Low Concentrations of Ibuprofen Had No Adverse Effects on Deleatidium spp. Mayfly Nymphs: A 7-Day Experiment

Concerns over pharmaceutical contaminants are increasing due to their high biological activity and ubiquity, with wastewater being the main source. Ibuprofen is extensively used worldwide and commonly detected in freshwaters due to its low degradability during wastewater treatment. Daphnia magna is the most-used model taxon for toxicity testing of ibuprofen, but this crustacean is known to be less sensitive to some contaminants than several freshwater insect groups. Our study assessed the toxicity of ibuprofen (nominal concentration range 2.0–2147.5 µg/L) to a native New Zealand mayfly, Deleatidium spp., in a 7-day static renewal experiment, with the neonicotinoid imidacloprid (1.4 µg/L) as a reference toxicant. Test concentrations of ibuprofen included three field-realistic and four higher concentrations that might occur in severely polluted streams. Mayfly responses indicated some negative trends (decreased survival and moulting propensity, increased impairment and immobility), but all patterns were non-significant. The imidacloprid control also had no significant impacts but tended to increase mayfly impairment. Overall, Deleatidium nymphs were largely unaffected by the entire range of experimental ibuprofen concentrations, suggesting that ibuprofen may be a relatively benign stressor for these organisms, although longer-term exposure experiments are needed to confirm if they demonstrate susceptibility to chronic exposure.