Iranian Journal of Soil and Water Research

Iranian Journal of Soil and Water Research

Temporal Monitoring of Silver Nanoparticle Toxicity on Some Biological Indicators in Two Sandy Loam and Clay Soil Textures

Document Type : Research Paper

Authors
1 Department of Soil Science, Ka,C., Islamic Azad University, Karaj, Iran
2 Department of Soil Science, Ka,C. Islamic Azad University, Karaj, Iran
Abstract
The increasing entry of silver nanoparticles (Ag-NPs) into soil ecosystems threatens biochemical health and biogeochemical cycles. This study evaluated the ecotoxicity and temporal dynamics (aging) of Ag-NPs on soil enzyme activities across two contrasting soil textures. A laboratory incubation experiment was conducted as a factorial based on a completely randomized design (CRD). Treatments included soil texture (sandy loam and clay), Ag-NP concentration (0, 100, 500, and 1000 mg/kg), and incubation time (7, 24, and 72 days). Urease, acid phosphatase, and alkaline phosphatase activities were measured as biomarkers. Results showed that Ag-NP inhibition strongly depended on soil texture and time. In sandy loam soil, urease was highly vulnerable; 1000 mg/kg reduced its activity by 54% on days 7 and 24 compared with the control. In contrast, clay soil showed greater buffering capacity. A pronounced hormesis effect occurred for alkaline phosphatase in clay soil: 100 mg/kg on day 7 increased activity by 109% relative to the control, and stimulation stabilized at a persistent 21% increase on days 24 and 72. For acid phosphatase in clay soil, initial inhibition at 1000 mg/kg almost fully recovered by day 24 (8% decline), but a 16% decline reappeared by day 72. Clay colloids and organic carbon likely mitigated Ag-NP toxicity through chelation and reduced bioavailability, whereas light soils remained highly vulnerable without this protective barrier. These findings highlight the importance of soil properties in determining nanoparticle ecological impacts. Nevertheless, temporal monitoring showed that pollutant aging remains a silent long-term ecological risk, even in colloid-rich soils.
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