I think people are confused what an endocrine disruptor is and how it works. A lot of people probably hear and talk about endocrine disruptors as "bad" yet don't understand what is actually happening. Even in the example Ed posted a lot of people will not understand what is truly happening.
1. The endocrine system is focused on hormones. Hormones are typically a concern during critical periods of growth in an organism.
2. A large number of species are wired to develop as females. If the animal has male chromosomes they will produce a protein. This protein is what makes the gonads stop developing into a female gonad and make them develop into a male gonad. So, in humans the SRY protein will make the gonads turn into testis. Once this development has occurred the endocrine system will become more important. (this is probably why almost all the genetically male frogs developed male gonads in the article, it is a DNA thing and not a hormone thing).
3. The male genitals will produce higher levels of male hormones, most widely referred to as testosterone. There are many types of testosterone. It is the production of testosterone that causes the primary external sexual development. So, testosterone will shut down the female sexual development and begin the male sexual development. This is why many articles will focus on the size and function of the sexual characteristics when looking at the effects of endocrine disruptors.
4. Endocrine disruptors are also important for other issues that are not often discussed. Hormones are also an important part of bone development. Yes, you need calcium and D3 for healthy bones. However, it is the testosterone that typically causes bones to grow longer and more dense (in humans, Ed can verify if this is the case for frogs). This is why people with Gigantism are known for tumors on or near the pituitary gland or malfunctions of the pituitary gland. The excess hormones causes the bones to continue to grow.
5. All this talk about endocrine disruptors will be hard to "witness", unless you are measuring your frogs genitals, doing sperm counts, or accurately measuring your frogs size.
6. The published article makes an important conclusion. "These findings suggest that the styrene monomer and trimer induced a weak estrogen-like effect on the pathways of testicular differentiation in genetically male tadpoles". This is referring to the statistical analysis. A weak effect in statistics is often an effect size less than 0.2 (I didn't pay for the article so I don't know what the true statistics were). This means that although it is a concern to see these effects, more frogs developed properly than those that had the problems. So, a lot of us will never see the effects when looking at our individual frogs. However, if we look at the frogs general health (everyone's frogs) the endocrine disruptor could be concerning.
