5. Non-biocidal paints, Danish Environmental Protection Agency

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Ecotoxocicological assessment of antifouling biocides and non-biocidal antifouling paints

5. Non-biocidal paints

5.1 Investigations of non-biocidal paints
5.2 Leaching and ecotoxicological tests
5.3 Assessment of non-biocidal paints

5.1 Investigations of non-biocidal paints

Field tests with mechanical cleaning of two non-biocidal marine bottom paints were carried out by the Danish Sailing Association and Hempel during the sailing season in 1998 (Danish Sailing Association and Hempel 1999).

Non-biocidal antifouling paints are defined and interpreted in various ways in different official connexions. In this report, the following definition applies: A non-biocidal antifouling paint does not contain any active substances (biocides) added in order to prevent fouling through the toxic effect of these substances. Examples of biocides that have been or are still used in antifouling paints in Denmark are: TBT, copper, Diuron, Irgarol, Nopcocide, Sea-Nine (active substance is DCOI), zinc pyrithione, etc.

In stead, the antifouling effect is achieved by a very smooth surface on which the fouling has difficulty in sticking to the paint (corresponding to a "non-stick" effect, often based on silicone). Also very hard epoxy-based paints are considered as non-biocidal alternatives. Very heavy fouling is then expected but these epoxy-based paints allow repeated mechanical cleaning without destroying the surface of the paint.

The two types of paint were an experimental silicone-containing paint, 86330, and an epoxy-based paint, High Protect 35651, which is a commercial product designed to prevent osmosis. The environmental properties of the two non-biocidal paints were examined in ecotoxicological laboratory tests of water samples from a leaching test with painted panels. The ecotoxicological tests included the marine green alga Skeletonema costatum and the marine crustacean Acartia tonsa. As effects of substances leaching from the paints were only examined in tests with two water-living organisms, a test setup ensuring a worst-case situation was applied in the leaching test.

In the leaching test, the ratio of the painted area to the surrounding amount of water was established in accordance with calculations based on the conditions in the pleasure craft harbour of Jyllinge. On the basis of estimations from the Danish Sailing Association (personal communication with Steen Wintlev-Jensen, Danish Sailing Association), the boats in the harbour are considered to be composed of 360 sailing boats with a total of immersed bottom area of 6840 m² (360 × 19 m²) and 60 motor boats with a total of immersed bottom area of 1320 m² (60 × 22 m²). In the pleasure craft harbour of Jyllinge, the area is approx. 31,500 m² and the average water depth is 2.3 m, after which the amount of water in the harbour can be calculated at 70,450 m³ (cf. Appendix, Table A.1.). Based on these assumptions, the ratio of the painted bottom area of the pleasure craft of the harbour to the amount of water in the harbour is calculated at 0.11 m²:1 m³. The ratio of the painted area to the total amount of water in the leaching tests was 1.5 m²:1 m³. The painted surface per volume unit was thus 13-14 times higher in the leaching test than this ratio would be if the boats in the pleasure craft harbour of Jyllinge were painted with the same paint.

5.2 Leaching and ecotoxicological tests

Test paints
The laboratory tests included two non-biocidal paints (1 and 2 below) and Hempel’s Antifouling Nautic 76800, which is an organotin-based bottom paint for large-scale navigation. The test paints in the study were as follows:

An experimental 86330 paint (silicone-containing)
High Protect 35651 (epoxy-based)
Hempel's Antifouling Nautic 76800 (organotin-based)

Leaching tests
The leaching tests were performed in cast solid glass aquaria with 38 litres of filtered seawater. Four panels painted on both sides with test paint were submerged into each aquarium so that only the painted part of the panels made contact with the seawater. The painted surface of each panel was 150 cm². The water in the aquaria was continuously aerated with a weak current of atmospheric air and vaporized liquid was replaced once a week. The aquaria were covered with black plastic and placed at 20°C. Water samples from the aquaria were sampled after 0, 6, 13, 20 and 34 days. On the first day of the leaching test (day 0), 0.5 litres were sampled from each aquarium after 3 hours while, at all other samplings, 9 litres were taken from each aquarium. At each sampling of 9-litre water samples, one panel was removed from the aquaria so that the ratio of the painted area to the liquid volume remained unchanged throughout the leaching test.

