Assessing the potential phytotoxicity of digestate from winery wastes

Evaluation of Toxicity and Genotoxicity of Concrete Cast with Steel Slags Using Higher Terrestrial Plants

The potential impact of concrete mixtures containing steel slag (SS) as a partial replacement of natural aggregates (NA) on the terrestrial ecosystem was assessed using a battery of plant-based bioassays. Leaching tests were conducted on four concrete mixtures and one mixture containing only NA (reference concrete). Leachates were tested for phytotoxicity using seeds of Lepidium sativum, Cucumis sativus, and Allium cepa. Emerging seedlings of L. sativum and A. cepa were used to assess DNA damage (comet test). The genotoxicity of the leachates was also analyzed with bulbs of A. cepa using the comet and chromosome aberration tests. None of the samples caused phytotoxic effects. On the contrary, almost all the samples supported the seedlings; and two leachates, one from the SS-containing concrete and the other from the reference concrete, promoted the growth of C. sativus and A. cepa. The DNA damage of L. sativum and A. cepa seedlings was significantly increased only by the reference concrete sample. In contrast, the DNA damage in A. cepa bulbs was significantly enhanced by the reference concrete but also by that of a concrete sample with SS. Furthermore, all leachates caused an increase in chromosomal aberrations in A. cepa bulbs. Despite some genotoxic effects of the concrete on plant cells, the partial replacement of SS does not seem to make the concrete more hazardous than the reference concrete, suggesting the potential use of SS as a reliable recycled material. Environ Toxicol Chem 2023;42:2193-2200. © 2023 The Authors. Environmental Toxicology and Chemistry published by Wiley Periodicals LLC on behalf of SETAC.

Allium cepa tests: A plant-based tool for the early evaluation of toxicity and genotoxicity of newly synthetized antifungal molecules

Many fungal genera such as Aspergillus, Penicillium, Fusarium and Alternaria are able to produce, among many other metabolites, the aflatoxins, a group of toxic and carcinogenic compounds. To reduce their formation, synthetic fungicides are used as an effective way of intervention. However, the extensive use of such molecules generates long-term residues into the food and the environment. The need of new antifungal molecules, with high specificity and low off-target toxicity is worth. The aim of this study was to evaluate: i) the toxicity and genotoxicity of newly synthesized molecules with a good anti-mycotoxic activity, and ii) the suitability of the Allium cepa multi-endpoint assay as an early screening method for chemicals. Eight compounds were tested for toxicity by using the A. cepa bulb root elongation test and for genotoxicity using the A. cepa bulb mitotic index, micronuclei and chromosome aberrations tests. Three molecules showed no toxicity, while two induced mild toxic effects in roots exposed to the highest dose (100 µM). A more pronounced toxic effect was caused by the other three compounds for which the EC50 was approximately 50 μM. Furthermore, all molecules showed a clear genotoxic activity, both in terms of chromosomal aberrations and micronuclei. Albeit the known good antifungal activity, the different molecules caused strong toxic and genotoxic effects. The results indicate the suitability of experiments with A. cepa as a research model for the evaluation of the toxic and genotoxic activities of new molecules in plants before they are released into the environment.

Hydrochar and hydrochar co-compost from OFMSW digestate for soil application: 2. agro-environmental properties

The work concerns the study of the hydrochar from digestate and hydrochar co-compost characterization as amendments. The processes for hydrochar and co-compost production were described in Part 1 of this work (Scrinzi et al., 2022). The amendment properties of hydrochar (produced at 180-200-220 °C for 3 h) and co-composts (25%, 50%, and 75% hydrochar percentage of digestate substitution) were assessed by phytotoxicity, plant growth bioassay, and soil effect. Different seeds species (Lepidium sativum, Cucumis sativus, and Sorghum bicolor sp.) were dosed at increased concentrations using both wet raw amendments and their water extracts. The chemical characterization showed phytotoxic compounds content depending on both the initial feedstock (digestate) and the HTC process; at the same time, the analysis highlighted the reduction of these compounds by composting (organic acid, polyphenols, salt concentration). The dose-response was analyzed by the Cedergreen-Streibig-Ritz model and the half-maximal effective concentration (EC50) was calculated based on this equation. The soil properties and GHG emissions measurements (CH₄, CO₂, N₂O, and NH₃) highlighted the effect on N dynamics and on soil respiration induced by substrates. The HC200 soil application determined a significant impact on CO₂ and N₂O emission and NH₃ volatilization (10.82 mol CO₂/m²; 51.45 mmol N₂O/m²; 112 mol NH₃/m²) and a significant reduction of total N and TOC (46% of TKN and 49% of TOC). The co-compost (75%) showed specific effects after soil application compared to other samples an increase of available P (48%), a greater content of nitrogen (1626 mg/kg dry basis), and a reduction of organic carbon (17%). Our results demonstrate the good quality of co-compost and at the same time the validity of this post-treatment for addressing many issues related to hydrochar use in the soil as an amendment, confirming the suitability of HTC process integration for digestate treatment in anaerobic digestion plants.

