Modeling in environmental chemistry

It is our pleasure to present this themed issue of Environmental Science: Processes & Impacts on “Modeling in Environmental Chemistry”. For many decades models have provided tools to environmental chemists for quantitatively formulating hypotheses, evaluating existing data and guiding new research and data collection. Of particular note is the prominent role that models have played in the regulatory assessment of environmental risks associated with the use of chemicals in commerce. Environmental fate, bioaccumulation and exposure models, sometimes coupled with property estimation models, are well-established policy support tools at national and international levels. Given the important role of models in environmental risk and hazard assessment, it is necessary to continually evaluate regulatory applications of models against the current scientific state-of-the-art. A workshop sponsored by the European Centre for Ecotoxicology and Toxicology of Chemicals (ECETOC) with the theme ‘Advances in Exposure Modelling: Bridging the Gap Between Research and Application’, was held in May of 2017 in Brussels, Belgium, and provided both the opportunity for reflection, and part of the motivation for this themed issue. The three of us were members of the planning committee for the workshop, which brought together users and developers of models for assessing the fate of chemicals released into the environment and levels of ecosystem and human exposure to chemicals. In addition to inviting authors to submit modeling papers at the intersection of science and policy, we also solicited contributions that would cover scientific applications of modeling in the entire field of environmental chemistry.

Three Perspective articles are closely aligned to the topic of the ECETOC workshop in that they present experiences and arguments related to the use of environmental fate and exposure models in a regulatory context. Chris Money (DOI: 10.1039/C7EM00434F) examines tiered and targeted approaches to acquiring information to support human health risk assessment in a European context, and Mark Bonnell and his co-authors from Environment and Climate Change Canada and Health Canada (DOI: 10.1039/C7EM00510E) reflect on two decades of fate and exposure modeling in support of Canada’s Chemicals Management Plan. Finally, with a focus on international regulation of chemicals, Michael McLachlan (DOI: 10.1039/C7EM00473G) argues for a more prominent role for environmental fate modeling in assessing chemicals that are candidates for addition to the Stockholm Convention on Persistent Organic Pollutants.

Two other Perspectives describe the development of specific modeling approaches. On the occasion of her retirement as Full Professor of Environmental Chemistry at Insubria University, Paola Gramatica, her longtime collaborator Ester Papa and Alessandro Sangion (DOI: 10.1039/C7EM00519A) review the development of quantitative structure–activity relationship (QSAR) models to describe multivariate endpoints such as environmental persistence, aquatic toxicity and PBT properties of organic chemicals. In another Perspective article, Roman Ashauer and Tjalling Jager (DOI: 10.1039/C7EM00328E) present a case for a dynamic energy budget model with a toxicity module (DEBtox) to be a tool that provides the theoretical underpinning to advance our understanding of physiological modes of action across species and toxicants.

Two of us (MacLeod & Gouin) together with Antonio Di Guardo and Martin Scheringer (DOI: 10.1039/C7EM00568G) authored a Critical Review of advances in environmental fate and exposure modeling over the last 25 years. We call for the formation of multi-stakeholder expert groups tasked with transferring scientific advances into regulatory models.

Four research papers are specifically concerned with aspects of modeling bioaccumulation of organic chemicals by fish. Don Mackay and collaborators (DOI: 10.1039/C7EM00485K) use a bioaccumulation model to illustrate the potential limitations of regulatory bioaccumulation criteria when applied to highly hydrophobic substances. Mackay also collaborates with Jon Arnot (DOI: 10.1039/C7EM00539C) to develop a new model of dietary absorption efficiency of chemicals, and to estimate the rate of chemical degradation that is assumed to occur in the lumen of the gastrointestinal tract of fish. Wolfgang Larisch and Kai-Uwe Goss (DOI: 10.1039/C7EM00495H) use a mechanistically based bioaccumulation model and experimental data collected from literature to argue that super-hydrophobic chemicals are subject to slow up-take and depuration by fish, which is contrary to suggestions in regulatory documents. Finally, Manoochehr Khazaee and Carla Ng (DOI: 10.1039/C7EM00474E) identify the critical gaps in parametrization of physiologically based pharmacokinetic models of perfluoroalkyl acids in zebrafish.

