MERCER02-14
11
These systems requiremore review regarding the environmental compliance of the copper leach
rates. Copper leaching rates are affected by biofilm development, water temperature, water flow,
age and condition of the metal, and other factors. Leaching rates are typically higher after a
disturbance or upon initial coating immersion (Wells and Sytsma 2009). Very little information
is available on the long-term performance or the copper release rate after long immersion times.
In static conditions, the copper release rate is 20 µg cm
-2
d
-1
, which is higher than the lower limit
of 10µg cm
-2
d
-1
, which is used to gauge antifouling action (Yebra et al. 2003).
5.1.1. BiocideTypes
5.1.1.1. Primary biocides
Primary biocides are typically heavymetals, as well as alloys and compounds of metals, such as
cuprous oxide. Highwater velocity, floating debris, or abrasive contact with entrained solids can
remove copper-based coatings, allowing foulants to attach in eroded areas. When most of the
toxicant is released from the coating or the leaching channels become clogged, the level of
cuprous oxide at the surface falls below the minimum necessary to control fouling (Mussalli
1984).
5.1.1.2. Biocide boosters
In an effort to find a suitable antifouling solution for paints without using TBT, companies have
developed substitutes able to complement the biocidal action of copper and yield good
antifouling properties. Booster biocides, such as herbicides, fungicides, and bactericides are
examples of some different substitutes. There are many uncertainties about different
environmental parameters associated with booster biocides. Some of these include the
environmental profiles of booster biocides; acute and chronic toxicity; validation of analytical
methods for biocides, monitoring and fate and toxicity in the environment; synergistic
interactions between pollutants; accumulation in the environment; and evaluation of the
performance of alternative antifoulants (Yebra et al. 2003).
5.1.1.3. Natural biocides
In natural environments, some organisms remain foul-free, while others become heavily fouled
on the surface. The foul-free organisms produce secondarymetabolites that may inhibit or repel
fouling organisms. The metabolites act enzymatically by dissolving the fouling organism’s
adhesive and inhibiting attachment. Examples of themetabolites include fatty acids, steroids, and
amino acids. Incorporating natural biocides into paint is currently being studied. Uncertainties
with this approach include proving that incorporation of the biocide into paints does not reduce
its effectiveness; showingwhether the compatiblematrix fulfills the same requirements as other
paints regarding mechanical properties, stability, and release characteristics; documenting
whether large scale production is possible; and production costs (Yebra et al. 2003).
5.1.2. BiocideContainingPaints
5.1.2.1. Self-polishing copolymers (SPC)
SPCs are based on a copolymer binder. Biocides, primarily copper, are attached as pendant
groups to the copolymer. SPCs release biocides by hydrolysis or an ion exchange reaction of an
acrylic polymer with water. The polymer backbone allows for a controlled and slow release of
the biocide (Watermann et al. 2004). When the biocide is released from the hydrophobic SPC
copolymers, it leaves a hydrophilic site on the polymer. When hydrophilic sites accumulate, the
