Specialized coatings can be effective in controlling zebra mussels in raw water systems. Traditional antifouling coatings leach an aquatic toxin, typically cuprous oxide, into the water to repel fouling organisms, such as the zebra mussel. These products are effective for approximately 2 to 5 years. Foul-release coatings present a slippery surface that minimizes the adhesion of the zebra mussel. These products are considered to be more environmentally sound because they do not leach aquatic toxins. However, they are subject to abrasion and therefore their use should be limited to areas that are not susceptible to damage caused by ice and debris. Thermal-spray coatings are metallic coatings such as zinc, copper and brass. Thermal-sprayed coatings are applied by melting a wire feedstock and propelling the molten droplets in a stream of compressed air on the surface to be treated. These coatings repel zebra mussels through the slow dissolution of metal ions into the water. Zinc thermal spray also provides excellent corrosion resistance on steel surfaces. Copper and brass should never be applied directly to steel because the steel will corrode. Thermal spray coatings should not be used on nonferrous metal substrates. With proper surface preparation they may be used on concrete. Thermal spray coatings are potentially the most durable and lasting zebra-mussel repellent coating.
The use of coatings as a control measure should be preceded by a complete understanding of recognized or predictable impact on the operation of the facility. Other control options should be considered as appropriate. HQUSACE (1995) recommended two coating systems described below for the control of zebra mussels. Coating system A is for use on mild steel or concrete and can be expected to provide effective protection for 10 or more years. Coating system B is for use on mild steel and on some previously painted surfaces. System B should provide approximately 3 years protection.
MIL-P-15931 may also be used over some existing coatings, including Systems 3, 3-A-Z, 4, and 5-A-Z, described in CWGS-09940, provided the receiving surface has been cleaned and is in good condition. Existing coating systems to be top-coated with MIL-P-15931 should be cleaned using high pressure water at 10,350 kPa. Prior to top-coating the cleaned surface should be dry and free of visible deposits that may interfere with intercoat adhesion.
Systems A and B described herein contain significant amounts of zinc and copper, respectively. Most states do not currently regulate the disposal of zinc and copper containing wastes; however, proposed legislation suggests that they may be more widely regulated at some future time. Disposal of regulated wastes can be expensive.
The effectiveness of these coating systems at preventing the attachment of zebra mussels is a direct result of the aquatic toxicity of copper and zinc. Systems A and B introduce measurable amounts of zinc and copper into the water that may affect nontarget organisms. The zinc and copper leach rates of these coatings have been measured in controlled laboratory experiments. The relatively low release rates and high dilution rates associated with their practical application suggests negligible or very low secondary effects on nontarget organisms. Cuprous oxide, the active constituent in System B, is subject to regulation under the Federal Insecticide, Fungicide, and Rodenticide Act, as amended. For additional information on this topic refer to Zebra Mussel Research Technical Note ZMR-1-15 (Howe et al. 1994).
The paints in System B may be regulated in some locations based on their volatile organic compound (VOC) content. Regulations affecting shop and field application of these coatings may be different from VOC content restrictions for shop-applied coatings. The specifier should learn the air quality regulations in their area.
For additional information on conducting environmental assessments for zebra mussel control, see Tippett, Cathey, and Swor (1993). additional information on the use of coatings to prevent zebra mussel fouling contact The Paint Technology Center, US Army Construction Engineering Research Laboratories, 1-800-USACERL, extension 6769 or 7237, can provide additional information on the use of coatings to prevent zebra mussel fouling.