Figure 1.
E x t e n t of Fouling at Dnytonn Beach i n 2.5 3\Ionths
ANTIFOULING PAINTS Test Procedures and General Observations G. H. YOUNG, G. W. GERHARDT W. IC. SCHNEIDER Mellon Institute, Pittsburgh, Penna.
HE problem of fouling of surfaces subjected to inimersion in sea water has long been serious. The major alleviative efforts to date have involved the use of an “antifouling” paint-applied in the too-often vain hope that, by its nature or content of “toxic” agencies, fouling growths would be prevented or a t least reasonably inhibite&. To this end an almost unlimited number of specific compositions, for which antifouling properties are claimed, appear i’n the patent and technical lfterature. I n many preparations the beneficial effect is attributed to the composition of the vehicle; in others, to the peculiar fashion in which the several ingredients are compounded together. In by far the greatest number the virtue is ascribed t o the presence of one or more “poisons” or toxic agents. The phototropicity of certain types of fouling organisms has frequently been demonstrated by biological studies. The suggestion has therefore been made that color alone is the most significant factor in autifouling paint performance; the argument of light us. dark paints is still unsettled. It has more recently been asserted that the only effective approach from the paint standpoint is to strive for extreme exfoliation or “underwater chalking’’ properties; but the question of chalking coatings or toxic‘coatings is still unanswered. In the research reported here additional light is thrown on these controversial phases of the problem of antifouling paint formulation. The experimental paints employed
do not necessarily represent practical or even usable coatings; rather, the several variables have been maintained under as rigid control as possible within the limitations of varnish cooking and formulating techniques. In every case, however, commercially available constituents have been used, of the purity represented by the products procurable on the market.
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THE FOULING PROCESS
The fouling of a ship’s bottom, which begins as soon as the ship is water-borne, can be divided into three phases taking place more or less simultaneously: the formation of the slimy microbiological film, the attachment of macroscopic fouling organisms (almost always in larval form), and their growth into the mature forms, visable as barnacles, mollusks, annelids, Bryozoa, algae, and other fouling growths ( 5 ) . The probable role in the fouling process of the microbiological film has been described by RoBell, Clapp, and others (2, 8, 9). That such films are universally present on surfaces shortly after submersion in sea water is unquestioned. Nevertheless, evidence that such prior film formation is essential for subsequent attachment of macroorganisms is inconclusive. Our own experiments indicate that slime formation on antifouling paints may eventually vitiate their effect by a simple blanketing action preventing lethal concentrations of the toxic agents from building up at the slime filmwater interface. This observation is in agreement with the 432
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INDUSTRIAL AND ENGINEERING CHEMISTRY
April, 1943
findings of the Navy (6). Where sufficiently high toxic concentrations can be realized, in spite of the slime film we have been able to maintain slime-covered surfaces free from macrogrowths for many months. The principal organisms with which one has to deal on underwater structures may be classified as follows: Or anisms building hard, calcareous, or chitinous shells
innelids: coiled or twisted tubes Barnacles : cone-shaped shells built up of laminated lates, attached directly or by means of long muscular staPks Bryoaoa (encrusting): flat, spreading, multicellular coral-like patches Mollusks: bivalves such as clams, mussels, oysters Organisms without hard shells Algae: green, brown, or red filament-like growths, generally near the water line Bryoaoa (filamentous): fern-like or tree-like growths, the branches not ex anded at the tips Hydroids: stalk-lite or branching growths, each branch terminating in an expanded tip Tunicates: soft, spongy masses (“sea squirts”) Boring organisms Teredo: soft-bodied worms with a cutting shell-like head (“ship worms”) Martesia: boring clam-like mollusks Limnoria: shrimp-like drilling arthropods These types of organisms are described in the Navy’s Docking Manual (6). Details concerning morphology and differences among subspecies are contained in most standard biological texts (4). PRIMARY TOXICITY
Certain preliminary measurements were made on a wide variety of toxic materials. As test object a fresh-water
Rating 10, perfect
I , medium fouling
Figure 2.
