Do environmental dynamics matter in fate models? Exploring scenario dynamics for a terrestrial and an aquatic system

Incorporating climate projections in the environmental risk assessment of pesticides in aquatic ecosystems

Global climate change will significantly impact the biodiversity of freshwater ecosystems, both directly and indirectly via the exacerbation of impacts from other stressors. Pesticides form a prime example of chemical stressors that are expected to synergize with climate change. Aquatic exposures to pesticides might change in magnitude due to increased runoff from agricultural fields, and in composition, as application patterns will change due to changes in pest pressures and crop types. Any prospective chemical risk assessment that aims to capture the influence of climate change should properly and comprehensively account for the variabilities and uncertainties that are inherent to projections of future climate. This is only feasible if they probabilistically propagate extensive ensembles of climate model projections. However, current prospective risk assessments typically make use of process-based models of chemical fate that do not typically allow for such high-throughput applications. Here, we describe a Bayesian network model that does. It incorporates a two-step univariate regression model based on a 30-day antecedent precipitation index, circumventing the need for computationally laborious mechanistic models. We show its feasibility and application potential in a case study with two pesticides in a Norwegian stream: the fungicide trifloxystrobin and herbicide clopyralid. Our analysis showed that variations in pesticide application rates as well as precipitation intensity lead to variations in in-stream exposures. When relating to aquatic risks, the influence of these processes is reduced and distributions of risk are dominated by effect-related parameters. Predicted risks for clopyralid were negligible, but the probability of unacceptable future environmental risks due to exposure to trifloxystrobin (i.e., a risk quotient >1) was 8%-12%. This percentage further increased to 30%-35% when a more conservative precautionary factor of 100 instead of 30 was used. Integr Environ Assess Manag 2024;20:384-400. © 2023 The Authors. Integrated Environmental Assessment and Management published by Wiley Periodicals LLC on behalf of Society of Environmental Toxicology & Chemistry (SETAC).

Spatially resolved environmental fate models: A review

Spatially resolved environmental models are important tools to introduce and highlight the spatial variability of the real world into modeling. Although various spatial models have been developed so far, yet the development and evaluation of these models remain a challenging task due to several difficulties related to model setup, computational cost, and obtaining high-resolution input data (e.g., monitoring and emission data). For example, atmospheric transport models can be used when high resolution predicted concentrations in atmospheric compartments are required, while spatial multimedia fate models may be preferred for regulatory risk assessment, life cycle impact assessment of chemicals, or when the partitioning of chemical substances in a multimedia environment is considered. The goal of this paper is to review and compare different spatially resolved environmental models, according to their spatial, temporal and chemical domains, with a closer insight into spatial multimedia fate models, to achieve a better understanding of their strengths and limitations. This review also points out several requirements for further improvement of existing models as well as for their integration.

Estimating temporal and spatial levels of PAHs in air using rain samples and SPME analysis: Feasibility evaluation in an urban scenario

There is a growing interest in evaluating the role of concentration changes of contaminants in temporal and spatial gradients. This is often relevant for fast moving environmental phases such as air and water. In this paper, small volumes of rainwater were sampled as proxy for air concentrations of Polycyclic Aromatic Hydrocarbons (PAHs): rain was collected in three sampling sites (high traffic, restricted traffic and a low traffic zone) in Como. Solid phase micro extraction (SPME) was used for the extraction to reduce required sample volumes, allowing the acquisition of more samples in time. Rain samples highlighted a spatial and temporal variability along a traffic gradient in the Como city, especially for the most abundant PAH, e.g. phenanthrene. Air concentrations were then estimated from rain concentrations. The results show that this is a cheap and promising method, although requiring rainfall/snowfall conditions, that can be used to perform monitoring campaign of air concentrations at a higher temporal and spatial resolution than the adopted standard methods (e.g. high-volume air samplers). The results could be employed for evaluation of the exposure, emission profiles and calibration of fate models.

A new dataset of PCB half-lives in soil: Effect of plant species and organic carbon addition on biodegradation rates in a weathered contaminated soil

This paper presents a new dataset of Polychlorinated Biphenyls (PCBs) half-lives in soil. Data were obtained from a greenhouse experiment performed with an aged contaminated soil under semi-field conditions, collected from a National Relevance Site (SIN) located in Northern Italy (SIN Brescia-Caffaro). Ten different treatments (combination of seven plant species and different soil conditions) were considered together with the respective controls (soil without plants). PCB concentration reduction in soil was measured over a period of 18 months to evaluate the ability of plants to stimulate the biodegradation of these compounds. Tall fescue, tall fescue cultivated together with pumpkin and tall fescue amended with compost reduced more than the 50% of the 79 measured PCB congeners, including the most chlorinated ones (octa to deca-PCBs). However, the data obtained showed that no plant species was uniquely responsible for the effective degradation of all isomeric classes and congeners. The obtained half-lives ranged from 1.3 to 5.6 years and were up to a factor of 8 lower compared to generic HL values reported in literature. This highlighted the importance of cultivation and plant-microbe interactions in speeding up the PCB biodegradation. This new dataset could contribute to substantially improve the predictions of soil remediation time, multimedia fate and the long-range transport of PCBs. Additionally, the half-lives obtained here can also be used in the evaluation of the food chain transfer of these chemicals, and finally the exposure and potential for effects on ecosystems.

