The SEPMERCURY project will focus on the development and evaluation of a sequential extraction protocol (SEP) for Hg fractionation in sediment and soil matrices. The approach of SEPMERCURY project will be:

1. To test and compare different Hg sequential extraction schemes in well characterised sediment and soil samples;

2. To combine the Hg sequential extraction study with a comprehensive analysis of the mineralogical and chemical characteristics of the soil and sediment samples as well as with the study of the toxicity of the different extracts; and

3. To select the most appropriate scheme that takes into account the specificity of this element.

Finally we will prepare reference materials to be tested in the scope of an international interlaboratory exercise (similar to a proficiency-testing exercise for total Hg in environmental samples recently organised by this team) which will be targeted to test the performance of the selected SEP.

It is well-know that information on total contents of Hg in soils is not sufficient to assess human health and environmental risks associated to contaminated sites. Elevated levels of Hg may in certain cases occur in soils and sediments and do not be available to be mobilised. Only "reactive" species of Hg correspond to the bioavailable and toxic chemical forms. Thus, Hg-speciation is the most critical measurement for enabling the prediction of Hg behaviour (mobility, bioavailability, and toxicity) in environmental systems.

The traditional sequential extraction schemes used for fractionation of the 'classic' trace elements (such as Cu, Co, Ni, Al, Cd, Zn) are generally not applicable to Hg. At present, neither specific extractants nor standard protocols exist for the isolation of particular Hg species in soil and sediment samples. Recent literature has vehemently highlighted the need for the development of such a protocol together with appropriate reference materials.

SEPMERCURY Project will therefore develop further research on the chemistry controlling the biogeochemical reactivity, mobility, bioavailability and toxicity of Hg in contaminated soils and sediments towards the establishment of a simplified sequential extraction, BCR-like (proposed by "The Standards, Measurements and Testing Programme of the European Comission (BCR)"), protocol for which, the used chemical reagents would take into account the particular chemistry of Hg in association with specific properties of soil/sediment sample. The SEP for Hg fractionation will be proposed on the basis of:

• production of valuable information regarding both the chemistry of Hg (in terms of its reactivity and potential bioavailability) and matrix characteristics;


• Hg-species extracted in each step;


• percentages of Hg extracted in each step;


• uncertainties associated;


• reproducibility of analysis.

The most relevant innovative aspects of our approach are:

i) the multivariate comparison of several chemical sequential extraction schemes to evaluate their differences/ similarities in describing the behaviour of Hg in the different fractions.

ii) the use of Factor analysis and Principal Component Analysis in the interpretation of patterns of Hg chemical fractionation obtained by the use of the different SEPs

iii) the consideration of the specificity of Hg, namely its preference to form complexes with soft ligands such as organic matter and Scontaining ligands in the selection of an appropriate SEP;

iv) the evaluation of toxicity associated to Hg extracted in each operationally defined fractions of the proposed SEP to relate toxicity with actual reactivity of the contaminant;

v) the preparation of new reference materials specifically targeted to test the performance of a SEP, which for the first time will be specific for Hg;

vi) the organisation of an interlaboratory analytical exercise which for the first time will be targeted to test the performance of a method for Hg fractionation in sediments and soils.

Within SEPMERCURY perspective, the development of such a SEP is of paramount importance since it will be crucial for an effective implementation of risk assessment methodologies in Hg contaminated sites and for a better understanding and prevention of risks arising from practices such as sewage sludge, fertilizers or pesticides application in agricultural soils.

In order to achieve the proposed objectives, SEPMERCURY will involve two R&D units of University of Aveiro: CESAM (Centre for Environmental and Marine Studies) and GeoBioTec (Geobiosciences Technology and Engineering), engaging researchers from three Departments, Chemistry, Biology and Geosciences. Researchers from IMAR (Intitute of Marine Research, University of Coimbra) will also participate in the project. This multidisciplinary team combines expertise on Hg contamination and speciation assessments; long-term experience in the geochemical characterisation and mineralogical characterisation of soil and sediment matrices; and the required expertise on ecotoxicological assessments.

Isabel Maria Cunha Antunes Lopes
Researcher

Sónia Alexandra Morais Rodrigues
Researcher