Fugacity superposition: a new approach to dynamic multimedia fate modeling

Mangrove guardians: Unearthing the enrichment patterns of PAHs in the Zhangjiang estuary ecosystem

Understanding the bioaccumulation of PAHs in mangrove plants is crucial as it reflects the ecosystem's ability to mitigate pollution and minimize its impacts on surrounding environments. The Zhangjiang Estuary mangrove ecosystem is a vital ecological asset in Fujian Province, however, the interactions between contaminants, such as polycyclic aromatic hydrocarbons (PAHs), and mangrove plant tissues remain underexplored. This study investigates the different bioaccumulation patterns and machanism of 26 PAHs in three mangrove species (Kandelia obovata, Aegiceras corniculatum, and Avicennia marina). PAHs concentrations in mangrove and estuarine sediments ranged from 55.68 to 247.76 ng/g and 119.16 to 346.03 ng/g, while Σ26PAHs in the mangrove plants ranged from 13.03 to 172.17 ng/g, which was dominated by two- and five-ring PAHs. The bioconcentration factors (BCFs) of plant tissues showed a wide range, from 0 to 330.17, stems exhibited the highest PAHs concentrations compared to roots and leaves, with BCFs in stems following average enrichment factors: two-ring PAHs (37.23 ± 13.33) > alkylated PAHs (9.40 ± 4.66) > three-ring PAHs (3.09 ± 2.20) > six-ring PAHs (2.29 ± 0.36) > five-ring PAHs (0.52 ± 0.06) > four-ring PAHs (0.03 ± 0.01). The BCFs in roots showed strong positive correlations with logKow and Koc values, while the trends in stems and leaves were reversed, suggesting that roots showed high affinity for hydrophobic compounds, while stems and leaves preferred more water-soluble PAHs. The bioaccumulation capacity was highest in Aegiceras corniculatum, followed by Kandelia obovata and Avicennia marina. Additionally, alkylated PAHs were more enriched than their parent compounds, indicating selective uptake potential in mangrove plants. These findings underscore the critical role of mangrove species in mitigating PAHs contamination through selective absorption and accumulation. The results provide valuable insights into the application of mangrove ecosystems in bioremediation and offer guidance for environmental management in coastal regions.

Analysis of the multi-media environmental behavior of polycyclic aromatic hydrocarbons (PAHs) within Haizhou Bay using a fugacity model

In this study, we aimed to quantify the transport and fate of PAHs in different environmental phases (air, seawater, soil, sediment and fish), verify application of the Level III fugacity model in a bay simulation, and understand the transport and fate of PAHs in the bay environment on a macroscopic scale. The simulated average concentrations of ∑₁₆PAH in the air and soil (23.8 ng/m³ and 1080.91 ng/g, respectively), which is as a background reference data for the Haizhou Bay. In addition, the soil (307 t), fish (29.4 t), and sediment (9.72 t) phases were found to be important reservoirs in the Haizhou Bay. Emissions from road vehicles (658 t) accounted for the largest share of PAH emissions in the area, and atmospheric deposition contributed most to the input of PAHs to the polluted area in the region. Whereas the contribution of river runoff input was small, and degradation loss was the main output pathway.

Contribution of Dietary Uptake to PAH Bioaccumulation in a Simplified Pelagic Food Chain: Modeling the Influences of Continuous vs Intermittent Feeding in Zooplankton and Fish

Dietary uptake is important for trophic transfer of polycyclic aromatic hydrocarbons (PAHs) in the freshwater pelagic ecosystem. In this study, we hypothesized that both the dietary uptake rate and interval significantly influenced its relative contribution to bioaccumulation. We developed a toxicokinetic model framework for the bioaccumulation of deuterated PAHs (PAHs-d₁₀) in aquatic organisms considering different feeding intervals ranging from none for phytoplankton to approximately continuous for zooplankton to discrete for fish and built a simple artificial freshwater pelagic food chain composed of algae Chlorella vulgaris, zooplankton Daphnia magna, and zebrafish. We conducted bioaccumulation experiments and simulations for Daphnia magna and zebrafish under different algal densities based on our model. The results showed that intermittent feeding led to a large fluctuation in the PAH-d₁₀ concentrations in zebrafish compared to a leveled-off pattern in Daphnia magna because of approximately continuous feeding. Trophic dilution of PAHs-d₁₀ occurred in the food chain when there was waterborne-only uptake, but dietary uptake largely mitigated its extent that depended on dietary uptake rates. The assimilation efficiency, dietary uptake rate, and its relative contribution to bioaccumulation of PAHs-d₁₀ in zebrafish were all higher than those in Daphnia magna, suggesting that dietary uptake played a more important role in bioaccumulation of PAHs at higher trophic-level organisms.

