Spatial environmental risk evaluation of potential toxic elements in stream sediments

Abstract

The occurrence of Potential Toxic elements (PTE) in a river system is influenced by different factors such are geology, mineralogy, hydrology, vegetation, chemical reactivity, land use pattern and biological productivity. In the herein study – Monfortinho area (Central Portugal) - stream sediments were used as a tool for contamination evaluation and definition of PTE enrichment clusters. The assessment of the studied PTE distribution and the evaluation of the associated ecological risk is the target goal of the herein study and went through a two-step methodology: 1. Data collection and preparation; 2. Spatial modeling and definition of spatial clusters of high (high rings) and low (low rings) significance. For this last issue, was adopted a geostatistical approach, namely variography for attributes spatial structure computation, Ordinary Kriging for content inference aiming to predict the variables’ values at any arbitrary spatial location within the study region; and finally, clusters definition using the Local G clustering algorithm. A broad discussion about PTE provenance and possible trends in spatial dissemination lead to the conclusion that the Monfortinho area is far affected by the mining legacy. It is worth noticing the Fe; Ni; Ba; Cu; B; Zn; V; Pb and As enrichment overlapping the areas of old abandoned Ba-Zn mineralizations (southern area) and the sedimentary gold concentrations along the Erges river banks (northern region). The multivariate geostatistical approach allowed the identification and quantification of anthropogenic impacts and therefore the definition of adequate monitoring actions for the contaminated zones. Future work involves an exhaustive identification of covariates to tackle PTE fate as well as to as to clarify their provenance and enrichment.