title: Ecotoxicity of neutral red (dye) and its environmental applications.
abstract: Neutral red (NR) is a synthetic phenazine with promising prospect in environmental biotechnology as an electron shuttle. Recently, NR injections into coal seam associated groundwater in Australia (final dissolved NR concentration: 8 µM ± 0.2) were shown to increase methanogenesis up to ten-fold. However, information about NR toxicity to ecological receptors is sorely lacking. The main aim of this study was to investigate the concentration dependent toxicity of NR in microorganisms and plants. Acute toxicity of NR was determined by the modified Microtox™ assay. Microbial viability was determined using Escherichia coli and Bacillus subtilis. Germination and early growth of plants was studied using Lactuca sativa, Daucus carota, Allium cepa and an Australian native Themeda triandra. Lastly, mutagenicity of the coal seam associated groundwater was assessed using the Ames test. The EC50 of acute NR toxicity was determined to be 0.11 mM. The EC50 of microbial viability was between 1 and 7.1mM NR. Among the concentrations tested, only 0.01, 0.10 and 100mM of NR significantly affected (p<0.001) germination of L. sativa. The EC50 for root elongation in seeds was between 1.2 and 35.5mM NR. Interestingly, root elongation in seeds was significantly stimulated (p<0.001) between 0.25 and 10mM NR, showing a hormetic effect. A significant increase in mutagenicity was only observed in one of the three wells tested. The results suggest that the average dissolved NR concentration (8 µM ± 0.2) deployed in the field trial at Lithgow State Coal Mine, Australia, appears not to negatively impact the ecological receptors tested in this study.
authors.affiliation: School of Biotechnology and Biomolecular Sciences, University of New South Wales, Sydney, NSW 2052, Australia; Centre for Environmental Risk Assessment and Remediation, University of South Australia, Mawson Lakes Campus, Adelaide, SA 5095, Australia. Electronic address: fkastury@gmail.com.
authors.forename: Farzana
authors.initials: F
authors.lastname: Kastury
authors.affiliation: Centre for Environmental Risk Assessment and Remediation, University of South Australia, Mawson Lakes Campus, Adelaide, SA 5095, Australia.
authors.forename: Albert
authors.initials: A
authors.lastname: Juhasz
authors.affiliation: School of Biotechnology and Biomolecular Sciences, University of New South Wales, Sydney, NSW 2052, Australia.
authors.forename: Sabrina
authors.initials: S
authors.lastname: Beckmann
authors.affiliation: School of Biotechnology and Biomolecular Sciences, University of New South Wales, Sydney, NSW 2052, Australia.
authors.forename: Mike
authors.initials: M
authors.lastname: Manefield
mesh_terms: D001315:Australia; D001412:Bacillus subtilis / Q000187:drug effects; D003032:Coal Mining; D004396:Coloring Agents / Q000633:toxicity*; D052918:Environmental Restoration and Remediation / Q000379:methods; D004926:Escherichia coli / Q000187:drug effects; D018525:Germination / Q000187:drug effects; D007220:Industrial Waste; D009152:Mutagenicity Tests; D009499:Neutral Red / Q000633:toxicity*; D063245:Plant Development / Q000187:drug effects; D018517:Plant Roots / Q000187:drug effects / Q000254:growth & development; D018520:Plant Shoots / Q000187:drug effects / Q000254:growth & development; D010944:Plants / Q000187:drug effects
chemical_list: D004396:Coloring Agents; D007220:Industrial Waste; D009499:Neutral Red
keywords: CFU: Colony forming units; Coal seam gas; Dye; EC(10): The concentration where ten percent of the maximum effect is observed; EC(50): The concentration where fifty percent of the maximum effect is observed; Hormesis; LOAEC: Lowest observed adverse effect concentration; NR: Neutral red; PAH: Polycyclic aromatic hydrocarbon; Phenazine; Polyaromatic hydrocarbon; SEM: Standard error of the mean; Toxicity