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In silico methods to prioritize chemicals with high exposure potential
Stockholm University, Faculty of Science, Department of Environmental Science and Analytical Chemistry.ORCID iD: 0000-0002-3426-1108
2017 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Chemicals offer a wide range of desired functions and are used in a variety of consumer goods and industrial sectors. The number of individual synthetic organic chemicals produced and the total global chemical production volume are increasing. The majority of these anthropogenic chemicals are not monitored in environmental matrices nor in the indoor environment even though some are associated with undesirable consequences and the range of possible chemical impacts is still far from being fully understood. Chemicals that remain in the environment for a long time and/or distribute over a large area have high exposure potential, and will present particularly acute challenges if a currently unknown undesirable effect is discovered. 

This thesis describes the development of a set of in silico methods to identify and prioritize chemicals with high exposure potential that are currently not subject to national or international restrictions. In brief, we i) compiled databases of contaminants of potential concern, ii) established models to predict key properties to fill data gaps in the absence of experimental data, and iii) developed and applied methods to screen chemicals to identify those that should be assigned high priority for future study. 

Paper I delivers screening-level models to predict partition ratios of organic chemicals between polymeric materials commonly found indoors, and both air and water. These models can be used in high-throughput exposure assessment studies, passive sampling experiments, and models of emissions, fate and transport of chemicals. 

Paper II presents a scoring method to prioritize 464 organic chemicals of emerging Arctic concern for their potential to fit a set of four exposure-based hazard profiles. These four profiles represent persistent organic pollutants (POPs) regulated under the Stockholm Convention, very persistent and very bioaccumulative substances (vPvBs) regulated under REACH and for two novel and unregulated profiles derived from the planetary boundary threats framework; airborne persistent contaminants (APCs) and waterborne persistent contaminants (WPCs). APCs and WPCs are chemicals that are mobile in air and water, respectively, and that contaminate the environment in a poorly reversible manner due to their persistence. The prioritization method is based on a reference set of 148 chemicals that is used to contextualize the scoring results. 

Paper III describes the prioritization of 8,648 chemicals that were reportedly produced in five OECD countries. Paper III elucidates the relationship between the elemental composition of these chemicals and the exposure-based hazard scores, and presents a strategy to disentangle overlaps among the four exposure hazard profiles by categorizing chemicals according to the spatial coverage of profiles they best fit. 

Paper IV focuses on refining the prioritization method described in Papers II and III using a set of 5,600 hypothetical chemicals. The refined method is used to prioritize the chemicals from Papers II and III, and an additional 4,567 chemicals from the REACH database. 

The in silico methods developed in this thesis can be applied to conduct screening-level exposure assessments using only chemical structures as a starting point. Substances prioritized as having high potential to be POPs, vPvB, APC, or WPC should be considered for more detailed study to unequivocally determine their identity and physicochemical properties.

Place, publisher, year, edition, pages
Stockholm: epartment of Environmental Science and Analytical Chemistry, Stockholm University , 2017. , p. 53
Keyword [en]
free energy relationship, solvation parameters, polymers, materials, partitioning, octanol, Arctic contaminants, AMAP, POPs, Stockholm Convention, vPvB, REACH, OECD, QSAR, planetary boundaries, persistence, bioaccumulation, long-range transport
National Category
Environmental Sciences
Research subject
Applied Environmental Science
Identifiers
URN: urn:nbn:se:su:diva-149358ISBN: 978-91-7797-065-1 (print)ISBN: 978-91-7797-066-8 (electronic)OAI: oai:DiVA.org:su-149358DiVA, id: diva2:1161008
Public defence
2018-01-18, Nordenskiöldsalen, Geovetenskapens hus, Svante Arrhenius väg 12, Stockholm, 10:00 (English)
Opponent
Supervisors
Funder
EU, FP7, Seventh Framework Programme, 316665
Note

At the time of the doctoral defense, the following papers were unpublished and had a status as follows: Paper 3: Manuscript. Paper 4: Manuscript.

Available from: 2017-12-18 Created: 2017-11-28 Last updated: 2017-12-20Bibliographically approved
List of papers
1. Screening-level models to estimate partition ratios of organic chemicals between polymeric materials, air and water
Open this publication in new window or tab >>Screening-level models to estimate partition ratios of organic chemicals between polymeric materials, air and water
2016 (English)In: Environmental Science: Processes & Impacts, ISSN 2050-7887, E-ISSN 2050-7895, Vol. 18, no 6, p. 667-676Article in journal (Refereed) Published
Abstract [en]

