The invisible threat in air, water, and food: how ammonia quietly harms liver, brain, and gut

Ammonia is everywhere in modern life—released by farms, industry, and waste systems—and it reaches people through more routes than most realize. A review published in The Innovation Reviews compiles the evidence that this colorless compound, at sufficient exposure, threatens health through the atmosphere, contaminated water, and the food chain alike. The health picture the authors assemble spans three fronts. Inhaled ammonia is linked to respiratory disease. The review also flags an elevated risk of gastrointestinal cancer associated with exposure. And through water eutrophication—nutrient runoff that fuels algal blooms—ammonia contributes to liver toxicity, closing a loop between environmental degradation and organ damage. The body normally holds ammonia in check with a two-part system. The liver's urea cycle converts ammonia into urea for excretion, while intestinal microorganisms transform what the gut cannot handle into relatively non-toxic compounds. The system fails in a characteristic way: when liver function is impaired, blood ammonia rises, producing hyperammonemia—a state with well-recognized neurological consequences—accompanied by an imbalance of the gut microbiota that normally assists ammonia processing. Liver injury and gut dysbiosis thus reinforce each other. Treatment options remain constrained. Drugs and dialysis, the mainstays for lowering ammonia, are limited by long treatment cycles and high costs. The review highlights a newer direction: fecal microbiota transplantation, rebuilt with engineered bacteria, which the authors describe as showing potential therapeutic promise for restoring the ammonia-processing capacity of the gut. The review closes on a less familiar frontier: ammonia-metabolizing bacteria themselves. It details the ammonia metabolism mechanisms and key enzyme systems of autotrophic and heterotrophic ammonia-oxidizing bacteria, and discusses how these genes might one day be used for therapeutic intervention—harnessing microbes' own chemistry to clear or neutralize ammonia in patients. As a review, the article sets a map rather than settling questions. The authors note that the full picture of how ammonia exposure acts on the body—and how the liver-gut axis can be therapeutically rebalanced—remains to be worked out. For environmental health researchers, the message is that ammonia's public-health footprint extends beyond the lungs; for clinicians, it is that the gut microbiome is becoming part of the ammonia-management conversation.