Abstract
Microplastic fibers (MF) are released from synthetic textiles during washing and end up in the wastewater. Similarly, silver nanoparticles (AgNP), incorporated in textiles as antimicrobial agents, are released in washing machines, also reaching the wastewater treatment plants. Therefore, both MF and AgNP co-exist in the environment and enter the soil compartment mainly via the application of biosolids. Yet, the combined effect of MF and AgNP has not been studied. Here, we assessed the effects of polyester MF on the toxicity of AgNP and AgNO3 to the earthworm Eisenia andrei and the enchytraeid Enchytraeus crypticus. The organisms were exposed to a range of concentration of AgNP (32, 100, 320, 1000, 3200 mg Ag/kg) and AgNO3 (12.8, 32, 80, 200, 500 mg Ag/kg) in LUFA 2.2 soil in the absence or presence of MF (0.01% DW). Reproduction tests were conducted and the toxicity outcomes compared between soils with and without MF. The exposure to MF caused a decrease in the number of juveniles and changed the biochemical composition of earthworms. Moreover, the presence of MF increased the toxicity of AgNP to earthworm reproduction (EC50 = 165 mg Ag/kg) when compared to AgNP exposure alone (EC50 = 450 mg Ag/kg), but did not alter the toxicity of AgNO3 (EC50 = 40 mg Ag/kg). For enchytraeids, no significant difference in Ag toxicity could be detected when MF was added to the soil for both AgNP and AgNO3. Overall, Ag bioaccumulation was not affected by MF, except for a decrease in earthworm body concentration at the highest Ag soil concentration (3200 mg Ag/kg). Our results suggest that the presence of MF in the soil compartment may be a cause of concern, and that the joint exposure to Ag may be deleterious depending on the Ag form, organism, and endpoint. The present work provides the first evidence that a realistic MF concentration in soil lowers AgNP concentration necessary to provoke reproductive impairment in earthworms. The influence of MF on the risk assessment of AgNP should be considered.
Highlights
The contamination of the soil compartment by microplastics has been recognized as an issue of concern
scanning electron microscopy (SEM) images of the Microplastic fibers (MF) confirmed the presence of elongated fibers as well as irregular shapes after the cryo-milling process (Figure SI2)
Fourier Transform Infrared (FTIR) analysis was performed to define the composition of polyester (Figure SI2)
Summary
The contamination of the soil compartment by microplastics has been recognized as an issue of concern. Studies have shown the ubiquitous presence of microplastics in soils, which can vary among sites with different land-uses. Floodplain sites in Switzerland had an average microplastic concentration of 0.0005% dry weight (DW), with the most contaminated site containing 0.0055% (DW) (Scheurer & Bigalke, 2018), equivalent to 5 and 55 mg/kg, respectively (Scheurer & Bigalke, 2018). In industrial areas in Australia, microplastic concentrations varied from 0.03 to 6.7% (DW) (Fuller & Gautam, 2016). Different sources can contribute to the increasing concentration of microplastics in the terrestrial compartment, such as local deposition of waste and atmospheric deposition. The main source is believed to be the land application of biosolids from wastewater treatment plants (WWTP) (Ng et al, 2018; Horton et al, 2017b)
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