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Pulp Mill Effluent and Fish Don't Mix (Well)

Canadian Pulp Mill

A Canadian pulp mill.

University of Minnesota scientists were the first to find that fish in the Duluth-Superior Harbor are exposed to chemicals that can interfere with their sex lives. They found that chemicals, called endocrine disrupters, are present in the wastewater from industries and homes that enters the Western Lake Superior Sanitary District (WLSSD).

Wastewater treatment plants like WLSSD do not have technologies in place to remove these chemicals because the findings are rather new and no technologies exist yet.

The problem with endocrine disrupters is that they mimic hormones (such as estrogen and testosterone) in the bodies of some animals, including humans, that control sexual development and reproduction.

Dalma Martinovic, currently a postdoctoral fellow at the Environmental Protection Agency (EPA) Laboratory in Duluth, described the results of her Sea Grant-funded research in April during a presentation at the Minnesota Pollution Control Agency. Martinovic and University of Minnesota Professor Peter Sorensen found that male fish exposed in the lab to WLSSD-treated wastewater effluent demonstrated a reduced ability to secure mates when competing with unexposed fish. They also found the presence of an egg yolk protein usually only produced by female fish in the blood of male fish.

Martinovic described the effluent as "quite estrogenic" and that it could have harmful effects on animals.

Where could these endocrine disrupters be coming from? Studies in North America and Europe have pinpointed pesticides, medicines, detergents, plasticizers, and effluent from pulp and paper mills. Papermaking is an important industry in Duluth, and its leftovers comprise over half of the waste stream entering WLSSD.

Scientists in neighboring Canada have been studying the effects of treated pulp mill wastewater on fish. Several gave presentations recently at the Duluth EPA Lab.

Mark McMaster with Environment Canada assessed fish populations in Jackfish Bay, a northern bay in Lake Superior opposite the Slate Islands. McMaster and his crew found that although wild fish exposed to treated pulp mill wastewater grew faster and were fatter, they had reduced levels of reproductive hormones and smaller sexual organs (ovaries or testes) than unexposed wild fish. It also took the fish about two years longer to reach sexual maturity.

They found these same conditions in fish across Canada in rivers with pulp mills. McMaster said the different processes the pulp and paper mills used didn't seem to matter fish all showed the same results.

Joanne Parrott, also with Environment Canada, said that lab minnows exposed to effluent grew well and looked great. "But they had smaller gonads and the males and females exhibited mixed sexual characteristics, which got more pronounced with higher levels of effluent exposure," Parrott said.

Female fish exposed to a concentration of 10 percent effluent or more produced no eggs. Parrott said that fish in the wild in rivers below the effluent outfall are typically exposed to ranges from one to 15 percent effluent.

"Why haven't we found a solution despite 18 years of research?" Mark Hewitt with Environment Canada asked as he discussed the cause-and-effect relationship of pulp mill effluent on fish reproduction in Canada. He attributes this to the complexity and sources of the chemicals, the fish's varying biological responses, and the difficulties inherent in comparing wild and laboratory fish.

He studied 10 mills and, like McMaster, didn't find a correlation between type of mill process or effluent treatment and effects on fish. So he went inside the mills. In the fresh slurry, Hewitt and his crew discovered that the wood itself is the source of the problem. They found five or six chemicals that are plant estrogens. These chemicals change quickly, so they aren't easily found later, when the effluent exits the mills.

Back outside the mills, the researchers examined white suckers, which had been exposed to mill effluent for four days. They found that the chemicals rapidly accumulate inside the fish's liver.

Hewitt said these findings have led Canada to develop a national project supported by the paper mills to remove these natural wood compounds from their effluent. They're on step two of a five-part process.

"We're working together to find solutions to a real-world problem," Hewitt said. "We're hoping this will serve as a model for other complex problems like metal mining and global warming."

Cooperation is made easier through a group called PAPTAC (Pulp and Paper Technical Association of Canada www.paptac.ca). This nonprofit group is composed of paper mills, universities, government departments, and consultants, and offers a mechanism for projects like the one Hewitt describes.

Another researcher, Rodney Johnson from the Duluth EPA Lab, has been looking into the effects that exposure to endocrine disrupters has on successive generations of fish (in this case, medaka, which look like guppies). His lab tests have shown that exposure to endocrine disrupters causes increased sensitivity in descendants. By the third generation, fish exhibited effects (such as sex change and physical characteristics of the opposite sex) at lower concentrations of the chemicals than would have affected their grandparents.

Johnson calls the results "disconcerting," and says they have implications for evaluating the risks of having these chemicals in the environment. "I almost hope the results aren't repeatable by other scientists," he said.

For more information on Martinovic and Sorensen's research, order Temporal Variation in the Estrogenicity of a Sewage Treatment Plant Effluent and its Biological Significance, (JR 535). For information about fish exposed to sewage treatment plant effluent, order JR 545.

By Marie Zhuikov
August 2008

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