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Public Radio's Environmental News Magazine (follow us on Google News)

The Search for Evidence in the Okefenokee

Air Date: Week of

Alligators have outlived the dinosaurs, and survived predation by human beings. But now, they’re facing a new threat: synthetic chemicals which interfere with their ability to reproduce. Steve Curwood visits the Okefenokee Swamp, where scientists are investigating the effects of estrogen-mimicking hormones found in common industrial compounds on the sexual development of alligators.


CURWOOD: This is Living On Earth. I'm Steve Curwood.

(Sound of an alligator bellowing)

CURWOOD: It's alligator breeding season in the Okefenokee swamp in Southeast Georgia. A male gator lifts his head from the marshy bog and roars. The sound, like a Harley-Davidson motorcyle being kickstarted, is the alligator's mating call and the way he stakes out his territory. The alligator's breeding behavior has helped ensure the species survival for 250 million years. Alligators have outlived the dinosaurs, survived the ice ages, and so far, they've even endured predation by humanity.

The Okefenokee swamp is one of the refuges the federal government has created to protect the once endangered animals. Hunting alligators here, in the primitive swamp, is strictly prohibited.

But Dr. Timothy Gross, a zoologist from the University of Florida, and a team of government and university scientists have special permission and have waited months for this opportunity to hunt young alligators from the Okefenokee.

(Sounds of a boat being launched into the water)

GROSS: That's gonna stay dry, it probably, I hope so, I'm not gonna guarantee ya.

CURWOOD: Dr. Gross helps push a swamp airboat into the water. Tonight the researchers will try to gather evidence of a new and insidious threat that could, in a generation or two, endanger the population of alligators in the refuge. In research elsewhere, Dr. Gross has found that toxic chemical pollutants can interfere with the sexual development of young alligators producing bizarre effects and disrupting their ability to reproduce.

GROSS: These contaminants exert huge effects on the embryo and the embryo therefore as it develops doesn't develop normally. It looks like a normal animal externally but internally certain systems are abnormal mainly the endocrine system and we find that these animals are not normal, primarily the males are very altered They're not normal, they're look semi-female, semi-male, they're halfway way, and they're probably non-functional.

CURWOOD: The second generation reproductive effects in alligators were first observed on Lake Apapka in central Florida. In 1981, 90 percent of the lake's alligators were dead form a pesticide spill. The lake was supposedly de-contaminated but a decade later the alligator population wasn't rebounding as the scientists expected. Something was terribly wrong with the offspring of the surviving animals. Most failed to hatch from eggs and the few that lived, developed reproductive abnormalities. To find out if this was an isolated or widespread effect, Dr. Gross and his team of scientists have obtained special permission to study alligators here.

GROSS: Okefenokee is a rather large population of alligators so it's one worth looking at. Also we have the aspect that there's many paper pulp operations around here, a lot of lumbering and so on and there are potentials, this is a very large drainage area for contaminants to also get into the Okefenokee like in any environmental system.

CURWOOD: So we don't know tonight if we're going to find any alligators that have problems, they might be fine here.

GROSS: They could be fine here. Actually this is a fairly pristine environment and what we're hoping to find is that indeed our findings will match what we would expect which is gators are probably fairly healthy here. We may get a surprise though in some of these areas but the only way we're going to begin to know is by looking.

(Sounds of a boat motor engaging)

CURWOOD: Dr. Gross, Dr. Greg Masson, a scientist with the U.S. Fish and Wildlife Service, and I board the bright yellow airboat. It's crowded.We've loaded it with burlap sacks, plastic specimin bags, syringes, test tubes, a scale, duct tape and a tape measure. Dr. Masson, perched high above in the pilot's seat steers a course down a narrow canal towards the headwaters of the Suwanee River made famous by the Stephen Foster song.

Dr. Gross passes out earplugs and hard hats with lights fixed to the top like the ones used by miners. The lights pierce the darkening canal where Spanish moss hangs from the cyprus and scrub pine along the marshy banks. Dr. Gross says, the best time to hunt gators is at night when they're more active and you can see their red eyes floating just above the water.

(Dr. Gross speaks loudly over the sound of the boat motor)

GROSS: Way you're going to find gators is once it gets pitch black, he'll have a que beam back there that's about 60-70 thousand candle power and you'll be able to shine at a fairly good distance, and also with our headlamps you see the eyes glow, they look like somebody's tiny little pen light flashlights, a pair of 'em, and you'll see 'em and that's how we'll know where they're at. Then otherwise than that, there's a big guy swimming across the water up there, that's how you find them.

