Abstract
BackgroundSilver nanoparticles (AgNPs) are widely used in many fields of application and consumer products due to their antibacterial properties. The aim of this study was to prepare a hazard assessment for one specific AgNP in soil, incorporated via sewage sludge (the sewage sludge pathway). The effects of pristine AgNPs on microorganisms, plants and earthworms were first determined in screening tests. Long-term tests over 140 days were then conducted with AgNPs added to soil via sewage sludge. AgNPs were incorporated into the sludge through a simulated sewage treatment plant (STP) over 10 days to allow transformation to occur and also by manual spiking over 2 h. The results of the most sensitive organism from the long-term tests, the soil microorganisms, are presented.ResultsThe STP simulations confirmed that at environmentally relevant concentrations >90% of AgNPs remain bound to sewage sludge. Effects of AgNPs bound to sewage sludge and added to soil were similar to that of pristine NM-300K after degradation of the sludge. The predicted no-effect concentration for NM-300K in soil of 0.05 mg/kg dry soil determined a maximum threshold of 30 mg/kg dry sludge per application, considering the maximum addition of sewage sludge in Germany (5 tons per hectare every 3 years).ConclusionAt environmentally relevant concentrations, AgNP absorption to sludge and aging in soil (even after transformation) cause toxic effects on soil microorganisms of the terrestrial ecosystem.
Highlights
Silver nanoparticles (AgNPs) are widely used in many fields of application and consumer products due to their antibacterial properties
A predicted no-effect concentration (PNEC) in soil of 0.05 mg NM-300K/kg dry soil was calculated. This value means sludge containing 30 mg NM-300K/kg dry sludge may be applied in a single application to soil before the microorganisms are affected
For NM-300K, a derived PNEC in soil of 30 mg/kg dry sludge, with incorporation of the sewage sludge from municipal wastewater treatment plants, can be classed as a risk to soil organisms. This assessment is limited by the missing differentiation between total silver and silver nanoparticle (AgNP) and the fact that the PNEC is for NM-300K only
Summary
Silver nanoparticles (AgNPs) are widely used in many fields of application and consumer products due to their antibacterial properties. The effects of pristine AgNPs on microorganisms, plants and earthworms were first determined in screening tests. Long-term tests over 140 days were conducted with AgNPs added to soil via sewage sludge. Toxic effects on organisms of terrestrial ecosystems are reported, e.g. on earthworm reproduction [8,9,10] and microbial biomass and enzyme activity in soil [11]. These studies provide important information for risk characterisation
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