Impact of sludge deposition on biodiversity

Amendment of soils with metal-rich sludge: Potential water toxicity due to metal release via over-time slaking

Industrial metal-rich sludge can improve soil properties, but it is potentially toxic to soils and adjacent aquatic systems. The soil-sludge-water interactions influence metals bioavailability over time, a phenomenon mostly regulated by the still debatable "sludge physical protection" or "sludge delayed release" hypotheses. The present study aimed to investigate: (1) whether sludge increases soil aggregate stability against slaking, (2) which hypothesis mostly regulates metal release from soils to water and (3) the ecotoxicity of the metals released during soil slaking for aquatic organisms. Under a realistic field scale, soils amended with an industrial sludge or spiked with equivalent metal solutions (of Cr, Cu, Ni, Zn) were collected over three months to test soil aggregate stability, the ecotoxicity of the slaking water and metal contents in soil and water. The "sludge physical protection" was verified for all metals, though for Cu the "sludge delayed release" hypothesis appears plausible after three months. Soil amendment with sludge did not lead to effects on the growth of the microalga Raphidocelis subcapitata, contrarily to the observed for the metal-spiked soil. Criteria regulating soils sludge-amendment management should thus include doses not hazardous to biota, and not only metal threshold levels.

Uptake and release of perfluoroalkyl carboxylic acids (PFCAs) from macro and microplastics

Microplastics and per- and polyfluoroalkyl substances (PFAS) are two of the most notable emerging contaminants reported in the environment. Micron and nanoscale plastics possess a high surface area-to-volume ratio, which could increase their potential to adsorb pollutants such as PFAS. One of the most concerning sub-classes of PFAS are the perfluoroalkyl carboxylic acids (PFCAs). PFCAs are often studied in the same context as other environmental contaminants, but their amphiphilic properties are often overlooked in determining their fate in the environment. This lack of consideration has resulted in a diminished understanding of the environmental mobility of PFCAs, as well as their interactions with environmental media. Here, we investigate the interaction of PFCAs with polyethylene microplastics, and identify the role of environmental weathering in modifying the nature of interactions. Through a series of adsorption-desorption experiments, we delineate the role of the fluoroalkyl tail in the binding of PFCAs to microplastics. As the number of carbon atoms in the fluoroalkyl chain increases, there is a corresponding increase in the adsorption of PFCAs onto microplastics. This relationship can become modified by environmental weathering, where the PFCAs are released from the macro and microplastic surface after exposure to simulated sunlight. This study identifies the fundamental relationship between PFCAs and plastic pollutants, where they can mutually impact their thermodynamic and transport properties.

Phyto-genotoxicity assessment of different associations between sludges from Water and Sewage Treatment Plants, before and after the bioremediation process

Water Treatment Plants (WTP) and Sewage Treatment Plants (STP) generate residues known as sludge (WS and SS, respectively). SS and WS present some positive characteristics for reuse in agriculture. The aim of the present study was to evaluate, using the Allium cepa test, the effectiveness of the bioremediation process in the detoxification of SS and WS sludges. In this study, the phytotoxic, cytotoxic, genotoxic, and mutagenic potentials of pure sludge samples (WS and SS) were evaluated, as well as the association of these two sludges with soil (S), before and after the bioremediation process. In the T0 period (before undergoing bioremediation), the SS, SS + S, and SS + WS samples totally inhibited the germination of A. cepa, proving the high phytotoxic potential of these samples. For the T1 period (after 6 months of bioremediation), phytotoxicity was observed for the SS, SS + S, SS + WS, and SS + WS + S samples, but there was not a complete inhibition of germination and radicles growth, allowing the evaluation of the other parameters (cytogenotoxic and mutagenic potential). No cytotoxicity was observed for any sample, both in T0 and T1. As for the genotoxicity parameter, a significant result was observed for the pure WS sample in T0 and for all samples in T1, when compared to NC. The genotoxic alteration most found in meristematic cells exposed to treatments was of binucleated cells. Mutagenic potential was also observed for samples of WS and WS + S in T0. From this study, we can conclude that, after six months of bioremediation, despite the SS phytotoxicity being reduced, all samples were genotoxic to the A. cepa organism test.

Speciation, controlling steps and pathways of silver release from the sludge generated from coagulation of wastewater spiked with silver nanoparticles

Sludge generated in wastewater treatment facilities is an integral part for the introduction of silver nanoparticles (AgNPs) to the terrestrial environment, which would cause some adverse ecosystem responses. The understanding of silver release process from the sludge is important to evaluate their risks. In this study, the amount and speciation of the released silver were investigated by taking the sludge generated by wastewater coagulation with AgNPs added (denoted as sludge_C-AgNPs) an example, and kinetic analysis and density functional theory (DFT) calculations were first used to explore the controlling steps and pathways about the silver release. The results showed that sludge_C-AgNPs could release the dissolved silver and the colloidal silver. Beside Cl^-, Ca²⁺ in the leaching solution could enhance the silver release of sludge_C-AgNPs, especially for the colloidal silver. The released colloidal silver restricted in size from 40 nm to 100 nm with irregular shape. Although the oxidative dissolution of Ag⁰ was the origin of the silver release pathways from the sludge_C-AgNPs, the silver diffusion was the controlling step due to the spontaneous binding between silver and the hydrolysates of polyaluminium chloride in sludge_C-AgNPs. However, Ca²⁺ in the leaching solution could occupy the binding site of silver on sludge_C-AgNPs, which would increase the diffusion rate of silver over the oxidative rate of Ag⁰. With this condition, the controlling step of silver release from sludge_C-AgNPs turned to the oxidative dissolution of Ag⁰. Our findings are important to assess the fate of AgNPs in wastewater treatment as well as sludge applications.