Role of photo- and biodegradation of two PAHs on leaves: Modelling the impact on air quality ecosystem services provided by urban trees

Urban trees provide important ecosystem services, including air quality improvement. Polycyclic aromatic hydrocarbons (PAHs) are among the most important pollutants in air, due to their elevated concentrations and toxicity. Plants can act as filters of PAHs and as "chemical reactors" for pollutant removal, therefore reducing air concentrations. Here, the first assessment of photo- vs. biodegradation of PAHs on leaves of urban trees is presented. A dynamic air-vegetation-soil model (SoilPlusVeg) was improved to simulate the fate of two representative PAHs with contrasting physico-chemical properties (phenanthrene and benzo[a]pyrene). Simulations were performed for two different environmental scenarios from Italy (Como and Naples), selected for their dissimilar meteorological parameters, plant species and emission levels. The effect of photo- and biodegradation on leaf concentrations and fluxes towards air and soil was investigated comparing deciduous (maple, cornel and hazelnut) and evergreen (holm oak) broadleaf woods. The results showed that biodegradation in the phyllosphere could not be neglected when evaluating the ecosystem services provided by urban trees, as this process contributed significantly to the reductions (up to 25% on average) in PAH leaf concentrations and fluxes to air and soil; however, the reductions revealed ample variations with time (up to more than two orders of magnitude) showing the dependence on meteorological parameters, air compartment structure, as well as type of woods. These findings permitted to improve the ecological realism of the simulations and obtain more accurate results when predicting organic contaminant uptake and release by plant leaves, including potential for food chain transfer and long-range transport.

ChemFate: A fate and transport modeling framework for evaluating radically different chemicals under comparable conditions

With the ever-increasing development on novel chemicals and materials, with radically different properties and environmental behavior, it is challenging to compare their environmental behavior under similar conditions. For example, pesticides may be non-ionizable organics, ionizable organics, metal ion-based, or nanomaterials. These very different chemicals behave very differently. To date, no single modeling platform can handle all adequately, in a dynamic framework that accounts for actual variability in meteorology, rates of release to the environment, and the actual characteristics of the region of interest. Here we present ChemFate, a framework to address this challenge, by incorporating four different fate and transport models, each to address these four classes of chemicals (non-ionizable organics, ionizable organics, metal ion-based, or nanomaterials). We build upon established models, but have incorporated a number of additional processes. After demonstrating that the individual models comparable favorably with observed data and the previous models, under similar conditions, we conducted a case study with four radically different fungicides, used in the Central Valley, California. We found that although the concentrations of the non-ionizable and ionizable organic fungicide spike after application and temporarily may exceed toxicity thresholds for Daphnia Magna, they do not accumulate over time, while the metal ion and metallic nanoparticle result in increasing accumulation of Cu²⁺, eventually exceeding the toxicity threshold during runoff events. This case study demonstrates the value of a framework that allows the comparison of different classes of chemicals under the same conditions.

New Data Set of Polychlorinated Dibenzo-p-dioxin and Dibenzofuran Half-Lives: Natural Attenuation and Rhizoremediation Using Several Common Plant Species in a Weathered Contaminated Soil

In this paper, a new data set of polychlorinated dibenzo-p-dioxin and dibenzofuran (PCDD/Fs) half-lives (HLs) in soil is presented. Data are derived from a greenhouse experiment performed with an aged contaminated soil under semi-field conditions, obtained from a National Relevance Site (SIN) located in Northern Italy (SIN Brescia-Caffaro). Ten different treatments (combination of seven plant species with different soil conditions) were considered together with the respective controls (soil without plants). The ability of the plants to stimulate the biodegradation of these compounds was evaluated by measuring the PCDD/F concentration reduction in soil over a period of 18 months. The formation of new bound residues was excluded by using roots as a passive sampler of bioaccessible concentrations. The best treatment which significantly reduced PCDD/F concentrations in soil was the one with Festuca arundinacea (about 11-24% reduction, depending on the congener). These decreases reflected in HLs ranging from 2.5 to 5.8 years. Simulations performed with a dynamic air-vegetation-soil model (SoilPlusVeg) confirmed that these HLs were substantially due to biodegradation rather than other loss processes. Because no coherent PCDD/F degradation HL data sets are currently available for soil, they could substantially improve the predictions of soil remediation time, long-range transport, and food chain transfer of these chemicals using multimedia fate models.