433
arthropod, Daphnia, more than superficially similar to the Cypris larva or embryonic Balanus, was used because i t was not practical to maintain colonies of Cypris larvae in an inland laboratory. Zoological affinities Size, mm.
Appearance
Cypris Larva Crustacea Cirripedia 1-3
.
Habitat
Light reaction Toxicological reaction
Daphnia Crustacea Cladocera 0.6-1.5
Shrimp-like form in a bivalve shell
Surface marine waters Strongly positive
Very sensitive to oopper
TESTPROCEDURE. Two or three grams of the substance were placed in 250 ml. of distilled water and shaken a t intervals for 24 hours; the resultant solution was arbitrarily assumed to be a saturated solution in water although there is no reason to suppose that complete saturation occurred in every case. Certain of the substances of relatively high solubility were adjusted to a concentration of approximately 1 X 10-6 molar. A stock culture oE Daphnia was started in 70 gallons of tap water to which were added 25 grams of sheep manure and 15 grams of dead fish; the medium was enriched a t intervals with a weak suspension of Fleischmann’s yeast. Healthy animals from this colony were placed in 20 ml. of their own medium in glass vials 4 inches long and 1 inch in diameter. Three such vials were used in each test. To the first was added distilled water; to the second was added 1 ml. of the “saturated test solution”, and the third received 5 ml. of the same solution. The distilled water control was discontinued after the first twenty-five tests demonstrated that it was without effect on Daphnia.
8, very slightly fouling
6, definite fouling
2, bad fouling
0, complete fouling
Arbitrary Rating of Over-all Fouling
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434
The experimental tubes were observed closely for the first minute for any immediate effect on the behavior of the animal, as determined by an increase in its speed of movement coupled with a certain irregularity of motion. The condition was further recorded after 15 and 30 minutes, 1, 6, 12, and 24 hours; in later experiments observations were discontinued after the sixth hour. The condition of the animals a t the time the observation was made is recorded as dead, dying, some effect, and no effect. “No effect” describes the appearance of the tube when the animals are swimming freely and without apparent discomfort. “Some effect” means that the animals are still swimming freely but are showing jerky irregular motion; recovery from this condition is not infrequent. “Dying” indicates that the animals are lying a t the bottom of the tube but are still exhibiting irregular movements of the antennae; some occasionally rise a few millimeters above the bottom of the tube and then sink back. Recovery from this condition was never observed. “Dead” refers to animals lying motionless on the bottom of the tube. (There is some reason to doubt the strict accuracy of this term, as a deep narcosis would have produced the same appearance; this possibility is not of any practical importance in relation to the purpose of these tests.) TESTS ON CHEMICALS
ORGANIC COMPOUNDS. A large number of representative organic compounds were evaluated by the test procedure, and certain of them were classified into four groups based on their apparent efficiency as toxic agents:
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Certain cyclic nitrogen bases, of the pyridine and quinoline family, particularly those boiling in the range 258263’ C.; and pitchy residues derived from the prior recovery of the lower boiling pyridines 3. Certain aromatic unsaturated aldehydes, of which cinnamic aldehyde is typical 2.
