Evidence for a causal link between exposure to an insecticide formulation and declines in catch of Atlantic salmon

We report a case study showing relationships between historical insecticide applications (1973 to 1990) of an aminocarb formulation (Matacil(R) 1.8D) containing 4-nonylphenol (4-NP) and catch data for Atlantic salmon (Salmo salar) populations. To address the hypothesis that Matacil(R) 1.8D caused reductions in Atlantic salmon catch, seven epidemiological criteria are used to evaluate causality between the stressor and effect. These criteria include: strength of association; consistency of association; specificity of association; time order; biological gradient; experimental support; and biological plausibility. We conclude that the general weight-of-evidence supporting the seven epidemiological criteria is consistent with a causal relationship between declines in salmon catch and Matacil(R) 1.8D exposure during parr-smolt transformation (PST). If the effects exerted by 4-NP are due to its activity as a weak estrogen, then hormonal activity stemming from other sources (e.g., domestic sewage, agricultural, industrial) might influence present day salmon populations.