LAUSR

Neonicotinoid insecticides have become of global concern for the aquatic environment. Harpacticoid copepods are amongst the most sensitive organisms to neonicotinoids. Here, we exposed the brackish copepod Nitocra spinipes to four neonicotinoid insecticides, i.e. clothianidin (CLO), imidacloprid (IMI), thiacloprid (TCP) and thiamethoxam (TMX) to investigate acute toxicity on adults (96-h exposure) and effects on larval development (7-d exposure). We used these results in combination with publicly available ecotoxicity data to derive Environmental Quality Standards (EQS). These EQS were ultimately used in a single-substance and mixture risk assessment for the Belgian part of the North Sea. Acute toxicity testing revealed that immobilization is a more sensitive endpoint than mortality, with 96h-EC50 values of 6.9, 7.2, 25 and 120 µg L-1 for CLO, TCP, IMI and TMX, respectively. In addition, the larval development tests resulted in 7d-NOECs of 2.5, 2.7, 4.2 and >99 µg L-1 for CLO, TCP, IMI and TMX, respectively. The derived saltwater Annual Average (AA-)EQS were 0.05, 0.0048, 0.002 and 0.016 µg L-1 for CLO, TCP, IMI and TMX, respectively. Finally, the risk characterization revealed some exceedances of the AA-EQS in Belgian harbors for IMI (number of exceedances, n = 2/4), TCP (n = 1/4), TMX (n = 1/4) and the mixture of the four neonicotinoids (n = 4/4), but not at the open sea. At the open sea site, the toxic unit sum relative to the AA-EQS was 0.72 and 0.22, suggesting no mixture risk, albeit with a relatively small margin of safety. Including short-term EC10 (96h) values of N. spinipes for the AA-EQS derivation led to a refinement of the AA-EQS for CLO and TMX, suggesting their use for the AA-EQS derivation since one of the overarching goals of the definition of EQS is to protect species at the population level. This article is protected by copyright. All rights reserved.