Influence of Traffic Activity on Heavy Metal Concentrations of Roadside Farmland Soil in Mountainous Areas

Abstract

Emission of heavy metals from traffic activities is an important pollution source to roadside farmland ecosystems. However, little previous research has been conducted to investigate heavy metal concentrations of roadside farmland soil in mountainous areas. Owing to more complex roadside environments and more intense driving conditions on mountainous highways, heavy metal accumulation and distribution patterns in farmland soil due to traffic activity could be different from those on plain highways. In this study, design factors including altitude, roadside distance, terrain, and tree protection were considered to analyze their influences on Cu, Zn, Cd, and Pb concentrations in farmland soils along a mountain highway around Kathmandu, Nepal. On average, the concentrations of Cu, Zn, Cd, and Pb at the sampling sites are lower than the tolerable levels. Correspondingly, pollution index analysis does not show serious roadside pollution owing to traffic emissions either. However, some maximum Zn, Cd, and Pb concentrations are close to or higher than the tolerable level, indicating that although average accumulations of heavy metals pose no hazard in the region, some spots with peak concentrations may be severely polluted. The correlation analysis indicates that either Cu or Cd content is found to be significantly correlated with Zn and Pb content while there is no significant correlation between Cu and Cd. The pattern can be reasonably explained by the vehicular heavy metal emission mechanisms, which proves the heavy metals’ homology of the traffic pollution source. Furthermore, the independent factors show complex interaction effects on heavy metal concentrations in the mountainous roadside soil, which indicate quite a different distribution pattern from previous studies focusing on urban roadside environments. It is found that the Pb concentration in the downgrade roadside soil is significantly lower than that in the upgrade soil while the Zn concentration in the downgrade roadside soil is marginally higher than in the upgrade soil; and the concentrations of Cu and Pb in the roadside soils with tree protection are significantly lower than those without tree protection. However, the attenuation pattern of heavy metal concentrations as a function of roadside distance within a 100 m range cannot be identified consistently.

Relationships between Heavy Metal Concentrations in Roadside Topsoil and Distance to Road Edge Based on Field Observations in the Qinghai-Tibet Plateau, China

“…Therefore, a further roadside study is needed to investigate these metals’ distribution to identify how far these contaminants can actually reach. However, Zhang et al [9] reported that the exponentially decreasing distribution pattern was not available in farm land soil due to agricultural activities and mixed metal resources. In the Qinghai-Tibet Plateau, the industrial facilities are very limited and its fossil fuel consumption is relatively low [30].…”

“…However, other research results showed that the special distribution patterns of heavy metals in roadside soils were not always significantly correlated with the roadside distance [3,4,9]. This may be attributed to mixed sources of metals, agricultural activities and roadside green belts [9].…”

“…Generally, the topsoil adjacent to the road edge is collected for analyzing the heavy metals pollution levels. Most observational studies on the concentrations of heavy metals in roadside soils were focused on Cu, Zn, Cd, and Pb [6,7,8,9]. Some research extended the monitored metals to Cr, Ni and As [3,10,11].…”

Assessment of forest soil contamination in Krakow surroundings in relation to the type of stand

“…Pollutants transferred from the Upper Silesian Industrial Region are deposited in the west while 35 km east of Krakow are deposited contaminants from Krakow, primarily from the steel producer ArcelorMittal Poland Unit in Krakow. According to Zhang et al (2012), wind direction and speed might change the heavy metal contaminants of soil. Ogunkunle and Fatoba (2014) studied the level of soil contamination by Pb, Cu, Cr, Cd and Zn and showed that these heavy metals are deposited at various distances depending on wind velocity.…”

Biogeochemical characterization of municipal compost to support urban agriculture and limit childhood lead exposure from resuspended urban soils

“…Correlations between Pb and other metals can yield insight into both the source of metal contamination and the mode of transport. In urban soils, a correlation between Pb and Zn has been suggested to be linked with traffic patterns and the combustion of leaded gasoline (Mielke et al, 1983;Zhang et al, 2012) while associations between Pb and Ti have been linked with Pb-based paint contamination (Clark et al, 2006). Within the municipally sourced matrix, the Pb/Ti ratio systematically varies, nearly linearly, when plotted against the major element ratio (Si/Ca).…”