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Coppel antifouling coatings.

Antifouling coatings applied to military vessels, commercial marine vessels, and pleasure craft prevent biofouling, or the attachment of aquatic organisms to the hull. Such organisms cause drag, leading to increased fuel consumption, and may also cause wear on propulsion systems, damage corrosion protection coatings, and lead to more rapid hull damage. In addition, nonnative aquatic invasive species present a significant threat, and the prevention of the migration of such destructive organisms from one marine environment to another is a significant challenge. Most antifouling coatings contain copper-based antifoulants, such as copper oxide, copper thiocyanate, and copper in powdered or flaked forms, due to their efficacy and economics. The extensive use of copper on both large vessels and pleasure craft has led to concerns about the impact of copper concentrations on marine life, particularly in harbors where large numbers of ships and boats are docked. In this article, focus is on recent studies and subsequent actions taken in California that may impact paint formulators and their efforts to control invasive species.

The cupric ion (C[u.sub.2+]), which is the biologically active copper species, has broad-spectrum activity against fouling organisms, an essential property given the thousands of marine organisms around the world that are capable of colonizing the portions of ship hulls immersed in water. Recent studies have shown that most of the cupric ion released from antifouling coatings, referred to as dissolved copper, is rapidly complexed with organic and particulate material present in the water. As a result, the amount of bioavailable copper is significantly reduced.

Although regulatory agencies traditionally established limits for total copper in aquatic environments, more recently, the importance of bioavailability has been recognized. In 2007, the U.S. Environmental Protection Agency (EPA) adopted a fresh water version of the Biotic Ligand Model (BLM), which uses water chemistry measurements in an area to calculate the amount of copper that is bioavailable to organisms in that water body. The agency was originally expected to implement a BLM for salt water in 2012, but that date has been extended to 2015. However, it is still common to establish one limit for all environments; for example, for California marinas, the California Toxics Rule (CTR) chronic criterion for dissolved copper is 3.1 [eta]g/I (ppb) as a statewide target. It is also the U.S. Clean Water Act criteria. This is despite the fact that the conditions at different California harbors and marinas are quite varied with respect to temperature, salinity, dissolved organic carbon, currents, and other parameters.

California, in particular, remains concerned about copper concentrations in its marinas where large numbers of boats are located and little water exchange occurs. Shelter Island Yacht Basin (SIYB) in San Diego has received much attention. Two studies of this area found that although the copper concentrations in the basin are above the current limit of 3.1 ppb, these levels have not resulted in increased toxicity, due to low bioavailability. In 2011, as part of the required annual monitoring of the basin by the San Diego Regional Water Quality Control Board, (1) it was found that there was an absence of acute toxicity at dissolved copper concentrations up to 11.5 ppb, and chronic toxicity was detected at only one station with a dissolved copper concentration of 8.1 ppb. The report concluded that these results "underscore the importance of considering site-specific factors that regulate copper bioavailability."

Separately in 2011, scientists at the University of San Diego and the Space and Naval Warfare Systems Command (SPAWAR) collected 62 water samples near the surface and the bottom of the SIYB at several locations during the wet (March) and dry (July) seasons, and found only one sample to be toxic to copper-sensitive Mytilus galloprovin-cialis mussel embryos. (2) The researchers concluded that the SIYB is not impaired due to copper, suggesting that the Water Quality Criteria (WQC) are overly conservative.

In addition, the scientists compared results obtained using EPA's traditional Water Effect Ratio (WER) method and a salt water version of the BLM. The WER approach involves toxicity testing of numerous samples from a site, which is both expensive and time-consuming. The BLM, which is rapid, simple, and cost-effective, was shown to be suitable for predicting copper toxicity in SIYB. For the evaluation, a site-specific modification to the saltwater criteria for copper was developed for SIYB using both the BLM (using the pH, temperature, salinity, and dissolved organic carbon content) and a WER approach based on the measured ambient copper toxicity to M. galloprovincialis. Bosse, et al. (2) also notes that the biotic ligand model is based on 700 test results, while the current database used to establish permit levels includes approximately 150, and is a significantly less robust data set to establish Water Quality Criteria.

