Atrazine fate and transport within the coastal zone in southeastern Puerto Rico

► Tropical storm events dominated atrazine residue transport to Jobos Bay. ► Rapid degradation in soil reduced the herbicide’s discharge to the Bay. ► Atrazine replacement with more persistent products may increase runoff risk. Agrichemical transport to coastal waters may have adverse ecological impact. This work examined atrazine fate and transport in a field adjacent to Puerto Rico’s Jobos Bay National Estuarine Research Reserve. The herbicide’s use was linked to residue detection in shallow groundwater and movement toward the estuary; however, data indicated that transport via this pathway was small. In contrast, surface runoff as tropical storm systems moved through the area appeared to have high potential for atrazine transport. In this case, transport to the estuary was limited by runoff event timing relative to atrazine application and very rapid atrazine dissipation (DT50=1–3days) in field soil. Soil incubation studies showed that accelerated degradation conditions had developed in the field due to repeated atrazine treatment. To improve weed management, atrazine replacement with other herbicide(s) is recommended. Use of products that have greater soil persistence may increase runoff risk.