Significance and Use
4.1 This test method is designed to provide a laboratory procedure to quantify and characterize changes in the release rate of organic biocide from antifouling coatings that occur during a period of immersion under specified laboratory conditions of constant temperature, pH, salinity, and hydrodynamics. Quantitative measurement of biocide release rate is necessary to help in selection of materials, providing quality control, and understanding the performance mechanism.
4.2 Results from this test method establish a pattern of biocide release from an antifouling coating over a minimum of 45 days exposure under controlled laboratory conditions. Biocide release rates of antifouling paints in-service vary over the life of the coating system depending on the formulation and on the physical and chemical properties of the environment. Factors such as differences in berthing locations, operating schedules, length of service, condition of paint film surface, temperature, pH, and salinity influence the actual release rate under environmental conditions. Results obtained using this test method do not reflect actual biocide release rates that will occur in service, but provide comparisons of the release rate characteristics of different antifouling formulations in substitute ocean water under the prescribed laboratory conditions.
4.3 By comparison with published copper and organotin release rate data4,5 obtained either by direct measurements from ship hulls or release rate measurements from harbor exposed panels, all data indicate that the results of this generic rotating-cylinder test method significantly overestimate the release rate of biocide when compared to release rates under in-service conditions. For example, published results demonstrate that this generic test method produces higher measurements of copper and organotin release rates than from direct in situ measurements for the same coating on in-service ship hulls and harbor-exposed panels. The difference between the results of this test method and the panel and ship studies was up to a factor of about 30 based on copper release rate data for several commercial antifouling coatings.4, 6 No direct release rate data from ship hulls or harbor-exposed panels have been generated to-date for the biocides covered by this method. However, the expectation is that the results of this test method, when compared with the direct measurements from ship hulls and harbor-exposed panels, could follow the same trend. Realistic estimates of the biocide release from a ship’s hull under in-service conditions can only be obtained from this test method where the difference between the results obtained by this test method and the release rate of an antifouling coating in service is taken into account.
4.4 Where the results of this test method are used in the process of generating environmental risk assessments, for environmental loading estimates, or for regulatory purposes, it is most strongly recommended that the relationship between laboratory release rates and actual environment inputs is taken into account to allow a more accurate approximation of the biocide release rate from antifouling coatings under real-life conditions. This can be accomplished through the application of appropriate correction factors.6
Scope
1.1 This test method covers the laboratory determination of the rate at which organic biocide is released from an antifouling coating exposed in substitute ocean water. The test is run entirely in the laboratory under controlled conditions of pH, temperature, salinity, and hydrodynamics. Analytical procedures are provided for the determination of the release rate of 4,5-dichloro-2-n-octylisothiazolin-3-one (DCOIT), zinc and copper pyrithione (ZPT and CuPT), and N-cyclopropyl-N′-(1,1-dimethylethyl)-6-(methylthio)-1,3,5-triazine-2,4-diamine (CDMTD). At predetermined intervals, substitute ocean water samples are analyzed for leached biocide using a suitable analytical technique.
1.2 In cases in which the antifouling coating contains both an organic biocide and a copper-based biocide, the release rate of copper may optionally be concurrently determined according to the procedure found in Test Method D6442.
1.3 The procedure contains the preparation steps for the determination of the release rate of biocide in substitute ocean water from antifouling paints including apparatus, reagents, holding tank conditions, and sampling point details. The procedure calls for the accurate determination of organic biocide concentrations in substitute ocean water at the low μg L-1  (parts per billion, ppb) level. To detect and correct for reagent impurities and allow a suitable level of analytical precision to be achieved, the analytical method to be used for the determination of the concentration of organic biocide in substitute ocean water must meet the acceptability criteria given in Annex A2. Where Annex A2 specifies a limit of quantitation (LOQ), the procedure for determining the LOQ for the organic biocide in substitute ocean water by the analytical method presented in Annex A3 is to be followed.
1.4 Suitable analytical methods that use high-performance liquid chromatography (HPLC) for determining the concentration of DCOIT, ZPT and CuPT, and CDMTD in substitute ocean water are given in Appendix X1-Appendix X3, respectively. Other methods may be used provided that they meet the appropriate criteria given in Annex A2.
1.5 When the release rate of a highly photosensitive organic biocide is being determined, steps must be taken to protect the apparatus and samples from exposure to natural and artificial visible light sources. Any such requirement for these steps to be taken for a particular biocide is indicated in Annex A2.
1.6 The practical limits for quantifying biocide release rates by this method are from 4.5 to 500 μg cm-2 d-1 for DCOIT, 0.36 to 500 μg cm-2 d-1 for CuPT, 0.36 to 500 μg cm-2 d-1 for ZPT, and 2.7 to 500 μg cm-2 d-1 for CDMTD. These ranges may be extended to 3.8 to 500 μg cm-2 d-1 for DCOIT, 0.16 to 500 μg cm-2 d-1 for CuPT, 0.2 to 500 μg cm-2 d-1 for ZPT, and 2.2 to 500 μg cm-2 d-1 for CDMTD if the procedures described in Appendix X1-Appendix X3 (as appropriate) are followed. The quantitation of release rates lower than these ranges will require the use of analytical methods with lower limits of quantitation than those specified in Annex A2.
1.7 The results of this test method do not reflect environmental biocide release rates for antifouling products, and are not suitable for direct use in the process of generating environmental risk assessments, environmental loading estimates, or for establishing release rate limits for regulatory purposes. See also Section 4.
