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Trace metals in antifouling paint particles and their heterogeneous contamination of coastal sediments
Marine Pollution Bulletin 58 (2009) 559–564
Contents lists available at ScienceDirect
Marine Pollution Bulletin journal homepage: www.elsevier.com/locate/marpolbul
Trace metals in antifouling paint particles and their heterogeneous contamination 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 Keywords: Antifouling paint Leisure boats Copper Zinc Trace metals Organometallics
i n f o
a b s t r a c t Antifouling paint residues collected from the hard-standings of a marine leisure boat facility have been chemically characterised. Scanning electron microscopy revealed distinct layers, many containing oxidic particles of Cu and Zn. Quantitative analysis indicated concentrations of Cu and Zn averaging about 300 and 100 mg g1, respectively, and small proportions of these metals (<2%) in organometallic form as pyrithione compounds. Other trace metals present included Ag, Cd, Cr, Ni, Pb and Sn, with maximum concentrations of about 330, 75, 1200, 780, 1800 and 25,000 lg g1, respectively. Estuarine sediment collected near a boatyard contained concentrations of Cu and Zn an order of magnitude greater than respective concentrations in ‘‘background” sediment, and mass balance calculations suggested that the former sample was contaminated by about 1% by weight of paint particles. Clearly, antifouling residues represent a highly significant, heterogeneous source of metallic contamination in the marine environment where boating activities occur. Ó 2008 Elsevier Ltd. All rights reserved.
1. Introduction Antifouling paints are applied to the hulls of boats and to other submerged structures to prevent the growth of fouling organisms, including algae, barnacles and bivalves. The slow, controlled release of biocides from such applications does, however, have important environmental ramifications, particularly in semi-enclosed environments with a high density of boats. Thus, elevated concentrations of biocidal components, including Cu and Zn and various organic boosters, are frequently reported (Comber et al., 2002; Helland and Bakke, 2002), while concern has been levelled at 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 biological impacts of spent paint particles derived from boat hull cleaning or that flake off structures, including grounded and abandoned vessels, in situ (Tolhurst et al., 2007; Turner et al., 2008). Regulations or codes of practice concerning the removal and subsequent disposal of antifouling residues from commercial and recreational boatyards exist in many countries. For example, with regard to the leisure boat industry in the UK, the British Marine Federation (2005) recommends that tarpaulin is emplaced below boats to collect paint fragments during hull cleaning or maintenance, and/or that debris is carefully vacuumed from the site; hazardous particulates should then be disposed of appropriately. In * Corresponding author. Tel.: +44 1752 584570; fax: +44 1752 584710. E-mail address: [email protected] (A. Turner). 0025-326X/$ - see front matter Ó 2008 Elsevier Ltd. All rights reserved. doi:10.1016/j.marpolbul.2008.11.014
many cases, however, marinas and boaters are unaware of these guidelines (Srinivasan and Swain, 2007). Consequently, paint particles of various sizes and colours are a common sight, both on the hard-standings in an around boat maintenance facilities and on the foreshore in the vicinity of boat moorings. These particles are readily transported into the local aquatic environment with washwater and runoff or as airborne dust. Their potential for long-range transport, coupled with a relatively high surface area and erodibility, suggests that antifouling boat paint particles may pose chemical and biological impacts that are more widespread than is generally acknowledged. In this study, we use qualitative and quantitative methods to chemically characterise individual spent paint particles and a composite of such collected from a marine leisure boat maintenance facility. We focus on the metallic components (organic booster biocides are the subject of a separate research programme) with an overall aim of evaluating the signature of and potential for contamination of the marine coastal environment from contemporary boat cleaning and maintenance activities.
2. Materials and methods Before use, all equipment for sampling, sample processing and sample storage was soaked in 10% HCl for at least 24 h and subsequently rinsed in distilled water. Reagents employed throughout were of analytical grade or better, and were purchased from Fluka, VWR or Fisher Scientific.