Hydrochar and hydrochar co-compost from OFMSW digestate for soil application: 1. production and chemical characterization

The best available technique (BAT) for managing the organic fraction of municipal solid waste (OFMSW) is represented by anaerobic digestion (AD) and subsequent composting. This research explored a new industrial model in the framework of the C2Land international project, with the insertion of hydrothermal carbonization (HTC) as a post-treatment for OFMSW digestate. The reaction was set for 3 h at three different temperatures (180 ÷ 220 °C); the wet solid hydrochar obtained after filtration was then co-composted with greenery waste as a bulking agent and untreated OFMSW digestate in four different proportions in bench-scale bioreactors. The hydrochars and the hydrochar co-composts were suitable for agro-industrial applications, while the HTC liquors were tested in biochemical methane potential (BMP) for internal recirculation to AD. The scenarios proposed can be beneficial for plant enhancement and increased biogas production. This study reports results connected to the production phase. Mass balances confirmed that, during HTC, phosphorus precipitated into the solid products, organic nitrogen partially mineralized into ammonium, and oxidizable organic matter solubilized. The selected hydrochar obtained at 200 °C had mean (dry) solid, liquid, and gaseous yields equal to 77, 20, and 3 %_db, respectively. The dynamic respirometric index (DRI) confirmed that the reproduced BAT for the composting process was effective in producing high-quality hydrochar co-composts in terms of biological stability. The BMP tests on HTC liquors showed some inhibitory effects, suggesting the need for future studies with inoculum adaptation and co-digestion, to dilute toxic compounds and enhance biogas production. Part 2 of this study describes the agro-environmental properties of hydrochars and hydrochar co-composts, including the beneficial effect of composting on hydrochars phytotoxicity.

The Effects of Soil Application of Digestate Enriched with P, K, Mg and B on Yield and Processing Value of Sugar Beets

The aim of this research was to find out if the supplementation of digestate, a by-product of the anaerobic digestion of sugar beet pulp, with phosphorus, potassium, magnesium and boron can improve digestate performance as a soil amendment. The materials of this study were: digestate and sugar beet roots (Beta vulgaris cv. Fighter). A field trial was carried out on sugar beet growth under soil application conditions of solid and liquid digestate fractions with or without supplementation with P, K, Mg and B. It was shown that the root yield obtained from the plots amended with digestate supplemented with P, K, Mg and B was higher compared to the yield of other treatments. Soil amendment with digestate supplemented with P, K, Mg and B affected quality parameters of sugar beet roots. An increase in the following parameters under the effects of enriched digestate application was found: sucrose content, dry residue, pomace content, inverted sugars, α-amino and amide nitrogen fractions, as well as sodium and potassium content. A reduction in the content of conductometric ash was noted but this difference was not proven. The enrichment of digestate with P, K, Mg and B resulted in the beneficial modification of beet roots’ processing parameters with the exception of the predicted content of sugar in molasses. In the case of the liquid fraction and its supplementation with P, K, Mg and B, six among eleven technological quality parameters were increased.

