1 Introduction
2 Literature survey on in vitro toxicity of combustion derived particles
2.1 Overview on studies
-
Objective category 1: Understanding the mechanism of health effects of combustion-derived particles is the most frequent objective (84% of studies).
-
Objective category 2: 46% of the authors wanted to compare the effects of different PM from different sources.
-
Objective category 3: 40% of studies intended to identify the effect-relevant compounds attached to the particles.
-
Objective category 4: 16% of the authors aimed to characterize the whole particles in order to identify effect-relevant parameters.
-
Objective category 5: 2 publications wanted to compare the applicability of in vivo versus in vitro methods for effect-detection of combustion-derived particles.
2.2 Studies’ conclusion on the potential of combustion-derived particles to induce toxic effects
3 Developing recommendations—the way towards suitable and adaptable criteria
3.1 Need for physical-chemical characterization in relation to the studies’ aims
No. | Aim | Requirements in particle characterization | Requirements in bioassay |
---|---|---|---|
1 | Mechanistic understanding of particle-induced health effects | Particle characterization, particle concentrations, analysis of attached compounds, particle behavior under test conditions | Reliable detection of effects for particles as well as chemicals, use of different bioassays indicating different modes of action Appropriate controls |
2 | Comparison of toxic effects from different PM sources | Combustion conditions, sampling site, substrate, particle concentrations, analysis of attached compounds | Reliable detection of effects for particles as well as chemicals Appropriate controls |
3 | Identification of the effect-relevant components attached to the particles Identification of most important substance Occurrence of mixture effects | Extract composition: identification of compounds, concentrations of compounds | Reliable detection of effects of chemicals, information on mode of action Bioavailability of attached compounds under biological conditions Appropriate controls |
4 | Assessing the toxicity of the whole PM | Identify changes in PM characteristics upon transfer from gas to liquid phase Particle’s physicochemical properties (e.g., components, size, shape); behavior of particles under test conditions in the medium (e.g., agglomeration), and over test duration (e.g., release of attached compounds, particle sedimentation) | Reliable detection of effects for particles as well as chemicals Appropriate controls |
5 | Applicability of in vitro methods for particle-induced toxicity, comparison of results of in vivo with in vitro studies | Appropriate dosimetry for comparison of air-based measures (i.e., particle number/volume) to liquid-based measured (i.e., mass/volume) Differences of airborne particles compared to suspended particles Preparation of test suspensions Particle behavior under test conditions and over test duration to account for changes in physicochemical parameters | Consideration of differences in exposure routes in vivo and in vitro Appropriate controls |
3.2 Development of a list of relevant characterization criteria
General methodology | • Source/generation of particles |
• Method of particle sampling (volume [m3/h], stages, sampler, sampling duration, filter) | |
• Filter preparation (before/after sampling, storage; preparation for chemical analysis- organic extracts, water-soluble fraction, whole particles) | |
Chemical characterization | • Analysis of attached compounds: |
– Composition of organic extracts, concentration of individual compounds | |
– Composition of water-soluble fraction, concentration of individual compounds | |
– endotoxin content | |
Particle characterization | • Average PM concentration [mass/volume; number/volume] |
• Particle composition (carbon, metals) | |
• Particle size, size distribution, aggregate size | |
• Surface chemistry (hydrophobic, hydrophilic)/surface reactivity and/or surface charge, surface area | |
• Particle morphology (shape) | |
Exposure conditions | • Method for preparation of suspensions (composition of dispersion medium, preparation of stock solution or direct dosing, way of dispersal, energy input, nominal concentration) |
• Type of exposure (air-liquid exp., suspended particles, extracts, direct contact, complexity of mixtures) | |
Consideration of particle behavior under test conditions | • Extent of agglomeration/aggregation resp. particle size distribution under experimental conditions |
• Evaluation of particle behavior over test duration (sedimentation of particles, floating) | |
• Dosage used classified clearly to be “non-overload” or “overload conditions” | |
• Interaction (particles with cells or organism) | |
• Release of attached components (e.g., chemicals, metals) |
3.3 Studies considering particle characteristics and particle behavior under test conditions
Author, year | Primary objective | Major achievements |
---|---|---|
Danielsen, 2011 [3] | Comparison of different PM | Characterization of particle’s shape, analysis of size distribution under experimental conditions |
Dilger, 2016 [71] | Identification of effect-relevant compounds | Characterization of particle’s shape, description of agglomeration and sedimentation under test conditions |
Diociauti, 2001 [36] | Comparison of different PM | Characterization of particle’s shape, description of particle-cell interaction |
Gauggel et al., 2012 [18] | Particle characterization | Characterization of particle’s shape, analysis of size distribution under experimental conditions, description of agglomeration |
Karlsson, 2005 [44] | Comparison of different PM | Characterization of particle’s shape, description of particle-cell interaction |
Kocbach, 2008 [70] | Comparison of different PM | Characterization of particle’s surface chemistry, comparison of toxicity of whole particles, washed particles and extracts, selection of doses: overload, as well as of human relevance |
Orona, 2014 [80] | Comparison of different PM | Characterization of particle’s shape, description of particle-cell interaction, comparison of toxicity of whole particles and extracts |
Carero, 2001 [30] | Comparison of different PM | Analysis of size distribution under experimental conditions, comparison of toxicity of whole particles, washed particles and extracts, selection of doses: overload, as well as of human relevance |
Gminski, 2011 [98] | Comparison of different toner dust | Characterization of particle’s surface chemistry and shape, comparison of toxicity of whole particles and extracts, description of agglomeration under test conditions, selection of doses: overload, as well as of human relevance |
Van Landuyt, 2016 [99] | Comparison of different dental composite dust | Characterization of particle behavior under test conditions. Selection of doses: overload, as well as of human relevance |