July 12, 2011 -- Reusable metal water bottles have lately gained a certain cachet as a greener, healthier alternative to some kinds of plastics, which can release trace amounts of a hormone-disrupting chemical into the liquids they hold.

But a new study shows that some kinds of aluminum bottles may be releasing more of that chemical, known as bisphenol A (BPA), than the hard, clear polycarbonate plastic bottles they were supposed replace.

Sales of one popular brand of reusable water bottles have roughly tripled in the four years since it was launched in the United States, according to The Aluminum Association, an industry trade group in Arlington, Va.

In a 2009 interview with the New York Times, the CEO of that company said sales had been driven by the “huge green wave” and “the BPA scare.”