Potential use of Schumannianthus dichotomus waste: the phytotoxic activity of the waste and its identified compounds

The phytotoxic potential of the leaves and twigs of Schumannianthus dichotomus, discarded in the mat-making industry against four test plants (lettuce (Lactuca sativa L.), rapeseed (Brassica napus L.), foxtail fescue (Vulpia myuros (L.) C.C. Gmel.) and timothy (Phleum pratense L.)) was investigated and found strong phytotoxic activity. An assay-guided fractionation of S. dichotomus extarcts against cress (Lepidium sativum L.) through a series of column chromatography steps yielded two compounds, 8-(5-oxo-2,5-dihydrofuran-2-yl) octanoic acid (ODFO) and (E)-6-hydroxy-2,6-dimethylocta-2,7-dienoic acid (8-carboxylinalool). ODFO and 8-carboxylinalool showed strong phytotoxic activity against cress and timothy. The concentrations required for 50% growth inhibition (I50 value) of the seedlings of cress and timothy were 111.94-128.01 and 36.30-91.75 µM, respectively, for ODFO, but the values were much higher at 315.98-379.13 and 107.92-148.41 µM, respectively, for 8-carboxylinalool, indicating the stronger phytotoxic activity of ODFO. This study is the first to isolate ODFO and 8-carboxylinalool from S. dichotomus and their phytotoxic potential while ODFO is firstly encountered from any natural source. The growth inhibitory activity of the identified compounds may explain their role in the phytotoxic activity of S. dichotomus, which suggests the possible use of its leaves and twigs or its active constituents as natural bioherbicides.

Effects of woody biochar on dry thermophilic anaerobic digestion of organic fraction of municipal solid waste

This study presents the results of semi-pilot scale anaerobic digestion tests conducted under dry thermophilic conditions with the addition of biochar (6% on fresh mass basis of inoculum), derived from an industrial gasification plant, for determining biogas and biomethane production from organic fraction of municipal solid waste. By using two types of inocula (from a full-scale dry anaerobic digestion plant and from lab-scale biomethanation tests), the obtained experimental results did not show significant increase in methane yield related to the presence of biochar (330.40 NL CH₄ kgVS^-1 using plant inoculum; 335.41 NL CH₄ kgVS^-1 using plant inoculum with biochar, 311.78 NL CH₄ kgVS^-1 using lab-inoculum and 366.43 NL CH₄ kgVS^-1 using lab-inoculum with biochar), but led to significant changes in the microbial community composition. These results are likely related with the specific biochar physical-chemical features and low adsorption potential. Resulting digestate quality was also investigated: biochar-enriched digestates were characterized by increased biological stability (809 ± 264 mg O₂ kgVS^-1 h^-1 vs. 554 ± 76 mg O₂ kgVS^-1 h^-1 for biochar-free and biochar-enriched digestates, respectively), lower heavy metals concentrations (with the exception of Cd), but higher polycyclic aromatic hydrocarbons content, with a reported maximum concentration of 8.9 mgPAH kgTS^-1 for biochar-enriched digestate derived from AD test with lab-inoculum, which could trigger non-compliance with regulation limits for agricultural reuse of digestates. However, phytotoxicity assessments showed a decreased toxicity of biochar-containing digestates when compared to biochar-free digestates.

Production of Microalgal Slow-Release Fertilizer by Valorizing Liquid Agricultural Digestate: Growth Experiments with Tomatoes

Anaerobic Digestion (AD) is a process that is well-known and fast-developing in Europe. AD generates large amounts of digestate, especially in livestock-intensive areas. Digestate has potential environmental issues due to nutrients (such as nitrogen) lixiviation or volatilization. Using liquid digestate as a nutrient source for microalgae growth is considered beneficial because digestate could be valorized and upgraded by the production of an added value product. In this work, microalgal biomass produced using liquid digestate from an agricultural biogas plant was investigated as a slow-release fertilizer in tomatoes. Monoraphidium sp. was first cultivated at different dilutions (1:20, 1:30, 1:50), in indoor laboratory-scale trials. The optimum dilution factor was determined to be 1:50, with a specific growth rate of 0.13 d−1 and a complete nitrogen removal capacity in 25 days of culture. Then, outdoor experiments were conducted in a 110 dm3 vertical, closed photobioreactors (PBRs) in batch and semi-continuous mode with 1:50 diluted liquid digestate. During the batch mode, the microalgae were able to remove almost all NH4+ and 65 (±13) % of PO43−, while the microalgal growth rate reached 0.25 d−1. After the batch mode, the cultures were switched to operate under semi-continuously conditions. The cell densities were maintained at 1.3 × 107 cells mL−1 and a biomass productivity around 38.3 mg TSS L−1 d−1 during three weeks was achieved, where after that it started to decline due to unfavorable weather conditions. Microalgae biomass was further tested as a fertilizer for tomatoes growth, enhancing by 32% plant growth in terms of dry biomass compared with the control trials (without fertilization). Similar performances were achieved in tomato growth using synthetic fertilizer or digestate. Finally, the leaching effect in soils columns without plant was tested and after 25 days, only 7% of N was leached when microalgae were used, against 50% in the case of synthetic fertilizer.

