Assessment of the impact of abiotic factors on the stability of engineered nanomaterials in fish embryo media

Current and potential beneficial applications of engineered nanomaterials (ENM) are outweighed by the potential concern of their environmental implications. Understanding the impact of ENM release in the aquatic systems is complicated by the transport of the nanoparticles (NPs) especially in presence of various biotic and abiotic factors. Several attempts have been made to understand the aggregation and sedimentation of ENM in presence of individual factors such as natural organic matter and clay and in presence of salts to address their transportation and fate. The objective of the current study is to compare the effect of abiotic factors on the pH dependent stability and aggregation of TiO2 and CuO NP in a relevant fish embryo (E3) medium as a function of time. The aggregation and the sedimentation are compared in presence of humic acid (HA) alone, montmorillonite clay alone, and their combination. It is observed that in presence of HA, the aggregation of TiO2 NP and CuO NP decreases at pH 6, 8, and 10 and heteroagglomeration of TiO2 NP and CuO NP occurs with clay minerals at pH 2 and 4. It is also found that CuO NP are more stable than TiO2 NP in E3 medium and are perturbed to a lesser extent by the abiotic factors as compared to TiO2. Clay and HA are interesting naturally occurring matter in the aqueous environment that can affect the size, charge, and sedimentation behavior of ENM and thus affect their bioavailability and eventual toxicological fate.