Ecotoxicological test
The toxicity of the water samples was determined in a growth inhibition test with the marine green alga Skeletonema costatum, which was conducted in accordance with the procedures in the OECD Guideline for Testing of Chemicals No. 201 "Algal Growth Inhibition Test" (OECD 1984). The algal test was performed with water samples taken after 0, 6, 13, 20 and 34 days’ leaching. The results from this test were used for selecting water samples for the examination of chronic effects on crustaceans and for determination of potentially bioaccumulable substances.

On the basis of the results from the algal test, the toxicity of water samples taken after 13 and 34 days was determined in tests with the marine crustacean Acartia tonsa. The toxicity towards A. tonsa was examined in a screening test for acute toxicity (ISO 1998) and in a test for chronic toxicity, which has been described in detail by the National Environmental Research Institute (NERI 1986) and Johansen and Møhlenberg (1987). The presence of hydrophobic, potentially bioaccumulable substances in the leachate was determined in accordance with the OECD Guideline for Testing of Chemicals No. 117 "Partition Coefficient (n-octanol/water), High Performance Liquid Chromatography (HPLC) Method" (OECD 1989).

The materials and methods used are described in detail in the report "Ecotoxicological tests of leachates of antifouling paints" (Bjørnestad et al. 1999), which also contains a detailed description of the study results. The most essential results are summarized below.

Growth inhibition test with algae
The toxicity test with S. costatum showed that the leachate from High Protect 35651 did not inhibit the growth of the algae. However, Hempel’s Antifouling Nautic 76800 as well as the experimental 86330 paint leached substances to the surrounding water, which caused an inhibition of the growth of the algae (Table 5.1).

Table 5.1
Inhibition of growth of Skeletonema costatum in tests of leachates in a concentration of 900 mL/L.

Test paint	Inhibition of growth (%)
Test paint	Day 0	Day 6	Day 13	Day 20	Day 34
Control	< 1	< 1	< 1	< 1	< 1
High Protect 35651	< 1	< 1	< 1	< 1	< 1
Experimental 86330	2	48	100	100	100
Hempel's Antifouling Nautic 76800	100	100	100	100	100

As the results with the experimental 86330 paint (Table 5.1) were astonishing, Hempel’s laboratory has performed more leaching tests using the method described above (personal communication with Susanne Holm Faarbæk, Hempel). In this test, leachates were sampled after 20 days, after which the toxicity of the coded water samples was determined by VKI. Water samples from two separate leaching tests with the experimental 86330 caused an inhibition of S. costatum of 78% and 100%, respectively. The leachate from another paint, 97003-057, which composition is very similar to that of the experimental 86330, caused no inhibition of the algal growth. The test with 97003-057 could, however, not be reproduced as a new laboratory batch of the paint, 97003-128, caused an inhibition of 90% of S. costatum (personal communication with Susanne Holm Faarbæk, Hempel).

While the additional leaching tests with the experimental 86330 paint generally confirmed the results in Table 5.1, the diverging results for the 97003 paint indicate that variations in the production or painting process has great influence on the leaching of substances from the painted surface. It has not been possible to shed light on these conditions in connection with this study.

Toxicity test with Acartia tonsa
Water samples from leaching test with High Protect 35651 caused no acute toxicity towards A. tonsa in screening tests. The chronic toxicity test, however, showed that undiluted water samples from the leaching test with High Protect 35651 inhibited the development of Acartia nauplii while no inhibition was observed when the water samples were diluted 10 times (100 mL/L) (Figure 5.1). As no effects were observed either on the egg production at a concentration of 100 mL/L, NOEC (No Observed Effect Concentration) was 100 mL/L for the leachate from High Protect 35651.

Contrary to High Protect 35651, the leachate from the test with the experimental 86330 paint was acutely toxic to A. tonsa as the lethality of adult Acartia was 100% for undiluted water samples taken after 20 and 34 days, respectively. Leachate diluted 10 times (100 mL/L) caused a lethality of 40% (20 days) and 20% (34 days), respectively. In the chronic toxicity tests, no nauplii developed into copepodites and adults at an impact of leachate diluted to 100 mL/L (water sample taken after 13 days) and 10 mL/L (water sample taken after 34 days) (Figures 5.2-5.3.). On the basis of these results, it is concluded that NOEC was less than 10 mL/L for the leachate from the experimental 86330 paint.

Figure 5.1 Look here...
Development of nauplii, copepodites and adults in leachate from High Protect 35651, day 13.