Plants radically change the mobility of PCBs in soil: Role of different species and soil conditions

The mobility of Polychlorinated Biphenyls (PCBs) in soil cultivated with different plant species was evaluated by means of a column experiment to investigate the specific plant influence on PCB environmental fate and the potential for leaching. The soil was collected at a National Relevance Site for remediation located in Northern Italy (SIN Brescia-Caffaro) and underwent a rhizoremediation treatment for 18 months with different plant species (Festuca arundinacea, Cucurbita pepo ssp pepo and Medicago sativa). The same but unplanted soil was also considered as control for comparison. The columns were leached with tap water and PCB concentrations were measured in the leachate after 7 days of soil/water contact. Soil previously cultivated with different plant species exhibited statistically different behavior in terms of chemical leaching among the different fractions. Total PCB bulk concentrations ranged from 24 to 219 ng/L. Leachate samples were enriched in tetra- to hepta-PCBs. While PCB concentrations in the dissolved phases varied within a factor of 2 between controls and treatments, PCB associated to particulate organic carbon (POC) differed by more than one order of magnitude. More specifically, Medicago sativa enriched the soil with POC doubling PCB leaching with respect to the other plant species and the unplanted controls.

Modelling peak exposure of pesticides in terrestrial and aquatic ecosystems: importance of dissolved organic carbon and vertical particle movement in soil

In the present work, an existing vegetation/air/litter/soil model (SoilPlusVeg) was modified to improve organic chemical fate description in terrestrial/aquatic ecosystems accounting for horizontal and vertical particulate organic carbon (POC) transport in soil. The model was applied to simulate the fate of three pesticides (terbuthylazine, chlorpyrifos and etofenprox), characterized by increasing hydrophobicity (log K_OW from about 3 to 7), in the soil compartment and more specifically, their movement towards surface and groundwater through infiltration and runoff processes. The aim was to evaluate the role of dissolved organic carbon (DOC) and POC in the soil in influencing the peak exposure of pesticides in terrestrial/aquatic ecosystems. Simulation results showed that while terbuthylazine and chlorpyrifos dominated the free water phase (C_W-FREE) of soil, etofenprox was mainly present in soil porewater as POC associated chemical. This resulted in an increase of this highly hydrophobic chemical movement towards groundwater and surface water, up to a factor of 40. The present work highlighted the importance of DOC and POC as an enhancer of mobility in the water of poor or very little mobile chemicals. Further studies are necessary to evaluate the bioavailability change with time and parameterize this process in multimedia fate models.

How good are the predictions of mobility of aged polychlorinated biphenyls (PCBs) in soil? Insights from a soil column experiment

A column leaching experiment was performed to evaluate the influence of some relevant environmental factors (soil/water contact time, temperature, saturation) on mobility of aged polychlorinated biphenyls (PCBs) in soil together with transport mediated by dissolved organic carbon (DOC) and mobile organic carbon (OC) coated fine particles/colloids. Consecutive fractions of leachates were collected after a variable pre-equilibration time (2, 5, 7, 48 days), using leaching solutions with different DOC content (tap water vs. Aldrich humic acid), in saturated vs. field capacity conditions and at different temperatures (25 °C vs. 15 °C). The data obtained were compared to the predicted values using a multimedia model (SoilPlusVeg) to evaluate model behaviour. Contact time and temperature determined a relevant effect on DOC and particle/colloid availability, with significant variations in leachate concentrations (up to 1 order of magnitude), typically overlooked by most environmental fate models. Results obtained at different temperatures show a modulation of the DOC/particles production with temperature and therefore the role of temperature changes in the environmental scenarios (e.g. seasonal variations). Transport of PCBs enhanced by Aldrich DOC was not linearly correlated to chemical hydrophobicity but revealed a threshold to ~Log K_OW 6.5, likely because of the slow sorption kinetics of more hydrophobic chemicals. Additionally, variation of the saturation conditions (e.g. drying-wetting cycles) can determine contamination peaks at the beginning of an irrigation/rainfall event because of the soil/water equilibration. Model simulations, even when including DOC in the water phase, but not accounting for the particle/colloidal transport and sorption/desorption kinetics, mismatched the ratio of dissolved vs. DOC-associated and particle-associated PCBs and substantially underpredicted concentrations, especially for the high chlorinated congeners. The results indicated that some of the common assumptions and paradigms in fate modelling of such hydrophobic compounds should be revisited and models updated.