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2.1. Sample collection and processing Fragments of boat paint, of between about 5 and 50 mm in length, were collected by hand from the hard-standings and slipways of a large (>100 berth) marine boat maintenance facility, catering for mainly (but not exclusively) leisure craft, in Plymouth during April 2007. Although we implicitly refer to the sample and fragments thereof as antifouling in nature, it is important to appreciate that some paint particles may have been derived from parts of the boat not associated with the hull (e.g. decking and cabin) but undergoing general maintenance. These particles have a different chemical makeup to antifouling fragments, but the net sample is representative of the signature of particulate contamination derived from the general, contemporary practice of marine leisure boat maintenance. In the laboratory, visible extraneous particulates (e.g. grit and macroalgae) were removed and the fragments pooled in two 150 ml screw-capped polyethylene canisters. The contents of one canister were ground with a pestle and mortar, a process aided by the occasional addition of a few ml of liquid nitrogen. The ground sample was then sieved through a 63 lm nylon mesh and the fine fraction stored in a polyethylene bottle. On the basis of colour and texture, a variety of paint fragments (n = 25) was selected from the second canister and stored individually in polyethylene tubes. Inter-tidal sediment was collected during December 2007 from two sites on the Plym Estuary, SW England; specifically, about 10 m from the foot of a hard-standing of a leisure boatyard, and at a location remote from significant boating activity. Surface, oxic scrapes were obtained using a polyethylene spatula and transferred to zip-locked plastic bags. In the laboratory, the contents of the samples were sieved through a 63 lm nylon mesh with the aid of a few ml of estuarine water. The fine fractions were freeze-dried and subsequently stored in polyethylene canisters under desiccation. 2.2. Sample digestion–extraction and metal analysis Three aliquots of both fractionated sediment samples, three subsamples of the fractionated paint composite and clippings taken from individual fragments (including replicates of some fragments) were chemically characterised. For the complete digestion of metals (and phosphorus), about 100 mg of sediment or 5– 10 mg of paint powder (composite) or paint clipping were accurately weighed into a 50 ml Pyrex beaker. Five millilitres of aqua regia (three parts HCl to one part HNO3) were added to each beaker, and after about 1 h the contents were covered with watch glasses and heated on a hot plate to about 75 °C for a further 2 h. The cooled contents and Milli-Q water rinsings were transferred to individual 25 ml Pyrex volumetric flasks and diluted to mark with 0.1 M HNO3. Digestions were undertaken in batches of ten, and procedural blanks, performed likewise but in the absence of solids, were undertaken in triplicate for each batch. To evaluate the contribution of organometallic compounds to the total metal content of the paint composite, triplicate subsamples were subject to solvent extraction according to the method outlined in Thomas et al. (2000) after some minor modifications. Thus, about 50 mg were weighed into a Pyrex beaker to which 30 ml of a 1:1 mixture of dichloromethane–ethylacetate were added. The beaker was covered with Al foil and agitated on a lateral shaker at about 100 rpm at room temperature for about 2 h. The contents were subsequently sonicated for 10 min and centrifuged at 2100g for 15 min. Ten millilitres of supernatant were pipetted into a clean beaker and the contents evaporated to dryness in a flow hood for about 24 h. The remaining, dried contents were redissolved in 5 ml of 0.1 M HNO3 and transferred to a 10 ml volumetric flask where they were diluted to mark with Milli-Q water.
