Gender Blender

Why Have Some Male Walleye in the Mississippi Stopped Producing Sperm?

The channel that carries treated sewage from the Twin Cities to the Mississippi River is not a bad-looking stretch of water. From its source at the Metro Sewage Treatment Plant across the river from the Downtown St. Paul Airport, it runs for about a quarter mile. Stately elms and oaks line the banks. There is a faint sweet smell in the air, but it doesn't stink. And surprisingly, the channel's waters, which consist entirely of treated effluent from the plant, are clearer than the Mississippi's--a result of a filtration process that removes sediments.

Because the effluent is always warm, it also attracts a lot of creatures. This time of year, cormorants, herons, and kingfishers busily hunt schools of shad. And mallards dabble in the shallows. Walleye, the state's most prized game fish, are also known to periodically roam the channel. "Even in the winter, the effluent remains at 62 degrees. That's a comfortable temperature for walleye," notes Ira Adelman, a professor with the University of Minnesota's Department of Fisheries and Wildlife. "A lot of fishermen will anchor right in the middle of the channel." Adelman should know: For the past two years, he has been visiting the channel in pursuit of walleye.

Unlike conventional hook-and-line fishermen, Adelman employs no-fail gear in his efforts to land the notoriously wily fish: a 220-volt generator, a transformer, and, connected to that, two long rods to pump the current into the water. The electrical field attracts the fish, which are then stunned and easily netted. Adelman is not capturing the walleye for their prized fillets, however ("I wouldn't eat anything out of that water," he says). He is hoping to answer a confounding question: Is the effluent somehow "feminizing" the male walleye and affecting their ability to reproduce?

So far, it appears the answer is yes. Suspicions about the gender-bending qualities of effluent first surfaced in the mid-Nineties after Department of Natural Resources scientists detected a female egg protein in the blood of male walleye taken from the St. Paul channel. The presence of the protein indicated that the fish were being exposed to an endocrine-disrupting compound (EDC). A growing source of environmental worry, EDCs are thought to interfere with sexual processes, particularly in male animals, by mimicking the hormone estrogen. In recent years, studies have revealed measurable quantities of EDCs in both sewage and agricultural run-off.

So two years ago, after receiving a $200,000 research grant from the Metropolitan Council (which operates the Metro Sewage Treatment Plant), Adelman and a group of U of M researchers initially set out to study walleye sperm for any signs of abnormality. Those plans were scrapped when it was discovered that the male fish were no longer producing sperm. "We were quite surprised," Adelman says. A microscopic examination of the fish turned up other peculiarities, including an "intersex" walleye, which displayed both male and female anatomical characteristics.

The culprit? Probably an EDC, Adelman says, although he is uncertain about its exact makeup; many different chemicals have been identified as EDCs. Human estrogen, the estrogenic compounds in birth-control pills, and even a common additive to laundry detergent are suspects, but there are as many as 20 other common EDCs found in wastewater. "This is a soup," Adelman says of the effluent. "There's a lot of stuff in there. But it's obvious from the high levels of vitellogenin [the female egg protein] in the walleye that they're being exposed [to EDCs]."

It is also possible, Adelman acknowledges, that the EDCs are a red herring. Vitellogenin has also been found in male carp collected from the channel, yet those fish are still producing normal sperm. Adelman says it is possible the male walleye are sterile because they are spending too much time in warm water. Previous studies have shown that male perch, a close relative of walleye, require a "winter chill period" to trigger sperm production.

Next spring Adelman plans to resolve the issue by studying male walleye who inhabit warm water discharges near a power plant in Bayport. If those fish produce normal sperm, which Adelman believes is likely, the warm-water theory would be eliminated. "I'm in favor of the EDC hypothesis," he says. "These walleye have such high levels of vitellogenin--much higher than the carp. That seems like pretty good, if not absolutely confirming, evidence [that EDCs are to blame]."

Meanwhile, the task of identifying the various EDCs in the St. Paul channel's sewage is proving difficult. "We're looking at some very minute exposures," says Deborah Swackhamer, an environmental chemist at the U who has been studying effluent as part of the Met Council grant. "These chemicals are in very low concentrations--parts per trillion. Because of that, it's hard to even tell what part of the effluent is estrogenic." Swackhamer is quick to point out that although concentrations of EDC in the water are low, that doesn't mean they aren't affecting the walleye's hormonal systems.

Additionally, it is still an open question whether the presence of EDCs in the environment poses a problem for human health. In the influential 1996 tome Our Stolen Future, researcher Theo Colborn linked EDCs to a variety of gender abnormalities in animals worldwide. Male alligators in Florida's Lake Apopoka, exposed to EDCs as a result of a pesticide spill, were found to have undersize penises and were unable to reproduce. Beluga whales near the St. Lawrence Seaway were showing similar symptoms. Colborn and others have warned that EDCs may also be taking a more understated but nevertheless significant toll on the human population. Testicular cancer, breast cancer, and shifting gender ratios in new births have all been cited as possible outcomes of EDC exposure.

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