Marine Pollution Bulletin 58 (2009) 559–564

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Marine Pollution Bulletin

journal homepage: www.elsevier .com/ locate /marpolbul

Trace metals in antifouling paint particles and their heterogeneouscontamination of coastal sediments

Nimisha Singh, Andrew Turner *

School of Earth, Ocean and Environmental Sciences, University of Plymouth, Drake Circus, Plymouth, Devon PL4 8AA, UK

a r t i c l e i n f o

Keywords:Antifouling paintLeisure boatsCopperZincTrace metalsOrganometallics

0025-326X/$ - see front matter � 2008 Elsevier Ltd. Adoi:10.1016/j.marpolbul.2008.11.014

* Corresponding author. Tel.: +44 1752 584570; faxE-mail address: aturner@plymouth.ac.uk (A. Turne

a b s t r a c t

Antifouling paint residues collected from the hard-standings of a marine leisure boat facility have beenchemically characterised. Scanning electron microscopy revealed distinct layers, many containing oxidicparticles of Cu and Zn. Quantitative analysis indicated concentrations of Cu and Zn averaging about 300and 100 mg g�1, respectively, and small proportions of these metals (<2%) in organometallic form as pyri-thione compounds. Other trace metals present included Ag, Cd, Cr, Ni, Pb and Sn, with maximum concen-trations of about 330, 75, 1200, 780, 1800 and 25,000 lg g�1, respectively. Estuarine sediment collectednear a boatyard contained concentrations of Cu and Zn an order of magnitude greater than respectiveconcentrations in ‘‘background” sediment, and mass balance calculations suggested that the former sam-ple was contaminated by about 1% by weight of paint particles. Clearly, antifouling residues represent ahighly significant, heterogeneous source of metallic contamination in the marine environment whereboating activities occur.

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1. Introduction

Antifouling paints are applied to the hulls of boats and to othersubmerged structures to prevent the growth of fouling organisms,including algae, barnacles and bivalves. The slow, controlled re-lease of biocides from such applications does, however, haveimportant environmental ramifications, particularly in semi-en-closed environments with a high density of boats. Thus, elevatedconcentrations of biocidal components, including Cu and Zn andvarious organic boosters, are frequently reported (Comber et al.,2002; Helland and Bakke, 2002), while concern has been levelledat their individual or combined effects on non-target organisms(Katranitsas et al., 2003; Koutsaftis and Aoyama, 2007).

Less well understood, however, are the environmental and bio-logical impacts of spent paint particles derived from boat hullcleaning or that flake off structures, including grounded and aban-doned vessels, in situ (Tolhurst et al., 2007; Turner et al., 2008).Regulations or codes of practice concerning the removal and subse-quent disposal of antifouling residues from commercial and recre-ational boatyards exist in many countries. For example, withregard to the leisure boat industry in the UK, the British MarineFederation (2005) recommends that tarpaulin is emplaced belowboats to collect paint fragments during hull cleaning or mainte-nance, and/or that debris is carefully vacuumed from the site; haz-ardous particulates should then be disposed of appropriately. In

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many cases, however, marinas and boaters are unaware of theseguidelines (Srinivasan and Swain, 2007). Consequently, paint parti-cles of various sizes and colours are a common sight, both on thehard-standings in an around boat maintenance facilities and onthe foreshore in the vicinity of boat moorings. These particles arereadily transported into the local aquatic environment with wash-water and runoff or as airborne dust. Their potential for long-rangetransport, coupled with a relatively high surface area and erodibil-ity, suggests that antifouling boat paint particles may pose chemi-cal and biological impacts that are more widespread than isgenerally acknowledged.

In this study, we use qualitative and quantitative methods tochemically characterise individual spent paint particles and a com-posite of such collected from a marine leisure boat maintenancefacility. We focus on the metallic components (organic booster bio-cides are the subject of a separate research programme) with anoverall aim of evaluating the signature of and potential for contam-ination of the marine coastal environment from contemporary boatcleaning and maintenance activities.

2. Materials and methods

Before use, all equipment for sampling, sample processing andsample storage was soaked in 10% HCl for at least 24 h and subse-quently rinsed in distilled water. Reagents employed throughoutwere of analytical grade or better, and were purchased from Fluka,VWR or Fisher Scientific.

