Engineered Nanoparticle (Eco)Toxicity: Towards Standardized Procedures for Hazard Identification

The present study investigated changes in suspension stability and ecotoxicity of engineered nanoparticles (ENPs) by addition of Suwannee River natural organic matter and aging of stock and test suspensions prior to testing. Acute toxicity tests of silver (Ag), zinc oxide (ZnO), and titanium dioxide (TiO2) ENPs with Daphnia magna were carried out following Organisation for Economic Cooperation and Development test guidelines. Daphnia magna was found to be very sensitive to Ag ENPs (48-h 50% effective concentration 33mg L ), and aging of the test suspensions in M7 medium (up to 48 h) did not decrease toxicity significantly. Conversely, the presence of Suwannee River natural organic matter (NOM; 20mgL ) completely alleviated Ag ENP toxicity in all testing scenarios and did not aid in stabilizing suspensions. In contrast, addition of Suwannee River NOM stabilized ZnO ENP suspensions and did not decrease toxicity. Aging for 48 h generated monotonous concentration–response curves in the presence and absence of Suwannee River NOM. At concentrations up to 100mgL 1 TiO2 ENPs did not cause immobilization ofD. magna under any of the tested conditions. Presence of Suwannee River NOM caused agglomeration in stock suspensions. The authors’ results suggest that aging and presence of Suwannee River NOM are important parameters in standard toxicity testing of ENPs, which in some cases may aid in gaining better control over the exposure conditions but in other cases might contribute to agglomeration or elimination of ENP toxicity. Therefore, modifications to the current guidelines for testing ENPs should be evaluated on a case-by-case basis. Environ Toxicol Chem 2015;34:497–506. # 2014 SETAC