Life cycle assessment of sewage sludge treatment and disposal based on nutrient and energy recovery: A review

With the acceleration of urbanization, the production of urban sludge is increasing rapidly. To minimize resource input and waste output, it is crucial to execute analyses of environmental impact and assessments of sustainability on different technical strategies involving sludge disposal based on Life Cycle Assessment (LCA), which is a great potential mean of environmental management adopted internationally in the 21st century. This review aims to compare the environmental sustainability of existing sludge management schemes with a purpose of nutrient recovery and energy saving, respectively, and also to include the substitution benefits of alternative sludge products. Simultaneously, LCA research regarding the emerging sludge management technologies and sludge recycling (cement, adsorbent, bricks) is analyzed. Additionally, the key aspects of the LCA process are worth noting in the context of the current limitations reviewed here. It is worth emphasizing that no technical remediation method can reduce all environmental damage simultaneously, and these schemes are typically more applicable to the assumed local conditions. Future LCA research should pay more attention to the toxic effects of different sludge treatment methods, evaluate the technical ways of adding pretreatment technology to the 'front end' of the sludge treatment process, and further explore how to markedly reduce environmental damage in order to maximize energy and nutrient recovery from the LCA perspective.

Occurrence and leaching of silver in municipal sewage sludge in China

Sewage treatment plants effectively remove silver (Ag) from sewage. Sewage sludge can therefore be important Ag sinks, polluting the environment with this element. In this work, we report a nation-wide survey on the Ag content of sewage sludge in China (0.23-19.02 mg kg^-1, average 2.72 mg kg^-1). Furthermore, we identify that sludge disposal represents an important Ag pollution source (84.48 tons in 2016) for the environment by estimating the national and provincial inventories of sludge-borne Ag in China. Also the positive correlations between the per capita gross domestic product (GDP)/provincial GDP and the content/mass loadings of Ag highlighted the impact of human activities on Ag pollution. In different samples, strong complexation of thiosulfate contributed to the highest leaching concentration (95.00-438.15 μg kg^-1) and ratio (1.9-8.8%) of Ag, emphasizing the necessity of a long-term risk assessment for landfill and land application of sludge.

Legislation for the Reuse of Biosolids on Agricultural Land in Europe: Overview

The issues concerning the management of sewage sludge produced in wastewater treatment plants are becoming more important in Europe due to: (i) the modification of sludge quality (biological and chemical sludge are often mixed with negative impacts on sludge management, especially for land application); (ii) the evolution of legislation (landfill disposal is banned in many European countries); and (iii) the technologies for energy and material recovery from sludge not being fully applied in all European Member States. Furthermore, Directive 2018/851/EC introduced the waste hierarchy that involved a new strategy with the prevention in waste production and the minimization of landfill disposal. In this context, biological sewage sludge can be treated in order to produce more stabilized residues: the biosolids. In some European countries, the reuse of biosolids as soil improver/fertilizer in arable crops represents the most used option. In order to control the quality of biosolids used for land application, every Member State has issued a national regulation based on the European directive. The aim of this work is to compare the different approaches provided by European Member States for the reuse of biosolids in agricultural soils. A focus on the regulation of countries that reuse significant amount of biosolids for land application was performed. Finally, a detailed study on Italian legislation both at national and regional levels is reported.

Organic amendment additions to rangelands: A meta-analysis of multiple ecosystem outcomes

Interest in land application of organic amendments-such as biosolids, composts, and manures-is growing due to their potential to increase soil carbon and help mitigate climate change, as well as to support soil health and regenerative agriculture. While organic amendments are predominantly applied to croplands, their application is increasingly proposed on relatively arid rangelands that do not typically receive fertilizers or other inputs, creating unique concerns for outcomes such as native plant diversity and water quality. To maximize environmental benefits and minimize potential harms, we must understand how soil, water, and plant communities respond to particular amendments and site conditions. We conducted a global meta-analysis of 92 studies in which organic amendments had been added to arid, semiarid, or Mediterranean rangelands. We found that organic amendments, on average, provide some environmental benefits (increased soil carbon, soil water holding capacity, aboveground net primary productivity, and plant tissue nitrogen; decreased runoff quantity), as well as some environmental harms (increased concentrations of soil lead, runoff nitrate, and runoff phosphorus; increased soil CO₂ emissions). Published data were inadequate to fully assess impacts to native plant communities. In our models, adding higher amounts of amendment benefitted four outcomes and harmed two outcomes, whereas adding amendments with higher nitrogen concentrations benefitted two outcomes and harmed four outcomes. This suggests that trade-offs among outcomes are inevitable; however, applying low-N amendments was consistent with both maximizing benefits and minimizing harms. Short study time frames (median 1-2 years), limited geographic scope, and, for some outcomes, few published studies limit longer-term inferences from these models. Nevertheless, they provide a starting point to develop site-specific amendment application strategies aimed toward realizing the potential of this practice to contribute to climate change mitigation while minimizing negative impacts on other environmental goals.

