Bakelite, the first synthetic plastic, is a rather unexplored material in the field of ecotoxicology, despite its long production and use. The aim of this study was to investigate the ecotoxicity of Bakelite microplastics (before and after leaching) and its leachates on four aquatic organisms: the crustacean Daphnia magna, the plant Lemna minor, the bacterium Allivibrio fischeri and the alga Pseudokirchneriella subcapitata. Bakelite microplastics before and after leaching and leachates affected all organisms, but to varying degrees. Leachates showed increased ecotoxicity to Daphnia magna, while Pseudokirchneriella subcapitata was more affected by particles. For Lemna minor and Allivibrio fischeri, the effects of particles before leaching and leachate were comparable, while the negative effect of particles after leaching was minimal or not present. All leachates were analysed, and phenol and phenol-like compounds were the predominant organics found. In addition, bioadhesion of Bakelite microplastics to the surface of Daphnia magna and Lemna minor was confirmed, but the particles were mainly weakly adhered. Results of this study suggest that, in addition to the recently studied microplastics from consumer products (e.g. from polyethylene and polystyrene), microplastics from industrial plastics such as Bakelite may be of increasing concern, primarily due to leaching of toxic chemicals.

A biological treatment method was tested in laboratory conditions for the removal of hydrocarbons contained in a waste disposal soil sample consisting of excavated sandy soil from a former fueling station. Two fractions of hydrocarbons were quantified by GC-FID: diesel (C₁₀–C₂₁) and lubricant oil (C₂₂–C₄₀). Meat and bone meal (MBM, 1% w/w) was used as a bio-stimulant agent for soil organisms. Cyclodextrin, an oligosaccharide produced from starch by enzymatic conversion, was also used to assess its ability to improve the bioavailability/biodegradability of hydrocarbons in the soil. Parameters such as temperature, pH, water content and aeration (O₂ availability) were monitored and optimized to favor degradation processes. Two different experimental tests were prepared: one to measure the degradation of hydrocarbons; the other to monitor the mobility of some elements in the soil and in the leachate produced by watering with tap water. Soil samples treated with MBM and cyclodextrin showed, over time, a greater removal of the more persistent hydrocarbon fraction (lubricant oil). MBM-treated soils underwent a faster hydrocarbon removal kinetic, especially in the first treatment period. However, the final hydrocarbon concentrations are comparable in all treatments, including control. Over time, the effect of cyclodextrin on hydrocarbon degradation seemed to be relevant. MBM-treated soils sequestered lead in the very first weeks. These results highlight the intrinsic capacity of soil, and its indigenous microbial communities, to degrade petroleum hydrocarbons and suggest that MBM-induced bioremediation is a promising, environmentally friendly technology which should be considered when dealing with hydrocarbon/heavy metal co-contaminated soils.

A large amount of disposable plastic face masks (DPFs) is produced and used during the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) pandemic, which results in an inevitable consequence of the dramatic increase of DPFs waste. However, the impact of DPFs exposure to the environment on their toxicity is rarely considered. In this study, a range of 76–276 items/L microplastics (MPs) was detected in the DPFs leachates, and fibrous (> 80.3%) and polypropylene (PP, > 89.2%) MPs were dominant. Co, Cu, Ni, Sr, Ti and Zn, were commonly detected in all leachates of the tested DPFs. Organics, such as acetophenone, 2,4-Di-tert-butylphenol, benzothiazole, bisphenol-A and phthalide, were found in the DPFs leachate, which were including organic solvents and plasticizer. Besides, we first found an emerging environmental risk substance, namely environmentally persistent free radicals (EPFRs), was generated in the DPFs leachates. The characteristic g-factors of the EPFRs was in a range of 2.003–2.004, identified as mixture of carbon- and oxygen-centered radicals. By means of in vitro toxicity assay, the DPFs leachate were confirmed to cause cytotoxicity and oxidative stress. Significantly, it is found that the formed EPFRs could contribute more toxic effects. Furthermore, when compared to N95 respirators, the tested surgical masks tend to release more MPs, leach more metals and organics, and generate more EPFRs. Surgical masks were thus showed higher risk than N95 respirators after exposure to water. This work highlights the importance of understanding the chemical complexity and possible toxicity of DPFs for their risk assessment.