Polymeric materials flowing through the technosphere are repositories of organic chemicals throughout their life cycle. Equilibrium partition ratios of organic chemicals between these materials and air (KMA) or water (KMW) are required for models of fate and transport, high-throughput exposure assessment and passive sampling. KMA and KMW have been measured for a growing number of chemical/ material combinations, but significant data gaps still exist. We assembled a database of 363 KMA and 910 KMW measurements for 446 individual compounds and nearly 40 individual polymers and biopolymers, collected from 29 studies. We used the EPI Suite and ABSOLV software packages to estimate physicochemical properties of the compounds and we employed an empirical correlation based on Trouton's rule to adjust the measured KMA and KMW values to a standard reference temperature of 298 K. Then, we used a thermodynamic triangle with Henry's law constant to calculate a complete set of 1273 KMA and KMW values. Using simple linear regression, we developed a suite of single parameter linear free energy relationship (spLFER) models to estimate KMA from the EPI Suite-estimated octanol-air partition ratio (KOA) and KMW from the EPI Suite-estimated octanol-water (KOW) partition ratio. Similarly, using multiple linear regression, we developed a set of polyparameter linear free energy relationship (ppLFER) models to estimate KMA and KMW from ABSOLV-estimated Abraham solvation parameters. We explored the two LFER approaches to investigate (1) their performance in estimating partition ratios, and (2) uncertainties associated with treating all different polymers as a single bulk polymeric material compartment. The models we have developed are suitable for screening assessments of the tendency for organic chemicals to be emitted from materials, and for use in multimedia models of the fate of organic chemicals in the indoor environment. In screening applications we recommend that K-MA and K-MW be modeled as 0.06 x K-OA and 0.06 x K-OW respectively, with an uncertainty range of a factor of 15.

National Category
Chemical Sciences Earth and Related Environmental Sciences Environmental Sciences
Research subject
Applied Environmental Science
Identifiers
urn:nbn:se:su:diva-132621 (URN)10.1039/c5em00664c (DOI)000378237000003 ()27158699 (PubMedID)
Projects
A-TEAM
Funder
EU, FP7, Seventh Framework Programme, 316665
Available from: 2016-08-23 Created: 2016-08-17 Last updated: 2017-11-30Bibliographically approved
2. Screening-level exposure-based prioritization to identify potential POPs, vPvBs and planetary boundary threats among Arctic contaminants
Open this publication in new window or tab >>Screening-level exposure-based prioritization to identify potential POPs, vPvBs and planetary boundary threats among Arctic contaminants
2017 (English)In: Emerging Contaminants, ISSN 2405-6650, E-ISSN 2405-6642, Vol. 3, no 2, p. 85-94Article in journal (Refereed) Published
Abstract [en]

A report that reviews Arctic contaminants that are not currently regulated as persistent organic pollutants (POPs) under international treaties was recently published by the Arctic Monitoring and Assessment Programme (AMAP). We evaluated 464 individual chemicals mentioned in the AMAP report according to hazard profiles for POPs, very persistent and very bioaccumulative (vPvB) chemicals, and two novel and distinct hazard profiles we derived from the planetary boundary threat framework. The two planetary boundary threat profiles assign high priority to chemicals that will be mobile and poorly reversible environmental contaminants. Utilizing persistence as a proxy for poor reversibility, we defined two exposure-based hazard profiles; airborne persistent contaminants (APCs) and waterborne persistent contaminants (WPCs) that are potential planetary boundary threats. We used in silico estimates of physicochemical properties and multimedia models to calculate hazard metrics for persistence, bioaccumulation and long-range transport potential, then we synthesized this information into four exposure-based hazard scores of the potential of each AMAP chemical to fit each of the POP, vPvB, APC and WPC exposure-based hazard profiles. As an alternative to adopting a “bright line” score that represented cause for concern, we scored the AMAP chemicals by benchmarking against a reference set of 148 known and relatively well-studied contaminants and expressed their exposure-based hazard scores as percentile ranks against the scores of the reference set chemicals. Our results show that scores in the four exposure-based hazard profiles provide complementary information about the potential environmental exposure-based hazards of the AMAP chemicals. Our POP, vPvB, APC and WPC exposure-based hazard scores identify high priority chemicals for further study from among the AMAP contaminants.

Keyword
Arctic contaminants, AMAP, Stockholm Convention, REACH, Planetary boundary threats
National Category
Environmental Sciences
Research subject
Applied Environmental Science
Identifiers
urn:nbn:se:su:diva-148267 (URN)10.1016/j.emcon.2017.06.001 (DOI)
Available from: 2017-10-19 Created: 2017-10-19 Last updated: 2017-12-04Bibliographically approved
3. In silico Screening-Level Prioritization of 8648 Chemicals Produced in OECD Countries to Identify Potential Planetary Boundary Threats
Open this publication in new window or tab >>In silico Screening-Level Prioritization of 8648 Chemicals Produced in OECD Countries to Identify Potential Planetary Boundary Threats
(English)Manuscript (preprint) (Other academic)
National Category
Environmental Sciences
Research subject
Applied Environmental Science
Identifiers
urn:nbn:se:su:diva-149356 (URN)
Projects
A-TEAM
Funder
EU, FP7, Seventh Framework Programme, 316665
Available from: 2017-11-28 Created: 2017-11-28 Last updated: 2017-12-13Bibliographically approved
4. Exploring the Chemical Space Occupied by Non-ionizing Organic Chemicals with Hazardous Environmental Exposure Potential
Open this publication in new window or tab >>Exploring the Chemical Space Occupied by Non-ionizing Organic Chemicals with Hazardous Environmental Exposure Potential
(English)Manuscript (preprint) (Other academic)
National Category
Environmental Sciences
Research subject
Applied Environmental Science
Identifiers
urn:nbn:se:su:diva-149354 (URN)
Projects
A-TEAM
Funder
EU, FP7, Seventh Framework Programme, 316665
Available from: 2017-11-28 Created: 2017-11-28 Last updated: 2017-12-04Bibliographically approved

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