Suspended particulate matter (SPM): The known unknown in nanomaterial risk assessment

Activity: Talks and presentationsTalk or oral contributionScience to Science

Description

In light of regulations’ requiring environmental fate assessment of engineered nanomaterials (ENMs), a major distinctive feature of ENMs – their particulate nature – precludes direct application of testing protocols or fate models designed for dissolved substances. In the aquatic environment particle-particle interactions (influencing ENM transport, behaviour and uptake) need to be considered. These include homoaggregation among ENMs and heteroaggregation with natural suspended particulate matter (SPM). From an ENM particle’s perspective, SPM surfaces are omnipresent, as size and most likely number concentrations exceed those expected for ENMs. Thus, heteroaggregation is assumed to be the dominant process. Covering heteroaggregation in fate assessment requires a thorough scientific process understanding and informed simplifications of the same, feeding into the design of controlled experiments that allow deriving fate parameters. The most blatant “known unknown” is the interaction of ENMs and natural SPM. To fill this gap, process-relevant, near-natural SPM analogues are needed: natural SPM is very complex, featuring flock-like structures composed of various minerals and organics from the molecular level to microorganisms or detritus. Compositions, concentrations and sizes are dynamic in space and time. Hence, a mere mineral analogue is too simplistic, while attempts to rebuild natural SPM from major mineral fractions identified did not arrive at similar flocks. Reviewing available literature on natural SPM, we identified the heterogeneity of physicochemical surface characteristics as a crucial feature and took a conceptual approach, selecting mineral and organic components based on the interplay of abundance, physicochemical heterogeneity and realistic mass ratios. Here we present our resulting SPM analogues: complex flocks consisting of illite, hematite, quartz and tryptophan (proxy for microbial exudates), representing heterogeneity of natural SPM. They are reproducible and stable in batches, but at the same time dynamic when varying hydrochemistry – reflecting natural processes of flock association/dissociation.
For the first time, such near-natural analogues were employed in heteroaggregation studies with ENMs, allowing more environmentally relevant conclusions for ENM fate assessment and modelling. However, the scope may also be extended to other particulate contaminants like micro-/nanoplastics, soot or tire wear – and perhaps beyond...
Period29 May 2019
Event titleSETAC EUROPE 29th Annual Meeting: One Environment. One Health. Sustainable Societies.
Event typeConference
LocationHelsinki, FinlandShow on map
Degree of RecognitionInternational