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

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

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

Research Area Cairns Location

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

Kuranda Range Road World heritage rainforest

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

Results

Results Cd (mg/kg) Cu (mg/kg) Pb (mg/kg) Ni (mg/kg) Zn (mg/kg) Kuranda Range Road (median, N=18) ANZECC Guidelines for sediments Background levels for local stream sediments (median, N=8) Heavy metal concentrations in Kuranda Range Road sediments (Results in mg/kg)

Results Grain size distribution in road sediments  Grain size distribution in road sediments Weight % of sediments 4mm Sediment size

Results Heavy metal concentrations (mg/kg) in different grain size fractions  Heavy metal concentrations (mg/kg) in different grain size fractions Cd CuPb NiZn CoarseFineCoarseFineCoarseFine CoarseFineCoarseFine

Results CdCuPbNiZn First Flush (January 03) ≤ Subsequent flushes (February 03) ≤ ANZECC Draft Guidelines – for sensitive environments Background stream levels (February 04) ≤ ≤5 Heavy metal concentrations in Kuranda Range Road runoff water samples (Results in μg/kg)

 Adsorption experiments CdCu Pb Ni Zn ppb 5 minutes 1 hour 24 hours Zeolite-treated leachate untreated leachate, contaminated with road sedimentsResults

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

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

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

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

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

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

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

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

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