Contaminants of emerging concern in Mediterranean groundwater: The more we analyse, the more diversity we observe

A review of case studies investigating contaminants of emerging concern (CECs) in Mediterranean groundwater (2006-2024) highlights where there are few investigations or limited CECs analysed, there is important information missing on CEC diversity. This was evident from the relatively high diversity of CECs reported in the 30 publications on Spanish groundwaters, including 127 types of pharmaceuticals and personal care products (PPCPs), 36 pesticides and 26 industrial products. In comparison, publications from other Mediterranean countries were fewer (≤ 7/country, and ≤ 3/country for southern Mediterranean countries), with significantly lower CEC diversity in groundwater: PPCPs ≤79 types/country, pesticides ≤8 types/country, and industrial products ≤5 types/country. The high CEC diversity present in Spanish groundwater may be due to the large land surface area (28,051 km²) of overlapping high anthropogenic activities and soil properties that favor the infiltration of CECs to groundwater. However, these factors were also observed over large areas in France, Turkey, Bulgaria, and Italy (> 9900 km²). The contaminant diversity in groundwater is also affected by CEC characteristics. 43% of the PPCPs and 50% of the pesticides observed at high concentrations in groundwater (140-50,000 and 950-18,721 ng/L respectively) have relatively high infiltration indices (based on CEC adsorption coefficients and half-lives). The PPCPs concentrations also showed a relatively high positive correlation with water-solubility (r² = 0.8). Whereas for industrial products, the infiltration index was only high for Bisphenol A. This review underscores the diversity of CECs present in groundwater, and a need for greater CECs investigation across all Mediterranean groundwaters.