From Field to Faucet: Phosphorus-Driven Harmful Algal Blooms, Cyanotoxin Exposure, and Clinical Implications for Primary Care Physicians-A Narrative Review.

BACKGROUND: Agricultural phosphorus enrichment of freshwater ecosystems drives eutrophication and cyanobacterial harmful algal blooms (HABs) that contaminate drinking water, recreational sites, and food webs with cyanotoxins. Translating this environmental science into clinical practice for primary care physicians remains limited.

OBJECTIVES: This narrative review traced the causal chain from agricultural phosphorus transport and cyanobacterial bloom ecology through cyanotoxin-mediated health consequences. The goal is to give primary care physicians a practical, One Health-based resource for recognizing, managing, and counseling patients on cyanotoxin exposure.

METHODS: A narrative, integrative review was conducted by searching PubMed, Web of Science, Scopus, and Google Scholar using terms related to phosphorus runoff, cyanobacterial HABs, cyanotoxin human health effects, and primary care environmental exposure. Peer-reviewed articles, key toxicology and epidemiology studies, and guidance documents from the World Health Organization, the United States Environmental Protection Agency, and the Centers for Disease Control and Prevention were prioritized and selected based on their relevance to the intersection of phosphorus contamination and human health outcomes in primary care settings. No statistical analysis was performed because this is a qualitative synthesis of existing literature.

RESULTS: The review found that phosphorus from agricultural fertilizers, livestock production, urban runoff, and legacy soil stores drives freshwater eutrophication and harmful algal bloom formation. Climate change is intensifying these processes through increased extreme precipitation and prolonged thermal stratification. Cyanotoxins enter human exposure pathways via drinking water, recreational contact, aerosol inhalation, and bioaccumulation in fish and irrigated crops. Children, pregnant individuals, rural communities on small water systems, and occupational groups such as fishers face disproportionate exposure risk. Broad regulatory gaps persist globally: although some regional bodies, such as the European Food Safety Authority, have issued risk assessments and provisional guidance, no internationally harmonized maximum permissible limits for cyanotoxins in food crops have been established.

CONCLUSIONS: This narrative review demonstrates that phosphorus-driven HABs pose a growing multisystem health threat through contamination of water and food supplies with hepatotoxic, neurotoxic, and cytotoxic cyanotoxins. Primary care physicians, particularly those serving rural communities and communities disproportionately burdened by environmental hazards, must integrate environmental exposure history-taking into routine clinical practice to improve early recognition and reduce the health burden of cyanotoxin exposure.