The spatiotemporal variability of ambient volatile organic compounds (VOCs) in Tehran, Iran, is not well understood. Here we present the design, methods, and results of the Tehran Study of Exposure Prediction for Environmental Health Research (Tehran SEPEHR) on ambient concentrations of benzene, toluene, ethylbenzene, p-xylene, m-xylene, and o-xylene (BTEX). To date, this is the largest study of its kind in a low- and middle-income country and one of the largest globally. We measured BTEX concentrations at five reference sites and 174 distributed sites identified by a cluster analysis method. Samples were taken over 25 2-weeks at five reference sites (to be used for temporal adjustments) and over three 2-week campaigns in summer, winter, and spring at 174 distributed sites. The annual median (25th–75th percentile) for benzene, the most carcinogenic of the BTEX species, was 7.8 (6.3–9.9) μg/m3, and was higher than the national and European Union air quality standard of 5 μg/m3 at approximately 90% of the measured sites. The estimated annual mean concentrations of BTEX were spatially highly correlated for all pollutants (Spearman rank coefficient 0.81–0.98). In general, concentrations and spatial variability were highest during the summer months, most likely due to fuel evaporation in hot weather. The annual median of benzene and total BTEX across the 35 sites in the Tehran regulatory monitoring network (7.7 and 56.8 μg/m3, respectively) did a reasonable job of approximating the 144 city-wide sites (7.9 and 58.7 μg/m3, respectively). The annual median concentrations of benzene and total BTEX within 300 m of gas stations were 9.1 and 67.3 μg/m3, respectively, and were higher than sites outside this buffer. We further found that airport did not affect annual BTEX concentrations of sites within 1 km. Overall, the observed ambient concentrations of toxic VOCs are a public health concern in Tehran.

The ability to characterize the composition of emerging unconventional Bakken tight oil is essential to better prepare for potential spills and to assess associated environmental concerns. The present work measured and compared the physical and chemical properties of Bakken crudes with conventional crude oils from various regions and different types of refined petroleum products. The physicochemical properties of Bakken crude are overall similar to those of conventional light crudes. The Bakken crude consists of high concentrations of monoaromatic hydrocarbons and alkylated PAHs with a clear dominance of the alkylated naphthalene homologues followed by the phenanthrene series. Its pyrogenic index (PI) values are considerably lower than typical conventional crude oils. The Bakken crude oils in this study exhibit a low abundance of petroleum biomarker such as terpanes, steranes and diamondoids and bicyclic sesquiterpanes. Since tight oil from the Bakken region is produced from low-permeability formations, variations in abundance and diagnostic ratios of common target petroleum hydrocarbons were found among these oils.

Understanding the colloidal stability of graphene is essential for predicting its transport and ecological risks in aquatic environments. We investigated the agglomeration of ¹⁴C-labeled few-layer graphene (FLG) at concentrations spanning nearly four orders of magnitude (2 μg/L to 10 mg/L) using dynamic light scattering and sedimentation measurements. FLG agglomerates formed rapidly in deionized water at concentrations >3 mg/L. From 1 mg/L to 3 mg/L, salt-induced agglomeration was decreased with dilution of FLG suspensions; the critical coagulation concentration of the more concentrated suspension (3 mg/L) was significantly lower than the dilute suspension (1 mg/L) in the presence of NaCl (1.6 mmol/L and 10 mmol/L, respectively). In contrast, FLG underwent slow agglomeration and settling at concentrations ≤0.1 mg/L in NaCl solutions and ambient waters with low ionic strength (<10 mmol/L). FLG nanoparticles with smaller lateral sizes (25 nm–75 nm) were shown to agglomerate more slowly than larger FLG, and these small FLG particles exhibited greater bioaccumulation in zebrafish embryo and stronger chorion penetration ability than larger FLG particles. These findings suggest that FLG at more environmentally relevant concentration is relatively stable and may have implications for exposure of small FLG to ecological receptors.

