Zero to 24 hour old specimens of Daphnia were exposed to 10 ppm 3-amino-1,2,4-triazole at 24° C until immobilized. The most consistent alteration in cell structure was expressed by the mitochondria especially those of muscle fibers. Not all muscle cells within a single animal nor all mitochondria within a single cell were affected equally. The most common alteration observed was folding of the outer membrane. This was accompanied by organelle swelling and a reduction in electron density of the ground matrix and number of cristae.
In addition other cytotoxic effects were observed. These included general tissue swelling, disarrangement of myofilaments and dissociation of membranes. Mobile 0-24 hr old daphnids which were exposed to the herbicide for up to 15 hr showed no cell or organelle damage regardless of length of exposure.
Data from acute static experiments suggest that the time of immobility is closely related to molt for 0-24 hr juveniles.
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