Mixtures of these three types of toxic compounds are apparently more rapidly effective than are the single reagents. I n all cases concentrations of the order of 10-5 molal were lethal to Daphnia. INORGANIC COMPOUNDS.For comparison, a similar evaluation was made of the relative toxicities of the familiar heavy metals used (in the form of oxides, salts, and as metals) in the usual antifouling paints. The death times for 0.001 M solutions of a number of the metal chlorides against Daphnia follow: Metal Ion Mercury (ic) Cadmium Copper Manganese (ous) Ammonium Calcium Selenium Tellurium Iron (ous)
Death Time, Hr. 0.25 1.0 1.5 1.5 1.5 1.5 1.5 1.5 2.0
Metal Ion Death Time, Hr. Zinc 2.5 Chromium (ous) 2.5 Barium 2.5 Cobalt (ous) 3.0 Iron (io) 3.0 Lithium 3.5 Sodium No effect Potassium No effect Lead (ous) No effect
It is apparent that known experience with heavy metal toxics is rather quantitatively predictable by death time tests on Daphnia. That is, the generally employed metallic compounds of mercury, copper, manganese, and zinc are seen to be effectively lethal to Daphnia. VEHICLE P E R M E A B I L I T Y
1,3-Xylenol p-Cresol
Early in the investigation it became apparent that one of the major controlling factors in antifouling performance Benzocaine must be the equilibrium permeability to sea water of any Trichloroethyl vehicle carrying a soluble toxic agent. Accordingly, the phosphate water permeability of a wide range of organic film-forming p-Cyclohexylphenol resin films was determined by the familiar method of Wray p-tert-Butylphenol Naphthalene and Van Horst (6). Relative permeability data for typical ptert-Amylphenol organic vehicles, together with data on several formulations Pyridine base containing solid toxic phenols and inert pigmentations, residues appear in Table I. Chlorinated cresols These figures show the wide range of permeabilities obtain(30% C1) Chlorinated cresols able with varnish and synthetic resin vehicles. Actual (50% 91) marine exposure, using selected vehicles of permeability Crude tripyridyl rate from 4 t o 300 with a constant toxic content, has clearly D. OUTSTANDINGLY EFFICIENT demonstrated that the optimum permeability range for effective antifouling performance is 75 to 150, with the Thymol preferred permeability approximating 100. o-tert-Amylphenol
o-Cyclohexylphenol 2-Chlorophenylphenol Quinaldine Chlorinated xylenols
o-Cresol Cinnamaldehyde Tar base (boiling at 260-263’ C.)
USELESS Tetrachlorobenzene Pentachlorobenzene Hexachlorobenzene Pentachlorophenyl benzoate Cinchophene Quinoidine Carbazole Chloral hydrate Orris gum p-Isopropylindene Benzyl polysulfide Polychloronaphthalene Tetramethylphenol sulfide Dichlorophenyl benzoate Dimethylphenol sulfide A.
C.
EFFICIENT
B. MODERATELY EFFICIENT p-Dichlorobenzene
In view of the fact that sea water abounds in microorganisms, supplementary experiments were carried out to determine whether a high concentration of such forms could blanket the effect of the outstandingly efficient substances. Thus similar tests to those described were carried out in culture medium to which had been added enough yeast to produce an opacity equivalent to that of milk. The results of these laboratory tests did not differ from those made in straight culture medium. I n general, three basic types of organic compounds (1) may be expected to be effective against shell-forming organisms resembling the Cypris larva in their embryonic stages: 1. Certain o- and p-substituted phenols and their halogenated
derivatives
TABLEI.
WATERPERMEABILITY RATES Water Mg. Permeability HsO/Mii/
Vehicle T y p e 25-gal. phenolic varnish 1
+
75% varnish 1 25% alkyd R-869 Polycyclopentadiene 25-gal. ester gum varnish 2 Copolymer of vinyl chloride a n d acetate
Methacrylate Linseed oil 4
Added Toxic or Pigment None 25% 1.3-xylenol None None 25 % ’ 2-chloro-4-phenyl-phenol None 2570 13-xylenol 2 5 7 i 3-xylenol pigmented w%h ‘TiOz” None 25% 13-xylenol 10% cblite 25% celjte 50% celite None 2 5 7 13-xylenol 25% 2&hloro-4-phenyl-phenol None
At p i g m e n t / v a r n l h ratio of 2/1.
Sq. In./24 Hr. 39.2 32.8
120.0 3.5 4.0 49.8 49.8 204.0
17.8 24.0 14.1 33.4 45.5 127.0 114.0 362.0 298.0
April, 1943
I N D U S T R I A L A N D E N G I N E E R I N G CHEMISTRY PANEL EXPOSURE TESTS
While laboratory tests are instructive, they cannot replace actual exposure under fouling conditions. The exposure site chosen is in the Ponce de Leon tidal inlet, one half mile from the Atlantic Ocean on the Florida sea coast, approximately 14 miles south of Daytona Beach. Marine fouling growth a t this location is heavy during the entire year. Water temperatures vary between relatively narrow
cases special priming paints or treatments suitable to the specific surface were used.) The method of rating exposed panels is demonstrated in Figure 2. The occurrence of type of fouling organism is rated on the scale at monthly intervals during the life of the test. For convenience in examination and reporting, the following classification is used : barnacles (all types), mollusks (oysters, clams, and mussels), tube worms (annelids),
Exposed side
Figure 3.