560 N. Singh, A. Turner / Marine Pollution Bulletin 58 (2009) 559–564

2.1. Sample collection and processing

Fragments of boat paint, of between about 5 and 50 mm inlength, were collected by hand from the hard-standings and slip-ways of a large (>100 berth) marine boat maintenance facility,catering for mainly (but not exclusively) leisure craft, in Plymouthduring April 2007. Although we implicitly refer to the sample andfragments thereof as antifouling in nature, it is important to appre-ciate that some paint particles may have been derived from partsof the boat not associated with the hull (e.g. decking and cabin)but undergoing general maintenance. These particles have a differ-ent chemical makeup to antifouling fragments, but the net sampleis representative of the signature of particulate contamination de-rived from the general, contemporary practice of marine leisureboat maintenance.

In the laboratory, visible extraneous particulates (e.g. grit andmacroalgae) were removed and the fragments pooled in two150 ml screw-capped polyethylene canisters. The contents of onecanister were ground with a pestle and mortar, a process aided bythe occasional addition of a few ml of liquid nitrogen. The groundsample was then sieved through a 63 lm nylon mesh and the finefraction stored in a polyethylene bottle. On the basis of colour andtexture, a variety of paint fragments (n = 25) was selected fromthe second canister and stored individually in polyethylene tubes.

Inter-tidal sediment was collected during December 2007 fromtwo sites on the Plym Estuary, SW England; specifically, about10 m from the foot of a hard-standing of a leisure boatyard, andat a location remote from significant boating activity. Surface, oxicscrapes were obtained using a polyethylene spatula and trans-ferred to zip-locked plastic bags. In the laboratory, the contentsof the samples were sieved through a 63 lm nylon mesh withthe aid of a few ml of estuarine water. The fine fractions werefreeze-dried and subsequently stored in polyethylene canisters un-der desiccation.

2.2. Sample digestion–extraction and metal analysis

Three aliquots of both fractionated sediment samples, threesubsamples of the fractionated paint composite and clippings ta-ken from individual fragments (including replicates of some frag-ments) were chemically characterised. For the complete digestionof metals (and phosphorus), about 100 mg of sediment or 5–10 mg of paint powder (composite) or paint clipping were accu-rately weighed into a 50 ml Pyrex beaker. Five millilitres of aquaregia (three parts HCl to one part HNO3) were added to each bea-ker, and after about 1 h the contents were covered with watchglasses and heated on a hot plate to about 75 �C for a further 2 h.The cooled contents and Milli-Q water rinsings were transferredto individual 25 ml Pyrex volumetric flasks and diluted to markwith 0.1 M HNO3. Digestions were undertaken in batches of ten,and procedural blanks, performed likewise but in the absence ofsolids, were undertaken in triplicate for each batch.

To evaluate the contribution of organometallic compounds tothe total metal content of the paint composite, triplicate subsam-ples were subject to solvent extraction according to the methodoutlined in Thomas et al. (2000) after some minor modifications.Thus, about 50 mg were weighed into a Pyrex beaker to which30 ml of a 1:1 mixture of dichloromethane–ethylacetate wereadded. The beaker was covered with Al foil and agitated on a lateralshaker at about 100 rpm at room temperature for about 2 h. Thecontents were subsequently sonicated for 10 min and centrifugedat 2100g for 15 min. Ten millilitres of supernatant were pipettedinto a clean beaker and the contents evaporated to dryness in aflow hood for about 24 h. The remaining, dried contents wereredissolved in 5 ml of 0.1 M HNO3 and transferred to a 10 ml volu-metric flask where they were diluted to mark with Milli-Q water.

Procedural blanks were undertaken likewise but in the absenceof paint particles.