The aim of this study was to recover Sc as the main product and Fe as a by-product from Hungarian bauxite residue/red mud (RM) waste material by solvent extraction (SX). Moreover, a new technique was developed for the selective separation of Sc and Fe from real RM leachates. The presence of high Fe content (∼38%) in RM makes it difficult to recover Sc because of the similarity of their physicochemical properties. Pyrometallurgical and hydrometallurgical methods were applied to remove the Fe prior to SX. Two protocols based on organophosphorus compounds (OPCs) were proposed, and the main extractants were evaluated: bis(2-ethylhexyl) phosphoric acid (D2EHPA/P204) and tributyl phosphate (TBP). The results showed that SX using diethyl ether and tri-n-octylamine (N₂₃₅) was efficient in extracting Fe(III) from the HCl leachate as HFeC1₄. Over 97% of Sc was extracted by D2EHPA extractant under the following conditions; 0.05 mol/L of D2EHPA concentration, A/O phase ratio of 3:1, pH 0–1, 10 min of shaking time, and a temperature of 25 °C. Sc(OH)₃ as a precipitate was efficiently obtained by stripping from the D2EHPA organic phase by 2.5 mol/L of NaOH with a stripping efficiency of 95%. In the TBP system, 99% of Sc was extracted under the following conditions: 12.5% vol of TBP, an A/O phase ratio of 3:1, 10 min of shaking time, and a temperature of 25 °C. The Sc contained in the TBP organic phase could be efficiently stripped by 1 mol/L of HCl with a stripping efficiency of 92.85%.

Rare earth elements (REEs) concentrated in soils have attracted increasing attention about their impact on soil health as emerging contaminants. However, the sources of REEs enriched in soils are diverse and need to be further investigated. Here, surface soil samples were collected from southern Jiangxi Province, China. REEs contents and soil physicochemical properties were determined, and cerium (Ce) and europium (Eu) anomalies were calculated. Moreover, we established a model to further identify the main sources of REEs accumulation in the studied soils. Results show that the abundance of soil REEs reveals larger spatial variation, suggesting spatially heterogeneous distribution of REEs. The median content of light REEs in soils (154.5 mg kg⁻¹) of the study area was higher than that of heavy REEs and yttrium (35.8 mg kg⁻¹). In addition, most of the soil samples present negative Ce anomalies and all the soil samples present negative Eu anomalies implying the combined effect of weathering and potential exogenous inputs on soil REEs. Positive matrix factorization modeling reveals that soil REEs content is primarily influenced by soil parent materials. Potential anthropogenic sources include mining-related leachate, traffic exhaust, and industrial dust. These results demonstrate that the identification of sources of soil REEs is an important starting point for targeted REEs sources management and regulation of excessive and potentially harmful REEs levels in the soil.

The study aimed to evaluate the ecotoxicity of soil (S) amended with biochars (BCKN) produced by the thermal conversion of sewage sludge (SSL) at temperatures of 500 °C, 600 °C, or 700 °C and SSL itself. The ecotoxicological tests were carried out on organisms representing various trophic levels (Lepidium sativum in plant, Folsomia candida in invertebrates, and Aliivibrio fischeri in bacteria). Moreover, the study evaluated the effects of three plants (Lolium perenne, Trifolium repens, and Arabidopsis thaliana) growing on BCKN700-amended soil on its ecotoxicological properties. The experiment was carried out for six months. In most tests, the conversion of sewage sludge into biochar caused a significant decrease in toxicity by adding it to the soil. The pyrolysis temperature directly determined this effect. The soil amended with the biochars produced at higher temperatures (600 °C and 700 °C) generally exhibited lower toxicity to the test organisms than the SSL. Because of aging, all the biochars lost their inhibition properties against the tested organisms in the solid-phase tests and had a stimulating influence on the reproductive ability of F. candida. With time, the fertilizing effect of the BCKN700 amended soil also increased. The aged biochars also did not have an inhibitory effect on A. fischeri luminescence in the leachate tests. The study has also demonstrated that the cultivation of an appropriate plant species may additionally reduce the toxicity of soil fertilized with biochar. The obtained results show that the conversion of sewage sludge to biochar carried out at an appropriate temperature can become a useful method in reducing the toxicity of the waste and while being safe for agricultural purposes.

Restoring woody vegetation to riparian zones helps to protect waterways from excessive sediment and nutrient inputs. However, the associated leaf litter can be a major source of dissolved organic matter (DOM) leached into surface waters. DOM can lead to the formation of disinfection by-products (DBPs) during drinking water treatment. This study investigated the DBPs formed during chlorination of DOM leached from leaf litter and assessed the potential toxicity of DBPs generated. We compared the leachate of two native Australian riparian trees, Casuarina cunninghamiana and Eucalyptus tereticornis, and a reservoir water source from a catchment dominated by Eucalyptus species. Leachates were diluted to dissolved organic carbon concentrations equivalent to the reservoir (~9 mg L⁻¹). E. tereticornis leachates produced more trihalomethanes (THMs), haloacetic acids (HAAs), and haloketones after chlorination, while C. cunninghamiana produced more chloral hydrate and haloacetonitriles. Leachate from both species produced less THMs and more HAAs per mole of carbon than reservoir water. This may be because reservoir water had more aromatic, humic characteristics while leaf leachates had relatively more protein-like components. Using in vitro bioassays to test the mixture effects of all chemicals, chlorinated E. tereticornis leachate induced oxidative stress in HepG2 liver cells and bacterial toxicity more frequently and at lower concentrations than C. cunninghamiana and reservoir water. Overall, this study has shown that the DOM leached from litter of these species has the potential to generate DBPs and each species has a unique DBP profile with differing bioassay responses. E. tereticornis may pose a relatively greater risk to drinking water than C. cunninghamiana as it showed greater toxicity in bioassays. This implies tree species should be considered when planning riparian zones to ensure the benefits of vegetation to waterways are not offset by unintended increased DBP production and associated toxicity following chlorination at downstream drinking water intakes.