435
Under side
Barnacles Embedded in Soft Paint Film
limits (65-80' F.) from midsummer to midwinter, and the area is free from extraneous contaminating influences such as bilge oil, industrial waste, sewage, etc. The average tide is 3 feet a t this site. The test racks are constructed of untreated grade C cypress, slotted to hold 6 X 12 inch metal panels. Wooden panels are usually 7 X 12 X l1/* inches in size; the relatively thick blocks enable teredo attack to be examined with ease. A number of studies were made using rubber. The method of mounting flexible rubber panels is shown in Figure 1. All panels are exposed vertically, a t a depth of 24 inches below low-tide level; the racks are reversed biweekly to ensure uniform exposure and to eliminate inshore-offshore effects. For comparative evaluation of antifouling paints, sandblasted steel panels are generally used; they are primed with a t least two different standardized priming paints (two coats), and finished with a single coat of the antifouling paint. For evaluation on wood, three primer coats of a 40-gallon phenolic spar varnish are applied before the antifouling coat. Unless otherwise noted, all paints are brushapplied. (Certain studies have involved other surfaces; typical are glass, rubber, and the light metals. In these
hydroids (and stalked corals), Bryozoa (encrusting and filamentous), algae and scum (all types). Examples of these growths are illustrated on the control panel in Figure 1, and the more heavily fouled panels (rating 6 or worse) in Figure 2. GENERAL OBSERVATIONS
Subsequent papers in this series will evaluate the various controlling factors in antifouling paint performance. Typical is the effect of vehicle permeability rate; another is that of toxic concentration. All the data substantially confirm Baerenfaenger's observation (1) that color as such has no effect on the fouling characteristics of a given vehicle-toxic combination. So far the reported sensitivity to pale greens and whites ( 3 ) has not been confirmed. Panels 4, 2, 10, and 8 shown in Figure 1 of the following paper (page 436) were selected from a set in which only the toxic content was varied in a series of pigmented vehicles a t constant pigment-binder ratio; one group of panels was gray-white and the other was dark brown. The only relation between extent of fouling and a controlled factor in these paints was an inverse
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INDUSTRIAL AND ENGINEERING CHEMISTRY
ratio with toxic concentration, an expected but conclusive finding. On the other hand, a general sensitivity to light has been confirmed. Panels were exposed in bright sunlight, and duplicates in the shade only a few feet away showed heavier fouling. The difference is not marked and certainly cannot influence choice of paint color. The consistency or hardness of the antifouling paint, independent of its permeability and exfoliating characteristics, may influence the type and extent of fouling. Figure 3 shows a stripped-off paint film which was initially soft and gummy and remained so during immersion. The photograph presents both sides of this stripped film; the embedding tendency of the barnacles, with consequent injury to the underlying surface by contact-corrosion effects, is conclusively demonstrated. I n general, we believe that the harder the exposed paint film can be, all other factors being equal, the better protection it will afford against fouling. ACKNOWLEDGMENT
It is a pleasure to record the cooperation and assistance of Peter Gray, associate professor of biology a t the University
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of Pittsburgh, under whose direction the laboratory evaluations of primary toxicity were carried out. LITERATURE C I T E D
Baerenfaenger, C., meeting of Verein Deutscher Ingenieure. Kiel, 1937. Clapp, W. F., Am. h s s o c . Advancement Sci., Symposium on Corrosion, Gibson Island, Md., 1941. Oshima, S., J. SOC.Chem. Ind. Japan, 37,589 (1934); 38, 69, 170 (1935). Pratt, H.S.,“Manual of the Common Invertebrate Animals”, rev. ed.. Philadelphia, P. Blakiston’s Son & Co., 1935. U. S. Navy Dept., Bur. of Ships, “Docking Report Manual”, p. 6 (1942)
Wray, R. I., and Van Horst, A. R., IND.ENG.CHEM.,28, 1268 (1936). Young, G. H.,and Gray, Peter, U. S Patent 2,287,218 (June 23, 1942). ZoBell, C. E., Natl. Paint, Varnish Lacguer Assoc., Sci. Sect.. Circ. 588 (1939). ZoBell, C. E., Oficial Digest Federatzon Paint & Varnish Production Clubs, 17, 379-285. CONTRIBUTION from t h e Multiple Fellowship of Stoner-Mudge, Ino., at Mellon Institute.
