Environmental Science: Processes & Impacts最新文献

The complex land use patterns in urban–rural rivers and the presence of diverse point and non-point source pollution pose significant challenges for tracing heavy metal(loid) sources in river sediments. This study employed a combined approach using lead (Pb) stable isotopes, positive matrix factorization (PMF), and a Bayesian mixture model (MixSIAR) to determine the concentrations of Cr, As, Cd, Mn, Cu, Zn, Ni, and Pb along with Pb isotope distribution characteristics in sediments from a typical urban–rural river (Yinghe River). Our investigation enabled the quantitative identification of heavy metal(loid) sources and revealed the contribution patterns of multi-source Pb pollution. The results showed that mean concentrations of all heavy metal(loid)s except Cr and Mn exceeded local soil background values. PMF analysis identified four potential sources: natural sources (19.6%) contributing primarily Cr and Mn; industrial sources (32.1%) associated with Cd, Pb, and Ni; agricultural sources (28.0%) linked to Pb, As, and Zn; and traffic sources (20.3%) related to Cu and Zn. Furthermore, by combining Pb stable isotopes with MixSIAR, the contributions of different Pb pollution sources were quantified as agricultural sources (32.1%), industrial sources (30.5%), traffic sources (27.2%), and natural sources (10.3%). The less-than-10% difference in contribution rates between PMF and MixSIAR for Pb source apportionment demonstrated model reliability. Based on the significant correlation between Pb pollution and land use patterns in the Yinghe River, corresponding pollution prevention strategies were proposed. These findings provide a novel perspective for quantitative source identification of heavy metal(loid) pollution in urban–rural river sediments, offering valuable support for river management and heavy metal(loid) pollution control.

Fecal contamination of coastal waters threatens human and ecosystem health. Microbial source tracking (MST) methods offer a strategy to identify sources of fecal contamination through the measurement of genetic markers associated with a particular animal host. In this study, we measured fecal indicator bacteria (FIB) and employed MST methods to evaluate the sources of fecal contamination in a coupled stream-beach system in Kailua Bay, Hawai'i where residents adjacent to the shoreline use onsite cesspools for sewage management. In a baseline campaign, we measured enterococci concentrations in surface water samples from the stream and beach (n = 36). Results indicated that the stream contained enterococci in exceedance of the state standard (50% of samples) and therefore represented a potential source of contamination to the coastal ocean. To identify potential fecal sources, five MST genetic markers – three indicative of human feces (HF183/BacR287, CPQ_056, and ToBRFV), one of dog feces (DG3), and one of avian feces (GFD) – were measured alongside enterococci concentrations and environmental parameters (water temperature, salinity, tidal stage, and rainfall) in stream and beach water samples from longitudinal (n = 78) and spatial (n = 25) sampling campaigns. During the two-week longitudinal campaign, detections were observed for the avian marker (78% of samples positive), human marker ToBRFV (40%), and dog marker (10%), while HF183/BacR287 and CPQ_056 were not detected. Marker detection frequency varied by sampling location, with GFD most frequently detected in the stream and ToBRFV most frequently detected at the site adjacent to cesspools. In the spatial campaign, enterococci concentrations significantly decreased along the stream towards the beach (p < 0.001) but similar trends were not observed for MST markers. The occurrence of human, avian, and canine MST genetic markers in this study confirms these are important sources of fecal contamination in the Kailua Bay area. This study is the first to implement the RNA-based ToBRFV digital PCR assay in tropical coastal waters.

