Abstract
Metal-based engineered nanomaterials (ENMs) are known to affect bacterial processes and metabolic activities. While testing their negative effects on biological components, studies traditionally rely on initial exposure concentrations and thereby do not take into consideration the dynamic behavior of ENMs that ultimately determines exposure and toxicity (e.g. ion release). Moreover, functional responses of soil microbial communities to ENMs exposure can be caused by both the particulate forms and the ionic forms, yet their relative contributions remain poorly understood. Therefore, we investigated the dynamic changes of exposure concentrations of three different types of ENMs (nano-ZnO, -Cu and -Pb) and submicron particles (SMPs) in relation to their impact on the capacity of soil bacterial communities to utilize carbon substrates. The different ENMs were chosen to differ in dissolution potential. The dynamic exposures of ENMs were considered using a time weighted average (TWA) approach. The joint toxicity of the particulate forms and the ionic forms of ENMs was evaluated using a response addition model. Our results showed that the effect concentrations of spherical nano-ZnO, -Cu and SMPs, and Pb-based perovskites expressed as TWA were lower than expressed as initial concentrations. Both particulate forms and ionic forms of spherical 18nm, 43nm nano-ZnO and 50nm, 100nm nano-Cu contribute to the overall response at the EC50 levels. The particulate forms for 150nm, 200nm and 900nm ZnO SMPs and rod-shaped 78nm nano-Cu mainly affected the soil microbial metabolic potential, while the Cu ions released from spherical 25nm nano-Cu, 500nm Cu SMPs and Pb ions released from perovskites mainly described the effects to bacterial communities. Our results indicate that the dynamic exposure of ENMs and relative contributions of particles and ions require consideration in order to pursue a naturally realistic assessment of environmental risks of metal-based ENMs.
Highlights
Metal-based engineered nanomaterials (ENMs) have been widely applied in various medical, industrial and environmental applications (Wang et al, 2016)
This study evaluated the effect of three different types of metalbased ENMs that differ in size, shape and dissolution potential on the metabolic potential of soil bacterial communities
The EC50 values of spherical nano-ZnO, spherical nano-Cu and submicron particles (SMPs), and Pb-based perovskites were shown to be significantly lower based on time weighted average concentrations compared to responses derived from the traditional approach relying on a constant initial concentration
Summary
Metal-based engineered nanomaterials (ENMs) have been widely applied in various medical, industrial and environmental applications (Wang et al, 2016). The use of the time weighted average concentrations (CTWA) has been proposed to offer a more environmentally realistic display for exposure concentrations compared to using initially measured concentrations (CI) This approach has gained interest for risk assessment of degradable compounds such as many pesticides (Belgers et al, 2011), and was recently explored for ENMs that show time-variable exposure, e.g. silver nanoparticles (Zhai et al, 2016). It remains uncertain how the dynamic behavior of ENMs exposure affects the expression of toxicity (Meesters et al, 2013), in particular in comparison to static or semi-static concentrations and in relation to the metabolic or functional potential of soil bacterial communities
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