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Toxic Contaminants in the Environment: Persistent Organochlorines

Technical Supplement: Eggshell thinning (additional info)

DATA SOURCES
Environment Canada, Canadian Wildlife Service, Ontario Region, D.V. Weseloh, personal communication.

Weseloh, D.V., S.M. Teeple, and M. Gilbertson. 1983. Double-crested Cormorants of the Great Lakes: egg-laying parameters, reproductive failure, and contaminant residues in eggs, Lake Huron 1972–73. Canadian Journal of Zoology 61(2):427–436.

Environment Canada, Department of Fisheries and Oceans, and Health and Welfare Canada. 1991. Toxic Chemicals in the Great Lakes and Associated Effects. Vol. 2, p. 590.

DATA COLLECTED
a) DDE concentrations in Double-crested Cormorant eggs, measured in mg/kg wet weight (data taken from Table 1 of this technical supplement).

b) Eggshell thickness in millimetres (mm).

GEOGRAPHICAL COVERAGE
Double-crested Cormorant colonies of the North Channel of Lake Huron, Ont.

DATA COLLECTION PERIOD
Discontinuous time series from 1971 to 1995.

METHODS
After emptying the egg of its contents, the eggshell was rinsed thoroughly with water and allowed to air dry for three months at room temperature. The thickness of the eggshell (plus attached membranes) was measured at three points around the girth of the egg with a ball micrometer (accurate to 0.001 mm), and a mean was determined.

DATA PRESENTATION
The data for Figure 3 are shown in Table 4.

Table 4. DDE concentration and percent eggshell thinning in Double-crested Cormorant eggs