CORRESPONDENCE/REBUTTAL pubs.acs.org/est
Comment on “Effects of Triclocarban, Triclosan, And Methyl Triclosan on Thyroid Hormone Action and Stress in Frog and Mammalian Culture Systems” n their recent article, Hinther et al.1 made the following statement. “Moreover, Xenopus laevis premetamorphic tadpoles exposed to TCS through prometamorphosis exhibited an increase in TRβ transcript levels in stage-matched tadpoles at metamorphic climax.21 This same study also found tadpole development was significantly accelerated upon exposure to TCS although thyroid morphology and thyroxine levels were unchanged (ref 22 for further information).” Unfortunately, the authors did not provide adequate detail of the findings of Fort et al.2 (cited as ref 21 in Hinther et al. (2011)1), and have thus misrepresented the results described in the paper. In addition, no acknowledgment or discussion of the supplemental data provided in our response3 to Helbing et al. (2011)4 (cited as ref 22 in Hinther et al. (2011)1) was provided in Hinther et al. (2011)1 which clarify the results presented. Our response to Helbing et al.4 indicated that a statistical acceleration of Xenopus laevis tadpole development and TRβ induction occurred only at the lowest concentration and an intermediate concentration tested. Thus, no concentration response relationship existed. Hinther et al. (2011)1 assertion that thyroid histopathology and thyroxin levels “were unchanged” was correctly cited. Further examination of the data from longer-term exposure in Fort et al. (2011)3 and Fort et al. (2011)5 in which Nieuwkoop and Faber6 stage 47 X. laevis tadpoles exposed to triclosan for 32-days indicated that triclosan accelerated tadpole growth as measured by whole body length, snout vent length, and whole body weight. However, thyroid axis-related end points including the rate of tadpole development (developmental stage), thyroid histopathology, and TRβ and deiodinase induction were not altered. Reduced plasma T4 levels were again noted in two intermediate test concentrations, but may have been the result of the inability to completely stage match all specimens due to histopathology and serum hormone end point demands. These clarifications are important for a complete understanding of the controversy that exists regarding triclosan and disruption of the thyroid axis. Our results in X. laevis suggest that triclosan does not alter thyroid axis driven metamorphosis, although triclosan is capable of increasing tadpole growth via apparent nonthyroidal processes.
I
’ REFERENCES (1) Hinther, A.; Bromba, C. M.; Wulff, J. E.; Helbing, C. C. Effects of triclocarban, triclosan, and methyl triclosan on thyroid hormone action and stress in frog and mammalian culture systems. Environ. Sci. Technol. 2011, 45, 5395–5402. (2) Fort, D. J.; Rogers, R. L.; Gorsuch, J. W.; Navarro, L. T.; Peter, R.; Plautz, J. R. Triclosan and anuran metamorphosis: No effect on thyroidmediated metamorphosis in Xenopus laevis. Toxicol. Sci. 2010, 113, 392–400. (3) Fort, D. J.; Rogers, R. L.; Pawlowski, S.; Champ, S. Triclosan and anuran metamorphosis: no effect on thyroid-mediated metamorphosis in Xenopus laevis. Toxicol. Sci. 2011, 119, 419–422. (4) Helbing, C.; Van Aggelen, G.; Velhoen, N. Triclosan affects thyroid hormone-dependent metamorphosis in anurans. Toxicol. Sci. 2011, 119, 417–418. (5) Fort, D. J.; Mathis, M. B.; Hanson, W.; Fort, C. E.; Navarro, L. T.; Peter, R.; B€uche, C.; Unger, S.; Pawlowski, S.; Plautz, J. R. Triclosan and thyroid-mediated metamorphosis in anurans: differentiating growth effects from thyroid-driven metamorphosis in Xenopus laevis. Toxicol. Sci. 2011, 121, 292–302. (6) Nieuwkoop, P. D. Faber, J. Normal Tables of Xenopus laevis (Daudin). Garland Publishing, London, 1994.
Douglas J. Fort* Fort Environmental Laboratories, Inc.
Michael Mathis Fort Environmental Laboratories, Inc.
Sascha Pawlowski Department of Product Safety, BASF SE
’ AUTHOR INFORMATION Corresponding Author
*E-mail:
[email protected]. r 2011 American Chemical Society
Published: July 25, 2011 7602
dx.doi.org/10.1021/es2021582 | Environ. Sci. Technol. 2011, 45, 7602–7602
