Decrease in DDT residues in young salmon after forest spraying in New Brunswick

Abstract

DDT residues were measured in Atlantic salmon parr ( Salmo salar L.) collected from streams which had been subjected to aerial forest spraying in preceding months or years. Six months after spraying, surviving salmon had averages of 0·5 to 2 ppm DDT in their whole bodies, and 2 to 4 ppm DDE. Slightly higher concentrations have been associated with declines in fisheries in other places. In 2·5 years or less after spraying, DDT decreased to low or undetectable concentrations. DDE, the common metabolite, decreased slowly during 12·5 years. The relation of total amount (y) in ppm, of all DDT residues, to the time (t) in years since the river was last sprayed, was simply described as y= 1·91 t Total residue showed little or no relation to other aspects of spray history, such as strength of DDT mixture applied, or total number of yearly sprayings received by the river. Salmon parr from a Nova Scotia river with no spray-history had undetectable or trace amounts of DDT residues, a relatively uncommon finding in recent years.