CURWOOD: Gators can grow to 13 or more feet and live 50 years and longer. As the airboat picks up speed the alligators slowly submerge into the water dousing their intense, fire-red- glowing eyes.

GROSS: Help yourself if you need insect repellent. The mosquitoes get pretty bad out here, they'll chew you up.

CURWOOD: The scent of honeysuckle and magnolia overwhelm the smell of bug spray. Dr. Greg Masson pushes hard on the throttle and swings the powerful que beam in an arc . Pairs of red eyes watch us as we head 9 miles deep, into the swamp.

Nearly an hour later, we enter a swampy prairie. The moon lights up the lake.

The boat slows as the propeller pitches down.

GROSS: Now this is beautiful, this is totally beautiful. This is what a swamp is supposed to look like.

CURWOOD: Our airboat pushes through some tall reeds and stops at the mouth of th prairie near some peat bogs.

GROSS: This is the type of stuff gators love to hang out in.

CURWOOD: The water is cool and clean but it's the color of tea and tastes like vinegar; acidic from the decaying vegetation. Okefenokee is the Native American word for "land of the trembling earth". 600 square miles, the Okefenokee is one of the largest primitive swamps in the United States.

(Sounds of frogs and crickets)

Pig frogs and crickets serenade us as we search for pairs of narrow spaced red-eyes, the tell-tale sign of young gators. Dr. Greg Masson's beam scans the surface of the water with high powered light but all we see staring back at us are beadie, yellow eyes - we're surrounded by frogs.

(Frogs sounds continuing)

MASSON: It's so nice out here though, beautiful. This is really tranquil, I love it.

CURWOOD: Dr. Masson knows the way through the primordial Okefenokee swamp better than Tim Gross, so Dr. Gross is elected chief gator grabber.

CURWOOD: So now what's the approved method here of catching a gator?

GROSS: Hang off the front of this boat, he pulls up on it and you basically reach in and you simply want to grab them right behind the head but in front of the front legs...

CURWOOD: You don't want to grab the tail?

GROSS: Don't want to grab the tail, no, that's when they can swing around and bite you.

CURWOOD: Tim checks his life vest and helmet light.We're looking for young animals five feet or less. In a few minutes, Greg spots something in the distance.

MASSON: About a 4 footer you see him? Are you ready for him?

(Sounds of boat motor revving up)

CURWOOD: Greg pushes hard on the throttle and I'm almost tossed into the water. Tim crawls on his stomach to the edge of the boat.

As we approach the clump of trees where we spotted the gator, we turn off the powerful light. We don't want to scare the alligator off. Greg throttles down and Tim lies in the bow, his hands in the water. But in the dimmer light of his headlamp, he catches a better glimpse of the animal and pulls back, its too big.

GROSS: I was goin' to try to see if I could get behind him and see how wide he looked but he probably was a good 6 foot.

(Sound of boat motor starting up again)

CURWOOD: We move on, gliding over lily pads and past peat islands. We spot plenty of gators, but they're all even bigger than the first. Tim says he's never gone this long without catching a gator. He thinks a lot of young gators died in a previous year's drought.

An hour later and still no luck. The stars are begining to look like blinking frog eyes.

GROSS: This stuff is not the easiest stuff to find in it is it Greg?

CURWOOD: Tim Gross and Greg Masson are frustrated. Dr. Masson hops down from the pilots chair and lights a cigar. Dr. Gross stretches out on the deck . It's time for a break. Dr. Gross starts telling us the story of how he and Dr. Masson became interested in the reproductive problems of alligators. It began when Dr. Masson was studying turtle eggs collected from Lake Apapka in Florida. It had been more than a decade since the devastating pesticide spill and the lake had been cleaned up. But the turtle eggs weren't hatching, their sexual development had been disrupted.

GROSS: We simply fell into this basically, it was serendipity. We began to look at turtles and we saw abnormal sexual development.

MASSON: Yeah, the anatomy's different. We found that the gonads were not differentiated. You couldn't really tell a male from a female turtle and their hormone levels were off also as far as the estrogen-testosterone ratios.

