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Potassium nitrate

Endpoint:
fish short-term toxicity test on embryo and sac-fry stages
Type of information: experimental study
Adequacy of study: supporting study
Study period: 2008
Reliability: 2 (reliable with restrictions)

Details on test organisms: TEST ORGANISM
- Common name: Fathead minnow
- Source: Fertilized fathead minnow eggs were collected in-house from fathead minnow breeding pairs.

Nominal and measured concentrations:
Five concentrations and a control were tested in duplo. However, it is not reported what concentrations were tested.

Details on test conditions:
These toxicity tests estimated the test chemical concentration that reduced hatch rate, fry survival, and fish weight over 32 d. Fertilized fathead minnow eggs were collected in-house from fathead minnow breeding pairs. When enough eggs were spawned on the same day, the eggs were consolidated into a beaker of control water by gently rolling them off the spawning substrate. Eggs were distributed in groups of five using a stratified-random procedure into egg cups suspended in the test aquaria (30x15x19cm, fill volume 6.75L, flow-through, renewal of test solution 24-25 times per day, peristatltic diluter, replacement of aquaria after 15d) with toxicant concentrations at the desired levels. Egg cups were constructed of glass jars that were 5 cm in depth and 5 cm in diameter. A stainless steel screen formed the bottom. Cups contained between 25 and 30 eggs each with two cups per aquarium giving four per treatment. The number of eggs was the same among treatments but varied among tests as spawning success of breeding pairs varied. As water levels in the aquarium rose and fell with each dosing apparatus cycle, water moved past the eggs, ensuring well oxygenated water and fresh toxicant. A 15:9 h light: dark photoperiod was provided. At 24-h intervals during the first 6 d, each egg cup was removed and placed in a Petri dish containing the test water, and the eggs were inspected under a magnifying glass. Dead eggs and those with fungus were recorded and removed. Hatched fry were removed from egg cups and placed in their appropriate test aquaria. All fry hatched within 6 d. Hatch success wasrecorded over the first 6 d as the percentage of successful hatch [hatch success = (total number of hatched fry/initial number of eggs) X 100]. Once hatched, fry were fed to satiation with freshly hatched brine shrimp ( <48 h old) augmented with finely ground flake food two to three times daily. Fry were counted on days 11, 18, 21, and 32, while transferring them with a large syringe from test aquaria into a temporary holding aquarium containing test water. Dead and missing fry, assumed to be dead, were recorded. Food was withheld 24 h prior to test conclusion. At the conclusion of the test, fish were given a lethal exposure to MS-222 and preserved in a 70% alcohol solution for approximately 2 weeks before weighing. Preserved individual fry weights were recorded to the nearest 0.001 g. Overall treatment effects on embryo and fry percentage survival (with arcsine transformation) and mean fry weight were determined using one-way ANOVA. Each treatment was compared to the control using Dunnett's test. The NOEC and LOEC were reported as in the growth tests.

Conc. based on: other: mg NO3-N
Basis for effect: growth rate
Details on results: The NOEC and LOEC were based on a significant reduction (p = 0.027) in weight of fish at the end of the test ( 11 mg in the middle treatment vs 16 mg for the controls). Although fry survival was significantly reduced (p = 0.007) from the control (23% survived vs 78% for the control), that reduction occurred at a higher nitrate concentration than for final weight. Nitrate concentrations had no effect on embryo survival.

Conclusions:
NOEC 157 mg/L (growth rate)
LOEC 294 mg/L (growth rate)