Calanoid copepods play an important role in the functioning of marine and brackish ecosystems. Information is scarce on the behavioral toxicity of engineered nanoparticles to these abundant planktonic organisms. We assessed the effects of short-term exposure to nonfunctionalized gold nanoparticles on the swimming behavior of the widespread estuarine copepod Eurytemora affinis. By means of three-dimensional particle tracking velocimetry, we reconstructed the trajectories of males, ovigerous and non-ovigerous females. We quantified changes in their swimming activity and in the kinematics and geometrical properties of their motion, three important descriptors of the motility patterns of zooplankters. In females, exposure to gold nanoparticles in suspension (11.4 μg L−1) for 30 min caused depressed activity and lower velocity and acceleration, whereas the same exposure caused minimal effects in males. This response differs clearly from the hyperactive behavior that is commonly observed in zooplankters exposed to pollutants, and from the generally lower sensitivity of female copepods to toxicants. Accumulation of gold nanoparticles on the external appendages was not observed, precluding mechanical effects. Only very few nanoparticles appeared sporadically in the inner part of the gut in some samples, either as aggregates or as isolated nanoparticles, which does not suggest systemic toxicity resulting from pronounced ingestion. Hence, the precise mechanisms underlying the behavioral toxicity observed here remain to be elucidated. These results demonstrate that gold nanoparticles can induce marked behavioral alterations at very low concentration and short exposure duration. They illustrate the applicability of swimming behavior as a suitable and sensitive endpoint for investigating the toxicity of nanomaterials present in estuarine and marine environments. Changes in swimming behavior may impair the ability of planktonic copepods to interact with their environment and with other organisms, with possible impacts on population dynamics and community structure.

Antibiotic resistance genes (ARGs) have been regarded as emerging contaminants and have attracted growing attention owing to their widespread presence in the environment. In addition to the well-documented selective pressure of antibiotics, ARGs have also become prevalent because of anthropogenic impacts. Coastal habitats are located between terrestrial and marine ecosystems, which are a hotspot for anthropogenic impacts. Excessive accumulation of polycyclic aromatic hydrocarbons (PAHs) has posed a serious threat to coastal habitats, but no information is available on the effect of PAHs on antibiotic resistance in the microbial community of coastal environments. In this study, the effect of two typical PAHs, naphthalene and phenanthrene, on antibiotic resistance propagation was investigated in a coastal microbial community. The results indicated that the presence of 100 mg/L of naphthalene or 10 mg/L of phenanthrene significantly enhanced the abundance of class I integrase gene (intI1), sulfanilamide resistance gene (sulI), and aminoglycosides resistance gene (aadA2) in the microbial community. Horizontal gene transfer experiment demonstrated that increased abundance of ARGs was primarily a result of conjugative transfer mediated by class I integrons. These findings provided direct evidence that coastal microbial community exposed to PAHs might have resulted in the dissemination of ARGs and implied that a more comprehensive risk assessment of PAHs to natural ecosystems and public health is necessary.

Simulating the storage of aerobic soils under water, the chemical speciation of heavy metals and arsenic was studied over a long-term reduction period. Time-dynamic and redox-discrete measurements in reactors were used to study geochemical changes. Large kinetic differences in the net-complexation quantities of heavy metals with sulfides was observed, and elevated pore water concentrations remained for a prolonged period (>1 year) specifically for As, B, Ba, Co, Mo, and Ni. Arsenic is associated to the iron phases as a co-precipitate or sorbed fraction to Fe-(hydr)oxides, and it is being released into solution as a consequence of the reduction of iron. The composition of dissolved organic matter (DOM) in reducing pore water was monitored, and relative contributions of fulvic, humic and hydrophylic compounds were measured via analytical batch procedures. Quantitative and qualitative shifts in organic compounds occur during reduction; DOM increased up to a factor 10, while fulvic acids become dominant over humic acids which disappear altogether as reduction progresses. Both the hydrophobic and hydrophilic fractions increase and may even become the dominant fraction.Reactive amorphous and crystalline iron phases, as well as dissolved FeII/FeIII speciation, were measured and used as input for the geochemical model to improve predictions for risk assessment to suboxic and anaerobic environments. The release of arsenic is related to readily reducible iron fractions that may be identified by 1 mM CaCl2 extraction procedure. Including DOM concentration shifts and compositional changes during reduction significantly improved model simulations, enabling the prediction of peak concentrations and identification of soils with increased emission risk. Practical methods are suggested to facilitate the practice of environmentally acceptable soil storage under water.

