Microplastics are an emerging contaminants of concern in aquatic environments. The aggregation behaviors of microplastics governing their fate and ecological risks in aquatic environments is in need of evaluation. In this study, the aggregation behavior of polystyrene microspheres (micro-PS) in aquatic environments was systematically investigated over a range of monovalent and divalent electrolytes with and without natural organic matter (i.e., Suwannee River humic acid (HA)), at pH 6.0, respectively. The zeta potentials and hydrodynamic diameters of micro-PS were measured and the subsequent aggregation kinetics and attachment efficiencies (α) were calculated. The aggregation kinetics of micro-PS exhibited reaction- and diffusion-limited regimes in the presence of monovalent or divalent electrolytes with distinct critical coagulation concentration (CCC) values, followed the Derjaguin-Landau-Verwey-Overbeek (DLVO) theory. The CCC values of micro-PS were14.9, 13.7, 14.8, 2.95 and 3.20 mM for NaCl, NaNO3, KNO3, CaCl2 and BaCl2, respectively. As expected, divalent electrolytes (i.e., CaCl2 and BaCl2) had stronger influence on the aggregation behaviors of micro-PS as compared to monovalent electrolytes (i.e., NaCl, NaNO3 and KNO3). HA enhanced micro-PS stability and shifted the CCC values to higher electrolyte concentrations for all types of electrolytes. The CCC values of micro-PS were lower than reported carbonaceous nanoparticles CCC values. The CCC[Ca2+]/CCC [Na+] ratios in the absence and presence of HA at pH 6.0 were proportional to Z−2.34 and Z−2.30, respectively. These ratios were in accordance with the theoretical Schulze–Hardy rule, which considers that the CCC is proportional to z−6–z−2. These results indicate that the stability of micro-PS in the natural aquatic environment and the possibility of significant aqueous transport of micro-PS.

Microplastics (MPs) are well-known emerging contaminants in the marine environment. A key route by which MPs can directly affect marine life is through ingestion. The objective of the present study was to evaluate the occurrence of MPs in marine life and seafood for human consumption in the Persian Gulf. We conducted a whole body analysis of MP (between 10 and 5000 μm in diameter) abundance in five species of molluscs with different feeding strategies, including both gastropods and bivalves from the littoral zone of the Iranian coast of the Persian Gulf. The mean number of total encountered MPs in all species ranged from 0.2 to 21.0 particles per g of soft tissue (wet weight) and from 3.7 to 17.7 particles per individual. Overall, microfibres followed by fragments were the most common type of MP isolated in each species (respectively > 50% and ≈26%). Film (≈14%) and pellets (≈2%) were less commonly observed. The observed MPs were classified into three size groups (ca. 10–25 μm, 25–250 μm and 250–5000 μm), and 37–58% of MPs fell into the smallest size group. Fourier transform infrared (FT-IR) analysis confirmed the presence of polyethylene (PE), polyethylene terephthalate (PET), and nylon (PA). Our results indicated that molluscan shellfish from the Persian Gulf contain MPs, with higher concentrations in a predatory species, suggesting trophic transfer of MPs in the food web. The consumption of edible species may be a source of human microplastic intake. We compared our results with those previously reported for other regions of the world and identified the need for further studies in the Persian Gulf.

The aim of this study was to evaluate the mobility of platinum (Pt) and palladium (Pd) emissions from automotive catalysts in soils and to contribute to the risk assessment of platinum group metals (PGMs) discharged from catalysts in the environment. To address this question, for the first time risk assessment code (RAC) was applied to consider the results from sequential extraction of different Pd and Pt species from soils. For this purpose, model soil samples were prepared spiking defined Pd or Pt species, respectively, at known concentrations. In order to mimic emitted species as well as possible transformation products of traffic-related Pd and Pt emissions in soils, coated and uncoated elemental nanoparticles (cPd/cPt NPs, Pd/Pt NPs) and ionic divalent metal species (Pd(II)/Pt(II)) were applied. All model samples were characterized in detail and the developed sequential extraction scheme was validated. RAC values ranged between 24 and 8% revealing medium to low risk. The order of mobility for the studied species was found to be Pt(II) > cPd NPs » Pd(II) > Pd NPs > Pt NPs > cPt NPs. Furthermore, migration of Pd species in gravity columns was studied confirming highest transport of cPd NPs.