Digests and extracts were analysed for Ca, Ba, Cu, Fe, Mn, P, Sr, Tiand Zn by inductively coupled plasma–optical emission spectrom-etry (ICP–OES) using a Varian 725 ES (Mulgrave, Australia), and forAg, Cd, Co, Cr, Ni, Sn and Pb by inductively coupled plasma–massspectrometry (ICP–MS) using a Plasma Quad PQ2+ (Thermoelemen-tal, Winsford, UK). Both instruments were calibrated using mixed,acidified standards, and internal standardisation was achieved bythe addition of either yttrium (ICP–OES) or indium and iridium(ICP–MS). Metals were detectable (greater than three standarddeviations of concentrations determined in the corresponding pro-cedural controls) in all cases with the exception of Ag, Cr, Mn, Niand Sr in a few fragments and Ag in the composite. Accuracy, eval-uated from triplicate digestions of a river sediment sample certifiedfor metal concentrations available to aqua regia (LGC 6187; Labora-tory of the Government Chemist, Teddington, UK) was better than90% for all elements where certified concentrations were available.

2.3. CHN analysis

Total concentrations of C, H and N were determined in 2 mg ali-quots (as a powder or clipping) of each sample by flash combustionusing a Carlo Erba EA 1110 elemental analyser calibrated withEDTA standards. Accuracy, based on analysis of C in a variety ofcertified soils and sediments, was better than 95%.

2.4. Scanning electron microscopy

The bulk physico-chemical characteristics of selected paint frag-ments (n = 20) were examined by scanning electron microscopycoupled with energy dispersive X-ray spectrometry (SEM–EDX). Be-tween six and eight fragments were glued, vertically, to the bottomof a 20 ml plastic mould which was then filled with resin and curedfor 24 h in a fume cupboard. After removing the mould, the resin waspolished with a series of sand papers of successively finer grain size(grit 400–1200) until paint layers were exposed and a smooth sur-face attained. Embedded samples were then sputter-coated with athin film in an EMITECH K 450 high vacuum carbon-coating unit.Individual fragments were labelled using conducting ink beforethe resin was attached to the SEM with adhesive tape. Samples werephotographed using a JEOL JSM-6100 operated at 20 kV and at aworking distance of 15 mm. Qualitative elemental analysis was per-formed using an Oxford Instruments Inca 200 system.

2.5. Fourier transform infrared analysis

In order to evaluate the nature of any organometallic com-pounds present, Fourier transform infrared (FTIR) spectra arisingfrom the analysis of selected paint fragments were recorded usinga Bruker IFS 66 spectrometer attached to a Hyperion 1000 IRmicroscope with a liquid nitrogen cooled mercury–cadmium–tel-luride (MCT) detector. Fragments were compressed between thewindows of a Specac diamond compression cell until an appropri-ate thickness was attained. Transmission spectra were acquired byaveraging 100 scans at a resolution of 4 cm�1 over the range 4000–400 cm�1. Compounds were identified by comparing peaks ob-tained in the finger region with literature or library data.

3. Results and discussion

3.1. Elemental composition of paint fragments and composite sample

Table 1 summarises the elemental composition of the individ-ual paint fragments. Concentrations do not, necessarily, reflect

Table 1Elemental concentrations in the boat paint composite and individual paint fragments.Concentrations are in lg g�1 and results are shown in descending order of meanmetal (and non-metal) concentration in the composite. AM, SD and GM denotearithmetic mean, standard deviation and geometric mean, respectively.

Element Composite (n = 3) Fragments (n = 25)a

AM ± SD GM Minimum Maximum

Cu 311,200 ± 20,600 40,490 956 402,100Zn 114,100 ± 7660 16,660 1180 261,200Fe 6770 ± 401 20,480 2390 341,900Ca 6380 ± 562 8300 1420 34,740Al 2870 ± 185 3720 195 13,300Ba 1050 ± 89 152 5.9 29,200Sn 550 ± 27.0 353 31.0 24,890Pb 525 ± 33.9 163 13.8 1780Ti 234 ± 18.5 271 10.3 4030Ni 149 ± 3.9 213 25.9 777Mn 75.1 ± 7.3 776 27.4 6470Sr 43.5 ± 3.6 350 81.6 1025Cr 34.0 ± 1.5 79.5 12.5 1240Cd 7.56 ± 1.02 5.74 1.11 74.5Co 5.49 ± 0.34 11.9 0.77 917Ag ndb 34.0 3.45 333

C 179,700 ± 2300 331,500 123,200 577,900H 22,000 ± 300 38,080 13,000 58,600N 7200 ± 300 8880 900 18,700P 3800 ± 330 1860 17.5 30,920

Total (%) 65.68 ± 3.27 60.53 39.57 93.14

a n < 25 for Ag, Cr, Mn, Ni and Sr.b Not detected in the composite.