Elevated temperatures and nutrients can favor phytoplankton dominance by cyanobacteria, which can be toxic to zooplankton. There is growing awareness that maternal effects not only are common but can also significantly impact ecological interactions. Although climate change is broadly studied, relatively little is known regarding its influence on maternal effects in zooplankton. Given that lakes are sentinels for climate change and that elevated temperatures and nutrient pollution can favor phytoplankton dominance by toxic cyanobacteria, this study focused on elucidating the effects of maternal exposure to elevated temperatures on the tolerance of zooplankton offspring to toxic cyanobacteria in the diet. Three different maternal thermal environments were used to examine population fitness in the offspring of two cladoceran species that vary in size, including the larger Daphnia similoides and the smaller Moina macrocopa, directly challenged by toxic Microcystis. Daphnia and Moina mothers exposed to elevated temperatures produced offspring that were more resistant to Microcystis. Such findings may result from life-history optimization of mothers in different temperature environments. Interestingly, offspring from Moina fed with toxic Microcystis performed better than Daphnia offspring, which could partially explain the dominance of small cladocerans typically observed during cyanobacterial blooms. The present study emphasizes the importance of maternal effects on zooplankton resistance to cyanobacteria mediated through environmental warming and further highlights the complexities associated with the abiotic factors that influence zooplankton-cyanobacteria interactions.

The Ordos region of Inner Mongolia is rapidly developing and suffers from poor air quality and unhealthy levels of fine particulate matter. PM2.5 concentrations in the Ordos region were found to exceed 75 μg/m3 on average, annually, with peak pollution days in excess of 350 μg/m3, but local air pollution emissions from surrounding sources are not sufficient to drive pollution levels to these concentrations. The current study was designed to quantify sources of PM2.5 and assess the local source contributions and effects of regional transport on local pollution. The results show that the Ordos region is primarily impacted by regional long-range transport of pollutants from anthropogenic sources located outside of the Inner Mongolia in Shanxi province areas but is also largely affected by regional dust transported from the deserts located in western Inner Mongolia. The analysis proved that approximately 77% of PM2.5 mass is transported long-range from the sites exterior to the study area and contributes 59.32 μg/m3 on average, annually, while the local sources contribute 17.41 μg/m3 (23%) on annual average to the PM2.5 mass in the study area. High spatial correlation coefficients (R2 > 0.6) were observed for most of the factors pointing to the transport of external emissions into the area. Spatial correlation analysis, bivariate polar plots and hybrid trajectory models for industrial and secondary inorganic factors provide evidence for the impact of long-range transport from Shanxi province areas. In addition, the deserts in western Inner Mongolia were found to be the source regions for dust. Finally, our analysis shows that the source of oil combustion and mobile factors are impacted by local sources in the Ordos region; however, some regional impacts from other regions were also observed for mobile source in the area.

Derelict mines pose potential risks to environmental health. Several factors such as soil structure, organic matter, and nutrient content are the greatly affected qualities in mined soils. Soil microbial communities are an important element for successful reclamation because of their major role in nutrient cycling, plant establishment, geochemical transformations, and soil formation. Yet, microorganisms generally remain an undervalued asset in mined sites. The microbial diversity in derelict mine sites consists of diverse species belonging to four key phyla: Proteobacteria, Acidobacteria, Firmicutes, and Bacteroidetes. The activity of plant symbiotic microorganisms including root-colonizing rhizobacteria and ectomycorrhizal fungi of existing vegetation in the mined sites is very high since most of these microbes are extremophiles. This review outlines the importance of microorganisms to soil health and the rehabilitation of derelict mines and how microbial activity and diversity can be exploited to better plan the soil rehabilitation. Besides highlighting the major breakthroughs in the application of microorganisms for mined site reclamation, we provide a critical view on plant−microbiome interactions to improve revegetation at the mined sites. Also, the need has been emphasized for deciphering the molecular mechanisms of adaptation and resistance of rhizosphere and non-rhizosphere microbes in abandoned mine sites, understanding their role in remediation, and subsequent harnessing of their potential to pave the way in future rehabilitation strategies for mined sites.