The hydrocarbon phenanthrene is an organic compound commonly found in the environment. In aquatic ecosystems, it is highly toxic to organisms, although little is known about its effects on sediment-dwelling organisms. The purpose of this study was to evaluate phenanthrene effects on biochemical, histological, and ontogenetic levels in larvae of the sediment-dwelling invertebrate Chironomus sancticaroli at acute and chronic exposure. Lethal concentrations were estimated and toxicity (acute-96 h and chronic- 8 d) tests were performed at phenanthrene concentrations from 0.12 to 1.2 mg L⁻¹. At acute and chronic exposure, we evaluated acetylcholinesterase (AChE), alpha esterase (EST-α), and beta esterase (EST-β) activities as well as histological alterations. In the assays with chronic exposure, effects on larval development were estimated using antennae length (instar estimative) and body length (growth estimative). The EST-α showed a significantly increased activity after 48 h at acute exposure to high concentrations of phenanthrene, while EST-β activity was increased after 48 and 72 h at acute exposure at higher concentrations and at 0.12 mg L⁻¹ at chronic exposure. At acute exposure, the midgut showed alterations such as brush border disruption, gastric caeca regression, and lumen area reduction; the fat body showed nuclear alteration in the trophocytes, while the Malpighian tubules showed brush border reduction and the salivary glands were subject to cytoplasm vacuolation. At chronic exposure, the same alterations were observed, in addition to vacuolar coalescence in the trophocytes of the fat body. Regarding larval development, a reduction of body length was observed with increasing phenanthrene concentrations. Similarly, molting was delayed; in the control group, all larvae were in the fourth instar, while at higher phenanthrene concentrations, larvae were predominantly in the third instar. Phenanthrene had toxic effects on this chironomid, indicating risks for natural populations.

Microcystins (MCs) are naturally occurring algal toxins in the aquatic environment and pose a serious threat to the ecosystem. In general, aquatic populations are structured by organisms of different ages, with varying degrees of biochemical and physiological responses. In this study, juvenile and adult marine mysids (Neomysis awatschensis) were exposed to MC-Leucine Arginine (MC-LR) (0.1, 1, and 10 μg L⁻¹) for 7 days, and the bioconcentration dynamics and responses of antioxidant defense system were measured during the exposure and additional depuration periods (7 days). MC-LR bioconcentrated in a dose-dependent manner, from a threshold concentration of 1 μg L⁻¹ in both stages, and the levels reduced gradually during the depuration phase. Bioconcentration patterns of MC-LR were highly age-specific, as juvenile mysids showed peaks during the exposure period, whereas adults exhibited a peak on the first day of depuration. After exposure to 10 μg L⁻¹ concentration, elevated levels of malondialdehyde (MDA) and glutathione (GSH) were observed during the late (days 5 and 7) exposure and early (days 1 and 3) depuration periods in juvenile mysids, while adult mysids showed a peak on day 7 of the exposure period. Age-specific responses were also observed in the enzymatic activities of glutathione S-transferase (GST), catalase (CAT), superoxide dismutase (SOD), glutathione peroxidase (GPx), and glutathione reductase (GR). Juvenile mysids showed a significant elevation in all enzymatic activities during the exposure and/or depuration phase upon exposure to 10 μg L⁻¹ MC-LR, but only CAT and SOD enzymes showed significant changes during the exposure and/or depuration periods in adults. Overall, our results indicate the bioconcentration potential of MC-LR and its threshold in the marine mysid, in addition to age-specific MC-LR dynamics and subsequent biochemical responses.

Herein, we utilize sequential extraction and high-throughput sequencing to investigate the effects of nanomaterial additives on As volatilization from flooded soils. We reveal that maximum volatilization is achieved in the fourth week and is followed by stabilization. The extent of volatilization decreased in the order of control > nano-zerovalent iron >40-nm hydroxyapatite > nano-Fe₃O₄ > 20-nm hydroxyapatite > multilayer graphene oxide > high-quality graphene oxide. The most abundant forms of As in soil corresponded to As-Fe and Al oxides. In soil with low levels of As pollution, the contents of these species increased after treatment with graphene oxides but decreased after treatment with other nanomaterials, with an opposite trend observed for soil with high levels of As pollution. The addition of nanomaterials influenced the activity of soil enzymes, e.g., hydroxyapatites affected the activities of urease and alkaline phosphatase, whereas graphene oxides significantly impacted that of peroxidase (P < 0.05). The addition of nanomaterials (which can potentially inhibit microbial growth) affected As levels by influencing the amount of As volatilized from polluted soil. Moreover, As volatilization, enzyme activity, and As speciation were observed to be mutually correlated (e.g., volatilization was negatively correlated to peroxidase activity and the contents of amorphous crystalline hydrous oxides of As-Fe and Al).

Sewage sludge from a municipal wastewater treatment facility employing activated sludge process was pre-incubated with varying substrates and mixtures of substrates including metformin (MET), guanylurea (GUA) and glucose. The biomass from enriched cultures separately utilising MET and glucose/GUA was then used to investigate the kinetics of aerobic biodegradation of MET and GUA, respectively, as individual substrates in batch reactors. The results showed that GUA can be completely degraded as a nitrogen source when glucose is provided as a carbon and energy source. On the contrary, MET can be biodegraded as a sole carbon and energy source. However, formation of by-product GUA in solution, which acts as a nitrogen source, rapidly increased the degradation rate of MET resembling autocatalytic behaviour. At low starting concentration of 5 mg/L, the specific substrate utilisation rates of MET and GUA were 0.0033 day⁻¹ and 0.0013 day⁻¹, respectively, which is reported first time in this study. Out of the five biodegradation kinetic models used to describe substrate utilisation, the Quiroga-Sales-Romero (QSR) model was found to predict the measured MET and GUA degradation profile well supported by the goodness of fit parameters. Furthermore, the QSR model was able to describe the autocatalytic degradation of MET and the incomplete biodegradation of GUA in solution.

