Summary

Presence of potentially toxic trace elements in soils has gained a greater attention from the research community and general public worldwide. Identification of polluted soils that have problematic concentrations of trace elements is crucial to recommend actions to minimize negative effects. A rich database of baseline concentrations of the elements is necessary to differentiate clean soils from polluted soils. In absence of such database, detection of minute or background concentrations of these elements in soils could be misinterpreted as environmental hazards. Further, formation of reliable regulatory standards that define maximum safe concentrations of the elements in soils is greatly supported by the knowledge of background and/or baseline concentrations in soils in the country. Based on above requirements, our laboratory initiated the assessment of baseline concentration of trace elements in soils in Sri Lanka (Sanjeevani et al., 2015). This study proposes an extension of the study to soils in the up and mid country Wet Zone of Sri Lanka with the objectives of determining the baseline concentrations of As, Cd, Cu, Ni, Pb and Zn; and their spatial variability in soils in relation to land use, elevation, geology and soil properties. Special attention will be given to study the potential bioavailability of trace elements in soils using standard, internationally established methods.

A soil sampling scheme comprised of 200 samples will be developed on the basis of geological and anthropogenic controllers (i.e. land use) of soil trace elements. The sampling locations will be selected using the Conditioned Latin Hypercube sampling method. Soil samples will be obtained at 0- 15 cm depth. Total concentrations, salt extractable fraction, Mehlich-III extractable fraction, In-vitro bioaccessibility will be analyzed with through quality assurance and quality control methods. A sequential extraction will be performed to describe speciation of trace elements to assess potential solubility of trace elements in detail.

Data will be subjected to exploratory data analysis. Baseline concentrations will be calculated as described in (Chen et al., 1999). Background concentrations of trace elements will be estimated based on geochemical indices such as total Fe and Mn concentrations in soils. Total concentrations and potential bioavailability will be compared with data elsewhere in the world and available safe limits defined by other countries. Impact of geologic and anthropogenic controllers of trace elements will be elucided using the principal component analysis. Maps of concentrations of trace elements will be developed for the region showing spatial variability across variable land uses using multivariate regression kriging technique. Spatial relationships between trace elements will be quantified using the variography. Probability (uncertainty) maps of trace elements will be constructed using the indicator kriging approach. These maps of trace elements will be validated by collecting and analyzing about 60 samples towards end of the project

Objectives

1. To determine the baseline concentrations of As, Cd, Pb, Ni, Cu and Zn in soils in relation to land use, elevation, geology and soil properties in Up- and mid-country Wet Zone- in Sri Lanka
2. To determine the solubility and potential bioavailability of above elements in the region
3. To identify areas with problematic concentrations of trace elements in soils (hot spots) in the region
4. To assess the spatial variability of trace elements in relation to the land use, elevation, geology and soil properties

Major Equipment Facilitated by Grant