Sea-NineTM211 has been introduced as a new biocide in antifouling paints with an immediate degradation when it is released from ship hulls. The active component of Sea-NineTM211 is 4,5-dichloro-2-n-octyl-isothiazoline-3-one (DCOI). In the present study, the toxicity of DCOI and the occurrence of Pollution Induced Community Tolerance (PICT) were tested in microcosms containing eutrophic coastal water with its natural composition of phytoplankton. The experiment was performed in closed systems with a single addition of the nominal concentrations 0, 3.2, 10, 32 and 100 nM DCOI, for a period of 16 days. Pollution induced community tolerance (PICT) was observed in the phytoplankton communities exposed to the nominal concentrations 32 and 100 nM DCOI. Chemical analysis of DCOI in the coastal water utilised in the toxicity and PICT experiment was performed by GC-MS using a solid- phase extraction method. Half-life was calculated to be 2.5 days for the nominal concentrations 32 and 100 nM DCOI. The results of the present study show that nominal concentrations of 32 and 100 nM DCOI significantly increased the community tolerance already after 2 days of exposure and that the tolerance was maintained for a period of 16 days even when DCOI was degraded during this period. The causes for the persistent tolerance are discussed in relation to the degradation of DCOI and structural changes in the phytoplankton communities.


In 1996 the new antifouling agent Sea-NineTM211 Biocide was introduced. The active ingredient of Sea-NineTM 211 Biocide, 4,5-dichloro-2-n-oc- tyl-4-isothiazoline-3-one (DCOI), has shown potential effects against a wide spectrum of bacteria, fungi and algae (Miller and Lovegrove, 1980; Vasishtha et al., 1995; de Nys et al., 1996; Will- emsen et al., 1998). A rapid degradation of DCOI in natural seawater has been observed with a half- life of generally less than 24 h (Shade et al., 1993). The environmental risk of Sea-Nine is considered by Shade et al. (1993) to be relatively low, due to the very rapid degradation when released from ship hulls.

However, present knowledge about effects and degradation of DCOI is insufficient since effects of DCOI are based on single species toxicity tests and evaluated from nominal concentrations of DCOI (Shade et al., 1993; Bjo ̈rk and Karlsson, 1992). As far as the degradation of DCOI, this has been estimated by the producer, but to a certain extent performed under non-realistic conditions and never directly related to the effects of DCOI (Shade et al., 1993; Jacobson et al., 1993). Thus, the sparse amount of effects data measured under realistic conditions and in response to actual concentrations of DCOI, highlights the need for further information about the fate and effects of DCOI in the environment.