Operational integration of time dependent toxicity impact category in dynamic LCA

Life Cycle Assessment (LCA) is the most widely used method for the environmental evaluation of an anthropogenic system and its capabilities no longer need to be proved. However, several limitations have been pointed out by LCA scholars, including the lack of a temporal dimension. The objective of this study is to develop a dynamic approach for calculating the time dependent impacts of human toxicity and ecotoxicity within LCA. A new framework is proposed, which includes dynamic inventory and dynamic impact assessment. This study focuses on the dynamic fate model for substances in the environment, combined with the USEtox® model for toxicity assessment. The method takes into account the noisy and random nature of substance emissions in function of time, as in the real world, and uses a robust solver for the dynamic fate model resolution. No characterization factors are calculated. Instead, a current toxicity is calculated as a function of time i.e. the damage produced per unit of time, together with a time dependent cumulated toxicity, i.e. the total damage produced from time zero to a given time horizon. The latter can be compared with the results obtained by the conventional USEtox® method: their results converge for a very large time horizon (theoretically at infinity). Organic substances are found to disappear relatively rapidly from the environmental compartments (in the time period in which the emissions occur) while inorganic substances (i.e. metals) tend to persist far beyond the emission period.

Weather dependent dynamics of the herbicides florasulam, carfentrazone-ethyl, fluroxypyr-meptyl and fluroxypyr in wheat fields through field studies and computational simulation

A dynamic model of dynamiCROP was applied to study environmental fate and behavior of four herbicides in wheat including florasulam, carfentrazone-ethyl, fluroxypyr-meptyl, and fluroxypyr. Meantime, their residue in wheat and dissipation half-lives in plant determined by field trials using QuEChERS liquid chromatography tandem mass spectrometry were used to verify modelling results. The combination of experimental verification and modelling prediction deciphered the fate of four pesticides in wheat field ecosystem. Besides, temperature difference of 3 °C only resulted in lower than 15% half-life difference. By quantifying the contribution of temperature, the predominant role of rain on pesticide dissipation was highlighted for the first time, namely higher precipitation leaded to faster degradation and vice versa.

Simulation of the transfer and fate of γ-HCH in epikarst system

The thin surface soil layer and karst features in karst terrains lead to poor filtration, poor pre-purification and rapid infiltration, so that karst groundwater systems are particularly vulnerable to contamination. Due to its extensive use in past, gamma-hexachlorocyclohexane (γ-HCH) is ubiquitous in various environmental compartments of China, even though it has been prohibited since 1984. However, very little is known about its movement and behavior in special karst system. In this study, a dynamic fugacity model was established for γ-HCH in epikarst system via dividing the karst soil into multiple layers coupled with the physical-chemical properties of γ-HCH. The simulated results in soil profile were in good agreement with the measured values of γ-HCH. The modeled results predict that only 18 g γ-HCH will be left in the studied area in 2020, which is only 0.4% of the largest reserves in 1983, and about 99.99% of γ-HCH will remains in soil. The concentrations of γ-HCH in air, plant and 0-20 cm layer soil in the studied area descended quickly after HCHs was prohibited in 1984, while its concentration in soil layer deeper than 20 cm (deeper soil) increased continuously till 1997. The dominant transfer process of γ-HCH between the adjacent compartments in the studied area was from 0-20 cm layer to the deeper soil. Sensitivity analysis results showed that emission rate, infiltration coefficient, total organic carbon of soil, degradation rate in soil, compartment area and volume were the top six influential parameters for predicting γ-HCH concentration.

Occurrence of chiral organochlorine compounds in the environmental matrices from King George Island and Ardley Island, west Antarctica

Chiral organochlorine compounds (OCs) were measured in various environmental matrices (air, soil and vegetation) from west Antarctica using high resolution gas chromatography coupled with high resolution mass spectrometry (HRGC/HRMS). They were generally detected at a global background level compared with the previous studies. α-HCH and PCB-183 was observed in all the matrices except PCB-183 in two soil samples, while PCB-95, -136, -149, -174, -176 and o,p’-DDT were detected in most air but only a few solid matrices. Enantiomeric fractions (EFs) indicated that nonracemic residues of chiral OCs occurred in all the matrices and a wide variation of the EF values was observed in the vegetation. There was significant discrepancy between the EF values of PCB-183 and the racemic values, indicating that stereoselective depletion of PCB-183 was probably associated with the water-air exchange. The EFs values of α-HCH were generally lower than the racemic values but no statistical difference was obtained in all the matrices except lichen, supporting the assumption that water-air exchange may make influence on long-range transport of α-HCH.

