BPA, or bisphenol A, is an organic synthetic compound that's used to make certain plastics and epoxy resins. Because it's clear and tough, it has been especially useful for making plastic water bottles, and therein lies the problem. BPA has been shown to dissolve into our water, and once ingested in can potentially cause hormonal problems.

That's because BPA can mimic the actions of estrogen in our bodies, a hormone known to be involved in breast development, regulating periods and maintaining pregnancies, as well as a host of other things. Concerns about the negative health effects of BPA have thus led to some bans, as well as a demand for BPA-free plastics.

So, problem solved, right? Not exactly. It turns out that a common chemical replacement for BPA, fluorene-9-bisphenol (or BHPF), has now been shown capable of messing with our estrogen levels too. And like BPA, it's dissolving into our water, according to New Scientist.

Jianying Hu of Peking University in Beijing and colleagues tested the effects of BHPF in mice, and found that it caused the animals to have smaller wombs, smaller pups, and more miscarriages than controls. It's not yet clear whether BHPF will have similar effects on people, but until further research is done, it's probably not something you want to test for yourself.

Hu's team also tested a variety of BHPF plastic bottles that were labeled as "BPA-free" to test the rates at which it dissolves into water. They found that dissolution was especially concerning in warm or hot bottles, since heat can prompt compounds like this to dissolve. (Ask yourself how often you leave your water bottle in your hot car.) All in all, the compound was released from 23 of the 52 items tested, including all three baby bottles examined in the study.

The U.S. Food and Drug Administration has established "safe" levels for BPA found in food and water, but it's too early for such standards to exist for BHPF. In theory, it's possible that it could disrupt our hormonal systems even at low levels, but more extensive testing will be needed to know for sure.