Figure 5.2 Look here...
Development of nauplii, copepodites and adults in leachate from the experimental 86330 paint, day 13.

Figure 5.3 Look here...
Development of nauplii, copepodites and adults in leachate from the experimental 86330 paint, day 34.

The water samples from the leaching test with Hempel's Antifouling Nautic 76800 had a high acute toxicity towards A. tonsa as the water sample taken after 20 days and diluted 100 times (10 mL/L) caused a lethality of 100%. No nauplii developed into copepodites and adults at an impact of leachate diluted to 0.1 mL/L (water sample taken after 13 days). On the basis of these results, it is concluded that NOEC was less than 0.1 mL/L for the leachate from Hempel's Antifouling Nautic 76800.

Table 5.2 gives the NOEC values for acute and chronic effects.

Table 5.2
NOEC values determined in tests with Acartia tonsa (NOEC, No Observed Effect Concentration).

	Day for sampling of leachate	NOEC acute (mL/L)	NOEC development (mL/L)	NOEC egg hatching (mL/L)
Control	34	1,000	1,000	1,000
High Protect 35651	34	1,000	100	100
Experimental 86330	34	<100	<10	10 ^A
Hempel's Antifouling Nautic 76800	34	<1	<0.1 ^A	-

^{A, test performed with leachate taken
after 13 days,

-, not determined.
n-Octanol-water partition coefficient

The n-octanol-water partition coefficient (log K_ow) is normally used as an
expression of the inherent ability of chemical substances to bioaccumulate in water-living
organisms. Substances with log K_ow >3 are considered potentially
bioaccumulative. The test performed was a qualitative test, in which log K_ow
was determined for substances in leachate but in which the concentration of the substances
was not determined.

Six compounds with log K_ow >3 were demonstrated in a
water sample from the leaching test with High Protect 35651 at neutral pH. There was,
however, some analytical uncertainty as these compounds caused small areas in the HPLC
chromatograms and four compounds were only demonstrated in one of the two analyses. At pH
2, twelve compounds with log K_ow >3 were found. Although the results should
be interpreted with caution, the examination demonstrates the presence of potentially
bioaccumulable substances in the leachate from High Protect 35651. Of these substances,
the majority is considered to have a log K_ow between 3 and 4.
Four compounds with log K_ow >3 were demonstrated in a
water sample from the leaching test with the experimental 86330 paint at neutral pH. At pH
2, 12-15 compounds were demonstrated with log K_ow >3. The results show that
potentially bioaccumulable substances are leached to the surrounding water in leaching
test with the experimental 86330 paint. As was the case with High Protect 35651, the
majority of these substances is considered to have a log K_ow between 3 and 4.
The examinations of log K_ow have thus demonstrated that
potentially bioaccumulable compounds may be leached from High Protect 35651 as well as
from the experimental 86330 paint. The leached substances are, however, considered to have
a low bioaccumulation potential as most of the substances have a log K_ow
<3-4 and no compounds with log K_ow >5 have been demonstrated. Substances
with log K_ow between 3 and 4 will typically have a bioconcentration factor of
100-575 (Veith and Kosian 1983).
5.3 Assessment of non-biocidal paints
The performed leaching tests were carried out with a ratio of the
painted area to the surrounding liquid volume that was at least 13-14 times higher than
the corresponding ratio in the pleasure craft harbour of Jyllinge (cf. Section 5.1). For
both non-biocidal paints, High Protect 35651 and the experimental 86330 paint, water
samples from leaching tests have markedly less effect than water samples from similar test
with the commercial paint, Hempel's Antifouling Nautic 76800. Table 5.2 shows that
leachates from High Protect 35651 and the experimental 86330 paint caused NOEC values for A.
tonsa that were at least 1,000 and 100 times, respectively, higher than NOEC for
leachate from Hempel's Antifouling Nautic 76800.
Water samples from the leaching test with High Protect 35651 caused no
inhibition of S. costatum and chronic effects on A. tonsa were only observed
with undiluted leachate (NOEC = 100 mL/L).
Water samples from the leaching test with the experimental 86330 paint
were toxic to S. costatum and in acute and chronic tests with A. tonsa
(NOEC, acute <100 mL/L; NOEC, chronic <10 mL/L). There are, however, problems in the
leaching of substances from this type of paint that have not been fully examined (cf. the
results with S. costatum). These problems should be further examined before a final
assessment is made of the environmental properties of the paint.

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