Pharmaceuticals and Illicit Drugs in Environmental Waters: A Systematic Review and Quantitative Analysis of Global Trends 2004-2021. Part 2.

Pharmaceuticals and illicit drugs are environmental contaminants of concern due to their persistence and health impacts. Whilst spatial and temporal patterns have been extensively studied, seasonal variations remain under-explored globally. This review examined studies across six continents, synthesising wastewater and surface water data to identify seasonal patterns. Rather than a uniform global trend, seasonal peaks are continent- and matrix-specific. In Europe, effluent concentrations were highest in summer, whereas in influent higher concentrations were more frequently observed in winter. Asia exhibited elevated autumn concentrations in influent and effluent wastewaters, while surface water loads peaked in winter. North America influent concentrations were highest in summer. Africa showed higher summer wastewater loads and winter peaks in surface waters. Data from Oceania and South America was comparatively limited. Seasonal differences may reflect interacting climatic and hydrological conditions, population dynamics, environmental degradation, and wastewater treatment highlighting the need for regionally and seasonally tailored monitoring strategies.