 historical aerial applications of the insecticide matacil 1.8d provide an opportunity to look for potential effects of the endocrine disrupting compound 4-nonylphenol ( 4-np ) on atlantic salmon ( salmo salar ) populations . 
 matacil 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 atlantic canada to control damage from the spruce budworm ( choristoneura fumiferana ) . after spraying , 
 estimated concentrations of 4-np in water fell within a range in which estrogenic effects might be anticipated . 
 the spraying coincided with final stages of smolt development in salmon . 
 salmon catch data were evaluated considering effects on survival of the smolt stage . 
 there was a significant negative relationship between the returns of salmon and the proportion of tributaries sprayed within the restigouche river drainage basin in 1977 . 
 there was also a broader event of unusually heavy salmon smolt mortality in 1977 , which contains a significant relationship indicating that where matacil 1.8d spraying occurred , the smolt mortality increased . for 16 rivers exposed to spraying between 1973 and 1990 , a significant proportion ( p<0.005 ) of the lowest salmon catches coincided with matacil 1.8d spraying . 
 a decline coinciding with the use of matacil 1.8d was also apparent in blueback herring ( alosa aestivalis ) catches in new brunswick . because similar relationships were not evident for matacil 1.8f or fenitrothion , neither of which were formulated with 4-np , we hypothesize that the 4-np in matacil 1.8d was the causal agent 
 . concentrations of 4-np described here are within current ranges encountered in industrial effluents and municipal sewage outfalls.imagesfigure 1figure 2figure 3 
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