Scholarly record

CHEMICAL LINE OF EVIDENCE FOR ECOLOGICAL RISK ASSESSMENT: HEAVY METAL FORMS AS INDICATORS FOR AN ADVISORY SYSTEM IN THE TOPOLNITSA RIVER BASIN

Mariana Hristova, Veselina Vasileva, Viktoriya Kancheva, Ana Katsarova, Nikolai Dinev

Abstract

The Topolnitsa River basin is a vulnerable agricultural area affected by mining and metallurgical pressure. Irrigation with surface waters and contrasting soil properties may increase secondary contamination. This study develops the Chemical Line of Evidence (Chem-LoE) within the TRIAD framework of an advisory system for ecological risk assessment. The focus is on riparian and floodplain agricultural soils, mainly alluvial-meadow and deluvial-meadow soils. Copper (Cu), lead (Pb), zinc (Zn), cadmium (Cd) and arsenic (As) are evaluated as fold exceedances of background, maximum permissible and intervention concentrations under Bulgarian Ordinance No. 3/2008. Interpretation considers pH(H2O), texture, land use, soil organic matter (SOM) and cation exchange capacity (CEC). Single extractions with CaCl2 and NH4NO3 indicate water-soluble and exchangeable forms. EDTA reflects potentially available forms, while Na4P2O7 indicates humus-associated pools. Data from the project and previous investigations show that total metal content alone is insufficient for risk interpretation. Cu reaches up to 6.8-fold above the maximum permissible concentration, and local values in the broader Zlatitsa-Pirdop area reach up to 65-fold. Chemical extractions are indicative, not definitive. CaCl2 and NH4NO3 are closest to immediate mobility risk. EDTA indicates potential availability. Na4P2O7 links metals to organic matter. Chem-LoE must be combined with ecotoxicological and ecological evidence within TRIAD.

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