The annual dyeing of the Chicago River green for St. Patrick’s Day is a highly anticipated spectacle, drawing large crowds to witness its vibrant transformation. This tradition creates a striking visual impact, painting the river an emerald hue. The spectacle often leads to questions about the dye’s nature and safety.
The Dye’s Composition and Purpose
The dye used to transform the Chicago River is a vegetable-based powder, orange when dry, turning green upon contact with water. The Chicago Journeymen Plumbers Local Union 130 has been responsible for this tradition for over 60 years, keeping the exact formula a closely guarded secret. Initially, in 1962, an oil-based fluorescein dye was used, but this was replaced by the current vegetable-based, low-impact dye in 1966 due to environmental concerns. Approximately 40 to 50 pounds of this powder are typically dispersed into a quarter-mile stretch of the river. The primary purpose of this dyeing is to celebrate St. Patrick’s Day, honoring Irish heritage and providing a festive visual for the city’s annual parade.
Human Safety Considerations
The dye used in the Chicago River is non-toxic and derived from food-grade ingredients. The Illinois Environmental Protection Agency (EPA) has stated that at the concentration used, the dye is completely non-toxic. It is also described as a food-grade dye used in medicine and as a tracer, meeting drinking water standards by the National Sanitation Foundation. While incidental skin contact is generally regarded as safe, direct ingestion or prolonged exposure is not advised. The event is managed with public safety in mind, ensuring the controlled application of the dye.
Environmental Impact and Dispersion
Environmental studies and monitoring efforts indicate minimal long-term negative impacts on the Chicago River’s aquatic life or ecosystem from the dye. The dye is biodegradable and dissipates naturally within a short period. Typically, the green color lasts for a few hours, returning to the river’s natural hue within 24 to 48 hours.
A study conducted by Austin Happel, a researcher at the Shedd Aquarium, tracked the behavior of tagged fish during the dyeing process. His findings suggest that fish in the river showed no significant changes in behavior or agitation during or immediately after the event. This contrasts with their reactions to other environmental stressors, such as sewage overflows, which cause fish to flee affected areas. While the dye itself is safe, some environmental groups, such as the Friends of the Chicago River, have expressed concerns that the tradition might send an unintended message, implying the river is merely a decoration rather than a living ecosystem. Despite these concerns, the amount of dye used is carefully controlled to minimize any transient effects, and the river now supports over 70 species of fish and other wildlife.