John Wiley & Sons, Ltd.

The influence of natural organic matter and aging on suspension stability in guideline toxicity testing of Ag, ZnO, and TiO2 nanoparticles with Daphnia magna

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This study investigated changes in suspension stability and ecotoxicity of engineered nanoparticles (ENPs) by addition of Suwannee River natural organic matter (SR‐NOM) and aging of stock and test suspensions prior to testing. Acute toxicity tests of Ag, ZnO, and TiO2 ENPs with Daphnia magna were carried out following OECD test guidelines. D. magna was found to be very sensitive to Ag ENPs (48‐hr EC50 of 33 μg L‐1) and aging of the test suspensions in M7 medium (up to 48 hours) did not decrease toxicity significantly. Conversely, the presence of SR‐NOM (20 mg L‐1) completely alleviated Ag ENP toxicity in all testing scenarios, and did not aid in stabilizing suspensions. In contrast, addition of SR‐NOM stabilized ZnO ENP suspensions and did not decrease toxicity. Aging for 48 hours generated monotonous concentration‐response curves in the presence and absence of SR‐NOM. TiO2 ENPs did not cause immobilization of D. magna under any of the tested conditions in concentrations up to 100 mg L‐1. Presence of SR‐NOM caused agglomeration in stock suspensions. The authors' results suggest that aging and presence of SR‐NOM are important parameters in standard toxicity testing of ENPs, which in some cases may aid in gaining better control over the exposure conditions, however, in other cases might contribute to agglomeration or elimination of ENP toxicity. Therefore, modifications to the current guidelines for testing ENPs should be evaluated in a case‐by‐case basis. This article is protected by copyright. All rights reserved

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