4.6 Article

Phenothiazinium dyes for photodynamic treatment present lower environmental risk compared to a formulation of trifloxystrobin and tebuconazole

Journal

Publisher

ELSEVIER SCIENCE SA
DOI: 10.1016/j.jphotobiol.2021.112365

Keywords

Ecotoxicity; Fungicides; Photodynamic treatment; Photosensitizers; Pollutants

Funding

  1. State of Sao Paulo Research Foundation (FAPESP, Brazil) [2016/24269-7, 2016/11386-5, 2018/24298-2, 2014/50945-4, 2018/06945-0]
  2. National Council for Scientific and Technological Development (CNPq, Brazil) [165191/2020-1, 425998/2018-5, 307738/2018-3, 465571/2014-0]
  3. Coordination for the Improvement of Higher Education Personnel (CAPES) [001]

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Antimicrobial photodynamic treatment (APDT) is a promising alternative to conventional chemical antifungal agents for overcoming the issue of resistant isolates, utilizing a photosensitizer (PS) and light to damage biomolecules of target organisms. Evaluation of the environmental toxicity of phenothiazinium PSs and the commercial antifungal NATIVO® showed lower toxicity of PSs and great potential of APDT against plant-pathogenic fungi.
The widespread use of conventional chemical antifungal agents has led to worldwide concern regarding the selection of resistant isolates. In this scenario, antimicrobial photodynamic treatment (APDT) has emerged as a promising alternative to overcome this issue. The technique is based on the use of a photosensitizer (PS) and light in the presence of molecular oxygen. Under these conditions, the PS generates reactive oxygen species which damage the biomolecules of the target organism leading to cell death. The great potential of APDT against plantpathogenic fungi has already been reported both in vitro and in planta, indicating this control measure has the potential to be widely used in crop plants. However, there is a lack of studies on environmental risk with ecotoxicological assessment of PSs used in APDT. Therefore, this study aimed to evaluate the environmental toxicity of four phenothiazinium PSs: i) methylene blue (MB), ii) new methylene blue N (NMBN), iii) toluidine blue O (TBO), and iv) dimethylmethylene blue (DMMB) and also of the commercial antifungal NATIVO (R), a mixture of trifloxystrobin and tebuconazole. The experiments were performed with Daphnia similis neonates and zebrafish embryos. Our results showed that the PSs tested had different levels of toxicity, with MB being the less toxic and DMMB being the most. Nonetheless, the environmental toxicity of these PSs were lower when compared to that of NATIVO (R). Furthermore, estimates of bioconcentration and of biotransformation half-life indicated that the PSs are environmentally safer than NATIVO (R). Taken together, our results show that the toxicity associated with phenothiazinium PSs would not constitute an impediment to their use in APDT. Therefore, APDT is a promising approach to control plant-pathogenic fungi with reduced risk for selecting resistant isolates and lower environmental impacts when compared to commonly used antifungal agents.

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