Bonding of Butylparaben, Bis(2-ethylhexyl)-phthalate, and Perfluorooctanesulfonic Acid to DNA: Comparison with Benzo[a]pyrene Shows Low Probability for Strong Noncovalent DNA Intercalation

Parabens, phthalates, and perfluorinated compounds are pollutant compounds used in cosmetics, plastics, and fire-fighting foams. All three compounds have been studied over several years for toxicity mechanism; however, a clear view of their ability to bind to DNA has not been supplied empirically. In this work, a simulation study is done to reveal the interaction of three of these pollutants, bis(2-ethylhexyl)-phthalate (DEHP), butylparaben (BPRB), and the protonated form of perfluorooctanesulfonic acid (PFOS(H)), with DNA. The results show that the DEHP, PFOS(H), and BPRB bind with a probability of 1/5 to DNA, with respective bonding energies -23.96 kJ/mol (PFOS(H)), -94.92 kJ/mol (BPRB), and -216.52 kJ/mol (DEHP). The positive control, benzo[a]pyrene diol epoxide (BAP), which is known for its notorious DNA intercalation, binds at a rate of 3/5 simulations, with bonding energies of -6544.52, -7034.66, and -7578.67 kJ/mol. The results are compared to empirical studies and conclusively show that all these pollutants can interfere with transcription and DNA related mechanisms by forming noncovalent interactions with DNA. The results show also that these pollutants are unlikely to undergo strong noncovalent intercalation to DNA, such as BAP, and do not possess the frontier orbital profiles to undergo adduct formation. After many years of research and several unanswered questions on the action of these pollutants on DNA, a calculation on their properties hence to the DNA confirms that there is a low probability for these to undergo a strong intercalation with DNA. Literature shows however that the pollutants are strongly interfering with the protein machinery and receptors on the cell surface and are therefore still priority pollutants for ecotoxicity research.

Do drivers of biodiversity change differ in importance across marine and terrestrial systems - Or is it just different research communities' perspectives?

Cross-system studies on the response of different ecosystems to global change will support our understanding of ecological changes. Synoptic views on the planet's two main realms, the marine and terrestrial, however, are rare, owing to the development of rather disparate research communities. We combined questionnaires and a literature review to investigate how the importance of anthropogenic drivers of biodiversity change differs among marine and terrestrial systems and whether differences perceived by marine vs. terrestrial researchers are reflected by the scientific literature. This included asking marine and terrestrial researchers to rate the relevance of different drivers of global change for either marine or terrestrial biodiversity. Land use and the associated loss of natural habitats were rated as most important in the terrestrial realm, while the exploitation of the sea by fishing was rated as most important in the marine realm. The relevance of chemicals, climate change and the increasing atmospheric concentration of CO₂ were rated differently for marine and terrestrial biodiversity respectively. Yet, our literature review provided less evidence for such differences leading to the conclusion that while the history of the use of land and sea differs, impacts of global change are likely to become increasingly similar.

Binding of Pollutants to Biomolecules: A Simulation Study

A number of cases around the world have been reported where animals were found dead or dying with symptoms resembling a thiamine (vitamin B) deficiency, and for some of these, a link to pollutants has been suggested. Here, we investigate whether biomolecules involved in thiamin binding and transport could be blocked by a range of different pollutants. We used in silico docking of five compound classes (25 compounds in total) to each of five targets (prion protein, ECF-type ABC transporter, thi-box riboswitch receptor, thiamin pyrophosphokinase, and YKoF protein) and subsequently performed molecular dynamics (MD) simulations to assess the stability of the complexes. The compound classes were thiamin analogues (control), pesticides, veterinary medicines, polychlorinated biphenyls, and dioxins, all of which are prevalent in the environment to some extent. A few anthropogenic compounds were found to bind the ECF-type ABC transporter, but none binds stably to prion protein. For the riboswitch, most compounds remained in their binding pockets during 50 ns of MD simulation, indicating that RNA provides a promiscuous binding site. In both YKoF and thiamin pyrophosphokinase (TPK), most compounds remain tightly bound. However, TPK biomolecules undergo pollutant-induced conformational changes. Although most compounds are found to bind to some of these targets, a larger data set is needed along with more quantitative methods like free energy perturbation calculations before firm conclusions can be drawn. This study is in part a test bed for large-scale quantitative computational screening of interactions between biological entities and pollutant molecules.