G . H . Y O U N G , G . W . G E R H A R D T W . K . S C H N E I D E R
M e ll o n I n s t i t u t e ,
T
H E problem of fouling of surfaces subjected to immersion 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 th a t, by its nature or content of “toxic” agencies, fouling growths would be prevented or a t least reasonably inhibited. To this end an almost unlimited number of specific compositions, for which antifouling properties are claimed, appear in the paten t and technical literature. In m any preparations the beneficial effect is attrib u ted 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 to the presence of one or more “poisons” or toxic agents.
The phototropicity of certain types of fouling organisms has frequently been dem onstrated by biological studies.
The suggestion has therefore been made th a t color alone is th e m ost significant factor in autifouling paint performance;
the argum ent of light vs. dark paints is still unsettled.
I t has more recently been asserted th a t the only effective approach from the pain t standpoint is to strive for extreme exfoliation or “underw ater chalking” properties; b u t the question of chalking coatings or toxic coatings is still un
answered.
In th e research reported here additional fight is thrown on these controversial phases of the problem of antifouling p ain t form ulation. T he experimental paints employed
u P e n n a .
do not necessarily represent practical or even usable coatings;
rather, the several variables have been m aintained under as rigid control as possible w ithin th e lim itations of varnish cooking and form ulating techniques. In every case, how
ever, commercially available constituents have been used, of the purity represented by th e products procurable on the market.
T H E F O U L I N G P R O C E S S
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 sim ultaneously: th e form ation of the slimy microbiological film, th e a tta c h m e n t of macro
scopic fouling organisms (alm ost always in larval form), and their growth into the m ature forms, visable as barnacles, mollusks, annelids, Bryozoa, algae, and other fouling growths (5). The probable role in the fouling process of the micro
biological film has been described b y ZoBell, Clapp, and others (2, 8 ,9 ). T h a t such films are universally present on surfaces shortly after submersion in sea w ater is unquestioned.
Nevertheless, evidence th a t such prior film form ation is essential for subsequent a ttac h m e n t of macroorganisms is inconclusive. Our own experim ents indicate th a t slime forma
tion on antifouling paints m ay eventually v itiate their effect by a simple blanketing action preventing lethal concentra
tions of the toxic agents from building up a t th e slime film - water interface. This observation is in agreem ent w ith the
A p r i l , 1 9 4 3 I N D U S T R I A L A N D E N G I N E E R I N G C H E M I S T R Y 4 3 3
findings of th e N av y (5). W here sufficiently high toxic concentrations can be realized, in spite of th e slime film we have been able to m ain tain slime-covered surfaces free from m acrogrow ths for m any m onths.
The principal organism s w ith which one has to deal on underw ater stru ctu res m ay be classified as follows:
Organisms building hard, calcareous, or chitinous shells Annelids: coiled or tw isted tubes
B arnacles: cone-shaped shells built up of lam inated plates, attach ed directly or by m eans of long m uscular stalks Bryozoa (encrusting): flat, spreading, multicellular coral-like
patches
M ollusks: bivalves such as clams, mussels, oysters Organisms w ithout h ard shells
Algae: green, brown, or red filam ent-like growths, gener
ally near the w ater line
Bryozoa (filam entous): fern-like or tree-like growths, the branches not expanded a t th e tips
H ydroids: stalk-like or branching grow ths, each branch te r
m inating in an expanded tip
Tunicates: soft, spongy masses (“ sea sq u irts” ) Boring organisms
Teredo: soft-bodied worms w ith a cu ttin g shell-like head (“ship w orm s” )
M artesia: boring clam-like mollusks Lim noria: shrim p-like drilling arthropods
These types of organism s are described in th e N av y ’s Docking M anual (5). D etails concerning morphology and differences among subspecies are contained in m ost sta n d ard biological texts (4).
