A proposed methodology for the definition of background and reference values for trace elements in fluvial sediments

Area of Science:

• Environmental Chemistry
• Ecotoxicology
• River Basin Management

Background:

• The Water Framework Directive (WFD) requires background trace element values for sediment quality standards.
• Distinguishing natural background from anthropogenic enrichment is crucial for environmental assessment.

Purpose of the Study:

• To propose and test a methodology for calculating background and reference trace element values in sediments.
• To assess anthropogenic impacts in European river basins using these proposed values.

Main Methods:

• Defined background as median upper confidence limit and reference as 90th percentile upper confidence limit.
• Utilized the Bootstrap method for calculations on sediment samples from Nalón and Esva basins.
• Analyzed 19 elements in 110 sediment samples using ICP-MS/ICP-AES.

Main Results:

• Calculated background and reference values showed consistency across geologically different basins.
• The method proved effective for small, skewed datasets, typical in environmental monitoring.
• Nalón basin (impacted) showed higher exceedance rates of reference values (e.g., As, Pb) than the Esva basin (unpolluted).
• Reference values in Nalón generally exceeded generic ecological thresholds (LEL, TEL), unlike in Esva.

Conclusions:

• The proposed method reliably distinguishes natural trace element variations from anthropogenic inputs.
• These background and reference values are valuable tools for identifying historical mining impacts and assessing ecological status.
• The methodology supports Water Framework Directive implementation for sediment quality assessment.