Ecotoxicity and fate of silver nanomaterial in an outdoor lysimeter study after twofold application by sewage sludge

Martin Hoppe,Kerstin Hund-Rinke,Karsten Schlich,Jan Köser

doi:10.1007/s10646-022-02529-3

Abstract

The increasing use of antibacterial silver nanomaterials (AgNM) in consumer products leads to their release into sewers. High amounts of AgNM become retained in sewage sludge, which causes their accumulation in agricultural soils when sewage sludge is applied as fertilizer. This increase in AgNM arouses concerns about toxicity to soil organisms and transfer within trophic levels. Long-term field studies simulating the sewage sludge pathway to soils are sparse, and the effects of a second sewage sludge application are unknown. In this perennial field lysimeter study, a twofold application of AgNM (NM-300K, 2 + 3 mg AgNM/kg dry matter soil (DMS)) and a onefold application of silver nitrate (AgNO3, 2 mg Ag/kg DMS) by sewage sludge to the uppermost 20 cm of the soil (Cambisol) were applied. The response of microorganisms to the applications was determined by measuring the inhibition of ammonium-oxidizing bacteria (AOB). Silver concentration in soil, leachates, and crops were measured after acid digestion by inductively coupled plasma mass spectrometry (ICP-MS). Almost no vertical Ag translocation to deeper soil layers and negligible Ag release to leachates suggest that soil is a large sink for AgNM and AgNO3. For AgNM, an increase in toxicity to AOB was shown after the second sewage sludge application. The application of AgNO3 resulted in long-term toxicity comparable to the toxicity of AgNM. Low root uptake from both AgNM- and AgNO3-spiked lysimeters to crops indicates their incomplete immobilization, which is why food chain uptake cannot completely be excluded. However, the root-shoot barrier for wheat (9.8 → 0.1 mg/kg) and skin body barrier for sugar beets (1.0 → 0.2 mg/kg) will further reduce the accumulation within trophic levels. Moreover, the applied AgNM concentration was above the predicted environmental concentration, which is why the root uptake might be negligible in agricultural practice.

Highlights

Silver nanomaterials are one of the most widely used nanomaterials (NM) in various consumer products because of their antimicrobial properties (Benn et al 2010)
The AgARD concentration was low in all control lysimeters
The measured AgARD in the other lysimeters can be assigned to the applied AgNM (L2 and Lysimeter 6 (L6)) and to the applied AgNO3 (L28)

Summary

Introduction

Silver nanomaterials are one of the most widely used nanomaterials (NM) in various consumer products because of their antimicrobial properties (Benn et al 2010). The production and use of AgNM-containing products lead to increased AgNM emissions into wastewater (Bundschuh et al 2018). The entry of AgNM into wastewater treatment plants (WWTPs) is inevitable (Kaegi et al 2013). High amounts of AgNM become retained in sewage sludge. Ecotoxicity and fate of silver nanomaterial in an outdoor lysimeter study after twofold application by. The transfer of sewage sludge to agricultural soils is one of the most important NM pathways into the environment (Tourinho et al 2012; Pan and Xing 2012). Several short-term studies showed a rather high retention of AgNM for most agricultural soils, which is why soils were considered a large sink for AgNM (Pan and Xing 2012; Cornelis et al 2014; Hoppe et al 2014, 2015; Wang et al 2018)

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