More recently, the results of a study conducted by the U.S. Navy and Scripps Institute of Oceanography on the extent of copper emissions associated specifically with in-water hull cleaning and passive leaching of copper-based antifouling coatings and their respective loading contributions to water and sediment was published.3 This study was directed by the California Department of Pesticide Regulations (DPR) and funded by manufacturers of antifouling coatings with registrations in California and by copper suppliers. "The principal aim of the study was to quantify the effect of cleaning on cumulative copper emissions as a result of passive leaching and particulate emissions associated with paint removal during cleaning, relative to the equivalent product that was not subjected to any cleaning protocol," says John Hopewell, director of international affairs for the American Coatings Association. "The results have answered questions about the extent of the copper emissions associated specifically with cleaning and passive leaching and their respective loading contributions to water and sediment," he adds.

Leach rates were determined using the Navy's Dome method, which is considered to be one of the most reliable in situ methods for determining biocide release rates from antifouling coatings, according to Patrick J. Earley, a scientist at SPAWAR Systems Center Pacific and a member of the team that conducted the study. An in-water hull cleaning sampling method designed to allow capture of all water and particulates generated during cleaning was employed to determine the effects of cleaning. The most contemporary antifouling paints used in SIYB, including both epoxy and ablative systems, were evaluated, and in situ loading factors, including initial exposure, passive leaching, and surface refreshment were measured, according to Earley. The effects of two different cleaning techniques commonly used by divers for underwater fouling removal--a soft-pile carpet and a medium duty 3M[TM] pad--were investigated.

It was found that passive copper leach rates peaked three days after both initial panel deployment and individual cleaning events, declined over approximately 15 days, and eventually reached a pseudo-steady state (equilibrium) at 30 days. In addition, the study found that copper bioavailability increased immediately following a cleaning, but not after initial panel deployment. Most important, it was determined that cleaning contributes from 40-60% of the copper loading to the environment, depending on the method used (soft-pile carpet or 3M[TM] pad respectively). Furthermore, the data generated from the study was used to develop a life-cycle model that can be used to estimate the annual copper loading for a given paint and cleaning method under various conditions based on a three-year cycle of painting, episodic cleaning (every three weeks as typically practiced in California), and passive leaching.

"This study revealed that a significant portion of the copper content in marinas is not due to passive leaching from copper-based antifouling coatings, but is generated as the result of in-water hull cleaning, and that cleaning/scrubbing also leads to a spike in toxicity," Hopewell states. Neal Blossom, director of global environmental and regulatory affairs with American Chemet Corporation, adds that on a positive note, the study shows that using best-management practices can reduce copper input and toxicity significantly. Consequently, according to Hopewell, any approach to the reduction of copper in California marinas must be holistic and include a significant reduction in scrubbing--it cannot only be achieved through the reformulation of coatings to reduce leach rates.

After this study was published, California passed Assembly Bill (AB) 425, which required DPR by February 2014 to "establish a leach rate for copper-based antifouling paint used on recreational vessels and make recommendations for appropriate mitigation measures that may be implemented to address the protection of aquatic environments from the effects of exposure to that paint if it is registered as a pesticide." The maximum allowable leach rates that DPR developed are based on the statewide limit of 3.1 [mu]g/I for dissolved copper and took into consideration 20 California salt water marinas of different sizes with various levels of copper loading and different cleaning methods. (4)

DPR recommends maximum allowable copper leach rates for antifouling paints of 9.5 [mu]g/ cm2/clay for paints that may undergo in-water hult cleaning using soft-pile carpet as recommended by the California Professional Divers Association, not more than once per month, and 13.4 pg/ cm2/day when in-water hull cleaning of any type is prohibited. DPR recognizes that these limits will require the reformulation of a significant percentage (-58% for the 9.5 pg/cm2/day rate) of currently registered antifouling coatings, but believes that "reformulation to [antifouling paint] products to reduce copper leach rates will dramatically decrease copper loading in marinas." The agency does agree, however, that "other critical activities need to also be implemented to ensure the overall success of this endeavor," including requiring the use of best management practices for hull cleaning and reducing in-water hull cleaning frequency to no more than once per month (which it says will reduce copper loading from 43% to 29% over the three-year lifespan of the paint), among others. In addition, the DPR recommends considering site-specific objectives (SS05) for copper for certain marinas or harbors.

