Bioavailability, Toxicity, and Fate of Manufactured Nanomaterials in Terrestrial Ecosystems

The use of manufactured nanomaterials (MNMs) in consumer products has increased steadily over the past decade. MNMs from these consumer products are being discharged into waste streams and subsequently entering terrestrial ecosystems, primarily via land application of biosolids. As a result, the concentrations of MNMs in terrestrial ecosystems are increasing exponentially. Despite this, the majority of research investigating the bioavailability, fate, and effects of MNMs has focused on aquatic ecosystems. We review the current state of the knowledge on the fate of MNMs in terrestrial ecosystems as well as their effects on critical terrestrial ecoreceptors, including plants, bacteria, fungi, and soil invertebrates. While research on the bioavailability, toxicity, and ultimate fate of MNMs in terrestrial ecosystems is in its infancy, we conclude that there are critical knowledge gaps and an incomplete picture is emerging, with many studies reporting contradictory results. We also conclude that major discrepancies in the literature are primarily related to methodological and experimental shortcomings, such as inadequate MNM characterization, lack of consideration of MNM aggregation or dissolution, lack of proper controls, or the use of environmentally irrelevant MNM concentrations and/or exposure conditions. However, it is now evident that, under certain circumstances, MNMs are bioavailable and toxic to several key terrestrial ecoreceptors. It is also evident that additional systematic research focusing on the most environmentally relevant MNMs, including MNM transformation products and exposure conditions, is required to assess the risks posed to terrestrial ecosystems by nanotechnology.