ASTM D6442 – Standard Test Method for Determination of Copper Release Rate From Antifouling Coatings in Substitute Ocean Water
Significance and Use
4.1 This test method is designed to provide a laboratory procedure to quantify and characterize the release rates of copper from antifouling coatings in substitute ocean water over a period of immersion under specified laboratory conditions of constant temperature, pH, salinity, and low copper concentration. Quantitative measurement of the release rate is necessary to help in selection of materials, in providing quality control, and in understanding the performance mechanism.
4.2 Results from this test method establish a pattern of copper release from an antifouling coating over a minimum of 45 days exposure under controlled laboratory conditions. Copper release rates from 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 copper release rates that will occur in-service, but provide comparisons of the release rate of different antifouling formulations in substitute ocean water under the prescribed laboratory conditions.
4.3 By comparison with copper release rate measurements obtained either by direct measurements of copper release rate from AF coating systems on ship hulls, or copper release rate measurements from AF coating systems from harbor exposed panels, all available data indicate that the results of this test method (Test Method D6442) significantly overestimate the release rate of copper when compared to release rates under in-service conditions. Published results demonstrate that this test method produces higher measurements of copper release rate 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 data for several commercial antifouling coatings.3,4 Realistic estimates of the copper 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 from an AF 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 copper release rate from antifouling coatings under real-life conditions. This can be accomplished through the application of appropriate correction factors.4
1.1 This test method covers the laboratory determination of the rate at which copper is released from an antifouling (AF) coating in substitute ocean water. The practical limits for quantifying copper release rates by this method are from 1.8 to 500 μg cm-2d-1. This range may be extended to 0.2 to 500 μg cm-2d-1 if the analytical procedure described in Appendix X1 is followed.
NOTE 1: The term “substitute ocean water” is used throughout this standard to refer to artificial or synthetic seawater prepared in accordance with Practice D1141.
1.2 The procedure contains the preparation steps for the release rate determination of copper from antifouling paints including apparatus, reagents, holding tank conditions, and sampling point details. Analysis for the concentration of copper in substitute ocean water requires the accurate determination of copper at the low parts μg L-1 (parts per billion, ppb) level. To detect and correct for reagent impurities, acceptable analytical precision standards are necessary. Therefore, the limit of quantitation (LOQ) for copper in substitute ocean water for the analytical method shall be 10 μg L-1 (10 ppb) or less. The procedure for determining the LOQ for copper in substitute ocean water for the analytical method is found in Annex A2.
1.3 A suitable method is described in Appendix X1 (graphite furnace atomic absorption spectroscopy, GF-AAS). Other analytical methods may be utilized with relevant procedural changes, as needed, to accommodate selected specific methods. Such methods must meet the limit of quantitation for copper in substitute ocean water of 10 μg L-1 (10 ppb) or less. See 1.2.
1.4 This results of this test method do not reflect environmental copper 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 on Significance and Use.
1.5 The values stated in SI units are to be regarded as the standard. The values given in parentheses are for information only.