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Widespread occurrence of two ectoparasiticide compounds in the aquatic environment, imidacloprid and fipronil, have prompted concerns about their potential environmental impacts. However, very little focus has been placed on water bodies in urban green spaces used for dog swimming. In this study, occurrence of both substances on Hampstead Heath, London, was compared in ponds with (n = 3) and without dog swimming activity (n = 3), as well as connecting streams above, between, and below these ponds (n = 6). Imidacloprid and fipronil were detected at main swimming points in dog swimming ponds at mean concentrations of 309 ± 104 ng/L and 32 ± 13 ng/L, respectively, indicating a high environmental risk in these samples. Measured concentrations in ponds not accessible for dog swimming were either below the limits of detection or limits of quantification for both chemicals. Across all ponds, there was a strong positive correlation between measured dog swimming activities and concentrations of imidacloprid (R 2  = 0.91) and fipronil (R 2  = 0.79). Some contamination was detected in connecting streams between ponds. A wider chemical analysis for the presence of urban waste water chemical residue signatures indicated minimal contamination, including in source waters. A survey of visitors who allow their dogs to swim in the sampled ponds confirmed frequent use of products containing imidacloprid and fipronil. In total, 86 % of 101 dog owners were unaware of the potential environmental impacts of products, and 94 % indicated that protecting nature would be an important consideration when selecting products. Besides the current practice of limiting dog access to ponds, information collected on product use and dog swimming practices identified additional opportunities to reduce contamination. We suggest that more cooperation between industry, regulators, veterinarians, green space managers, and the public can reduce risks to urban biodiversity while maintaining recreational benefits for dog owners and dogs., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2024 The Authors. Published by Elsevier B.V. All rights reserved.)

The SARS-CoV-2 pandemic had huge impacts on global urban populations, activity and health, yet little is known about attendant consequences for urban river ecosystems. We detected significant changes in occurrence and risks from contaminants of emerging concern (CECs) in waterways across Greater London (UK) during the pandemic. We were able to rapidly identify and monitor large numbers of CECs in n = 390 samples across 2019-2021 using novel direct-injection liquid chromatography-mass spectrometry methods for scalable targeted analysis, suspect screening and prioritisation of CEC risks. A total of 10,029 measured environmental concentrations (MECs) were obtained for 66 unique CECs. Pharmaceutical MECs decreased during lockdown in 2020 in the R. Thames (p ≤ 0.001), but then increased significantly in 2021 (p ≤ 0.01). For the tributary rivers, the R. Lee, Beverley Brook, R. Wandle and R. Hogsmill were the most impacted, primarily via wastewater treatment plant effluent and combined sewer overflows. In the R. Hogsmill in particular, pharmaceutical MEC trends were generally correlated with NHS prescription statistics, likely reflecting limited wastewater dilution. Suspect screening of ∼ 1,200 compounds tentatively identified 25 additional CECs at the five most impacted sites, including metabolites such as O-desmethylvenlafaxine, an EU Watch List compound. Lastly, risk quotients (RQs) ≥ 0.1 were calculated for 21 compounds across the whole Greater London freshwater catchment, of which seven were of medium risk (RQ ≥ 1.0) and three were in the high-risk category (RQ ≥ 10), including imidacloprid (RQ = 19.6), azithromycin (15.7) and diclofenac (10.5). This is the largest spatiotemporal dataset of its kind for any major capital city globally and the first for Greater London, representing ∼ 16 % of the population of England, and delivering a foundational One-Health case study in the third largest city in Europe across a global pandemic., Competing Interests: Declaration of Competing Interest The authors declare the following financial interests/personal relationships which may be considered as potential competing interests: Leon Barron reports financial support was provided by Imperial College London., (Copyright © 2023 The Authors. Published by Elsevier Ltd.. All rights reserved.)