The primary objective of this study was to identify the capacity and mechanism of extracellular polymeric substance (EPS) adsorption on soil colloids of Alfisol and Ultisol at different pH and ionic strengths. Two kinds of EPS were extracted from Bacillus subtilis and Pseudomonas fluorescens by centrifugation, and their adsorption on Ultisol and Alfisol was investigated using a batch adsorption experiment and attenuated total reflectance–Fourier transform infrared spectroscopy (ATR-FTIR). The average diameter of EPS from B. subtilis and P. fluorescens was 1825 and 1288 nm, respectively, and both the EPS were negatively charged. The zeta potentials of the two EPS became more negative with increasing solution pH from 3 to 8 and less negative with increasing ionic strength from 0 to 80 mM. The maximum adsorption capacity of EPS-C and EPS-N on Alfisol was higher than that on Ultisol, whereas the maximum adsorption capacity of EPS-P on Alfisol was lower than that on Ultisol. The adsorption of EPS-C, EPS-N, and EPS-P of both the EPS on Ultisol and Alfisol decreased with increasing solution pH from 3 to 8. Adsorption of EPS-C, EPS-N, and EPS-P of both the EPS on Alfisol significantly increased with increasing ionic strength from 0 to 10 mM, whereas it remained constant, slightly increased, or reduced, when the ionic strength was increased from 10 to 80 mM. The adsorption of EPS-C, EPS-N, and EPS-P on Ultisol slightly increased with increasing ionic strength from 0 to 80 mM. Saturation coverage determined by ATR-FTIR showed that adsorption of whole EPS on Ultisol was higher than that on Alfisol at pH 6 after 60 min. Thus, electrostatic force between EPS and soil colloids played an important role in EPS adsorption. Besides, proteins and phosphate groups in EPS also contributed to EPS adsorption on soil colloids.

The widely used Di-(2-ethylhexyl) phthalate (DEHP) has been reported to exhibit ubiquitous environmental and global health hazards. The bioaccumulation and environmental persistence of DEHP can cause serious health hazards in wildlife animals and human. However, DEHP-induced nephrotoxicity in bird is remained unknown. Thus, this study explored the related mechanism of DEHP nephrotoxicity in quail. For this purpose, quail were exposed with DEHP at doses of 0, 250, 500, and 1000 mg/kg body weight daily by gavage administration for 45 days. The results showed that DEHP exposure induced renal injury, oxidative stress, and endoplasmic reticulum (ER) degeneration. Low level DEHP (250 mg/kg) exposure inhibited Nrf2 signaling pathway and induced renal injury via oxidative stress and suppressed the unfolded protein response (UPR) signaling pathway and induced ER stress in the kidney. But surprisingly, high level DEHP (500 mg/kg and 1000 mg/kg) exposure activated Nrf2 and UPR signaling pathways and protected kidney, but they still couldn't resist the toxicity of DEHP. Our study demonstrated that DEHP-induced nephrotoxicity in quail was associated with activating Nrf2-mediated antioxidant defense response and UPR signaling pathway.

Accurate measuring n-octanol/water partition coefficients (log Kₒw) of perfluoroalkyl carboxylic acids (PFCAs) using experimental approach has been proven to be very difficult due to their special properties. The ionizable carboxyl groups in PFCAs make their log Kₒw dependent on pH. In this study, the log Kₒw values of neutral species of PFCAs (C₄≤ₙ≤₁₄) were measured based on reversed-phase high-performance liquid chromatography (RP-HPLC) with the mobile phase pH varying in the range of 1.09–5.00. The relationship between log Kₒw and retention times was established using some reference compounds (including agrochemicals, polycyclic aromatic hydrocarbons) with known log Kₒw values, and then validated with alkyl fatty acids, which have similar chemical structures as PFCAs. The apparent log Kₒw (i.e., log Dₒw) of the C₄–₁₄ PFCAs were calculated based on their retention times using the established model, and they displayed a negative linear relationship with the mobile phase pH in the range of 1.09–4.00. Consequently, the log Dₒw values were converted to the corresponding log Kₒw values (1.05–7.19) based on the relationship of log Dₒw = log Kₒw + pKₐ – pH. The log Kₒw increased with perfluorinated carbon chain length with a greater rate for C₄ to C₅ PFCAs than for C₅–₁₄ PFCAs.