GROSS: Because of that we went back and we looked at gators and we saw abnormal sexual development. Before that we were basically pulling at straws trying to find out why they weren't doing as well. Contaminants was only one of the many theories we had and reproductive development was one of the things we hadn't even thought of looking at.

CURWOOD: Neither Dr. Gross nor Dr. Masson knew at the time that other scientists were also discovering similar bizarre reproductive effects in other animals. In the Great Lakes a high number of gull eggs weren't hatching. Many of the birds that were born were unable to reproduce. British scientists were finding male fish from polluted rivers were producing huge amounts of female hormones. And U.S government scientists studying the nearly-extinct Florida panther found that the male panthers seemed to be chemically castrated.

Drs. Masson and Gross are among a growing number of scientists who believe that these effects are due to some synthetic compounds which can mimic the action of hormones during fetal development.

GROSS: Basically, I think you would agree, Greg, we're finding that a number of contaminants can alter various physiological functions, mainly the endocrine system. And the endocrine system is one of the more important regulatory systems within any physiological system. It helps to regulate neuro-endocrine function or brain function. It helps to regulate immune function, it also regulates reproduction, stress, thyroid or metabolic function and when you have various agents that can mimick and alter the function of the system you have rather far ranging major potential effects.

CURWOOD: One of the most surprising aspects is the large number of chemicals that seem to be able to produce endocrine disrupting effects. They include some of the most common industrial compounds. Many are organochlorines including pesticides, and plastics made from chlorine.

CURWOOD: So what do you think? What makes it work like an estrogen? Or an androgen? Or any of the body's hormones?

GROSS: Looking at the structure, I wouldn't predict it's got an estrogenic effect, would you Greg? I don't think any of us would. The structure is so vastly different, it's not going to act like an estrogen, and yet it does.

MASSON: And unfortunately, most of these effects are sublethal so we don't have any indication that something is going on. Either now people look at toxicity testing or carcinogenicity. It either has to kill the animal or become cancerous. And they're just now becoming aware that there are sub-lethal effects that don't manifest themselves to the human eye.

CURWOOD: And the quantities required for these non-fatal effects are pretty tiny, is that what your research says?

GROSS: Exteremly small, most contaminants we measure at a level of one part per million or multiple parts per million. Hormones characteristically are measured in parts per billion and even more specifically very often in the case of estrogens, parts per trillion. They're extremely small, they're picogram amounts and it obviously doesn't take a lot of mass to possibly create a problem.

MASSON: And unfortunately, a lot of the compounds we're using nowadays have other compounds mixed in with it so there's an addititivity or even a synergenism we don't know about, and some of these compounds, the dioxins and some of the furans are in parts per quatrillion and we know they have an effect at that level which is extremely minute.

GROSS :And the whole system gets exacerbated a little bit by the fact that in addition, these compounds have a long life in the body. Estrogens for instance don't last more than several hours on the average in the body, they're cleared, they're removed, they're excreted and thery're gone. They're broken down, altered, so they're no longer biologically active at least... right natural estrogens...these artificial estrogenic-like contaminants or other endocrine disruptors stay in the body long term, they get stored, the body has no natural mechanisms to remove them, so they can continue to exert an effect again and again and again, much more so than natural.

(A thumping noise is heard)

CURWOOD: Dr. Masson spots something, flicks on his searchlight, and jumps up.

(Sound of boat motor)

MASSON: About 15 feet off the left side. See him..right where my light is, ok. See him? He's going under the water, he'll be up in a minute.

CURWOOD: Tim almost falls into the water but comes up with a smile and a gator.

GROSS: Finally, about a 4 year old.

CURWOOD: So what are you doing now?

GROSS: Taping his mouth shut and then he's pretty well under control.

CURWOOD: You going to take a look at his business department?

GROSS: Thats' what Greg's doing now, roll him over and check him out good.

CURWOOD: Now what do you have for gender?

GROSS: A little boy. That's about average size....not bad....not bad at all.

(Sound of a thump)

MASSON: Oh munchkin'.

GROSS: He's yurking.

(Sounds of alligator making throaty sounds)

MASSON: That was an alarm call, to say they were in some kind of distress.so they give that alarm call for the female. Let's tape his eyes down. We can just either put him in a bag or process him right away.

CURWOOD: Now when you say process right away, what do you mean?