Three papers describe new modeling tools and approaches to model chemical fate, transport and exposure at different spatial and temporal scales. Yoshitaka Imaizumi and colleagues from the National Institute for Environmental Studies in Japan (DOI: 10.1039/C7EM00517B) present their PeCHREM method for modeling spatio-temporal variability of concentrations of rice paddy herbicides in rivers. Cedric Wannaz, Peter Fantke, Joe Lane and Olivier Jolliet (DOI: 10.1039/C7EM00523G) introduce their Pangea framework for chemical fate and exposure modeling at variable spatio-temporal scales, and provide a case study for over 4000 point sources of benzene in Australia. Finally, Melissa Morselli, Elisa Terzaghi and Antonio Di Guardo (DOI: 10.1039/C7EM00530J) use dynamic exposure assessment models to demonstrate that variability in environmental factors such as primary producer biomass can lead to high variability in exposure estimates, which highlights the importance of accounting for environmental dynamics in some assessments.

Two papers from different teams of researchers at Radboud University confront the challenge of understanding degradation of organic chemicals in complex natural and engineered systems. Tom Nolte and his co-authors (DOI: 10.1039/C7EM00375G) describe the development of QSAR models to predict biodegradation of neutral and charged chemicals in surface waters. And, in a paper that straddles the boundary with our sister journal, Environmental Science: Water Research & Technology, Mélanie Douziech and collaborators from Radboud and Unilever (DOI: 10.1039/C7EM00493A) apply meta-regression modeling to a large database of wastewater treatment plant removal efficiencies of surfactants, fragrances and pharmaceuticals, and identify research priorities and key considerations for future monitoring campaigns.

Two papers describe case studies of environmental chemistry models applied to specific chemicals and environmental systems. Dimitri Panagopoulos and one of us (MacLeod) (DOI: 10.1039/C7EM00524E) present a systematic 5-stage model-based assessment of the fate of volatile methylsiloxanes, with a focus on the residence time of these chemicals in aquatic systems after release from wastewater treatment plants. And, in a study that includes natural and social scientists among the team of authors, Judith Perlinger et al. (DOI: 10.1039/C7EM00547D) use a suite of models to examine the sensitivity of modeled atmospheric deposition and bioaccumulation of mercury in the Great Lakes region to policy changes that affect emission rates and other major drivers.

Two research papers present modeling that supports the application of passive samplers in environmental analytical chemistry. Nicholas Herkert leads a team including Tom Harner and Keri Hornbuckle (DOI: 10.1039/C7EM00360A) who present a model of the effective volume of air sampled by passive air samplers deployed anywhere on Earth. And, a team led by Patricia Tcaciuc and Philip Gschwend (DOI: 10.1039/C7EM00501F) demonstrate that reaction–diffusion modeling of passive samplers in sediments deployed with carefully chosen performance reference compounds can provide estimates of in situ degradation rates of persistent hydrophobic contaminants.

Finally, two research papers describe modeling of biogeochemical processes. Yingying Sun, Ninh Pham and David Waite (DOI: 10.1039/C7EM00497D) use a model to evaluate the hypothesis that release of dopamine is a critical part of the allelopathic “chemical warfare” perpetrated by the benthic marine algae Ulvaria obscura var. blyttii that is present in green tides in the northern Pacific and Atlantic oceans. And, Chen Wang, Frank Wania and Kai-Uwe Goss (DOI: 10.1039/C7EM00451F) present a model that suggests aerosol growth in the atmosphere should be viewed as being determined by simultaneous kinetic processes rather than by thermodynamic equilibrium.

We hope you, the readership of Environmental Science: Processes & Impacts, enjoy reading this collection of papers, which represent a broad and exciting field. We thank all contributors to this themed issue, the staff at the Royal Society of Chemistry offices in Cambridge, and especially all of the anonymous reviewers who volunteered their time and expertise. We hope this collection of papers helps you find inspiration for new research that builds on these studies or opens new frontiers for modeling in environmental chemistry!

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