NASHVILLE, Tenn. -- The No. 1 birth defect in Tennessee is one most people haven’t heard of, but it certainly can complicate the lives of young boys.

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In just 30 years, a defect that has to do with how a baby boy’s sex organs develop has more than doubled nationwide, and only one state in the country has a higher rate than Tennessee.

No one knows what's causing it, but there are suspicions and fears that there's no system in place in Nashville or anywhere in Tennessee to test drinking water for what might be doing the harm.

By some counts, hypospadias is happening to one out of every 100 baby boys.

"Hypospadias is an abnormality of the development of the penis, and there are many different severities of hypospadias; some that are really, really mild and then those that are really quite severe. … It can be so severe that it's almost difficult to determine whether it's a boy or a girl at birth," said Dr. John Brock.

There's not a lot of data to study because the state just started keeping track of birth defects less than 10 years ago.

"Because of the definitions that we use and how we collect our data in Tennessee differs from other states, so sometimes it's difficult to compare our rates with that of other states in the United States," said Dr. Veronica Gunn.

In California, a large and densely populated state, the rate for hypospadias runs 2.26 for every 10,000 live births. Iowa also has a low incidence rate of just more than seven in 10,000.

The current rate for hypospadias in Tennessee is 47.4, and some counties approach double that number.

More than one-third of Tennessee counties have cases of hypospadias, which is well above what's considered average in the state or in the nation.

"I've been doing this for over 20 years. There's no question we're seeing more children who have hypospadias," Brock said.

Studies are pointing to something in the environment as a possible cause.

"Something that's actually changing the development of the penis, which happens in the seventh to eighth week of gestation early on in the pregnancy that we may be doing to create increased incidents of it as well," said Brock.

Channel 4 News recently reported how traditional wastewater treatment is not removing the many drugs, lotions and pharmaceuticals residents use and flush every day.

A leading pharmacist who has pioneered safe drug disposal said that even hospitals routinely sent large amounts of unused drugs down the drain.

"In most hospitals, even today, probably 80 percent of them, if it’s an IV that’s being discarded and if it’s not a chemotherapy drug, it’s probably going down the drain, and it really hasn't been documented. … We are talking significant poundage, probably tons eventually," said Charlotte Smith.

Scientists in Canada said they found estrogen that goes down the toilet both naturally and from birth control is enough to make entire fish species too feminine to reproduce.

Recently, one brand of birth control skin patch added a warning to its packaging, but hormones aren't the only problem.

One study honed in on the chemicals widely used to disinfect wastewater, and there's been great suspicion about plastic.

"(There are) things in plastics called phthalates. … Phthalates are everywhere; they're in nail your polish, they're throughout everything that we use today in what we call plasticizers to make them pliable, which may be increasing the risk of hypospadias because they change the hormonal environment the child lives in," Brock said.

In most cases, hypospadias can be surgically repaired before the baby is a year old, but it could lead to infertility problems later in life.

Doctors said the best advice is for pregnant women to be especially careful about what they eat or are exposed to very early on in pregnancy.

The only state with a higher rate of hypospadias than Tennessee is Colorado.