Procedural blanks were undertaken likewise but in the absence of paint particles. Digests and extracts were analysed for Ca, Ba, Cu, Fe, Mn, P, Sr, Ti and Zn by inductively coupled plasma–optical emission spectrometry (ICP–OES) using a Varian 725 ES (Mulgrave, Australia), and for Ag, Cd, Co, Cr, Ni, Sn and Pb by inductively coupled plasma–mass spectrometry (ICP–MS) using a Plasma Quad PQ2+ (Thermoelemental, Winsford, UK). Both instruments were calibrated using mixed, acidified standards, and internal standardisation was achieved by the addition of either yttrium (ICP–OES) or indium and iridium (ICP–MS). Metals were detectable (greater than three standard deviations of concentrations determined in the corresponding procedural controls) in all cases with the exception of Ag, Cr, Mn, Ni and Sr in a few fragments and Ag in the composite. Accuracy, evaluated from triplicate digestions of a river sediment sample certified for metal concentrations available to aqua regia (LGC 6187; Laboratory of the Government Chemist, Teddington, UK) was better than 90% for all elements where certified concentrations were available. 2.3. CHN analysis Total concentrations of C, H and N were determined in 2 mg aliquots (as a powder or clipping) of each sample by flash combustion using a Carlo Erba EA 1110 elemental analyser calibrated with EDTA standards. Accuracy, based on analysis of C in a variety of certified soils and sediments, was better than 95%. 2.4. Scanning electron microscopy The bulk physico-chemical characteristics of selected paint fragments (n = 20) were examined by scanning electron microscopy coupled with energy dispersive X-ray spectrometry (SEM–EDX). Between six and eight fragments were glued, vertically, to the bottom of a 20 ml plastic mould which was then filled with resin and cured for 24 h in a fume cupboard. After removing the mould, the resin was polished with a series of sand papers of successively finer grain size (grit 400–1200) until paint layers were exposed and a smooth surface attained. Embedded samples were then sputter-coated with a thin film in an EMITECH K 450 high vacuum carbon-coating unit. Individual fragments were labelled using conducting ink before the resin was attached to the SEM with adhesive tape. Samples were photographed using a JEOL JSM-6100 operated at 20 kV and at a working distance of 15 mm. Qualitative elemental analysis was performed using an Oxford Instruments Inca 200 system. 2.5. Fourier transform infrared analysis In order to evaluate the nature of any organometallic compounds present, Fourier transform infrared (FTIR) spectra arising from the analysis of selected paint fragments were recorded using a Bruker IFS 66 spectrometer attached to a Hyperion 1000 IR microscope with a liquid nitrogen cooled mercury–cadmium–telluride (MCT) detector. Fragments were compressed between the windows of a Specac diamond compression cell until an appropriate thickness was attained. Transmission spectra were acquired by averaging 100 scans at a resolution of 4 cm1 over the range 4000– 400 cm1. Compounds were identified by comparing peaks obtained 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 individual paint fragments. Concentrations do not, necessarily, reflect
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N. Singh, A. Turner / Marine Pollution Bulletin 58 (2009) 559–564 Table 1 Elemental concentrations in the boat paint composite and individual paint fragments. Concentrations are in lg g1 and results are shown in descending order of mean metal (and non-metal) concentration in the composite. AM, SD and GM denote arithmetic mean, standard deviation and geometric mean, respectively.
10000
Minimum
Maximum
40,490 16,660 20,480 8300 3720 152 353 163 271 213 776 350 79.5 5.74 11.9 34.0
956 1180 2390 1420 195 5.9 31.0 13.8 10.3 25.9 27.4 81.6 12.5 1.11 0.77 3.45
402,100 261,200 341,900 34,740 13,300 29,200 24,890 1780 4030 777 6470 1025 1240 74.5 917 333
C H N P
179,700 ± 2300 22,000 ± 300 7200 ± 300 3800 ± 330
331,500 38,080 8880 1860
123,200 13,000 900 17.5
577,900 58,600 18,700 30,920
Total (%)
65.68 ± 3.27
60.53
39.57
93.14
n < 25 for Ag, Cr, Mn, Ni and Sr. Not detected in the composite.
