Abstract
BackgroundThe procedure described in The Organisation for Economic Co-operation and Development (OECD) test guideline (TG) 216 is used to assess the effects of chemicals on microbial nitrogen transformation in soil, and the results are considered in regulatory risk assessments. We investigated the suitability of this method to characterize the effects of two silver nanomaterials and a soluble silver salt. We applied three different test procedures: (i) nitrogen transformation using the complex organic nitrogen source lucerne meal (OECD TG 216), (ii) nitrogen transformation using the inorganic nitrogen source (NH4)2SO4 (following OECD TG 216), and (iii) ammonium oxidation (ISO 15685). The results were compared with substrate-induced respiration (OECD TG 217).ResultsThe standard nitrogen transformation test using lucerne meal suggested that the test materials had no effect, whereas significant effects were identified with the other two test procedures. The absence of effects with lucerne meal probably reflected the sorption of silver ions to the additional organic nitrogen source, thus reducing its bioavailability, or blocking the silver nanomaterial oxidation sites by sorption of organic matter.ConclusionsThis common test used in the context of chemical registration is therefore unsuitable for the detection of potential effects caused by silver nanomaterials and soluble silver salts because it can yield false negative results. We instead recommend the use of an inorganic nitrogen source. The observed effects were not specific to nanomaterials. The time course of the effect in the nitrogen transformation test based on (NH4)2SO4 and the potential ammonium oxidation test varied according to the test substance, indicating different kinetic behaviors of ion release.
Highlights
The procedure described in The Organisation for Economic Co-operation and Development (OECD) test guideline (TG) 216 is used to assess the effects of chemicals on microbial nitrogen transformation in soil, and the results are considered in regulatory risk assessments
Nitrogen transformation test The N-transformation test according to OECD TG 216 monitors the formation of nitrate from a nitrogen source
The procedure described in OECD TG 216 is often used to assess chemical effects on the soil microflora responsible for nitrate accumulation under the framework of the REACH regulation and the resp
Summary
The procedure described in The Organisation for Economic Co-operation and Development (OECD) test guideline (TG) 216 is used to assess the effects of chemicals on microbial nitrogen transformation in soil, and the results are considered in regulatory risk assessments. We applied three different test procedures: (i) nitrogen transformation using the complex organic nitrogen source lucerne meal (OECD TG 216), (ii) nitrogen transformation using the inorganic nitrogen source (NH4)2SO4 (following OECD TG 216), and (iii) ammonium oxidation (ISO 15685). Several guidelines are currently used to investigate the effects of chemicals on selected microbial activities, as outlined in chapter R7c of the ECHA guidance for the implementation of Regulation (EC) 1907/ 2006 - the Registration, Evaluation, Authorisation and Restriction of Chemicals (REACH) [1]. The antimicrobial mechanisms of silver nanomaterials have recently been reviewed [8] and may include the formation of pits on the cell surface, the generation of free radicals that damage the cell membrane, the release of silver ions which affect Gram-positive and Gram-negative bacteria [7] - and the interaction between silver ions and the thiol and phosphate groups of enzymes and other organic molecules
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