Occurrence and transport of Irgarol 1051 and its major metabolite in coastal waters from South Florida

Irgarol 1051, a boosting antifouling agent often used to supplement copper based paints was found in surface waters from South Florida at stations collected from the Miami River, Biscayne Bay and selected areas of the Florida Keys. Concentrations of the herbicide ranged from below the method detection limit (1 ng/L) to as high as 182 ng/L in a canal system in Key Largo. The herbicide was present at 93% of the stations and often found in conjunction with its descyclopropyl metabolite (M1) previously reported to be the major degradation product of Irgarol under natural environmental conditions. The 90th percentile concentration calculated for all South Florida samples was 57.6 ng/L. Based on available data on the toxicity of Irgarol to algae and coral, only two stations (approximately 3%) ranked above the LC50 of 136 ng/L reported for the marine algae Naviculla pelliculosa and above the 100 ng/L level reported to reversibly inhibit photosynthesis of intact corals. However, a basic dissipation model for Irgarol using the Key Largo Harbor station as a point source indicated that concentrations of the herbicide decreased rapidly and concentrations below the MDL are observed within 2000 m of the source. No major coral based benthic habitats are documented for all the stations surveyed at distances that Irgarol may pose a substantial risk. However, other types of submerged vegetation like seagrasses are common around the marinas and the effects of Irgarol to such endpoints should be investigated further.