P R I M A R Y T O X I C I T Y
Certain prelim inary m easurem ents were m ade on a wide variety of toxic m aterials. As te s t object a fresh-w ater
Zoological affinities Size, mm.
Appearance H abitat Light reaction Toxicological reaction
arthropod, D aphnia, more th a n superficially sim ilar to the Cypris larva or em bryonic Balanus, was used because it was n o t practical to m aintain colonies of Cypris larvae in an inland laboratory.
Cypris Larva Daphnia
Crustacea Cirripedia Crustacea Cladocera
1 - 3 0 . 6 - 1 . 5
Shrimp-like form in a bivalve shell Surface marine waters
Strongly positive Very sensitive to copper
Test Procedure. Two or three grams of the substance were placed in 250 ml. of distilled w ater and shaken a t intervals for 24 hours; the resu ltan t solution was arbitrarily assumed to be a sa tu ra te d solution in w ater although there is no reason to suppose th a t com plete sa tu ra tio n occurred in every case. C ertain of th e substances of relatively high solubility were adjusted to a concentration of approxim ately 1 X 10-6 molar.
A stock culture of D aphnia was sta rted in 70 gallons of ta p w ater to which were added 25 grams of sheep m anure and 15 grams of dead fish; th e m edium was enriched a t intervals w ith a weak suspension of Fleischm ann’s yeast.
H ealthy anim als from this colony were placed in 20 ml. of their own m edium in glass vials 4 inches long and 1 inch in diam eter. Three such vials were used in each te st. To th e first was added distilled w ater; to th e second was added 1 ml. of th e “satu rated te st solution” , and th e th ird re
ceived 5 ml. of th e same solution. The distilled w ater control was discontinued after th e first tw enty-five tests dem onstrated th a t it was w ithout effect on D aphnia.
R a t i n g 1 0 , p e r f e c t 8 , v e ry s l i g h t l y f o u l i n g 6 , d e f i n i t e f o u l i n g
4 , m e d i u m f o u l i n g 2 , b a d f o u l i n g 0 , c o m p l e t e f o u l i n g
F ig u r e 2. A r b itr a ry R a t in g o f O v e r -a ll F o u lin g
I N D U S T R I A L A N D E N G I N E E R I N G C H E M I S T R Y still swimming freely b u t are showing jerky irregular motion, recovery from this condition is not infrequent. Dying indicates th a t the animals are lying a t the bottom of the tube b u t 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. “D ead” refers to animals lying motionless on the bottom of the tube. (There is some
organisms, supplem entary 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 th a t of milk. The results of these laboratory tests did no t differ from those m ade in straight culture medium.
In general, three basic types of organic compounds (1) m ay be expected to be effective against shell-forming or
ganisms resembling the Cypris larva in their embryonic stages:
1. C ertain o- and p-substituted phenols and their halogenated derivatives heavy metals used (in the form of oxides, salts, and as metals) in the usual antifouling paints. T he death tim es for 0.001 compounds of mercury, copper, manganese, and zinc are seen to be effectively lethal to D aphnia.
V E H I C L E P E R M E A B I L I T Y
Early in the investigation it becam e ap p aren t th a t one of the major controlling factors in antifouling performance m ust be the equilibrium perm eability to sea w ater of any containing solid toxic phenols and in e rt pigmentations, appear in Table I.
These figures show the wide range of perm eabilities obtain
able with varnish and synthetic resin vehicles. Actual marine exposure, using selected vehicles of permeability rate from 4 to 300 w ith a constant toxic content, has clearly
P A N E L E X P O S U R E T E S T S
While laboratory tests are instructive, they cannot re
place actual exposure under fouling conditions. T he ex
posure site chosen is in th e Ponce de Leon tidal inlet, one half mile from th e A tlantic Ocean on th e F lorida sea coast, approxim ately 14 miles south of D ay to n a Beach. M arine fouling grow th a t th is location is heavy during th e entire year. W ater tem peratures v ary betw een relatively narrow April, 1943
cases special prim ing paints or treatm en ts suitable to the specific surface were used.)
