This document presents an example of a tiered environmental exposure assessment for titanium dioxide nanoparticles used in road coatings. A higher tier assessment is conducted when lower and intermediate tiers indicate a potential risk. The higher tier assessment uses a complex water-soil-organism model to produce spatially detailed predictions of nanoparticle concentrations over time in soil, surface water, and sediment. The results from the higher tier assessment show lower predicted environmental concentrations than the intermediate or lower tiers, demonstrating the increased accuracy provided by more complex modeling. Tiered assessments efficiently evaluate risk by only requiring the most hazardous nanomaterials to undergo all assessment levels.

1. Presentation Name
Name Surname
Date
Environmental Exposure Assessment Framework
Higher tier exposure assessment worked example
- Workflow level 3
Prepared by Dr Stephen Lofts, UKRI-CEH
With Joris Quik (RIVM) and Samuel Harrison (CEH)
Sept. 2019
Detailed NanoFASE guidance here

2. Overview of tiered environmental exposure
assessment: Aim and logic of higher tier
Lower tier assessment
START
Data collection/collation, model choice
END
No
Intermediate tier assessment
No
Yes
Risk?
Data collection/collation, model choice
Higher tier assessment
No
Yes
Yes
Additional risk
management measures
Yes
Yes
Risk?
Data collection/collation, model choice
Risk?
END
END
A higher tier environmental exposure
assessment is engaged when the intermediate
tier assessment yields an indication of risk.
The assessment will then use:
 Calculation of exposure in space and time
 Environmetal behaviour of nanomaterial
 Heteroagglomeration/heteroaggregation/at
tachment properties
 Dissolution
 Influence of size and density
 Environmental scenario
 Multiple environmental subcompartments
and transfer between them
 Flow of material out of system e.g. by burial
in deep sediments
 Spatial variability within environmental
compartments e.g. soil types, river reaches
 Variable river flow, soil erosion over time
 Spatial distribution of inputs

3. Recap – the example used for our assessment
workflow
Commercially sourced TiO2
Dispersed in polymer resin
Sprayed onto road surface Application rate 2.49 g/m2
Anatase type material
Primary particle size range 10–20 nm
Application rate 2.49 g TiO2/m2
Annual loss rate 0.95 g TiO2/m2
i.e. 38% of amount applied
Released as particles of polymer/nanoparticle aggregate, 0.5–5.0µm diameter
Standardized equipment used
to perform the wheel abrasion
simulation
Titanium dioxide (TiO2) used as a coating on urban roads
See our FCCCO case study and detailed release assessment in NanoFASE Report D4.2

4. NanoFASE Water-Soil-Organism (WSO) model
Example of soil concentration predictions
(this is for all uses of TiO2 and emissions from 2000-2020)
Surface water
(blue = point sources,
orange = diffuse sources)
Soil
Spatial distribution of annual inputs for the example
London
Considers spatiotemporal patterns of
river and estuary flow, soil erosion,
spatial pattern of land use, locations of
point source discharges to waters.
100
50
0
5.0
4.0
3.0
2.0
1.0
Nano-TiO2concentration(µg/dm3)
Freshwater (tidal limit)
Estuary
Example temporal concentration profiles for surface waters

5.  Complex model produces detailed outputs
Not single values (as at lower and intermediate tiers)
Spatial distribution of predicted environmental
concentrations (PECs)
 Next slides: results shown in comparison with
those for the lower and intermediate tier
 Reminder: two scenarios were run for the
intermediate tier
 ‘Matrix’: all particles remain within the polymer matrix, as
on release from the road surface
 ‘Pristine’: all particles are initially in their pristine form, as if
released from the polymer matrix
Results

6. Soil PECs (1 year exposure)
Results from three assessment tiers compared
Higher tier (spatial distribution)
Intermediate tier
Lower tier
median
maximum
minimum
5th %ile
95th %ile
Particles in polymer matrix Particles in pristine form

7. Freshwater PECs (1 year exposure)
Results from three assessment tiers compared

8. Sediment PECs (1 year exposure)
Results from three assessment tiers compared

9.  The most realistic level of exposure assessment
Only done where lower tier assessments indicate risk
‘Last chance’ to demonstrate safe use of nanomaterial
In a regulatory context, choice of scenario details is likely
to require discussion with regulatory body
 A reflexive situation - generic guidance probably not present
 Relies on complex modelling
 Detailed spatiotemporal scenario required, including
emissions
Higher tier assessment and decision making

10.  An example was provided of a tiered approach
to exposure assessment (detailed guidance here)
 Higher tier assessments increase in both
complexity and data needs for computations
 Results show how PECs tend to decrease from
lower to intermediate to higher tiers
 This is an efficient approach to assessment: only
the most hazardous nanomaterials (those
demanding management response) would be
assessed at all tiers
Summary: Tiered exposure assessment