Nitrate leaching caused by overusing or misusing nitrogen (N) fertilizers in field vegetable cropping systems in China is a leading contributor to nitrate contamination of groundwater. Identification of the critical fertilizer N input rate could support management decisions that maintain yields while reducing the impact of nitrate leaching on groundwater. A four-season field experiment involving six N treatments (0, 60, 120, 180, 240, and 300 kg N ha⁻¹) was undertaken to investigate the impacts of various N rates on N use efficiency (NUE), seasonal nitrate leaching loss (SNLL), nitrate residue (NR), and radish yield, and to identify the critical N fertilizer rate for both optimum yield and minimum nitrate leaching loss in a field vegetable (radish, Raphanus sativus L.) cropping system in northern China. The results showed that radish yield enhanced quadratically and NUE reduced linearly with increasing N addition, while the NR and SNLL increased exponentially. The yield did not increase markedly when N fertilization exceeded 180 kg N ha⁻¹. SNLL and nitrate concentrations in the leachate averaged 11.5–71.5 kg N ha⁻¹ and 5.1–35.6 mg N L⁻¹, respectively, under N rates of 60–300 kg N ha⁻¹. The results showed that N fertilizer rate ranging from 180 to 196 kg N ha⁻¹ resulted in high yields and low nitrate leaching losses. Compared with those in response to the N fertilizer amount applied by local farmers, the NUE, NR, and SNLL in response to the N fertilizer amount identified in this study increased, decreased by 30.9%–35.0%, and decreased by 49.9%–55.7%, respectively, without any yield loss. Thus, a critical N fertilizer rate ranging from 180 to 196 kg N ha⁻¹ is recommended to obtain optimum yields with minimal environmental risks in radish fields in northern China.

Microplastic pollution is emerging as a global environmental issue, and its potential for transferring hazardous chemicals to aquatic organisms is gaining attention. Studies have investigated the transfer of chemicals, mainly sorbed chemicals, through ingestion of microplastics by organisms, but limited information is available regarding chemical additives and uptake via the aqueous route through plastic leaching. In this study, we compared two bioaccumulation pathways of the additive hexabromocyclododecane (HBCD) by exposing mussels (Mytilus galloprovincialis) to two different sizes of expanded polystyrene (EPS): inedible size (4.2–5.5 mm) for leachate uptake and edible size (20–770 μm) for particle ingestion and leachate uptake. Over 10 days, the HBCD concentration increased significantly in mussels in the EPS exposure groups, indicating that EPS microplastic acts as a source of HBCD to mussels. The concentration and isomeric profiles of HBCD in mussels show that uptake through the aqueous phase is a more significant pathway for bioaccumulation of HBCD from EPS to mussels than particle ingestion. HBCD levels measured in EPS, leachate and exposed mussels from this study are environmentally relevant concentration. The fate and effects of chemical additives leached from plastic debris in ecosystem requires further investigation, as it may affect numerous environments and organisms through the aqueous phase.

Plastic polymers such as polyvinyl chloride (PVC) may contain chemical additives, such as lead (Pb), that are leachable in aqueous solution. The fragmentation into microplastics (MPs) of plastics such as PVC may facilitate desorption of chemical additives and increase exposure of aquatic animals. In this study, the role of chemical additives in the aqueous toxicity of PVC, high-density polyethylene (HDPE) and polyethylene terephthalate (PET) MPs were investigated in early-life stage zebrafish (Danio rerio) by assessment of changes in expression of biomarkers. Exposure of zebrafish larvae to PVC for 24 h increased expression of metallothionein 2 (mt2), a metal-binding protein, but no changes in expression of biomarkers of estrogenic (vtg1) or organic (cyp1a) contaminants were observed. HDPE and PET caused no changes in expression of any biomarkers. A filtered leachate of the PVC also caused a significant increase in expression of mt2 and indicated that a desorbed metal additive likely elicited the response in zebrafish. Metal release was confirmed by acid-washing the MPs which mitigated the response in mt2. Metal analysis showed Pb leached from PVC into water during exposures; at 500 mg PVC L⁻¹ in water, 84.3 ± 8.7 μg Pb L⁻¹ was measured after 24 h. Exposure to a Pb-salt at this concentration caused a comparable mt2 increase in zebrafish as observed in exposures to PVC. These data indicated that PVC MPs elicited a response in zebrafish but the effect was indirect and mediated through desorption of Pb from PVC into the exposure water. Data also indicated that PVC MPs may act as longer-term environmental reservoirs of Pb for exposure of aquatic animals; the Pb leached from PVC in 24 h in freshwater equated to 2.52% of total Pb in MPs leachable by the acid-wash. Studies of MPs should consider the potential role of chemical additives in toxicity observed.