. The Canadian field-naturalist. Natural history. 118 The Canadian Field-Naturalist Vol. 84 Table 1.—DDT and DDD residue levels in ppm wet weight before and after PCB separation in tissues and eggs of female California Gulls. Mean DDT Mean DDD Tissue No. Sam. sample Before After % Before After % Abdom. fat 10 28 3 Ovary 10 16 16 Liver 10 3 13 Brain 10 5 4 Eggs 10 31 ND 0 ND = none detected = < ppm bation in the first week of May, 1969. Gull tissues and eggs were analyzed
. The Canadian field-naturalist. Natural history. 118 The Canadian Field-Naturalist Vol. 84 Table 1.—DDT and DDD residue levels in ppm wet weight before and after PCB separation in tissues and eggs of female California Gulls. Mean DDT Mean DDD Tissue No. Sam. sample Before After % Before After % Abdom. fat 10 28 3 Ovary 10 16 16 Liver 10 3 13 Brain 10 5 4 Eggs 10 31 ND 0 ND = none detected = < ppm bation in the first week of May, 1969. Gull tissues and eggs were analyzed for the purpose of comparing pesticide residue levels between arriving and incubating gulls as well as between incubating females and their own eggs. One type of tissue analysed was fat, taken from the abdominal cavities of the gulls. The contents of eggs and bird tissues were stored in glass jars and preserved by freezing. Laboratory Analysis For extraction of the organochlorine residues. the frozen egg sample was thawed out and homogenized in a Waring Blender. An aliquot (2-5 g) of the blend was weighed into a 50 ml beaker to the nearest milligram and dried in a vacuum oven at 45 °C with slight vacuum to constant weight (approximately 36 hours needed). The per cent moisture was then calculated from the difference in weights. After constant weight was obtained, the dried sample was broken up by adding 5-10 g an- hydrous Na:: SOi and grinding with a flattened glass rod. The dried material was removed from the sides and bottom of the beakers by grinding and scraping. The mixture was poured into a Soxhlet thimble and the beaker rinsed several times with ether : n-hexane (1:1). A glass wool plug was used to cover the sample in the thimble which was then extracted in a Soxhlet apparatus for 2 hours, using about 150 ml of 1:1 ether-hexane mixture at a rate of 10 siphonings per hour. After extraction, the solvent was removed in a flash evaporator and the dried flask was weighed. T
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