Pesticide fate in cultivated mountain basins: The improved DynAPlus model for predicting peak exposure and directing sustainable monitoring campaigns to protect aquatic ecosystems

Agricultural activities can involve the use of plant protection products (PPPs) and the use of such chemicals can occur near surface waters bodies, thus creating a potential for adverse effects on aquatic ecosystems. In mountain watersheds, where runoff fluxes are particularly rapid due to side slopes, exposure is generally characterized by short but intense concentration peaks. Monitoring campaigns are often inadequate or too expensive to be carried out and modelling tools are therefore vital for exposure assessment and their use is encouraged by current legislation. However, currently adopted models and scenarios (e.g., FOCUS for PPPs) are often too conservative and/or "static" to accurately capture exposure variability, and the need for more realistic and dynamic tools is now one of the major challenges for risk assessment. In a previous work, the new fate model DynAPlus was developed to improve pesticide fate predictions in cultivated mountain basins and was successfully evaluated against chlorpyrifos water concentrations measured in a mountain stream in Northern Italy. However, the need for some model improvements (e.g., the inclusion of dissolved organic matter and macrophytes in water) was highlighted. In this work, DynAPlus was improved by replacing the water-sediment unit with ChimERA fate, a recently-published model capable of predicting bioavailable chemical concentrations in shallow water environments accounting for the presence and temporal variations of particulate/dissolved organic carbon and primary producers. The model was applied to preliminarily characterize the risk associated to the use of four PPPs (two insecticides and two fungicides) in a sub-basin of the Adda River (Valtellina Valley, Northern Italy), surrounded by apple orchards. Results revealed the potential magnitude of exposure peaks for the four PPPs and suggested that monitoring campaigns should prioritize, in the selected case study, chlorpyrifos, etofenprox and fluazinam. The potential role of DynAPlus in providing more realistic exposure predictions for ecological risk assessment, as well as for planning efficient monitoring campaigns and help pesticide management practices, was also stressed.

Improving the SoilPlusVeg model to evaluate rhizoremediation and PCB fate in contaminated soils

Tools to predict environmental fate processes during remediation of persistent organic pollutants (POPs) in soil are desperately needed since they can elucidate the overall behavior of the chemical and help to improve the remediation process. A dynamic multimedia fate model (SoilPlusVeg) was further developed and improved to account for rhizoremediation processes. The resulting model was used to predict Polychlorinated Biphenyl (PCB) fate in a highly contaminated agricultural field (1089 ng/g d.w.) treated with tall fescue (Festuca arundinacea), a promising plant species for the remediation of contaminated soils. The model simulations allowed to calculate the rhizoremediation time (about 90 years), given the available rhizoremediation half-lives and the levels and fingerprints of the PCB congeners, to reach the legal threshold, to show the relevance of the loss processes from soil (in order of importance: degradation, infiltration, volatilization, etc.) and their dependence on meteorological and environmental dynamics (temperature, rainfall, DOC concentrations). The simulations showed that the effective persistence of PCBs in soil is deeply influenced by the seasonal variability. The model also allowed to evaluate the role of DOC as a possible enhancer of PCB degradation as a microorganism "spoon feeder" of PCBs in the soil solution. Additionally, we preliminary predicted how the contribution of PCB metabolites could modify the PCB fingerprint and their final total concentrations. This shows that the SoilPlusVeg model could be used in selecting the best choices for a sustainable rhizoremediation of a POP contaminated site.

Environmental fate and exposure models: advances and challenges in 21st century chemical risk assessment

Environmental fate and exposure models are a powerful means to integrate information on chemicals, their partitioning and degradation behaviour, the environmental scenario and the emissions in order to compile a picture of chemical distribution and fluxes in the multimedia environment. A 1995 pioneering book, resulting from a series of workshops among model developers and users, reported the main advantages and identified needs for research in the field of multimedia fate models. Considerable efforts were devoted to their improvement in the past 25 years and many aspects were refined; notably the inclusion of nanomaterials among the modelled substances, the development of models at different spatial and temporal scales, the estimation of chemical properties and emission data, the incorporation of additional environmental media and processes, the integration of sensitivity and uncertainty analysis in the simulations. However, some challenging issues remain and require research efforts and attention: the need of methods to estimate partition coefficients for polar and ionizable chemical in the environment, a better description of bioavailability in different environments as well as the requirement of injecting more ecological realism in exposure predictions to account for the diversity of ecosystem structures and functions in risk assessment. Finally, to transfer new scientific developments into the realm of regulatory risk assessment, we propose the formation of expert groups that compare, discuss and recommend model modifications and updates and help develop practical tools for risk assessment.