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.
Highlights
The risk posed by heavy metals to food safety and the environment are of great concern to governments and society in many countries
This study involving factorial design analyses was focused on heavy metal accumulation in roadside farmland soils along a highway across mountainous areas in Nepal
It was observed that the average concentrations of Cu, Zn, Cd, and Pb at the sampling sites are lower than the tolerable levels, a few maximum Zn, Cd, and Pb concentrations are close to or higher than the tolerable level
Summary
The risk posed by heavy metals to food safety and the environment are of great concern to governments and society in many countries. Heavy metal pollution in agricultural soils is becoming serious with the rapid industrialization and urbanization in developing countries [1]. This is a typical environmental issue due to anthropogenic activities in the countries in the Third Pole region which consists of the Tibetan Plateau and surrounding mountains. The Third Pole region covers parts of eight countries, consisting China, India, Russia, Bhutan, Myanmar, Nepal, Pakistan and Afghanistan, in which a fifth of the World’s population live [2]. The pressure on the unique ecosystem in the anthropogenic living areas of the Third Pole region is predictably increasing [3]
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