The registrants manufacturing copper antifouling active ingredients, as well as coatings manufacturers through the American Coatings Association, are working with the California DPR to reduce copper leach rates and to develop other mitigation strategies, such as limiting in-water hull cleaning and educating the recreational boating public as to how best to manage the coatings on their vessels, according to Blossom. "The determinations of SSOs will also ensure that the dissolved copper concentration specified as the environmentally protective goal is accurate for each California water body and not the default one-size-fits-all value of 3.1 [mu]g/L, which is an important improvement," observes Blossom. Hopewell is also gratified that DPR is recommending a reduction in underwater cleaning, but believes that the first proposals are insufficient. "ACA will continue to work closely with the legislators in California, as well as DPR, to ensure fair treatment for effective antifouling coatings in the state," he says.

The researchers at SPAWAR also continue to explore other issues related to copper and nickel toxicity. In one study, the scientists are using the Dome method to determine copper leach rates and accumulation in aquaculture materials, using a three-dimensional hydrodynamic model for San Diego Bay as a representative Mediterranean environment and Sinclair Inlet as an example of a cold water estuary with fast-moving water. Earley and his colleagues are negotiating a site-specific revision of nickel permit levels in Guam, based on a toxicity study (Rosen, et al., in press) following EPA guidelines about using a locally important collector urchin. The previous levels were set based on nickel toxicity associated with a collector urchin that is ultra-sensitive but not present in the waters around Guam.

On the international scene, concern over the transfer of invasive species appears to have overtaken concerns about copper toxicity, according to Blossom. "At the International Congress on Marine Corrosion and Fouling held in Singapore in July 2014, for example, the focus was on the prevention of invasive species transfer from one location to another. In particular, there are concerns that in places that are looking to restrict the use of copper in antifouling coatings--such as California--there will be an increasing likelihood that invasive species issues will arise," he explains. In many cases, the people dealing with copper concentrations in the water are different from those trying to prevent the spread of invasive species, and as a result they are often working against one another. "What is needed is a risk-benefit analysis with respect to the potential toxicity of copper and its effectiveness at preventing invasive species transfer (or the potential devastation to important marine environments if copper is not used and invasive species are spread)," asserts Blossom. He also adds that most people do not realize that a small pleasure craft could distribute an invasive species all along the California coast very rapidly, and the ecosystem and economic consequences could be very severe.

The coatings industry will be paying close attention to developments in the regulation of, and technological advances in, antifouling coatings on all fronts. Collecting and correctly interpreting data on copper concentrations, guiding cleaning techniques, reformulating antifouling coatings where necessary, and controlling invasive species are all part of the challenge in keeping both our waters and our marine vessels clean.


(1.) Port of San Diego Shelter Island Yacht Basin Dissolved Copper Total Maximum Daily Load 2011 Monitoring and Progress Final Report, prepared as required by Investigative Order R9-2011-0036 by the Port of San Diego for the San Diego Regional Water Quality Control Board.

(2.) Bosse, C., Rosen, G., Colvin, M., Earley, P., Santore, R., and Rivera-Duarte, I. "Copper bioavailability and toxicity to Mytilus galloprovincialis in Shelter Island Yacht Basin, San Diego, CA," Mar. Pollut. Bull., article in press, 2014.

(3.) Earley, P., Swope, B., Barbeau, K., Bundy, R., McDonald, J., and Rivera-Duarte, I. "Life cycle contributions of copper from vessel painting and maintenance activities," Biofouling, 30(1), 51-68 (2014).

(4.) California Department of Pesticide Registration, memorandum dated January 30, 2014: Determination of maximum allowable leachate and mitigation recommendations for copper antifouling paints per AB 425,

by Cynthia Challener, Coatings Tech Contributing Writer
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Author:Challener, Cynthia
Publication:JCT CoatingsTech
Geographic Code:1U9CA
Date:Sep 1, 2014
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