Disinfection byproducts (DBPs) have been receiving global attention because they may have detrimental effects on organisms. Cytotoxicity and genotoxicity are two toxicity endpoints that are of wide concern in the field of DBP hazard assessment. Hitherto, only around one hundred out of thousands of identified DBPs had available experimental cytotoxicity and genotoxicity data. It is important to fill this data gap of thousands of DBPs by employing an efficient and high-throughput method. Herein, we first summarized the extensive and heterogeneous cytotoxicity (184-DBPs) and genotoxicity (105-DBPs) data sets related to DBPs. Then, quantitative and qualitative models with acceptable internal and external prediction performance were developed for cytotoxicity and genotoxicity, respectively. Next, a user-friendly tool named “DBPCytoGenoTOX Predictor” was developed using the optimal models. This tool was further applied to fill the missing cytotoxicity and genotoxicity data gaps of an updated DBP inventory with 1816 substances. Finally, the high-priority DBPs were screened from the DBP inventory based on the experimental and predicted cytotoxicity and genotoxicity data as well as the previously reported endocrine-disrupting effects and aquatic toxicity data. As a result, 385 high-priority DBPs were identified. More efforts should be taken to confirm the potential adverse effects of these high-priority DBPs on organisms in the future.

Wildfires drastically alter biogeochemical cycling and transport of nutrient elements, including nitrogen (N), from terrestrial to aquatic ecosystems, with the potential to degrade water quality. Understanding the impact of characteristics of wildfire-derived ashes and burned soils on the mobilization of N is essential for effectively managing wildfires and mitigating adverse effects on watershed functions. This study quantified the mobility of N in soils and ashes influenced by wildfires in the northern California/Nevada region in the western United States (Dixie, Beckwourth, and Caldor fires) and the impact of soil/ash characteristics. The mobile fraction of N ranged from 0.025–0.070 for the ashes, and the mobile fraction of N was composed of 13.1–39.6% as NO₃⁻, up to 0.011% as NO₂⁻, 0.004–86.9% as NH₃/NH₄⁺, and up to 49.4% as dissolved organic N. The speciation indicates possible nitrification occurring during the wildfires, but suggests no substantial denitrification. The mobile fraction of N was 11.3 ± 7.4 times that of organic carbon (OC), due to the high mobility of inorganic N (mainly NO₃⁻ and NH₃/NH₄⁺) and nitrogenous organic compounds. The mobile N fraction was associated with redox reactions of iron during wildfires, and was regulated by the redox reactivity of OC. N mobility in the ashes was lower than in control soils, potentially due to the transformation in the speciation of N. However, the total amount of mobile N was increased by wildfire, with the amount of increase being closely related to the severity of wildfires. Overall, wildfires lead to more mobile N, including both organic and inorganic N regulated by redox reactions and severity of wildfires, with subsequent concerns for water quality and water/wastewater treatment processes.

Isoprene, the most predominant biogenically emitted volatile organic compound (VOC) in the atmosphere, undergoes oxidation to yield hydroxymethyl methyl α-lactone (HMML) in the presence of NO. While the particle-phase chemistry of HMML has been explored to some extent, its gas-phase chemistry remains unexplored. In this study, we have performed an extensive computational investigation involving the thermodynamics and kinetics of the oxidation reaction of HMML in the gas phase, driven by hydroxy radicals (OH) and chlorine (Cl) atoms. The oxidation of HMML proceeds via hydrogen atom abstraction reactions, all of which are exothermic in nature. The potential energy profile diagram representing all possible reaction routes has been constructed using CCSD(T)//M06-2X/6-311++G(d,p) level of theory. The rate coefficients of all the reaction pathways were estimated using the variational transition state theory (VTST), corrected with a tunneling factor, across the 200 to 400 K temperature range at the M06-2X/6-311++G(d,p) level of theory. At 298 K, the atmospheric lifetime of HMML was determined to be 9.6 days in the marine boundary layer (MBL) and 62.5 days in the normal tropospheric conditions. Furthermore, the degradation study of the product radicals revealed various end products with much higher reactivity and shorter lifetimes, such as diketones, α, β-unsaturated carboxylic acids, formic acid, pyruvic acid, methylglyoxal, and dioxopropanoic acid.

