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Excised embryos of the grass shrimp (Palaemonetes pugio) were exposed to single pulse concentrations of selected pollutants for 4 days. The following toxicity endpoints were monitored: rate of embryonic development, embryo mortality, and types of embryo malformation. Each endpoint exhibited concentration—response relationships which were modified by the embryonic age (hence stage) at which exposure commenced. Developmental retardation of up to 3 days was effected by phenol at 0.01% (V/V) and complete developmental arrest occurred at 0.05% and 0.1% (V/V). Similarly for methylene chloride, developmental retardation of 1–3 days were observed at 0.1% (V/V) depending on the age of the embryos at the start of the tests. At concentrations of > 0.5% (V/V), there was complete developmental arrest irrespective of the embryonic stage. With ethanol, developmental retardation of between 1 and 2 days resulted when embryos in stages 3–6 were exposed to 1 and 1.5% (v/v). Developmental retardation of 2 days was consistently observed at an exposure concentration of 2% (v/v) for all embryonic stages tested. Complete developmental arrest occurred at 2.5 and 5.0 % (v/v) when stages 3–6 were exposed. For potassium dichromate, exposure of stages 3–6 embryos to nominal concentrations of 50 – 500 mg/L did not produce any effect (except for tests with stage 6 which showed a 1 day delay). At 1 000 mg/L there was retardation of 0.5 –1 day, while 2 000 mg/L resulted in complete arrest. The morphological abnormalities of the embryos are described. The ecological significance of these findings and implications for the development of short-term toxicity tests using grass shrimp embryos are discussed.
grass shrimp, developmental arrest, embryo malformation, toxicants, aquatic toxicology, developmental retardation
Associate professor and director, Morgan State University, Baltimore, MD