Pollutant Waits to Smite Salmon at Sea


Science News Magazine Vol 155 #19 May 8 1999

Canadian scientists have identified the likely culprit behind some historic, regional declines in Atlantic salmon. The researchers find that a near-ubiquitous water pollutant can render young, migrating fish unable to survive a life at sea.

Heavy, late-spring spraying of forests with a pesticide laced with nonylphenol during the 1970s and '80s was the clue that led the biologists to unmask that chemical's role in the transitory decline of salmon in East Canada. Though these sprays have ended, concentrations of nonylphenols in forest runoff then were comparable to those in the effluent of some pulp mills, industrial facilities, and sewage-treatment plants today. Downstream of such areas, the scientists argue, salmon and other migratory fish may still be at risk.

Nonylphenols are surfactants used in products from pesticides to dishwashing detergents, cosmetics, plastics, and spermicides. Because waste-treatment plants don't remove nonylphenols well, these chemicals can build up in downstream waters (SN: 1/8/94, p. 24).

When British studies linked ambient nonylphenol pollution to reproductive problems in fish (SN: 2/26/94, p. 142), Wayne L. Fairchild of Canada's Department of Fisheries and Oceans in Moncton, New Brunswick, became concerned. He recalled that an insecticide used on local forests for more than a decade had contained large amounts of nonylphenols. They helped aminocarb, the oily active ingredient in Matacil 1.8D, dissolve in water for easier spraying.

Runoff of the pesticide during rains loaded the spawning and nursery waters of Atlantic salmon with nonylphenols. Moreover, this aerial spraying had tended to coincide with the final stages ofsmoltification--the fish's transformation for life at sea.

To probe for effects of forest spraying, Fairchild and his colleagues surveyed more than a decade of river-by-river data on fish. They overlaid these numbers with archival data on local aerial spraying with Matacil 1.8D or either of two nonylphenol-free pesticides. One contained the same active ingredient, aminocarb, as Matacil 1.8D does.

Most of the lowest adult salmon counts between 1973 and 1990 occurred in rivers where smolts would earlier have encountered runoff of Matacil 1.8D, Fairchild's group found. In 9 of 19 cases of Matacil 1.8D spraying for which they had good data, salmon returns were lower than they were within the 5 years earlier and 5 years later, they report in the May Environmental Health Perspectives. No population declines were associated with the other two pesticides.

The researchers have now exposed smolts in the laboratory to various nonylphenol concentrations, including some typical of Canadian rivers during the 1970s. The fish remained healthy--until they entered salt water, at which point they exhibited a failure-to-thrive syndrome.

"They looked like they were starving," Fairchild told Science News. Within 2 months, he notes, 20 to 30 percent died. Untreated smolts adjusted normally to salt water and fattened up.  Steffen S. Madsen, a fish ecophysiologist at Odense University in Denmark, is not surprised, based on his own experiments.

To move from fresh water to the sea, a fish must undergo major hormonal changes that adapt it for pumping out excess salt. A female preparing to spawn in fresh water must undergo the opposite change. Since estrogen triggers her adaptation, Madsen and a colleague decided to test how smolts would respond to estrogen or nonylphenol, an estrogen mimic.

In the lab, they periodically injected salmon smolts with estrogen or nonylphenol over 30 days, and at various points placed them in seawater for 24 hours. Salt in the fish's blood skyrocketed during the day-long trials, unlike salt in untreated smolts. "Our preliminary evidence indicates that natural and environ- mental estrogens screw up the pituitary," Madsen says. The gland responds by making prolactin, a hormone that drives freshwater adaptation.

Judging by Fairchild's data, Madsen now suspects that any fish that migrates between fresh and salt water may be similarly vulnerable to high concentrations of pollutants that mimic estrogen.


Brown, S.B. . . . and W.L. Fairchild. 1998. Effects of water-borne 4-nonylphenol on Atlantic salmon (Salmo salar) smolts. SETAC 19th Annual Meeting. November.

Charlotte, N.C.

Fairchild, W.L., et al. 1999. Does an association between pesticide use and subsequent declines in catch of Atlantic salmon (Salmo salar) represent a case of  endocrine disruption? Environmental Health Perspectives 107(May):349.

Further Readings:

Madsen, S.S., A.B. Mathiesen, and B. Korsgaard. 1997. Effects of 17b-estradiol and 4-nonylphenol on smoltification and vitellogenesis in Atlantic salmon (Salmo salar).

Fish Physiology and Biochemistry 17:303.

Madsen, S.S., and B. Korsgaard. 1991. Opposite effects of 17b-estradiol andcombined growth hormone-cortisol treatment on hypo-osmoregulatory performance in sea trout presmolts, Salmo trutta. General and Comparative Endocrinology 83:276.

______. 1989. Time-course effects of repetitive oestradiol-17b and thyroxine injections on the natural spring smolting of Atlantic salmon, Salmo salar L. Journal of Fish Biology 35:119.

Raloff, J. 1997. Hormone mimics get harder to pigeonhole. Science News 151(April 26):254.

______. 1994. Sperm changes linked to drinking water. Science News 145(Feb. 26):142.

______. 1994. The role of chlorine-and its future. Science News 145(Jan. 22):59.

______. 1994. That feminine touch. Science News 145(Jan. 22):56.

______. 1994. The gender benders. Science News 145(Jan. 8):24.


Wayne L. Fairchild

Fisheries and Oceans Canada

Gulf Fisheries Centre

P.O. Box 5030

343 Archibald Street

Moncton, N.B. E1C 9B6


Steffen S. Madsen

Odense University

Institute of Biology

Campusvej 55

DK-5230 Odense M