Silver nanoparticles (AgNPs) from industrial use, discharged via the land application of sewage sludge, are interacting with soil biota, including earthworms. In affected organisms, excessive production of reactive oxygen species can result in lipid peroxidation, shifting the balance between oxidants and antioxidants to cause oxidative stress. We determined selected lower‐tier biomarkers such as antioxidant responses and lipid peroxidation in Aporrectodea caliginosa earthworms exposed to soils spiked with AgNPs or silver nitrate (AgNO3). Aporrectodea caliginosa were exposed to AgNPs at 0 (control), 0.3, 3, 30, and 300 mg/kg or Ag+ (as AgNO3) at 0, 0.03, 0.3, 3, and 10 mg/kg in soil for 4 wk. At 1, 2, 3, and 4 wk, the activity of the antioxidant enzymes superoxide dismutase, catalase, glutathione peroxidase, glutathione S‐transferase, as well as lipid peroxidation (malondialdehyde content), increased as a function of concentration, with a much larger response for Ag+ than AgNPs. Given the likelihood of ever‐increasing AgNP concentrations in soil, where AgNPs can transform to ionic Ag (Ag+), our findings of antioxidant response to oxidative stress in a common indicator organism even at an environmentally realistic exposure concentration of 0.03 mg/kg demonstrate that AgNPs may affect soil fertility and, thus, agricultural production. Evaluating selected lower‐tier biomarkers offers a meaningful assessment of AgNPs and Ag+ effects on terrestrial earthworms. Environ Toxicol Chem 2020;39:1257–1266. © 2020 SETAC

The widespread use of silver nanoparticles (AgNPs) as a bactericide will ultimately result in their increased concentration in soils. We sought to determine the likely mobility, toxicity, and plant uptake of Ag applied to soil as either AgNPs or Ag + . We measured the solubility, toxicity, and plant uptake of both AgNPs and Ag + in an immature Pallic soil, a Templeton loamy silt (pH = 5.1), and a granular silt loam (pH = 6.0). The sorption of AgNPs by the test soils was significantly greater than Ag + , and both moieties were more strongly sorbed at lower concentrations and higher pH values. Between pH 4 and 8, distribution coefficient (K D ) values increased from <10 up to ?500 L kg −1 for Ag + , and from 100 to 10,000 L kg −1 for AgNPs. There was strong evidence that our citrate-coated AgNPs were transformed into Ag + during the course of the plant growth experiments, and plant responses were similar for both the Ag + and AgNP treatments. Soil concentrations >100 mg kg −1 significantly reduced the biomass of Lolium perenne L. and resulted in foliar concentrations of up to 10 mg kg −1 dry matter. At a soil concentration of 70 mg kg −1 , silverbeet [Beta vulgaris L. ssp. maritima (L.) Arcang.] and spinach (Spinacia oleracea L.) accumulated 5 to 10 mg Ag kg −1 , which may present a human health risk. Regarding citrate-coated AgNPs, the environmental impact of release is largely determined by the equivalent mass concentration of Ag + , into which they will ultimately transform. Given the widespread interest in AgNPs, there is limited knowledge on the behavior of Ag + in soil and this should be the subject of future research.

When soil is contaminated with silver (Ag), plants take up Ag and is concentrated in roots and leaves, with its effects reflected in crop health and yield. This study investigated the toxicity of silver nanoparticles (AgNPs) and silver nitrate (AgNO 3 as Ag +) to sunflower seeds grown in soils amended with 150 mg/kg of Ag either as AgNPs or AgNO 3. Exposure of the sunflower seeds to soils amended with Ag increased plant lipid peroxidation, activities of antioxidants enzymes (catalase, superoxide dismutase, glutathione-S-transferase), peroxidases (glutathione peroxidase pyrogallol peroxidase, guaiacol peroxidase), oxidases (ascorbate oxidase), urease, total phenolic compounds, vitamins (retinols, alpha-tocopherol and L-ascorbic acid) but inhibited chlorophyll, total carotenoids, total soluble carbohydrates, phenolic compounds and total soluble proteins. In general, AgNO 3 increased the above-mentioned parameters in sunflower more than did AgNPs, except for the tested vitamins, which were more affected by AgNPs. The results showed that Ag accumulation in the root > leaf > stem and human food security risk is enhanced in sunflower seeds exposed to Ag compounds.

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