C:H = 9.13

0

1

2

3

4

5

6

7

0 10 20 30 40 50 60 70

C, %

H, %

0.1

1

10

100

1000

10000

100000

1000000

0 1 10 100 1000 10000 100000 1000000

µg g-1

µg

g-1

Cd-Co

Al-Ca

Ti-Zn

Pb-Sn

Cd-Cu

Zn-Co

Fe-Cu

P-Ba

Fig. 1. Scatter plots of (a) different metal (and P) concentrations and (b) H versus Cin individual paint fragments.

N. Singh, A. Turner / Marine Pollution Bulletin 58 (2009) 559–564 561

concentrations in the corresponding original applications becauseof the differential leaching rates of the various components, espe-cially in non-self-polishing formulations (Fay et al., 2005). Of themetals analysed, Cu and Zn are most abundant in many of the frag-ments, consistent with their use in the principal pigments (cuprousoxide, cuprous thiocyanate and zinc oxide) of contemporary anti-fouling formulations (Comber et al., 2002; Yebra et al., 2004). Asidethe polymeric constituents, carbon and hydrogen, other compo-nents of antifouling paints (and topside paints and primers) thatare reflected in the results of our chemical analysis include extend-ers (e.g. barium sulphate and calcium carbonate), additional pig-ments (e.g. anatase titanium, barium metaborate, chromiumoxide, iron oxide, tin oxide, various cadmium and lead compounds)and corrosion inhibitors (e.g. zinc phosphate and strontium chro-mate). The presence of metals such as Mn and Ni in many samplesmay also reflect components of metallic base materials which, insome cases, were visibly attached to paint fragments, or to non-sil-ica-based particles of spent abrasives.

Concentrations of a given metal (and P) are highly variableamong the fragments, with a range spanning orders of magnitudeand, in most cases, a standard deviation in excess of the arithmeticmean. Variability was also evident within duplicate digestions/analyses of the same sample (results not shown); for Cu, Zn, Feand Al, duplicate concentrations sometimes differed by an orderof magnitude. Inter-fragment variability may be largely attributedto an inherent variation in the chemical composition of individualformulations (including non-antifouling paints), although hetero-geneous contamination by small adherent particulates or compo-nents of the base matrix (e.g. hull) may also be significant insome cases. Heterogeneous, extraneous contamination may alsobe responsible for intra-fragment variability of some chemicalcomponents, although we suspect that layering and the inconsis-tent subsampling of these layers in duplicate clippings is a moreimportant factor.

The chemical heterogeneity of the paint fragments was re-flected by the lack of correlations among the elements analysed,

and as exemplified by the composite of scatter plots shown inFig. 1. The only chemical pair that was significantly (p < 0.05) cor-related was carbon and hydrogen, also shown in Fig. 1, with anaverage C:H ratio of about nine. Lack of dispersion in these data re-flects the narrow range of C–H among different polymers and res-ins and other (extraneous) source materials.

Table 1 also shows the elemental composition of the fine frac-tion of the composite sample of boat paint fragments. Replicatedigestions–analyses indicate a relative standard deviation of below15% for all elements, suggesting that grinding and fractionationprovides a good means of sample homogenisation. In total, around65% of the paint composite mass was accounted for from our quan-titative analysis. Given the chemical makeup of most paints and re-sults of our SEM analysis described below, we surmise that theprincipal remaining elements of the sample were Si, Cl, O, Mgand S.

3.2. Physico-chemical forms of Cu and Zn

Information on the physico-chemical forms and speciation ofthe metallic biocidal components was gained by further quantita-tive and qualitative analysis of individual paint fragments andthe ground composite. The electron micrograph of the cross sectionof a paint fragment shown in Fig. 2 is typical of the many obtained

Fig. 2. Cross sectional SEM image of a typical fragment of antifouling paint. Spectra correspond to the locations denoted by the upper left corners of the respectivelynumbered boxes. The upper layer contains granular Cu as cuprous oxide (white grains) and cuprous thiocyanate (darker grains) embedded in an inert matrix. The middlelayer illustrates finer granules of Zn oxide and the presence of pores in the matrix. The lower layer contains grains of silica and Zn phosphate.