GROSS: We're going to basically go ahead and take a blood sample, we've already sexed it, we'll get a body length and a snout vent length, and obviously with no more than we're having luck finding a lot of them he'll be one of the five that we're gonna take off the lake and sacrifice to take samples from to actually find out what kind of pesticides and other contaminant levels are actually occurring within his tissues.

MASSON: I don't like sacrificing any animals you know If we do have to sacrifice an animal then we get as much information as we can from that animal and get as many people to collaborate on that as we can.

CURWOOD: Our luck improves and within an hour we catch four more small aliigators.

They're placed alive in burlap bags and stowed in the bow of the boat.

(Sounds of soft rain shower and birds chirping)

CURWOOD: A gentle rain falls the next morning in a field not far from where our trip into the Okefenokee began the night before.

GROSS: Do you have a scalpel blade by any chance, got a scalpel around?

ARNOLD HILL: I've got a scalpel but yeah, I'll need to get those vacutainers out of the boat.

CURWOOD: The back of a pick-up truck serves as a makeshift dissection table.

Dr. Gross is assisted by Dr. Gross and Beverly Arnold Hill, a graduate student from the University of Georgia.

GROSS: So how much blood do you want acid-free, how much do you want in tubes, what would you like?

ARNOLD HILL: Let me go ahead and do two vactainer tubes and so I'll have one and I'll send one to Florida.

CURWOOD: The dissection takes a better part of an hour for each of the gators.

CURWOOD: So what are you cutting through there?

GROSS: Cartilage and olifacia and fat and muscle.

CURWOOD: Four of the animals seem normal, later tests would confirm this. But it's immediately obvious to Dr. Masson that one of the small female alligators has a serious problem. He holds up a specimen jar. Inside is a pearly white, fleshy lump in formaldehyde, it's one of the gator's ovaries. She had the sexual development of an alligator twice as old as she was.

MASSON: Well on this one it' s amazing, we have this tissue is about 3 times the diameter of the other tissue we got out of the same size female and approximately 2 times longer. That's a tremendous amount of growth in this one compared to the others.

CURWOOD: So something would have to stimulate this growth?

compounds that stimulate this kind of gonadal tissue development.

(Frog sounds)

CURWOOD: Dr. Tim Gross believes the estrogen, or estrogen mimicking chemical that might have caused this young female alligators unusual reproductive development came from her mother. The daughter may have been exposed to chemicals in the envrionrment that had built up in the mother and were passed on to her during fetal development.

GROSS: The effects between the generation, that's I think the most important thing that this work is showing, is that these effects are not effecting the mom, or dad, or basically us at this point, what they're affecting is your subsequent abilty to reproduce adequately and more so, the subsequent ability of your offspring to reproduce and function in a normal physiological reproductive pattern. So it means that you may get exposed you won't see any effect in your lifetime, but your children, you'll see an effect in once they reach puberty once they're reproducing.

CURWOOD:There are lumber mills and farms not far from here. They're potential sources of endocrine disrupting chemicals. But these scientists don't believe they're the problem. Beverly Arnold Hill says the Okefenokee is clean. If there are pollutants here she says, they're coming from somewhere else carried in the air and deposited by the rain.

ARNOLD HILL: If its accumulating in this area which is very pristine, no point sources, no farms, no dumps or anything that we know of, then what about some of these rivers and streams and wetlands that are right near towns and where all this stuff is being dumped. I mean, if we have a problem here, then there's got to be a bigger problem elsewhere.

MASSON: People should take heed, I mean they should be scared. It's frightening.

CURWOOD: Earlier I had joked with Dr. Greg Masson of the U.S Fish and Wildlife service about the Okefenokee, how many of us knew the place only through Walt Kelly's cartoon strip: Pogo. "We have met the enemy," Pogo warned, "and he is us". I asked Dr. Masson about an equally prophetic book with a similiar message:

CURWOOD: You know thirty years ago Rachel Carson wrote a book, Silent Spring. What do you think she would say about this if she were here today?

MASSON: She had the foresight to see what was going on at that time, and to see that it's been magnified over the last 30 years. Not knowing her, but , in her writings she doesn't seem to be too facetious but I think she could easily say, "I told you so."

(Sound of an alligator call and rainfall)

CURWOOD: And a gentle, almost silent rain falls on the Okefenokee Swamp, and a gator's roar fills the air with an eternal call.

And for this week, that's Living On Earth.



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