An inorganic “non-targeted” characterization platform for comprehensive monitoring of elements in surface water

Background

The concept of bioavailability influencing environmental risk from metals has gained European regulatory and scientific support, but routine implementation remains a challenge due to the scarcity of physico-chemical data obtained from national surface water monitoring networks for assessing metal complexation with abiotic ligands. It is essential to remain vigilant and to ensure that the narrow focus of our routine analytical equipment does not limit our perspective. The focus blinders in our surface water monitoring networks should not transform into vision blinders, preventing us from considering broader insights and possibilities. Thanks to advancements in analytical instrumentation and data processing capabilities, this study presents an inorganic “non-targeted” characterization platform for wide-eyed and time-efficient high-quality surface water monitoring.

Results

This study evaluated the feasibility of a comprehensive inorganic quantitative non-targeted analysis (NTA) combined with geochemical modeling as holistic monitoring, i.e., a complete and comprehensive characterization of matrix and trace elements in Flemish surface water samples. For this purpose, state-of-the-art inductively coupled plasma–tandem mass spectrometry (ICP–MS/MS) and Discrete Analyzer instrumentation were employed to perform quantitative analysis of more than 70 elements in the periodic table. The obtained quantitative analysis data served as input for the PHREEQC geochemical model to calculate the chemical species of the elements and estimate the concentration of the free metal ion. For elements contributing to standard exceedances in Flemish waterways (e.g., Co), holistic monitoring can enhance understanding of their “(biological) availability” and ecological impact relative to environmental quality standards derived from chronic ecotoxicity data (NOEC or EC10). Various Risk Characterization Ratio (RCR) approaches were compared for Co, Cu, Ni, Zn, and Pb, utilizing the free ion concentration and the bioavailable metal concentration. Besides, the multi-element ICP–MS/MS analysis revealed a “gadolinium anomaly,” indicating the presence of Gd-based contrast agents in some Flemish surface waters.

Conclusions

As a proof of concept, benefits of the holistic monitoring, i.e., coupling of a non-targeted characterization platform with geochemical modeling, are given in terms of (i) improved analysis quality on the entire sample and not limited to individual analytes, (ii) Improved data interpretation, not only the dissolved concentration per element but the concentration for each element species, and (iii) future contaminants: concentration of elements that are currently not monitored on a routine basis.