Does an association between pesticide use and subsequent declines in catchof Atlantic salmon (Salmo salar) represent a case of endocrine disruption?

Historical aerial applications of the insecticide Matacil 1.8D provide an o pportunity to look for potential effects of the endocrine disrupting compou nd 4-nonylphenol (4-NP) on Atlantic salmon (Salmo salar) populations. Matac il 1.8D contained the carbamate insecticide aminocarb, with 4-NP as primary solvent. Between 1975 and 1985 Matacil 1.8D was applied to forests in Atla ntic Canada to control damage from the spruce budworm (Choristoneura fumife rana). After spraying, estimated concentrations of 4-NP in water fell withi n a range in which estrogenic effects might be anticipated. The spraying co incided with final stages of smelt development in salmon. Salmon catch data were evaluated considering effects on survival of the smelt stage. There w as a significant negative relationship between the returns of salmon and th e proportion of tributaries sprayed within the Restigouche River drainage b asin in 1977. There was also a broader event of unusually heavy salmon smel t mortality in 1977, which contains a significant relationship indicating t hat where Matacil 1.8D spraying occurred, the smolt mortality increased. Fo r 16 rivers exposed to spraying between 1973 and 1990, a significant propor tion (p<0.005) of the lowest salmon catches coincided with Matacil 1.8D spr aying. A decline coinciding with the use of Matacil 1.8D was also apparent in blueback herring (Alosa aestivalis) catches in New Brunswick. Because si milar relationships were not evident for Matacil 1.8F or fenitrothion, neit her of which were formulated with 4-NP, we hypothesize that the 4-NP in Mat acil 1.8D was the causal agent. Concentrations of 4-NP described here are w ithin current ranges encountered in industrial effluents and municipal sewa ge outfalls.