-1
GM
311,200 ± 20,600 114,100 ± 7660 6770 ± 401 6380 ± 562 2870 ± 185 1050 ± 89 550 ± 27.0 525 ± 33.9 234 ± 18.5 149 ± 3.9 75.1 ± 7.3 43.5 ± 3.6 34.0 ± 1.5 7.56 ± 1.02 5.49 ± 0.34 ndb
1000
µg g
AM ± SD Cu Zn Fe Ca Al Ba Sn Pb Ti Ni Mn Sr Cr Cd Co Ag
100 Cd-Co Al-Ca
10
Ti-Zn Pb-Sn Cd-Cu
1
Zn-Co Fe-Cu P-Ba
0.1 0
1
10
100
1000
10000
100000 1000000
-1
µg g 7 6 5
H, %
Composite (n = 3)
a
100000
Fragments (n = 25)a
Element
b
1000000
C:H = 9.13
4 3 2
concentrations in the corresponding original applications because of the differential leaching rates of the various components, especially in non-self-polishing formulations (Fay et al., 2005). Of the metals analysed, Cu and Zn are most abundant in many of the fragments, consistent with their use in the principal pigments (cuprous oxide, cuprous thiocyanate and zinc oxide) of contemporary antifouling formulations (Comber et al., 2002; Yebra et al., 2004). Aside the polymeric constituents, carbon and hydrogen, other components of antifouling paints (and topside paints and primers) that are reflected in the results of our chemical analysis include extenders (e.g. barium sulphate and calcium carbonate), additional pigments (e.g. anatase titanium, barium metaborate, chromium oxide, iron oxide, tin oxide, various cadmium and lead compounds) and corrosion inhibitors (e.g. zinc phosphate and strontium chromate). The presence of metals such as Mn and Ni in many samples may also reflect components of metallic base materials which, in some cases, were visibly attached to paint fragments, or to non-silica-based particles of spent abrasives. Concentrations of a given metal (and P) are highly variable among the fragments, with a range spanning orders of magnitude and, in most cases, a standard deviation in excess of the arithmetic mean. Variability was also evident within duplicate digestions/ analyses of the same sample (results not shown); for Cu, Zn, Fe and Al, duplicate concentrations sometimes differed by an order of magnitude. Inter-fragment variability may be largely attributed to an inherent variation in the chemical composition of individual formulations (including non-antifouling paints), although heterogeneous contamination by small adherent particulates or components of the base matrix (e.g. hull) may also be significant in some cases. Heterogeneous, extraneous contamination may also be responsible for intra-fragment variability of some chemical components, although we suspect that layering and the inconsistent subsampling of these layers in duplicate clippings is a more important factor. The chemical heterogeneity of the paint fragments was reflected by the lack of correlations among the elements analysed,
1 0 0
10
20
30
40
50
60
70
C, % Fig. 1. Scatter plots of (a) different metal (and P) concentrations and (b) H versus C in individual paint fragments.
and as exemplified by the composite of scatter plots shown in Fig. 1. The only chemical pair that was significantly (p < 0.05) correlated was carbon and hydrogen, also shown in Fig. 1, with an average C:H ratio of about nine. Lack of dispersion in these data reflects the narrow range of C–H among different polymers and resins and other (extraneous) source materials. Table 1 also shows the elemental composition of the fine fraction of the composite sample of boat paint fragments. Replicate digestions–analyses indicate a relative standard deviation of below 15% for all elements, suggesting that grinding and fractionation provides a good means of sample homogenisation. In total, around 65% of the paint composite mass was accounted for from our quantitative analysis. Given the chemical makeup of most paints and results of our SEM analysis described below, we surmise that the principal remaining elements of the sample were Si, Cl, O, Mg and S. 3.2. Physico-chemical forms of Cu and Zn Information on the physico-chemical forms and speciation of the metallic biocidal components was gained by further quantitative and qualitative analysis of individual paint fragments and the ground composite. The electron micrograph of the cross section of a paint fragment shown in Fig. 2 is typical of the many obtained
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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 respectively numbered boxes. The upper layer contains granular Cu as cuprous oxide (white grains) and cuprous thiocyanate (darker grains) embedded in an inert matrix. The middle layer illustrates finer granules of Zn oxide and the presence of pores in the matrix. The lower layer contains grains of silica and Zn phosphate.
in this study. Thus, most fragments consisted of distinct layers, presumably reflecting multiple applications removed concurrently during boat hull maintenance. Pits and holes of various dimensions in 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 containing any combination of Si, Ca, Mg, Al, Fe and Ti; and (iii) a matrix containing, additionally, Cu or Zn. Copper mainly occurred in the form of particles of various shapes and sizes, but generally between about 5 and 20 lm in diameter, and spectra indicated that the metal existed largely as cuprous oxide or, given its coincidence with S, as cuprous thiocyanate. Zinc occurred as oxidic grains ranging from about 0.1–5 lm in diameter and, in some layers, as less well dispersed grains of Zn phosphate. A measure of organometallics in the paint composite was obtained 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/w concentration and as a percentage of the respective total metal content. Although organometallic forms represent only a few per-
cent or less of total metal, with respect to Cu and Zn this is equivalent to considerable absolute concentrations. The identity of the organometallic compounds was inferred from FTIR analysis of selected individual fragments of paint. Results suggested the presence of the booster biocide, zinc pyrithione (peak band = 821.5 cm1), in most samples, and the presence of copper pyrithione (peak band = 831.5 cm1) in some fragments. Zinc pyrithione is employed as a booster biocide in many antifouling formulations (Maraldo and Dahllöf, 2004) and, although Cu pyrithione is sometimes employed, this compound may also form in situ by the transchelation of Zn pyrithione (Grunnet and Dahllöf, 2005). The Sn–C bond, with a spectral peak in the region 590–520 cm1 (Rehman et al., 2005), was not, however, observed in the samples. It is possible that any organotin present was heterogeneously dispersed within a few fragments and not, therefore, detected from our limited number of FTIR scans. Alternatively, given the small concentrations of Sn extracted by the solvent (Table 2), the majority of organotin originally present in older formulations may have undergone degradation.
