Le coupable serait le triclosan, ajouté dans les savons depuis les années '80. Une fois dans les égouts, le triclosan peut se transformer chimiquement en dioxines, une famille de composés chimiques toxiques pour les humains et l'environnement. Il semblerait que 3/4 des savons à main liquides en contiennent. Quand le triclosan coule dans l'évier avec l'eau chlorée du robinet, il se forme du super triclosan chloriné.
Dans les usines de traitement des eaux usées, 1 ou 2 atomes de chlore de l'eau du robinet sont souvent détachées, mais à la dernière étape de traitement des eaux usées, les usines ajoutent du chlore, ce qui rajoute des molécules de chlore au triclosan qui se déversent ainsi dans les rivières.
En laboratoire, il a été démontré qu'en présence de rayons du soleil, le triclosan ainsi chloriné peut se transformer et générer une série de dioxines, incluant les 2,8-dichlorodibenzo-p-dioxin, le 2,3,7- et le 1,2,8-trichlorodibenzo-p-dioxin et du 1,2,3,8-tetrachlorodibenzo-p-dioxin. Ce sont des dioxines qui se développent aussi dans l'environnement. Un ingénieur en environnement aux É.-U. affirme que c'est toujours inquiétant quand nous créons des composés qui semblent stables dans l'environnement et parviennent à se concentrer encore davantage, surtout quand leur innocuité est mise en doute.
Car une autre étude scientifique aurait mis des petits poissons mâles en contact avec du triclosan en concentration élevée pendant un mois: les poissons mâles se sont mis à produire une protéine du jaune d'oeuf, une charactéristique des femelles. Les mâles se sont aussi mis à produire moins de sperme, 1/3 de moins que la normale. La conclusion est que le triclosan imite légèrement les hormones et a un potentiel à devenir un perturbateur endocrinien pour la faune aquatique.
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"A new source of dioxins: Clean hands
Manufacturers have been adding the germ fighter triclosan to soaps, hand washes, and a range of other products for years. But here’s a dirty little secret: Once it washes down the drain, that triclosan can spawn dioxins. Patented in 1964, triclosan quickly found use in medical supplies. By 1987, manufacturers were adding it to liquid hand soaps for the consumer market. Within a little more than a dozen years, three-quarters of all such liquid hand soaps would contain the chemical. And as these soaps were used, triclosan washed down residential drains along with chlorinated tap water, forming super-chlorinated triclosan.
In wastewater treatment plants, the bonus chlorine atom or two that tap water had added to the molecule tends to be stripped off, notes William Arnold, an environmental engineer at the University of Minnesota in Minneapolis. But in the finishing stage at those treatment plants, most water gets one last chlorine-disinfection step, which “will re-chlorinate the triclosan,” he says, before the water is released out into rivers.
Arnold’s group and others have demonstrated in the lab that that in the presence of sunlight, the super-chlorinated triclosan can undergo transformations that beget a series of dioxins. They include 2,8-dichlorodibenzo-p-dioxin, 2,3,7- and 1,2,8-trichlorodibenzo-p-dioxin, and 1,2,3,8-tetrachlorodibenzo-p-dioxin. The genesis of these compounds isn’t just some laboratory curiosity. Triclosan's odd dioxins also develop in the environment — big time, Arnold’s group reported May 18 online, ahead of print, in Environmental Science & Technology.
“It’s always of concern when we’re generating compounds that appear to be stable in the environment and increasing in concentration,” Arnold says — especially when any risk they might pose remains unclear. That’s why he describes the triclosan-dioxin trend that his team unearthed as “disconcerting.”
Oh, and intact triclosan may pose its own environmental risks, another study finds. It exposed male mosquitofish that had come from relatively clean water to triclosan for a month. Concentrations were high, about 100 times what is usually found in water. The treatment induced the guys to produce notable amounts of egg-yolk protein — something only females are supposed to do. Sperm production in these fish also took a big hit, falling by a third when compared to untreated males.
Bottom line: These data indicate the pollutant is “weakly estrogenic” and “imply that triclosan has the potential to act as an endocrine-disrupting agent in aquatic organisms,” according to Robert Angus of the University of Alabama at Birmingham and Samiksha Raut of Dalton State College in Georgia. They describe their findings in the June Environmental Toxicology and Chemistry."
Excerpts from article written by Janet Raloff published in Science News here: http://www.sciencenews.org/view/generic/id/59333/title/A_new_source_of_dioxins_Clean_hands
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