Evaluation of microbial shifts caused by a silver nanomaterial: comparison of four test systems

Abstract

Background: Before chemicals, pesticides and biocides are registered and approved, their effects on soil microorganisms must be tested, specifically their impact on nitrogen transformation. Following a request from the European Food Safety Authority (EFSA), the Panel on Plant Protection Products and their Residues provided an opinion document evaluating the science behind the risk assessment of plant protection products in the context of soil-dwelling organisms. The EFSA document concludes that the most relevant community-based microbial test systems should cover the widest possible range of metabolic processes without compromising test sensitivity. The EFSA document refers to the MicroResp test system, stating that although it has not been used to study the effects of pesticides on soil microbial processes, its capability should be investigated in the future. In the scope of harmonization approaches, the recommendations in the EFSA document covering pesticides could also influence the risk assessment and regulation of other kinds of chemicals, including silver nanomaterials. We therefore used the silver nanomaterial NM-300K as a model substance to evaluate the sensitivity of three functional tests covering the activities of different microbial fractions: (1) the potential ammonium oxidation (PAO) test, which considers the first step in nitrification; (2) the Micro-Resp test, which determines respiratory activity by measuring CO 2 evolution; and (3) a colorimetric test system for exoenzyme activity. We also surveyed bacterial 16S rRNA sequence diversity by next-generation sequencing (NGS). Results: There was no major difference in the general sensitivity of the tests, each of which revealed significant effects at silver nanomaterial concentrations of at least 1.67 mg/kg. The PAO test was a robust and sensitive indicator of toxicity, and concentration-effect relationships were calculated for every time interval. The effects on respiration and exoenzyme activities were more variable. Among the three functional tests, the selected exoenzyme activities showed the weakest concentration-effect relationships, although silver concentrations were clearly related to two of the four activities we tested (glucosidase and arylsulfatase). We also observed a relationship between silver concentrations and respiration activity on glucose, cellobiose and alanine substrates. The bacterial orders identified by NGS differed in sensitivity to the silver nanomaterial. We found that the adverse impact on nitrifiers matched the inhibition of PAO activity. EC 50 values calculated for each functional test did not identify a generally superior method. Conclusion: We found that all four test approaches were similar in sensitivity towards the model silver nanomaterial, an ion-releasing substance. We observed advantages and limitations for each test, which must be considered when selecting tests for the registration or approval of substances. It is unclear whether the sensitivity of the tests would be comparable when testing substances that do...

Considerations for the inclusion of metabarcoding data in the plant protection product risk assessment of the soil microbiome

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Threats to the soil microbiome from nanomaterials: A global meta and machine-learning analysis

“…The better prediction performance of the RF model may reflect the modest number of features in the current datasets. The results indicate that there are complex nonlinear relationships between the effect size of NMs and each feature variable, including NM characteristics, soil properties, and exposure conditions (Hund-Rinke et al, 2019;Kim et al, 2013). Although both machine-learning models had acceptable performance, there is room for improvement in accuracy for practical applications.…”

Current Progress and Open Challenges for Combined Toxic Effects of Manufactured Nano-Sized Objects (MNO’s) on Soil Biota and Microbial Community

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