Influence of different types of nanomaterials on soil enzyme activity: A global meta-analysis

Engineered nanomaterials (NMs) have been widely used and could be released to soil environments, yet a consensus has not been reached on how soil enzyme activity, one of the most important indicators of soil health, responds to NMs exposure. Here, a global meta-analysis of 73 studies was carried out to examine the influence of NMs exposure on soil enzyme activity. Our results showed that the NM type was the most decisive factor, as Ag and Cu NMs had significant negative effects on soil enzyme activity. Carbon (C) NMs showed a negative effect on microbial biomass carbon (MBC) and most enzymes except dehydrogenase and soil respiration. Ti NMs only reduced soil respiration and urease activity. Zn NMs exerted no negative effect on all tested enzymes except dehydrogenase. Fe NMs had no negative effect on all tested enzymes, but stimulated the activity of acid phosphatase. The results also revealed that the response of β-glucosidase and dehydrogenase to NMs were similar to soil MBC and soil respiration, respectively. In addition, the inhibition of C, Ag, and Cu NMs on enzymes increases with dose. The exposure duration also regulated the effect of NMs on enzymes, which decreased with exposure longer than 10–20 days. Effects of NMs are also highly dependent on soil properties, for instance, the effect of Ag NMs on soil enzyme activity was weaker in organic matter-rich soils (>2%) or acidic soils (pH <7). Our meta-analysis suggests that soil enzyme activity could be negatively impacted by specific NMs, such as Ag, Cu, and even C NMs, of which high dose and prolonged exposure should be prevented, especially in low organic matter and/or neutral-alkaline soils. Therefore, these results can provide insights into the guideline for the future design and potential safe use of certain NMs, such as Zn and Fe NMs.