An ecological risk assessment for the use of Irgarol 1051 as an algaecide for antifoulant paints

Irgarol 1051 is an algaecide used in copper-based antifoulant paints for controlling fouling organisms on the hulls of recreational and commercial watercraft. Paints containing this algaecide have been used in Europe since the mid-1980s. In 1998, the first antifouling paints containing Irgarol 1051 were registered for use in the U. S. To examine the risk that Irgarol may pose to aquatic ecosystems, a probabilistic ecological risk assessment was conducted using distributions of exposure and toxicity data. Exposure data for this assessment were derived from 11 monitoring studies (146 stations) conducted in marinas, estuaries, and coastal waters from 1992 to 1997 in six European countries. A comparison of 90th percentile concentrations pooled by station types across all regions showed that concentrations in marinas (316 ng/l) were higher than in estuaries and coastal waters (41 and 19 ng/l, respectively). A 90th percentile of 133 ng/l was reported for all pooled stations. Temporal trends showed that Irgarol concentrations typically peaked in early summer after launching of small boats with much lower concentrations occurring during the spring, fall, and winter. Toxicity data used for this risk assessment were derived primarily from unpublished studies submitted to regulatory agencies. Because Irgarol is a photosynthesis-inhibiting herbicide, it is much more toxic to plants than animals. Toxicity values for animals (fish and invertebrates) were much greater than concentrations of Irgarol reported in the environment. Therefore, a conservative approach using a distribution of only plant toxicity data (EC50s for plant growth) was used to derive a 10th percentile of 136 ng/l. This plant toxicity benchmark of 136 ng/l was used for risk characterization. Results from probabilistic analysis showed that ecological risk from Irgarol exposure was low in estuaries, coastal areas, and various open-type marinas. However, 10% or more of the plant species in enclosed marinas with low flushing rates may be exposed to Irgarol concentrations that would reduce photosynthesis activity and growth during the summer. Ecological risk to these sensitive plant species in enclosed marinas will likely be moderated because of the reversibility of Irgarol's inhibition of photosynthesis and the rapid recovery potential of plant communities. The ecological significance of marinas that generally contain numerous stressors such as trace metals, tributyltin, petroleum hydrocarbons, high nutrient concentrations, and low dissolved oxygen concentrations is a management issue that needs to be addressed.