Yes, the main toxic action of nitrate is due to the conversion of oxygen-carrying pigments to forms that are incapable of carrying oxygen. Nitrate toxicity to aquatic animals increases with increasing nitrate concentrations and exposure times.A genotoxin is a chemical or agent that can cause DNA or chromosomal damage. Such damage in a germ cell has the potential to cause a heritable altered trait (germline mutation). DNA damage in a somatic cell may result in a somatic mutation, which may lead to malignant transformation (cancer). The clastogenic or aneugenic effects from the genotoxic damage will cause an increase in frequency of structural or numerical aberrations of the genetic material. This is similar to the micronucleus test and chromosome aberration assay, which detect structural and numerical chromosomal aberrations in mammalian cells40.

Yes, nitrates can be toxic to aquatic microorganisms. The toxicity of nitrates to aquatic organisms is a result of their conversion to nitrites. Nitrites are more acutely toxic to aquatic organisms than ammonia and nitrate under most conditions. The sublethal effects of nitrite on aquatic organisms have been relatively understudied. However, nitrate pollution has been found to cause growth reduction, histopathological changes, neurotoxicity, endocrine disruption, and ultimately death to aquatic organisms. Nitrate toxicity shows swimming alteration, growth retardation, and eventually death among aquatic organisms. In fishes, it causes histopathological alteration of gills, esophagus, and brain.

The genotoxicological effects and molecular mechanisms of nitrates are related to their conversion to nitrites in the body. Approximately 5%-10% of the total nitrate intake is converted to nitrite by bacteria in the saliva, stomach, and small intestine. This in vivo conversion of nitrates to nitrites significantly enhances nitrates’ toxic potency2. The known toxic effects of nitrate exposure result from the conversion of nitrate to nitrite. The effects of nitrite are the same whether nitrite-containing compounds are ingested or inhaled, or nitrite is produced in vivo from nitrate. Methemoglobinemia is the critical health effect from exposure to nitrates and nitrites. Depending on the percentage of total MetHb, the clinical presentation may be one of oxygen deprivation with cyanosis, cardiac dysrhythmias and circulatory failure, and progressive central nervous system (CNS) effects1. CNS effects can range from mild dizziness and lethargy to coma and convulsions.