『Abstract
　While the global increase in the use of nitrogen-based fertilizers has been well recognized, another change in fertilizer usage has simultaneously occurred: a shift toward urea-based products. Worldwide use of urea increased more than 100-fold in the past 4 decades and now constitutes ＞50％ of global nitrogenous fertilizer usage. Global urea usage extends beyond agricultural applications; urea is also used extensively in animal feeds and in manufacturing processes. This change has occurred to satisfy the world's need for food and more efficient agriculture. Long thought to be retained in soils, new data are suggestive of significant overland transport of urea to sensitive coastal waters. Urea concentrations in coastal and estuarine waters can be substantially elevated and can represent a large fraction of the total dissolved organic nitrogen pool. Urea is used as a nitrogen substrate by many coastal phytoplankton and is increasingly found to be important in the nitrogenous nutrition of some harmful algal bloom (HAB) species. The global increase from 1970 to 2000 in documented incidences of paralytic shellfish poisoning, caused by several HAB species, is similar to the global increase in urea use over the same 3 decades. The trend toward global urea use is expected to continue, with the potential for increasing pollution of sensitive coastal waters around the world.

Key words: Agricultural runoff; Eutrophication; Global change; Harmful algal blooms; Nitrogen fertilizer; Organic nitrogen; Phytoplankton; Urea』

Introduction
Global production and consumption
Range of global uses of urea
Urea in sewage and excretory products
Natural and anthropogenic enrichment of urea in coastal waters
Urea concentrations and contribution to total organic nitrogen in receiving waters
Urea uptake by phytoplankton
Implications and future trends
Acknowledgements
References