Long-term monitoring of contaminants of emerging concern (CECs) across coastal lagoon–marine remains scarce, particularly in protected ecosystems where understanding land-based pollution is essential for achieving the objectives of the UN Ocean Decade Challenge 1: Understand and Beat Marine Pollution. Here, we investigated the occurrence, persistence, and ecological risk of CECs in the protected Laguna de Rocha (Uruguay) and the adjacent marine environment (within 2 nautical miles from the coastline) using a seven-year monitoring dataset (2018–2024). Target screening by liquid chromatography coupled to high-resolution mass spectrometry (LC-HRMS) identified more than thirty pharmaceuticals, pesticides, lifestyle compounds, and other CECs.
More than thirty pharmaceuticals, pesticides and lifestyle compounds were detected across the lagoon–marine continuum. Observed concentrations ranged from 0.001 µg/L (carbendazim) to 6.9 µg/L (atrazine) in the lagoon, and from 0.0011 µg/L (atrazine-desethyl) to 6.15 µg/L (metolachlor) in adjacent marine waters. To evaluate contaminant conservation during transport, a Frequency Retention Ratio (FRR) was calculated as the ratio between detection frequencies in marine waters and in the lagoon. Several compounds exhibited limited attenuation along the gradient and were identified as indicators of sustained anthropogenic pressure, including nicotine (FRR = 0.90), atrazine desethyl (0.87), azoxystrobin (0.84), irbesartan (0.84) and valsartan (0.79). A second group of compounds showed even higher detection frequencies in marine waters than in the lagoon, including carbendazim (FRR = 2.17), lidocaine (2.00), buspirone (1.67), venlafaxine (1.54) and carbamazepine (1.20), highlighting their persistence and/or differential transport dynamics. In contrast, trimethoprim (0.20), acetaminophen (0.19), phenylbutazone (0.14), naproxen (0.30) and imidacloprid (0.00) displayed strong attenuation between systems.
Ecological risk assessment revealed that persistence patterns were not directly associated with environmental risk. While most highly retained contaminants showed low risk quotients (RQ < 1), metolachlor and atrazine presented the highest estimated risks in marine waters (RQmax = 85 and 17.7, respectively), despite occurring at substantially lower mean concentrations than in the lagoon (metolachlor: 0.0012 vs 1.0 ppb; atrazine: 0.06 vs 5.8 ppb). These results reflect the greater sensitivity of marine organisms represented in available ecotoxicological thresholds and highlight the importance of integrating occurrence, persistence and risk metrics when prioritizing contaminants in coastal environments. This study demonstrates that contaminants of emerging concern can persist across the lagoon–marine continuum of a protected coastal ecosystem and identifies priority compounds for future monitoring and ecotoxicological evaluation.