Effect of farmland type on the transport and spatial distribution of metal(loid)s in agricultural lands near an abandoned gold mine site: Confirmation of previous observations

Abstract

In many parts of the world, metal(loid)s resulting from mining activities are causing significant environmental concern, in particular because they are contaminating agricultural lands. In this respect, a previous study in South Korea suggested that a specific agricultural practice, associated with the growing of rice in paddy fields, could contribute specifically to the geographic spread of metal(loid)s contamination away from mine sites. The purpose of the research described in this article was to confirm this hypothesis at a different site. Samples from the surface soil of agricultural lands were collected from 374 sites (267 paddy soils and 107 dry field soils). The concentrations of As, Pb, Cd, Cu and Zn from the samples were analyzed and descriptive statistics and multivariate statistical analysis were carried out to identify potential sources of these various elements. In addition, geographical information systems (GIS) technology was applied to analyze the interrelationship between the mining activities and the distribution of meta(loid)s in agricultural lands. The results clearly show that the transport and distribution of As and Pb originating from the abandoned mine are distinct depending on the agricultural practice that was adopted locally. The highest concentrations of As and Pb are in agricultural soils nearest the abandoned mine site (<1km) because of climatic factors such as wind and precipitation that affect the direct mobilization of metal-bearing mine wastes. However, the distribution characteristics of As and Pb in the oxidizing environment of dry field soils in general suggest that the degree of pollution by these elements fell notably as the distance from the abandoned mine increased. In the alternatingly oxidizing and reducing environment of paddy soils, by contrast, the distribution of As and Pb is noticeably different from those of the dry field soils. Arsenic in particular is widely distributed across the study area with a high level of pollution regardless of the distance from the abandoned mine. These results confirm the hypothesis that the transport characteristics of metal(loid)s initially mobilized from an abandoned mine site into the paddy soils are predominantly governed by the specific submerged environment of rice paddy soils and these specific environments impact a wider area than climatic factors.