The research, conducted by biologists with the Canadian Wildlife Service of Environment Canada, is part of a growing body of international evidence indicating that many species are suffering from exposure to so-called gender-bending chemicals, industrial pollutants that have been found to mimic sex hormones.
These changes so far have been observed most in fish, but researchers have noted genital abnormalities in other species ranging from Florida panthers to alligators.
The turtles with abnormal penis size were found in Ontario: in the Detroit River near Windsor, the St. Clair River near Sarnia, and the harbour of Wheatley, a small fishing community on Lake Erie. All three sites are pollution hot spots.
Snapping turtles in cleaner environments, such as Algonquin Park and in a marsh near Midland, Ont., lacked the abnormalities.
The turtles that produced egg yolk protein were found around Wheatley. That protein is normally "only produced by females when they're laying eggs," said Kim Fernie, a biologist with the wildlife service, who was part of the team conducting the research. "You would not expect to find it in a male turtle."
Additional work by the scientists on herring gulls discovered the egg protein in some male birds along the Detroit River.
Female reproductive characteristics in male turtles and birds are a sign of contact with chemicals that act like female sex hormones.
More than 50 synthetic compounds have been found to affect hormone systems, among them dioxins, polychlorinated biphenyls, pesticides and some plastics.
Sarnia has Canada's largest concentration of petrochemical plants; the Windsor-Detroit area is heavily industrialized. Wheatley is in an agricultural area.
Young turtles showed other biological abnormalities, such as impaired thyroid function, at all three sites.
Researchers say they don't know yet which compounds caused the developments they observed.
"As this is relatively new, we don't know what is causing that yet," said Laird Shutt, a toxicologist with the wildlife service who conducted the research on the gulls.
Ms. Fernie said her results are preliminary, and she has done more field work trying to verify the extent of the turtle abnormalities. But the newer samples are being analyzed, and results are not expected until next year because of laboratory backlogs at Environment Canada's testing facilities.
"We did find these changes in the first year, but is that going to be consistent over multiple years or not, I don't know at this point," she said.
Environment Canada has issued a summary of the research on its website but has not publicized the findings.
Mr. Shutt said the levels of egg yolk protein he observed in male birds were not high enough to affect their chances of survival.
However, environmentalists said the research is worrisome because chemicals powerful enough to affect hormones are a potential health threat.
"As soon as you're disrupting hormone systems, there is a chance of cancer; there is a chance of other diseases," said Bailey Mylleville, a spokesman for Great Lakes United, an environmental group based in Buffalo.
In the turtle research, Ms. Fernie said she calculated penis size by measuring the distance between the reptile's shell and anus, and from that made an estimate of penis length.
She would not say how much the organs were reduced in size. Taking actual penis measurements would have required killing the turtles and opening up their shells.
The research also found excessive production of some liver enzymes in young snapping turtles and adult herring gulls from the Detroit River area.
They said high production of the enzymes occurs when animals are exposed to dioxin-like substances.
At Wheatley, the researchers were unable to find any signs of reproductive activity by the snapping turtles.
Along the St. Clair River, scientists found less hatching success than at the non-polluted sites.
Gulls from the Detroit River showed impaired immune systems. There were also high numbers of dead gull embryos in nests along the Detroit River and in western Lake Erie, compared to cleaner sites, and a single male bird with what the Environment Canada research summary called a "significantly feminized reproductive tract."