N. Singh, A. Turner / Marine Pollution Bulletin 58 (2009) 559–564 Table 2 Concentrations of solvent-extractable (organometallic) compounds in the boat paint composite and the percentage contribution of these compounds to total metal concentrations. The arithmetic mean ± one standard deviation of three independent determinations is given. Concentration (lg g1)
%
Cu Zn Sn
463 ± 60.9 1310 ± 73.1 16.4 ± 2.6
0.15 ± 0.02 1.15 ± 0.11 3.07 ± 0.63
Table 3 Elemental concentrations in fractionated (<63 lm) Plym estuarine sediment collected from the vicinity of a leisure boatyard (BY) and remote from any boating activity (ES). Concentrations are in lg g1, and the arithmetic mean ± one standard deviation of three independent determinations is given. EF represents the enrichment factor of a trace metal as calculated using Eq. (1). BY
ES
21,600 ± 1800 19,500 ± 940 30,000 ± 2000
18,600 ± 2100 17,400 ± 950 29,000 ± 5000
Cu Zn Ni Cr Co Pb Cd Sn
2230 ± 1900 916 ± 600 31.1 ± 6.1 34.8 ± 3.8 11.2 ± 0.7 163 ± 16.3 0.97 ± 0.25 12.3 ± 0.9
EF
98.5 ± 9.3 129 ± 15.0 11.1 ± 1.2 18.0 ± 1.7 5.9 ± 0.3 85.9 ± 11.8 0.57 ± 0.03 8.2 ± 2.5
19.49 6.09 2.41 1.67 1.64 1.63 1.46 1.30
3.3. Contribution of antifouling paint particles to metal concentrations in sediment Elemental contents of size fractionated (<63 lm) inter-tidal particles collected from the Plym Estuary, SW England, both in the vicinity of a boatyard (BY) and remote from any obvious boating activity (ES), are shown in Table 3. Given that concentrations of Al, Fe and C are similar in both samples, it is reasonable to assume that the particles are geochemically consistent. Enrichment factors (EF) for trace metals in the vicinity of the boatyard, also shown in Table 3, were computed from arithmetic mean metal concentrations, [Me], after normalisation with respect to Al as follows:
EF ¼
½MeBY =½AlBY ½MeES =½AlES
½MeBY ½MeES ½MePC ½MeES
The elemental content of the composite of paint fragments collected from a leisure boat maintenance facility is consistent with what is known about the composition of the most popular contemporary antifouling formulations (Comber et al., 2002; Yebra et al., 2004). Clearly, paint residues represent an important local source of particulate metallic contamination to the coastal marine environment through the cleaning, maintenance, grounding and abandonment of boats, and the flaking from a variety of underwater structures in situ. Given the compositional variation observed among the individual paint fragments collected from the leisure boat industry, this source is likely to be highly heterogeneous, exhibiting both temporal and geographical variation that is dependent on the precise formulations applied and removed. The magnitude of contamination from boatyards will depend on additional factors such as the size and layout (e.g. enclosure and drainage) of the facility, the time of year, and whether safe disposal of particulates is enforced or practiced. Copper and Zn exhibit greatest enrichment in the paint composite compared with estuarine sediment uncontaminated by boating activity but, because of the range in metal concentrations encountered in individual fragments, other metals such as Ag, Cd, Cr and Pb could pose more local or transient threats to the benthic community. Ultimately, the risk and impacts arising from spent paint particulates will be dependent on the solubility or rate of geochemical and biological mobilisation of toxic metals (and additional organic boosters) from the paint matrix. Accordingly, we are currently investigating the release of metals from paint particles suspended in sea water under different environmental conditions, along with in vitro measures of metal bioaccessibility to suspension-feeding and deposit-feeding invertebrates using digestive enzymes and proteins. Regardless of the precise outcome of ongoing experiments, stricter enforcement of the safe disposal of antifouling paint particles from the leisure boating industry is recommended.