562 N. Singh, A. Turner / Marine Pollution Bulletin 58 (2009) 559–564

in this study. Thus, most fragments consisted of distinct layers,presumably reflecting multiple applications removed concurrentlyduring boat hull maintenance. Pits and holes of various dimensionsin the different layers were evidence of leaching out of the biocidal(and non-biocidal) components. Layers could be categorised as: (i)enriched in Cu or Zn (or sometimes both); (ii) a matrix containingany combination of Si, Ca, Mg, Al, Fe and Ti; and (iii) a matrix con-taining, additionally, Cu or Zn. Copper mainly occurred in the formof particles of various shapes and sizes, but generally betweenabout 5 and 20 lm in diameter, and spectra indicated that the me-tal existed largely as cuprous oxide or, given its coincidence with S,as cuprous thiocyanate. Zinc occurred as oxidic grains ranging fromabout 0.1–5 lm in diameter and, in some layers, as less well dis-persed grains of Zn phosphate.

A measure of organometallics in the paint composite was ob-tained by solvent extraction of subsamples prior to metal analysis.Results for Cu, Zn and Sn are shown in Table 2 in terms of both w/wconcentration and as a percentage of the respective total metalcontent. Although organometallic forms represent only a few per-

cent or less of total metal, with respect to Cu and Zn this is equiv-alent to considerable absolute concentrations. The identity of theorganometallic compounds was inferred from FTIR analysis of se-lected individual fragments of paint. Results suggested the pres-ence of the booster biocide, zinc pyrithione (peakband = 821.5 cm�1), in most samples, and the presence of copperpyrithione (peak band = 831.5 cm�1) in some fragments. Zinc pyri-thione is employed as a booster biocide in many antifouling formu-lations (Maraldo and Dahllöf, 2004) and, although Cu pyrithione issometimes employed, this compound may also form in situ by thetranschelation of Zn pyrithione (Grunnet and Dahllöf, 2005). TheSn–C bond, with a spectral peak in the region 590–520 cm�1

(Rehman et al., 2005), was not, however, observed in the samples.It is possible that any organotin present was heterogeneously dis-persed within a few fragments and not, therefore, detected fromour limited number of FTIR scans. Alternatively, given the smallconcentrations of Sn extracted by the solvent (Table 2), the major-ity of organotin originally present in older formulations may haveundergone degradation.

Table 2Concentrations of solvent-extractable (organometallic) compounds in the boat paintcomposite and the percentage contribution of these compounds to total metalconcentrations. The arithmetic mean ± one standard deviation of three independentdeterminations is given.

Metal Concentration (lg g�1) %

Cu 463 ± 60.9 0.15 ± 0.02Zn 1310 ± 73.1 1.15 ± 0.11Sn 16.4 ± 2.6 3.07 ± 0.63

Table 3Elemental concentrations in fractionated (<63 lm) Plym estuarine sediment collectedfrom the vicinity of a leisure boatyard (BY) and remote from any boating activity (ES).Concentrations are in lg g�1, and the arithmetic mean ± one standard deviation ofthree independent determinations is given. EF represents the enrichment factor of atrace metal as calculated using Eq. (1).

BY ES EF

Al 21,600 ± 1800 18,600 ± 2100Fe 19,500 ± 940 17,400 ± 950C 30,000 ± 2000 29,000 ± 5000

Cu 2230 ± 1900 98.5 ± 9.3 19.49Zn 916 ± 600 129 ± 15.0 6.09Ni 31.1 ± 6.1 11.1 ± 1.2 2.41Cr 34.8 ± 3.8 18.0 ± 1.7 1.67Co 11.2 ± 0.7 5.9 ± 0.3 1.64Pb 163 ± 16.3 85.9 ± 11.8 1.63Cd 0.97 ± 0.25 0.57 ± 0.03 1.46Sn 12.3 ± 0.9 8.2 ± 2.5 1.30

