Fate and Transport of Lead Pollution Along a Highway Corridor

Annual source indicators for lead have dropped drastically with the phasing out of tetra ethyl lead as a fuel additive more than 15 years ago. Deposited lead concentrations along highway corridors continue to exceed the standard set in the B.C. Contaminated Site Regulation. The Ministry of Transportation and Highways is obliged to mitigate risks, without consideration of the mobility of the contaminant. This project was to determine whether it is acceptable to leave lead-contaminated roadside soil in place. Lead accumulations up to 1628 mg/kg were found in the highway soils. Lead contamination was found mainly in the top 0.3 m surface soil, with Pb concentrations rapidly decreasing to the background level at a depth of 0.6 m. The top 0.3 m contains more organic material and has a high adsorption capacity. Highway soils were found to have 3–10 times higher adsorption capacity for lead than the amount currently deposited on site. Therefore, it is unlikely that adsorption capacity will be saturated in the near future. Batch desorption tests using H2O at pH 5.5 and a HNO3 solution of pH 4.0 as leaching solutions indicated leachant concentrations below 2 ppm with a detection limit of 0.1 ppm. Despite the high total Pb concentration found in the soil, all sample leachants were below the B.C. Environmental Drinking Water Standard (10 ppm in solution). These results suggest that Pb has very limited mobility in highway soil and leaving the Pb contaminated soil in place may be acceptable.

• INTRODUCTION

• MATERIALS AND METHODS

• RESULTS AND DISCUSSION

• CONCLUSIONS

• AUTHORS CONCERNS AND COMMENTS

• ACKNOWLEDGEMENTS

• REFERENCES