Metal oxide nanoparticles (MO-NPs) with multifunctional properties are used extensively in various industries and released into the environment as industrial effluents and waste nano-products. These non-degradable, toxic MO-NPs are accumulating in the environment, debilitating the ecosystem and their biological communities. In this review article, a real-time scenario of MO-NP toxicity towards the soil and aquatic ecosystem and their mode of toxicity have been addressed in detail. The up-to-date information presented here suggests serious consideration of the consequences before random utilization of MO-NPs. © 2018, Springer Science+Business Media, LLC, part of Springer Nature.