N. Singh, A. Turner / Marine Pollution Bulletin 58 (2009) 559–564 563

3.3. Contribution of antifouling paint particles to metal concentrationsin sediment

Elemental contents of size fractionated (<63 lm) inter-tidalparticles collected from the Plym Estuary, SW England, both inthe vicinity of a boatyard (BY) and remote from any obvious boat-ing activity (ES), are shown in Table 3. Given that concentrations ofAl, Fe and C are similar in both samples, it is reasonable to assumethat the particles are geochemically consistent. Enrichment factors(EF) for trace metals in the vicinity of the boatyard, also shown inTable 3, were computed from arithmetic mean metal concentra-tions, [Me], after normalisation with respect to Al as follows:

EF ¼ ½Me�BY=½Al�BY

½Me�ES=½Al�ESð1Þ

Values are greater than unity for all trace metals analysed andgreatest enrichment is exhibited by the two metals that are mostabundant in the paint composite. Clearly, therefore, metal contam-ination of this sample is attributable to local leisure boating activ-ity. Moreover, substantial variability among the replicate analysesof Cu and Zn (rsd > 50%) and visible paint fragments remaining onthe sieve used to fractionate the sediment strongly suggest thatpaint particles are responsible. Contamination may arise directly,from spent fragments themselves, and indirectly, through leachingof metals into interstitial waters and subsequent readsorption tosediment particles.

Neglecting small granular and textural differences between theestuarine samples, the following mass balance equation may beused to evaluate the fractional, mass contribution of paint particlesto the contaminated sediment, fPC, as follows (Turner et al., 2008):

fPC ¼½Me�BY � ½Me�ES

½Me�PC � ½Me�ESð2Þ

where [Me]PC denotes the concentration of a metal in the paintcomposite. Using the arithmetic mean data for Cu and Zn reportedin Tables 1 and 3, contamination of background estuarine sediment

by around seven parts per 1000 of antifouling paint particles is re-quired to attain the concentrations measured in the sediment sam-ple near to the boatyard.

3.4. Nature and impacts of antifouling paint particle contamination

The elemental content of the composite of paint fragments col-lected from a leisure boat maintenance facility is consistent withwhat is known about the composition of the most popular contem-porary antifouling formulations (Comber et al., 2002; Yebra et al.,2004). Clearly, paint residues represent an important local sourceof particulate metallic contamination to the coastal marine envi-ronment through the cleaning, maintenance, grounding and aban-donment of boats, and the flaking from a variety of underwaterstructures in situ. Given the compositional variation observedamong the individual paint fragments collected from the leisureboat industry, this source is likely to be highly heterogeneous,exhibiting both temporal and geographical variation that is depen-dent on the precise formulations applied and removed. The magni-tude of contamination from boatyards will depend on additionalfactors such as the size and layout (e.g. enclosure and drainage)of the facility, the time of year, and whether safe disposal of partic-ulates is enforced or practiced.

Copper and Zn exhibit greatest enrichment in the paint compos-ite compared with estuarine sediment uncontaminated by boatingactivity but, because of the range in metal concentrations encoun-tered in individual fragments, other metals such as Ag, Cd, Cr andPb could pose more local or transient threats to the benthic com-munity. Ultimately, the risk and impacts arising from spent paintparticulates will be dependent on the solubility or rate of geo-chemical and biological mobilisation of toxic metals (and addi-tional organic boosters) from the paint matrix. Accordingly, weare currently investigating the release of metals from paint parti-cles suspended in sea water under different environmental condi-tions, along with in vitro measures of metal bioaccessibility tosuspension-feeding and deposit-feeding invertebrates using diges-tive enzymes and proteins. Regardless of the precise outcome ofongoing experiments, stricter enforcement of the safe disposal ofantifouling paint particles from the leisure boating industry isrecommended.

Acknowledgements

We are grateful to Dr. Andy Fisher, Dr. Roy Moate andMr. Andrew Tonkin (UoP) for assistance with sample analysis. NSwas supported by an Erasmus Mundus studentship to undertakea Joint European Masters in Water and Coastal Management. Thisstudy was funded, in part, by the Green Blue initiative of the RoyalYachting Association/British Marine Federation.

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