Understanding the microbial processes involved in ammonium loss in highly productive marine systems is crucial for reconstructing the global nitrogen cycle. This study is the first to examine the anaerobic ammonium oxidation coupled with dissimilatory Fe(III) reduction (Feammox) and the abundance of iron-reducing bacteria (IRB) in a seagrass-dominated coastal lagoon exposed to two contrasting upwelling conditions. Potential Feammox rates varied from 6.0 to 39.2 mg N per m² per day and were positively correlated with the abundance of IRB (Acidomicrobiaceae A6 spp. and Geobacteraceae spp.), suggesting that IRB mediated the Feammox process. The limited impact of near-mouth productivity conditions on Feammox activity and IRB was largely inherent to sediment type (eelgrass or adjacent bare bottom) and station-specific, depending on the degree of confinement relative to the nearby ocean. The partial least squares structural equation modeling approach revealed that dissimilatory Fe(III) reduction exerted a direct effect on potential Feammox rates, while upwelling conditions indirectly influenced the process through sediment characteristics. The contribution of Feammox to total ammonium loss exceeded 60% and increased with the distance from the mouth of the lagoon. A minimum of 3.7 ± 0.5 mg N per m² per day was catalyzed by electron acceptors besides Fe(III), highlighting the co-occurrence of alternative chemoautotrophic pathways in ammonium removal. Furthermore, an average loss of 38.4 ± 6.7 t N per year was attributed to the anaerobic ammonium oxidation processes, accounting for 5.1 ± 1.6% of the annual oceanic N transported into the lagoon. These findings extend our current understanding of N and Fe cycles in coastal environments linked to eastern boundary upwelling systems.

Lake Kivu is distinguished by several unique characteristics that set it apart from other lakes around the world. One of the notable features is a temperature increase with depth, accompanied by unusual staircase-like patterns in the thermodynamic and environmental parameters. The lake also experiences suppressed vertical mixing due to stable density stratification, with its deep water separated from the surface water by chemoclines. Additionally, Lake Kivu contains high concentrations of dissolved methane (CH₄) and carbon dioxide (CO₂), and there is no standard method for measuring their concentrations. The lake is also recognized as a renewable energy source due to its continuous supply of CH₄, and it demonstrates a quadruple-diffusive convection transport mechanism. These factors contribute to the lake's distinctiveness. The occurrence of catastrophic limnic eruptions at Lakes Nyos and Monoun, along with the structural similarities between these lakes and Lake Kivu, raises serious concerns about the likelihood of a similar disaster in Lake Kivu in the future. The scale of threats posed in Lake Kivu can be orders of magnitude greater than the other two lakes, given its 3000 times larger size, two to four orders of magnitude higher content of dissolved CO₂, containing substantial quantities of CH₄ in addition to CO₂ in solution, and holding a far denser population living in its much wider catchment area. The present study aims to assess the probability of a future gas outburst in this giant lake by numerical modeling of its hydrodynamics over the next half a millennium. The turbulent transport is calculated using the extended k–ε model. An implicit Euler method is applied to solve the governing partial differential equations on a vertically staggered grid system, discretized using a finite-volume approach. Since the previously calibrated model successfully reproduces the measured lake profiles, the same tuned parameter values are used in this study, assuming a stable steady-state condition in the future. The results of our simulations effectively address common concerns regarding the risk of a gas burst in the lake due to buoyancy instability-triggered overturn and/or supersaturation of the water column.

Microbial-Induced Calcite Precipitation (MICP) is an effective bioremediation method for heavy metals, which often co-exist with organic pollutants in soils. Organic pollutants such as hydrocarbons inhibit soil urea hydrolysis critical in MICP whilst its feasibility in such enviroments is poorly understood. This study presents an investigation on the potential of biostimulation and bioaugmentation of MICP in soils polluted by polycyclic aromatic hydrocarbons (PAH) and their effect on ureolyisis at cell and enzyme level. Biostimulation of urea hydrolysis by soil autochthonous ureolytic bacteria was not detected over 62 days. Flow cytometry revealed Sproposarcina pasteurii at initial OD₆₀₀ = 0.01 was able to grow in soil water extracts of increasing hydrocarbon concentration (TOC = 0.035–35 mg L⁻¹), showing no negative effects on cell membrane stability. Urease activity assays in soil water extracts inoculated with S. pasteurii (OD₆₀₀ = 0.01 and 1) and soybean Glycine Max urease enzyme (1 and 100 g L⁻¹) indicated hydrocarbons negative effect on cell and enzyme urease activity was dependant on hydrocarbon and cell/enzyme concentrations, indicating the mechanism of inhibition was competitive. Glycine Max urease activity was unaffected at 100 g L⁻¹ but at 1 g L⁻¹ decreased with increasing hydrocarbon concentration up to 61%, whilst S. pasteurii urease activity (OD₆₀₀ = 1) readily decreased at the lowest hydrocarbon concentration (TOC = 0.35 mg L⁻¹) to an overall reduction of 31% at the highest TOC concentration. Bioaugmentation of S. pasteurii (OD₆₀₀ = 1) inoculated in the soil matrix successfully hydrolysed urea within 24 h. These results evidence for the first time the ability of model MICP bacteria S. pasteurii to grow and maintain relevant metabolic ureolytic activity in soils significantly polluted by PAH.