Heavy Metal Compounds as Toxic Agents G. H. YOUNG AND W. IC. SCHNEIDER
HE previous paper described a procedure for the preliminary evaluation of toxic compounds designed for use in antifouling paints. It was demonstrated that the ions of a variety of heavy metals might be expected to have lethal action on Cypris larva and other embryonic fouling organisms. Accordingly, an extensive series of test panels was prepared for marine exposure a t Daytona Beach, Fla., involving controlled concentrations of representative heavy metal compounds in a suitable oleoresinous short-oil vehicle. Several commercial antifouling paints were included in the series for comparison purposes.
T
PREPARATION OF PANELS
The wood panels were 7 X 12 X l1j8inch seasoned poplar, primed with three brush coats of a 40-gallon phenolic spar varnish. The steel panels were prepared in duplicate, freshly sandblasted, and primed with two brush coats of two selected anticorrosive primers. A 25-gallon, 60 per cent tung oil-40 per cent linseed oil, phenolic varnish pigmented with zinc tetroxy chromate was one primer; an 8gallon, 50 per cent tung oil-50 per cent linseed oil, coumarone varnish pigmented with red lead was the other. The latter varnish was also selected to carry the toxic components because the permeability measurements had demonstrated its optimum moisture transniission characteristics. The experimental antifouling compositions evaluated are described in Table I ; a series of paints comprising two or more toxic agents was prepared from these primary formulations, and the combinations are listed in Table 11. Additional panels were painted with four commercial antifouling paints and with two paints made up according t o a Navy formula (1). I n one case red cuprous oxide was used; in the other, yellow.
EXPOSURE OF M E T A L COMPOUNDS
The panels were placed on test in December, 1941, and examined a t monthly intervals. At the end of one month the following paints still rated 9 or better; a t this stage the controls (containing no toxic) rated 7-8: AF-1,2, 7, 9, 11, 13, 14, 16, 17; proprietary paints 1, 2, and 3; Navy formula 16 with red and with yellow cuprous oxides. At the end of 2-month immersion, the following paints rated 8 or better, the controls rating 5-6: AF-2, 9, 11, 13, 16; proprietary paints 1and 3; both Navy formula 16 paints. At the end of 4.5 months the following paints rated 8 or better, the controls rating 2-3: AF-2 and 11; proprietary paints 1 and 3. The relative appearance of these paints is shown in Figure 1. .1
PAINTS CONTAINING SINGLE TOXICS TABLE I. EXPERIMENTAL [Vehicle, 50-50 tung-linseed, 8-gallon coumarone varnish (65 % ’ solids) ; pigment-vehicle ratio 2/11 Pigment Composition Toxic component % Inert % Code No. AF-1 AF-2 AF-3 AB-4 AF-5 AF-0
Yellow mercuric oxide Copper powder Copper arsenite Red cuprous oxide Zinc oxide Sublimed blue lead
60 60 GO 60 60 60
Barytes Barytes Barytes Barytes Barytes Barytes
40 40 40 40 40 40
At 6.5-month exposure only AF-2 and proprietary paints 1 and 3 were still actively antifouling, rating 8 or better. Figure 2 illustrates these paints, together with certain of the others, now failing. After 9 months the two good proprietaries and AF-2 still rated 8 or better; all the remaining panels were rated at 3 or worse and hence were removed.
