Behaviour and fate of chemicals in aquatic systems
Behaviour and fate of the algicide Irgarol in water and sediment of flowing and stagnant water systems
Irgarol 1051® (2-[tert-Butylamino]-4-[cyclopropylamino]-6-methyltio-s-triazine) is an antifouling boosting agent, which has increasingly been used as a biocidal agent in antifouling coatings for ship hulls after the EU ban on tributyltin (TBT). Irgarol is a photosynthesis inhibitor and is therefore very toxic for higher plants, algae and aufwuchs organisms. Irgarol is also very persistent in aquatic systems.
Due to these properties, high levels of pollution of water and sediment in coastal areas (ports and marinas in particular) led to restrictions and even bans on the use of antifouling coatings with Irgarol content in Denmark, Sweden, the Netherlands and Great Britain. A general ban was imposed on the use of biocidal antifouling coatings in inland waters in four countries. With the exception of a few regional bans on the general use of antifouling agents which contain biocides, Germany has no restrictions on use (except for TBT).
There is little literature up to now on freshwater systems exposure to Irgarol. The maximum known concentrations are 0.145 µg/l in Lake Geneva. The latest measurements by UBA showed levels of Irgarol of up to 0.23 µg/l in stretches of water with relatively high numbers of marinas in the region of Müritz (Mecklenburg-Western Pomerania). In general, however, there is very little data available on the fate of Irgarol and its degradation products (metabolites) in freshwater systems.
To close the gap in knowledge, Irgarol was applied to the artificial stream and pond mesocosm (FSA) of the Federal Environment Agency. The chemical's spread and fate as well as formation of metabolites were then analysed.
The decrease of Irgarol in the water is illustrated by a second-order biokinetic model (R²: 0.98). There are at least 2 parallel processes which can account for the decrease in open water:
- rapid elimination and e.g. sorption to organic particles, coupled with rapid accumulation in sediment, and
- slow elimination, an indication of time-related processes such as biodegradation or photolytic processes and the formation of metabolites M1.
The half-life (DT50) for Irgarol in the water was initially 8d, increasing to > 32d in the course of the study. The process seems to further slow down at concentrations of <0.2 µg/L.
M1 is formed from Irgarol, for example, in degradation processes such as that caused by the effects of UV radiation and showed little evidence in summer of decrease in water and sediment. M1 would thus appear to be even more persistent than the mother substance.
A European risk assessment within the framework of the Biocidal Products Directive 98/8/EC will decide on the future use of Irgarol as a biocidal anti-fouling agent. The present study represents a significant contribution to the knowledge on freshwater systems.