiobarbituric acid reactive substance (TBARS) concentration in the whole earthworm's body were higher after the exposition to lower concentration of the DS. Furthermore, histopathological changes revealed damage to earthworm body wall tissue layers as well as to the epithelial and chloragogen cells in the typhlosole region. These changes were proportional to SS concentration in tested soils and to exposure duration. Obtained results may contribute to the understanding of SS-induced toxic effects on terrestrial invertebrates exposed through soil contact and to identify defence mechanisms of earthworms.

Optimization of ZnO-NPs to Investigate Their Safe Application by Assessing Their Effect on Soil Nematode Caenorhabditis elegans

Zinc oxide nanoparticles (ZnO-NPs) are increasingly receiving attention due to their widespread application in cosmetics, pigments and coatings. This has raised concerns in the public and scientific communities regarding their unexpected health effects. Toxicity effect of ZnO-NPs on the environment was assessed in the present study using Caenorhabditis elegans. Multiple toxicity end points including their mortality, behaviour, reproduction, in vitro distribution and expression of stress response mtl-1 and sod-1 genes were observed to evaluate safe application of ZnO-NPs. C. elegans were exposed to 10, 50, and 100 nm ZnO-NPs (0.1 to 2.0 g/l). Application of 10 nm ≥0.7g/l adversely affects the survivability of worms and was significantly not affected with exposure of 50 and 100 nm ≤1.0 g/l. However, reproduction was affected at much low concentration as compared to their survivability. LC50 was recorded 1.0 ± 0.06 (g/l) for 100 nm, 0.90 ± 0.60 for 50 nm and 0.620 ± 0.08 for 10 nm. Expression of mtl-1 and sod-1 was significantly increased with application of 10 nm ≥0.7g/l and significantly unaffected with exposure of 50 and 100 nm at the same concentration. ZnO-NPs (10 nm) had shown even distribution extended nearly the entire length of the body. The distribution pattern of ZnO-NPs indicates that the intestine is the major target tissues for NP toxicity. Study demonstrates that small-sized (10 nm) ZnO-NPs ≥0.7g/l is more toxic than larger-sized particles. This may be suggested on the basis of available data; application of 50 and 100 nm ≤1.0 g/l ZnO-NPs may be used to the environment as this shows no significant toxicity. However, further calibration is warranted to explore safe dose on soil compartments prior to their field application.

ZnO Nanoparticles Treatment Induces Apoptosis by Increasing Intracellular ROS Levels in LTEP-a-2 Cells

Owing to the wide use of novel nanoparticles (NPs) such as zinc oxide (ZnO) in all aspects of life, toxicological research on ZnO NPs is receiving increasing attention in these days. In this study, the toxicity of ZnO NPs in a human pulmonary adenocarcinoma cell line LTEP-a-2 was tested in vitro. Log-phase cells were exposed to different levels of ZnO NPs for hours, followed by colorimetric cell viability assay using tetrazolium salt and cell survival rate assay using trypan blue dye. Cell morphological changes were observed by Giemsa staining and light microscopy. Apoptosis was detected by using fluorescence microscopy and caspase-3 activity assay. Both intracellular reactive oxygen species (ROS) and reduced glutathione (GSH) were examined by a microplate-reader method. Results showed that ZnO NPs (≥ 0.01 μg/mL) significantly inhibited proliferation (P < 0.05) and induced substantial apoptosis in LTEP-a-2 cells after 4 h of exposure. The intracellular ROS level rose up to 30-40% corresponding to significant depletion (approximately 70-80%) in GSH content in LTEP-a-2 cells (P < 0.05), suggesting that ZnO NPs induced apoptosis mainly through increased ROS production. This study elucidates the toxicological mechanism of ZnO NPs in human pulmonary adenocarcinoma cells and provides reference data for application of nanomaterials in the environment.