Effect of metal vehicle emissions on physiochemical and biological properties of a roadside soil
Creators: name: De Silva, Shamali
Publisher: name: RMIT University
Year: 2024
Subjects: classificationCode: 401199
subject: Environmental engineering not elsewhere classified
classificationCode: 410402
subject: Environmental assessment and monitoring
classificationCode: 410604
subject: Soil chemistry and soil carbon sequestration (excl. carbon sequestration science)

description: Concentrations of vehicular emitted heavy metals in roadside soils result in long term environmental damage. This study assessed the (1) relationships between traffic characteristics (traffic density, road age and vehicular speed) and roadside soil metals, (2) the bioavailability of these metals [CaCl2 and Diffusive Gradients in Thin-films (DGT)] (3) relationships between metals in roadside soil and biological accumulation using Stenotaphrum secundatum (buffalo grass), Triticum aestivum (wheat) and Folsomia candida (springtail) species and (4) the effects of metals on soil microbial functioning using enzyme assays and polymerase chain reaction-denaturing gradient gel electrophoresis (PCR-DGGE). Significant concentrations of roadside soil metals were recorded for Cd (0.06-0.59 mg/kg ), Cr (18-29 mg/kg ), Cu (4-12 mg/kg ), Ni (7-20 mg/kg ), Mn (92-599 mg/kg ), Pb (16 -144 mg/kg ) and Zn (10.36-88.75 mg/kg ), with Mn concentrations exceeding the Australian Ecological Investigation Level. Significant correlations were found between roadside soil metal concentration and vehicular speed (R=0.90), road age (R=0.82) and traffic density (R=0.68). Recently introduced metals in automotive technology (e.g. Mn and Sb) were higher in younger roads, while the metals which have been present for many years (e.g. Cd, Cu, Pb, Zn) were higher in medium and old age roads. Soil pH was reduced adjacent to older roads. Total metal concentrations and pore water concentrations were found to be the best measure of the bioavailability of metals to plants. The Mn uptake by plants appeared to be regulated by soil pH.<br><br> This study also detected signs of metal aging effect in soil. The study showed that the dissociation time (TC) of metal release from the solid phase to the solution phase was a good indicator of the soil metal aging effect. The results showed that TC was pH dependent for Cd, Ni and Zn. Metals accumulated on roadside soil showed a significant (P&lt;0.05) effect on the growth of F. candida. Copper concentrations were found at toxic concentrations, as demonstrated by the correlation of survival % with total metal concentrations (r= -0.941, P&lt;0.05). Additionally, it was found that F. candida Zn accumulation in body was suppressed by the presence of Cu (r= -919, P&lt;0.05) and Ni (r= -0.962, P&lt;0.05) in soil. Both survival and metal accumulation of F. candida was found to be independent of a metal aging effect in soil; however their biomass was found to be affected by metal aging in soil (r= -0.896, P&lt;0.05). The findings demonstrated the importance of soil physical properties on soil enzyme activity. DGGE gels separated bacterial profiles from the soils examined into three distinct clusters representing recent exposure, moderate exposure and long term exposure to metals. No equivalent clusters were found for roadside soil fungi. Roadside grown fungi were found to be more sensitive to soil metal concentration than soil bacteria. Overall this research demonstrated the risk of metal accumulation on roadside soil and risk of metal retention in soil. The accumulated metals were able to uptake by plants and organisms causing potential effects on soil microbial functioning. Considering the relationships found in this study, the present results are considered to be applicable to other similar urban areas.