The transformation and stability of iron (Fe) minerals in coastal sediments are closely linked to the sulfur (S) cycle, influencing the fate of nutrients, carbon, and contaminants. However, in situ studies of these interactions in coastal sediments remain limited. We investigated the transformation of lepidocrocite, goethite, and mackinawite in three intertidal field plots with contrasting Fe and S biogeochemistry. Fe minerals were enriched with ⁵⁷Fe and mixed with the sediment, allowing close contact with the other inorganic and organic components of the sediment. After 8 weeks, transformation products were assessed using ⁵⁷Fe Mössbauer spectroscopy. Regular porewater analysis complemented solid-phase analyses, supporting the understanding of transformation pathways and extents. Under low-sulfide, Fe-reducing conditions, lepidocrocite did not transform to more crystalline Fe-oxides such as goethite or magnetite. Instead, ∼20% of the lepidocrocite transformed, mostly into a disordered Fe-phase, due to reductive dissolution and a small extent of sulfidation. Goethite, in contrast, remained apparently unchanged under the same conditions. These results indicate that both Fe-oxides may persist during extended anoxic periods under Fe-reducing conditions in coastal sediments and thus may influence elemental cycles. However, in sulfidic environments, lepidocrocite and goethite transformed into amorphous, nonstoichiometric Fe–sulfide and greigite. We hypothesize that amorphous Fe–sulfide precipitated first, later transforming into greigite; a potential precursor of pyrite formation. This is further supported by the transformation of synthetic mackinawite into greigite under high sulfide conditions, suggesting a sulfidation pathway that may eventually lead to pyrite formation in coastal sediments.

Globally, recycling of otherwise waste materials into new products is desired. End-of-life tyres are increasingly incorporated into new pavement materials but leaching of entrained chemicals from such products is not well quantified. Chemical concentrations in runoff from pavements may pose environmental and human health risks. High liquid–solid ratio, batch-agitated leaching is standard practice for assessing leachability and hazards of chemicals-of-potential-concern in contaminated soil and wastes but is not reflective of important exposure scenarios and may mislead. A new static surface leaching procedure (SSLP) is introduced that is more representative of chemical leaching from pavement reuse materials whilst in contact with rainfall/runoff water. SSLP was evaluated over 2–14 d intervals against batch-agitated leaching for two rubberised pavement products containing 10-fold different proportions of crumbed end-of-life tyres. Although, batch leaching showed high mass removal of 1,3-diphenylguanidine (1,3-DPG, 34%) and hexamethoxymethylmelamine (HMMM, 30%), both batch- and SSLP-leached concentrations of 1,3-DPG, HMMM and N¹-(4-methylpentan-2-yl)-N⁴-phenylbenzene-1,4-diamine quinone (6PPD-Q) were below ECOSAR-predicted toxicity thresholds for fish and daphnids. SSLP highlighted differences in chemical leachability based on rubber content of pavement products and offers a method applicable to other scenarios, such as PFAS leaching from concrete/asphalt pavements. The SSLP was shown to approximate one-dimensional leaching from the surface of the pavement and to be dominated by diffusive processes, thus yielding a simple repeatable approach.