T he m ethod of ratin g exposed panels is dem onstrated in Figure 2. The occurrence of ty p e of fouling organism is rate d on the scale a t m onthly intervals during th e fife of th e test. F or convenience in exam ination an d reporting, th e following classification is used: barnacles (all types), mollusks (oysters, clams, and mussels), tube worms (annelids),
I N D U S T R I A L A N D E N G I N E E R I N G C H E M I S T R Y 435
■zX*..
E x p o s e d s i d e U n d e r s id e
F ig u r e 3. B a rn a c le s E m b e d d e d in S o ft P a in t F ilm
limits (65-80° F .) from m idsum m er to m idw inter, and the area is free from extraneous contam inating influences such as bilge oil, industrial waste, sewage, etc. The average tide is 3 feet a t this site. T he te st 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 1 Vs inches in size; th e relatively thick blocks enable teredo a ttac k to be examined w ith ease. A num ber of studies were m ade using rubber. T he m ethod of m ounting flexible rubber panels is shown in F igure 1. All panels are exposed vertically, at a depth of 24 inches below low -tide level; th e racks are reversed biweekly to ensure uniform exposure and to elimi
nate inshore-offshore effects.
For com parative evaluation of antifouling paints, sand
blasted steel panels are generally used; th e y are prim ed with a t least tw o different standardized prim ing paints (two coats), and finished w ith a single coat of th e antifouling paint. F or evaluation on wood, three prim er coats of a 40-gallon phenolic spar varnish are applied before th e a n ti
fouling coat. Unless otherwise noted, all p ain ts are brush- applied. (C ertain studies have involved o ther surfaces;
typical are glass, rubber, an d th e light m etals. In these
hydroids (and stalked corals), Bryozoa (encrusting and filamentous), algae and scum (all types).
Exam ples of these growths are illustrated on th e control panel in Figure 1, and th e more heavily fouled panels (rating 6 or worse) in Figure 2.
G E N E R A L O B S E R V A T I O N S
Subsequent papers in this series will evaluate th e various controlling factors in antifouling p a in t perform ance. T ypical is th e effect of vehicle perm eability ra te ; another is th a t of toxic concentration.
All th e d a ta substantially confirm B aerenfaenger’s ob
servation (1) th a t color as such has no effect on th e fouling characteristics of a given vehicle-toxic com bination. So far th e reported sensitivity to pale greens and whites (3) has no t been confirmed. Panels 4, 2, 10, and 8 shown in Figure 1 of th e following paper (page 436) were selected from a set in which only th e toxic content was varied in a series of pigm ented vehicles a t constant pigm ent-binder ratio ; one group of panels was gray-w hite an d th e other was d ark brown. T he only relation between extent of foul
ing and a controlled factor in these p ain ts was an inverse
i n d u s t r i a l a n d e n g i n e e r i n g c h e m i s t r y independent of its permeability and exfoliating character
istics, m ay influence the type and extent of fouling. igure 3 shows a stripped-off paint film which was initially soit and gummy and remained so during immersion. The photo
graph 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 con
clusively dem onstrated. In general, we believe th a t the harder the exposed paint film can be, all other factors being equal, the better protection it will afford against fouling.
A C K N O W L E D G M E N T
I t is a pleasure to record the cooperation and assistance of Peter Gray, associate professor of biology a t the University
4 3 6
of Pittsburgh, under whose direction th e laboratory evalua
tions of prim ary toxicity were carried out.
l i t e r a t u r e c i t e d
(9) ZoBell, C. E., Official Digest Federation Paint & Varnish Produc
tion Clubs,17, 379-285.
Co n t r ib u t io n fro m th e M u ltip le F e llo w s h ip o f S to n e r - M u d g e , I n c ., a t M el- Ion I n s tit u te .