Diagnostic tool for source apportionment of heavy metals around roads 2005 Kym Jarvis and Susan Parry Centre for Environmental Policy, Imperial College Sponsored by Environment Agency Contractors: TRL & Viridian Partnership 1

Project outline  To look at sources of heavy metal contamination in road dust and to apportion the relative contribution, where possible, of different sources  Identify contrasting sites wrt traffic flow  Similarities wrt road surface type, road furniture, soil, constant speed  First site - TRL Limited Small Roads research facility at Crowthorne  Second site - A243, south of Chessington, Surrey north of J9 of the M25 motorway.  similar density of road furniture, rural location  constancy of traffic flow along the areas sampled  TRL research track less than 50 vehicles/day & A243 ~30,000 vehicles/day. 2

Sample types  Surface sweepings from concrete and asphalt road and footway  Scrapings from metal surfaces including ferrous and non-ferrous metals and alloys  Surface soils  Paint from road markings 3

A243 Kingston Road, Chessington 4

TRL – Small Road System – showing sampling locations 5

Comparison of trace elements in soils 6

Comparison of soil composition with barrier sweeping TRL 7

Comparison of sweeping and scraping from barrier with soil, TRL 8

Comparison of sweepings from tarmac, tarmac under lamp post and TRL soil 9

Element concentration ranges for sweepings from Asphalt surfaces compared with soil TRL Test Track FootwayRoadSoil Sc Cr Cu <3 Zn Sr Nb Mo< <1.8 Sn <0.9 Sb Ce U

Normalised data for sweepings from tarmac and concrete at TRL 11

A243 Kingston Road, Chessington 12

Element concentration ranges for sweepings from Asphalt surfaces compared with soil A FootwayRoadSoil Sc Cr Cu Zn Sr Nb Mo<1.8-12< <1.8 Sn Sb Ce U

Ce normalised concentration ranges 14 CrCuZnMoSnSb TRL A Ref (a) Ref (b) Range Key: (a) Abeyawickrama, 2003, (b) Cook et al.,2003

Road Furniture A FurnitureType VCrMnCuZnMoCdSnSbPb Lamp PostGalvan Lamp PostGalvan Manhole coverIron < Sign PostSteel < Asphalt Soil <

Conclusions  Comparison of road dusts from both sites with their respective local soils indicates that soil is not a major metal contributor to road dust.  The similarity between the heavy metal contamination in road dust at the Research Track, on the A243 and from a wide variety of urban roads suggests that traffic has a smaller influence than currently perceived.  The heavy metal contamination in road dust from motorways, carrying very high traffic flows, reflect those measured at the experimental sites confirming the view that traffic input to surface dusts is less important than predicted.  It is suggested that the road surface and street furniture are significant factors in contamination in road dust. 16

Conclusions  There are four key sources of heavy metals related to road surfaces and street furniture: asphalt, zinc galvanising, iron and steel.  Source apportionment is currently difficult to assess due to the preferential dissolution of some elements, such as zinc, during weathering and corrosion.  Concentrations of zinc seem to be an underestimate of those predicted from the concentration of trace elements present in dust sweepings. 17

Apportioning source contributions to PM 10 & PM 2.5  Assess relative contribution of metals from road furniture  Age  Corrosion  Address mass balance issues resulting from preferential solubilisation of zinc  Establish/test key element ratios in air particulates to fingerprint sources  Assess relative particulate contribution from asphalt and concrete surfaces at different road locations and situations  Traffic density, speed, breaking, acceleration 18

Apportioning source contributions to PM 10 & PM 2.5  Assess relative contribution of metals & particulates from aggregate and bitumen in asphalt  Track particle movement from, & along, road surfaces using labelled micro-particulates  Develop model for quantifying relative contributions for source apportionment 19

Stage 1 – Characterisation of asphalt at selected sites  Selection of 1-2 sites with existing PM monitoring stations  Surface (few cm) and spatial sampling of asphalt  Separation of aggregate and bitumen  Inorganic characterisation of bulk asphalt, bitumen, aggregate and associated PM samples  Assessment of potential importance of asphalt as a source of metals in PM samples 20

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