Unionized Ammonia Risk Calculator

Ammonia Equilibrium Chemistry

In aqueous solution, ammonia exists in a pH- and temperature-dependent equilibrium:

The fraction of total ammonia that is unionized (NH₃) is determined by the dissociation constant (pKa) and the water pH:

The pKa of ammonia decreases with increasing temperature (Emerson et al., 1975):

where T is temperature in °C. This means that at higher temperatures, a greater fraction of TAN exists as toxic NH₃. Salinity further reduces pKa (Khoo et al., 1977), increasing the NH₃ fraction in brackish or marine systems.

Zebrafish Ammonia Toxicity

Zebrafish are relatively sensitive to ammonia compared to many other freshwater species. Key toxicity thresholds:

• < 0.02 mg/L NH₃: Safe for long-term culture
• 0.02–0.05 mg/L NH₃: Sublethal stress; reduced growth, altered behavior, and immune suppression
• 0.05–0.2 mg/L NH₃: Dangerous; gill hyperplasia, increased mucus production, fin erosion
• > 0.2 mg/L NH₃: Potentially lethal; acute gill necrosis, neurological damage

Larvae and embryos are more sensitive than adults. Chronic low-level exposure can confound experimental results by inducing stress-related gene expression changes, making ammonia monitoring essential for reproducible research.