Paper pulp and fish kills.

In the mid-1980s, Swedish scientists found stunted rates of growth and reproduction among fish breeding near papermaking plants in the Gulf of Bothnia, which separates Sweden and Finland. They correlated these effects with adsorbed organic halogens, a class of compounds present in pulp and paper mill wastes.

Since these compounds are rich in chlorine, the scientists assumed that the chlorinated compounds had adversely affected the fishes' health.

While environmental agencies in Sweden, Finland, and Denmark moved ahead to lessen concentrations of chlorinated pollutants dumped into marine waters, researchers in the United States and Canada continued looking for the specific culprit behind the fishes' ills.

B. Kent Burnison, a microbiologist at Canada's National Water Research Institute in Burlington, Ontario, and his colleagues now report that chemicals other than the chlorinated ones appear to be harming the fish.

Examining various chemicals present in effluents from papermaking, they found that wastewater from "kraft pulping mills" harmed the fish most seriously--even though it contains no chlorinated compounds. High concentrations of certain compounds extracted from the wood itself proved toxic to fish, regardless of chlorine's presence.

Burnison therefore concludes that simply targeting the discharge of chlorinated compounds is "unlikely" to ease fish suffering.