How paper mill wastes may imperil fish.

For years, biologists have observed that some fish downstream of pulp and paper mills reach sexual maturity much later than normal. For the white sucker, a distant relative of the salmon, that delay can be up to 2 years, "effectively reducing its lifetime fecundity by almost 50 percent," notes Glen J. Van Der Kraak of the University of Guelph in Ontario.

For lake whitefish, another commercially important species, "we have no indication of natural reproduction occurring," he says.

Other symptoms--such as exceptionally small reproductive organs and abnormally low concentrations of sex hormones circulating in the blood--suggested that something had greatly perturbed the fish's hormone systems.

Veterinary pathologists had traced similar symptoms in sheep and pigs to estrogenlike compounds in the plants they ate. So Van Der Kraak and Deborah L. MacLatchy, now at the University of New Brunswick in Saint John, looked into a tree-derived estrogen that researchers with Environment Canada had identified in paper mill effluent.

They injected goldfish--the aquatic equivalent of laboratory rats-- with this beta-sitosterol, then assayed each animal's blood a few days later. In the just-issued October Toxicology and Applied Pharmacology, they report that the pollutant significantly depressed concentrations of estrogen, the primary female sex hormone, and testosterone, the primary male reproductive hormone, in both male and female fish.

The new study showed that sitosterol affects "predominantly. . . the gonads--the ovary and testis," explains Van Der Kraak. "And this pattern tends to parallel what we see in wild fish populations." His team has begun experiments to evaluate whether sitosterol can also affect gonad size.

"I don't think beta-sitosterol is going to explain the entire picture," Van Der Kraak cautions. Fish downstream of pulp and paper operations frequently exhibit detoxifying liver enzymes. "And we're not seeing that with beta-sitosterol," he points out. "So there must be other chemicals the fish are exposed to--such as some chlorinated organics--[activating] those enzymes."

Certain chlorinated organic compounds--especially dioxins--not only trigger these detoxifying enzymes but also act as hormones, impairing the reproductive development of mammals (SN: 7/15/95, p.44). Moreover, chlorine bleaching of wood pulp generates dioxins (SN: 5/12/90, p.303).

Van Der Kraak doubts, however, that such agents pose the primary endocrine risk from paper-making operations. "We've sampled fish before and after normal mill shutdowns--such as for annual holiday maintenance--and we see a recovery [of normal hormone concentrations] in wild fish. This was one clue that dioxins weren't the causative agents." These long-lived chemicals would not have disappeared during the mill shutdowns.

"That plants would develop compounds that are reproductively active in animals is perfectly understandable" as a strategy for keeping predators in check, maintains Louis J. Guillette Jr. of the University of Florida in Gainesville. Though most predators would develop a tolerance to these hormone mimics, Guillette says, it would take generations. Thus, when animals such as these fish encounter what for them is a novel phytoestrogen, they may suffer dramatically--at least initially.

Indeed, says Peter Thomas of the University of Texas Marine Science Institute in Port Aransas, "the importance of the [Guelph study] is that it's showing that we should be concerned about other components of effluent, not just dioxins."

The study may also point to a solution to the fish's problems, he says. "Because most of these phytoestrogens are on the outside of plants, where insects can get to them, [industry] might solve this problem by debarking the wood before they ground it up."