Fate simulation and risk assessment of endocrine disrupting chemicals in a reservoir receiving recycled wastewater

A fugacity based model was applied to simulate the distribution of three endocrine disrupting chemicals (EDCs), namely estrone (E1), 17β-estradiol (E2) and 17α-ethynylestradiol (EE2) in a reservoir receiving recycled wastewater in Australia. At typical conditions, the majority of estrogens were removed by degradation in the water compartment. A sensitivity analysis found that the simulated concentrations of E1, E2 and EE2 were equally sensitive to the parameters of temperature (T), reservoir water volume (V) and equivalent biomass concentration (EBC), but E1 was more sensitive to estrogen concentration in the recycled water (C(e)) and recycling rate (F(r)). In contrast, all three estrogens were not sensitive to reservoir water releasing rate (F(d)). Furthermore, a probabilistic health risk assessment showed that the simulated concentrations were below fish exposure threshold value (ETV) and human public health standard (PHS). Human equivalent dose of EDCs from fish consumption was about 10 times higher than that from drinking water consumption. The highest risk quotient among the three estrogens was found for EE2 with less than 9.5×10(-2), implying negligible health risks.

Application of a level IV fugacity model to simulate the long-term fate of hexachlorocyclohexane isomers in the lower reach of Yellow River basin, China

A level IV multimedia fugacity model was established to simulate the fate and transfer of hexachlorocyclohexane (HCH) isomers in the lower reach of the Yellow River basin, China, during 1952-2010. The predicted concentrations of HCHs are in good agreement with the observed ones, as indicated by the residual errors being generally lower than 0.5 logarithmic units. The effects of extensive agricultural application and subsequent prohibition of HCHs are reflected by the temporal variation of HCHs predicted by the model. It is predicted that only 1.8 tons of HCHs will be left in 2010, less than 0.06% of the highest contents (in 1983) in the study area, and about 99% of HCHs remain in soil. The proportions of HCH isomers in the environment also changed with time due to their different physicochemical properties. Although beta-HCH is not the main component of the technical HCHs, it has become the most abundant isomer in the environment because of its persistence. The dominant transfer processes between the adjacent compartments were deposition from air to soil, air diffusion through the air-water interface and runoff from soil to water. Sensitivity analysis showed that degradation rate in soil, parameters related to major sources, and thickness of soils had the strongest influence on the model result. Results of Monte Carlo simulation indicated the overall uncertainty of model predictions, and the coefficients of variation of the estimated concentrations of HCHs in all the compartments ranged from 0.5 to 5.8.

Evaluating the fate of p,p'-DDT in Tianjin, China using a non-steady-state multimedia fugacity model

Studies showed that DDT levels were still high in Tianjin, China, even though its use was banned in 1983. To estimate current risk of DDT to human health in Tianjin area, a non-steady-state (Level IV) multimedia fugacity model was used to simulate the fate and transfer of p,p'-DDT before and after the ban. The ordinary linear equations of Level IV model were solved with a matrix approach. The calculated p,p'-DDT concentration in air, water, soil, and sediment reached a maximum in the 1980s and then decreased, and agree well with those measured. The biggest bulk sinks of p,p'-DDT were soil and sediment, which accounted for 90% of total amount of p,p'-DDT in the environment. Air deposition and diffusions through the interfaces of water-air and water-sediment were the major intermedia transfer processes, while the degradation in soil and sediment were the key eliminating routes for p,p'-DDT in the environment.

Development and evaluation of an environmental multimedia fate model CHEMGL for the Great Lakes region

This paper describes the development of a multimedia compartmental model--CHEMGL--which predicts the fate and transport of chemicals in the Great Lakes region and can be used for risk assessment. CHEMGL includes 10 compartments that describe a given region: air boundary layer, free troposphere, lower stratosphere, surface water, sediment, surface soil, vadose soil, groundwater zone, plant foliage and plant root. The model assumes that the compartments are completely mixed and chemical equilibrium between the phases within each compartment is assumed (e.g., suspended solids and biota in water). The attenuation mechanisms include advection, transformation reactions, and diffusive and nondiffusive intermedia transport between compartments. Input parameters include a description of each environmental media, emission rates, and chemical-specific properties and reaction rates. The numerical model results are in good agreement with the analytical solution for an example that examines the fate of benzene. Accordingly, the mathematical and computational components of the model were verified. CHEMGL predicted the concentration of four representative chemicals (atrazine, benzo[a]pyrene, benzene and hexachlorobenzene) in all five basins: Superior, Michigan, Huron, Erie and Ontario. The predicted concentrations fell within one to two orders of magnitude of data reported in the literature. These results suggest that the model is appropriate for estimating the fate and exposure of chemicals for a screening level risk assessment.