Evaluation of the endocrine disrupting potential of the antimicrobial triclosan on early embryonic and larval development in zebrafish.

Abstract

Triclosan is a widely used chlorinated phenolic antimicrobial used in a variety of soaps, toothpastes, cosmetics, fabrics, and plastics. (Walker and Kimmel 2007). Triclosan is structurally similar to bisphenol A and dioxin, a well documented endocrine disruptor and potent carcinogen, respectively. Triclosan has recently been shown to have endocrine disrupting effects on multiple aquatic organisms and in human cells in culture, including effects on genes regulated by various estrogens, androgens, and thyroid hormones. Current concerns regarding the continued use of triclosan includes its increasing detection in urban streams and its ability to bioaccumulate in the lipid‐dense tissues of exposed organisms. Relevance to the importance of these concerns to humans includes, a report from 2008 demonstrating that 74.6% of human urine samples collected for testing contained triclosan in quantities ranging from 2.3 ug/L to 3, 790 ug/L. Triclosan, considered to be physiologically harmless, may have detrimental effects on organisms during early embryonic development. These effects may vary dramatically based on the timing of exposure. Statistically significant changes in variables such as eye diameter in zebrafish larvae can be observed when exposure times to sublethal concentrations of triclosan (200 ug/L) are prolonged through the first week of embryonic development. Preliminary results also indicate an effect on larval zebrafish heart rates. We hypothesize that this may be the result of an endocrine disrupting effect on the expression of receptors that control heart rate, such as the beta‐adrenergic and muscarinic receptors in the larval heart. Changes in several genes known to be regulated by estrogens, androgens, and thyroid hormones will be analyzed using by RT‐PCR and presented.