Correspondence/Rebuttal pubs.acs.org/est
Comment on “Determining the Ecological Impacts of Organic Contaminants in Biosolids Using a High-Throughput Colorimetric Denitrification Assay: A Case Study with Antimicrobial Agents”
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T
he paper by Holzem et al.1 reports a colorimetric denitrification assay for determining the ecological impacts of organic contaminants present in biosolids. The main shortcoming of this study is that no biosolids was used. The authors simply used a suspension of lab-grown P. denitrificans bacteria in minimal medium, spiked with the selected antimicrobial agents (e.g., triclosan and triclocarban), and quantified the changes in the denitrification rate, gene expression and cell viability. The results were then extrapolated to biosolids, and the assay was suggested as “an attractive alternative for meeting the initial testing regulatory framework for the Federal Insecticide, Fungicide, and Rodenticide Act, and recommended for the Toxic Substances Control Act, in determining the ecotoxicity of biosolids-derived emerging contaminants”. In order to develop a reliable method for biosolids and to determine the ecological impacts of organic contaminants in biosolids, the experimental design must include testing and verification with biosolids. Application rate of biosolids, exposure times, biosolids and soil characteristics, environmental factors, and more importantly biodegradation and transport mechanisms will ultimately determine the toxicity caused by the organic contaminants in biosolids. Therefore, the way the paper is written (e.g., title, graphical abstract that shows a picture of a truck land applying biosolids, introduction, etc.) fails to accurately represent the scope of the actual work that was carried out. The proposed denitrification assay can be useful for certain applications and organic contaminants. However, its value is questionable in the evaluation of the ecotoxicity of antimicrobial agents as it is proposed. When antimicrobial agents are directly spiked in a suspension of bacteria, they will invariably cause loss of cell function and viability, the magnitude of which will depend on the concentration of the antimicrobial agent and exposure time. The decreases observed in denitrification rates with the assay will therefore be mainly due to the disinfection effect of the antimicrobial agents. In order to evaluate the ecotoxicity of antimicrobial agents, particularly in relation to land application of biosolids, using the assay to quantify the changes in denitrification rates of P. denitrif icans in soil before and after amendment with biosolids would be a more meaningful approach.
REFERENCES
(1) Holzem, R. M.; Stapleton, H. M.; Gunsch, C. K. Determining the ecological impacts of organic contaminants in biosolids using a highthroughput colorimetric denitrification assay: A case study with antimicrobial agents. Environ. Sci. Technol. 2014, 48, 1646−1655.
Banu Ö rmeci*
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Professor and Canada Research Chair, Department of Civil and Environmental Engineering, Carleton University, 1125 Colonel By Drive, Ottawa Ontario K1S 5B6, Canada
AUTHOR INFORMATION
Corresponding Author
*E-mail:
[email protected]. Notes
The authors declare no competing financial interest. © 2014 American Chemical Society
Published: October 1, 2014 12469
dx.doi.org/10.1021/es503333m | Environ. Sci. Technol. 2014, 48, 12469−12469
