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  1. Paper Title: Remediation of Heavy Metal Impacts in Roadside Corridors, Wet Tropics World Heritage Area, Australia

  2. Heavy metals in roadside corridors • Heavy metals derived from motor vehicles accumulate in road sediments • These metals are mobilised by rainwater runoff into streams and soils in roadside corridors • Exposure of organisms to elevated heavy metal loads

  3. Sources of heavy metals in roadside corridors Tyres = Zn Brake pads, engine wear = Cd, Cu, Ni Exhaust = Pb

  4. Location Research Area Cairns

  5. Reasons for investigation • Upgrading Kuranda Range Road • Previous Honours investigations identified elevated heavy metal concentrations in roadside soils in the Cairns area

  6. World heritage rainforest Kuranda Range Road World heritage rainforest

  7. Research aims Determine: • Heavy metal levels in road sediments along Kuranda Range Road • Heavy metal levels in runoff waters along Kuranda Range Road • Potential of zeolites to adsorb metals from runoff waters; limit their dispersal into roadside rainforest streams, soils

  8. Results

  9. Results Heavy metal concentrations in Kuranda Range Road sediments (Results in mg/kg)

  10. Results • Grain size distribution in road sediments Weight % of sediments <38 μm >4mm Sediment size

  11. 90 2500 90 0.40 120 80 80 0.35 100 2000 70 70 0.30 60 60 80 0.25 1500 50 50 0.20 60 40 40 0.15 1000 40 30 30 0.10 20 20 500 0.05 20 10 10 0.00 0 0 0 0 Results Cd Cu Pb • Heavy metal concentrations (mg/kg) in different grain size fractions Coarse Fine Coarse Fine Coarse Fine Ni Zn Coarse Fine Coarse Fine

  12. Results Heavy metal concentrations in Kuranda Range Road runoff water samples (Results in μg/kg)

  13. Results Cd Cu Ni • Adsorption experiments ppb ppb ppb 5 minutes 1 hour 24 hours 5 minutes 1 hour 24 hours 5 minutes 1 hour 24 hours Pb Zn Zeolite-treated leachate ppb ppb untreated leachate, contaminated with road sediments 5 minutes 1 hour 24 hours 5 minutes 1 hour 24 hours

  14. Conclusions and recommendations • Road sediments on Kuranda Range Road contaminated with elevated levels of heavy metals, particularly in fine-medium sized particles

  15. Conclusions and recommendations • Runoff waters also contain high dissolved heavy metals loads, particularly during early rainfall events

  16. Large-scale wetland, inappropriate for rugged terrain Active remediation – too expensive, not warranted Conclusions and recommendations

  17. Runoff waters PVC drum/container Treated water Plastic grate to keep zeolites at base Zeolites, adsorber Outlet Conclusions and recommendations Small-scale adsorption traps

  18. Conclusions and recommendations • Zeolites show strong potential to adsorb elevated dissolved Zn loads in runoff, but ineffective for other metals

  19. Conclusions and recommendations • Still, Zn is most abundant, dissolved levels of other metals is quite low • Further testing of zeolite’s potential to adsorb these other metals may involve agitation of solution to increase exposure of reactive surfaces of zeolites

  20. Conclusions and recommendations • Zeolites seen as useful substances to incorporate into filter traps in drains along Kuranda Range Road and other roads of similar nature

  21. Weaknesses in the research: remediation of runoff waters • Main problem - zeolites only effective for Zn, need options for reducing other metal concentrations especially Cu • Need to ensure that adsorptive material has long enough time to react with runoff waters without blocking drains – need to ensure constant flow of runoff • How to treat runoff waters that flow directly over soils that do not collect in drains

  22. Weaknesses in the research: remediation of runoff waters • Limitation of remediation to sediment bound metals – does not address airborne metal phases that settle in soils or on roadside vegetation