Effects of ammonium perchlorate, 4(TERT-OCTYL) phenol and their mixture on Zebrafish (Danio rerio)

The toxic effects of ammonium perchlorate AP and 4-(teri-octyl) phenol OP on zebrafish (Danio rerio) embryo/larvae were examined. AP inhibits thyroid function and OP is a weak xenoestrogen. Because reproduction and development occur under precise physiological regulation, use of chemicals during the perihatch period helps understand biological and ecological effects posed by the exposure to contaminant mixtures. Fertilized eggs were collected from unexposed parents and exposed to sublethal nominal concentrations of AP (8 X 10-8 M), OP (1 X 10-8 M) or their mixture. Exposures occurred during three periods: 0 to 3 days (embryo), 3 to 6 days (larval), and 0 to 6 days (embryo-larval) after fertilization. Hatching and mortality were determined through day 30. Control mortality by day post fertilization (dpf) 30 was 55.6 %. OP treatment had mortalities of 85.3 %, embryo; 77.3 %, larval; and 78 %, embryo-larvae on dpf 30. AP treatment had mortalities of 84.4 % (embryos), 82.1 % (larvae), and 63.8 % (embryolarvae) on dpf 30. The mixture treatment yielded mortalities of 83.3 % (embryos), 75 % (larvae), and 93.3 % (embryo-larvae) on dpf 30.

The swimming behavior involved the response to chasing in a Petri dish over a minute period on dpf 6; during the initial 30 seconds, the zebrafish exposed to OP as embryo/larvae were the only group to show effects by having a decreased swimming performance; this is also true for the final 30 seconds. Exposure duration had an effect on escape behavior; for the zebrafish exposed to AP and OP, the embryo/larvae exposed organisms were the most affected; the mixture exposed organisms did not show an effect. Reproductive success was assessed for fish that survived to Day 180; no significant differences were found in egg production, egg size, or fertilization rates between treatments when three females and two males were set to spawn weekly for three weeks. Similar effects were found in the exposure period comparisons for egg size; there was reduced fertilization rate in fish that were exposed as embryos to OP and MIX, and the total egg production was affected in fish exposed as embryos to OP