River of no return

 作者:梁堪     |      日期:2019-03-08 06:10:02
By Debora MacKenzie A CHEMICAL that mimics oestrogen may be responsible for the disappearance of North America’s Atlantic salmon, whose stocks have plummeted by 90 per cent over the past 20 years despite the efforts of conservationists. Biologists think that “gender-benders” in sewage and industrial effluent could be harming fish. In March, the European Commission’s scientific committee on toxicity said such compounds could pose a threat. The commission wants to study 500 of them to see if they should be banned. The effects of oestrogen mimics have mainly been seen in laboratory studies. However, Wayne Fairchild and colleagues at the Canadian Department of Fisheries and Oceans in Moncton, New Brunswick, have now shown that the number of mature salmon returning to rivers is closely related to the amount of a chemical, 4-nonylphenol, sprayed on them as young fish (Environmental Health Perspectives, vol 107, p 349). Salmon are born in rivers, migrate to sea for one to three years, then return to their native streams to spawn. In various years between 1973 and 1990, areas containing salmon streams in Atlantic Canada were sprayed with an insecticide called aminocarb to kill spruce budworm, a timber pest. One formulation, Matacil 1.8D, included 4-nonylphenol as a surfactant. Fairchild’s team compared the numbers of adult salmon returning to different tributaries of the Restigouche River in New Brunswick in 1977 with the amounts of Matacil spray washing into the streams when those fish were preparing to go to sea. More spray in the rivers resulted in fewer mature salmon coming back in later years. “No one had thought to look two or three years later for an effect of spraying,” says Fairchild, “The relationship was so close, we thought we’d made a mistake.” In years when the area was sprayed with a formulation of aminocarb that did not include 4-nonylphenol, however, there was no correlation between the amount of spray and the number of salmon that later returned to spawn. When they move to seawater, salmon undergo profound changes, some under the control of oestrogen. Steffen Madsen at Odense University in Denmark has shown that this process, called smoltification, is impaired in salmon fed or injected with oestrogens, including nonylphenols—and that such smolts are more likely to die when they reach salt water. “The result is intriguing,” says Fred Whoriskey, fisheries scientist for the Atlantic Salmon Federation, a conservation group in St Andrews, New Brunswick. Spraying with 4-nonylphenol has been discontinued in recent years, but Fairchild has evidence that the chemical is still present at similar concentrations from sewage, pulp and textile plant run-off. He believes oestrogens “could be why, even in rivers where they have made real improvements, salmon are still going to sea,