The agricultural use potential of the detoxified textile dyeing sludge by integrated Ultrasound/Fenton-like process: A comparative study

Enhancing industrial sludge detoxification is of scientific and practical significance in confronting urban development and stringent environmental regulations. A strategy combining ultrasound (US) with the zero-valent iron/EDTA/Air (ZEA) process was proven to be eco-friendly, being efficient in the removal of toxic compounds from textile dyeing sludge in our previous studies. In this paper, therefore, the detoxification effects of three advanced oxidation processes (US, ZEA, US/ZEA) on textile dyeing sludge were comparatively evaluated for the first time through alteration of the sludge's physico-chemical parameters (e.g., macronutrients, heavy metals, and persistent organic pollutants) and toxicity (plants and aquatic biota), by which the appropriateness of industrial sludge's agricultural use was assessed. The results showed that US led to the least alteration of the physico-chemical properties, and the treated sludge became less biodegradable, as demonstrated by XPS. With ZEA treatment, persistent organic pollutants (POPs) were degraded by oxidation, and heavy metals were more leachable, leading to effective detoxification with a relatively low sludge dose, but an excessive amount of EDTA would negatively change the fertilizing properties of the sludge. However, the integration of US and ZEA could avoid this situation, as US promoted the degradation of EDTA and POPs, thus causing the least inhibition or even a noticeable stimulation of plant growth when the sludge dosage was 7.5 t_dw/ha (recommended dosage by the latest legislation in China). Aquatic organism toxicity tests further confirmed that US/ZEA treatment realized the most significant toxicity reduction, leading to the slightest environmental disruption. This study could be instructive in providing guidance for industrial sludge management considering agricultural use.

Human and veterinary antibiotics induce hormesis in plants: Scientific and regulatory issues and an environmental perspective

Veterinary and human pharmaceuticals have been widely used in the developed world, thus increasing their accumulation in the environment and thereby posing ecological risks. Earlier studies report that active pharmaceutical ingredients induce hormesis in plants, i.e. at low doses may enhance plant health whereas at high doses may suppress plant vigor. There is hitherto no study critically reviewing the effects of antibiotics on plants within a hormetic context despite effects of low doses on plants can have implications to animals, including humans, and to ecological processes. This study critically reviews for first time antibiotic-induced hormesis in plants, both quantitatively and qualitatively. Hormesis was induced by several antibiotics in a variety of species and endpoints. The maximum stimulatory response (MAX) was commonly <1.5-fold the control response and the distance from MAX to no-observed-adverse-effect level (NOAEL) was commonly up to 10-fold. Further quantitative and qualitative evaluations are provided and discussed in relation to scientific and regulatory aspects. Low doses of antibiotics are equally important as high doses as they can negatively affect plants, depending on plant tissues and the time tissues are subject to exposure. Antibiotic-induced hormesis in plants provides a significant environmental perspective and should be incorporated into the hazard and risk assessment process.

CAPSULE

Common antibiotics released in the environment induce hormesis in plants, urging for re-examination of the risk assessment practices by worldwide regulatory agencies.

Effects of sludge enhanced aeration on nutrient contents and phytotoxicity of anaerobically digested centrate

In this study, we investigated the impact of intensive aeration pre-treatment on nutrient contents and phytotoxicity of anaerobically digested manure centrate. Activated sludge from conventional wastewater treatment plants was added to reinforce the aeration process. Results show that the addition of activated sludge did not negatively affect the nutrient contents, but significantly reduced the phytotoxicity of digested centrate, as indicated by an enhancement of seed germination index, during the aeration treatment. Based on the orthogonal experiment and following statistical analysis, the lowest phytotoxicity of digested centrate could be achieved under the aeration conditions: sludge concentration of 6 g/L, aeration time of 2 h, gas/water ratio of 40:1, and pH = 6.5. Of these operational parameters, the digested centrate pH dominantly determined its nutrient contents (e.g., amino acids, total phosphorus, and ammonium) and phytotoxicity. These results were further verified by hydroponic experiments, which showed that using digested centrate after sludge enhanced aeration as the nutrient solution facilitated the growth and dry biomass of maize.