Acknowledgements
ð1Þ
Values are greater than unity for all trace metals analysed and greatest enrichment is exhibited by the two metals that are most abundant in the paint composite. Clearly, therefore, metal contamination of this sample is attributable to local leisure boating activity. Moreover, substantial variability among the replicate analyses of Cu and Zn (rsd > 50%) and visible paint fragments remaining on the sieve used to fractionate the sediment strongly suggest that paint particles are responsible. Contamination may arise directly, from spent fragments themselves, and indirectly, through leaching of metals into interstitial waters and subsequent readsorption to sediment particles. Neglecting small granular and textural differences between the estuarine samples, the following mass balance equation may be used to evaluate the fractional, mass contribution of paint particles to the contaminated sediment, fPC, as follows (Turner et al., 2008):
fPC ¼
by around seven parts per 1000 of antifouling paint particles is required to attain the concentrations measured in the sediment sample near to the boatyard. 3.4. Nature and impacts of antifouling paint particle contamination
Metal
Al Fe C
563
ð2Þ
where [Me]PC denotes the concentration of a metal in the paint composite. Using the arithmetic mean data for Cu and Zn reported in Tables 1 and 3, contamination of background estuarine sediment
We are grateful to Dr. Andy Fisher, Dr. Roy Moate and Mr. Andrew Tonkin (UoP) for assistance with sample analysis. NS was supported by an Erasmus Mundus studentship to undertake a Joint European Masters in Water and Coastal Management. This study was funded, in part, by the Green Blue initiative of the Royal Yachting Association/British Marine Federation.
References British Marine Federation, 2005. Environmental code of practice. Practical advice for marine businesses sailing clubs and training centres. BMF, Egham, Surrey. Comber, S.D.W., Gardner, M.J., Boxall, A.B.A., 2002. Survey of four marine antifoulant constituents (copper, zinc, diuron and Irgarol 1051) in two estuaries. Journal of Environmental Monitoring 4, 417–425. Fay, F., Linossier, I., Langlois, V., Haras, D., Vallee-Rehel, K., 2005. SEM and EDX analysis: two powerful techniques for the study of antifouling paints. Progress in Organic Coatings 54, 216–223. Grunnet, K.S., Dahllöf, I., 2005. Environmental fate of the antifouling compound zinc pyrithione in seawater. Environmental Toxicology and Chemistry 24, 3001– 3006. Helland, A., Bakke, T., 2002. Transport and sedimentation of Cu in a microtidal estuary, SE Norway. Marine Pollution Bulletin 44, 149–155. Katranitsas, A., Castritsi-Catharios, J., Persoone, G., 2003. The effects of a copperbased antifouling paint on mortality and enzymatic activity of a non-target marine organism. Marine Pollution Bulletin 46, 1491–1494.
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Koutsaftis, A., Aoyama, I., 2007. Toxicity of four antifouling biocides and their mixtures on the brine shrimp Artemia salina. Science of the Total Environment 387, 166–174. Maraldo, K., Dahllöf, I., 2004. Indirect estimation of degradation time for zinc pyrithione and copper pyrithione in seawater. Marine Pollution Bulletin 48, 894–901. Rehman, W., Baloch, M.K., Badshah, A., 2005. Comparative study of structure– activity relationship of di- and triorganotin (IV) complexes of monomethyl glutarate. Journal of the Brazilian Chemical Society 16, 1–8. Srinivasan, M., Swain, G.W., 2007. Managing the use of copper-based antifouling paints. Environmental Management 39, 423–441.
Thomas, K.V., Blake, S.J., Waldock, M.J., 2000. Antifouling booster biocide contamination in UK marine sediments. Marine Pollution Bulletin 40, 739–745. Tolhurst, L.E., Barry, J., Dyer, R.A., Thomas, K.V., 2007. The effect of resuspending sediment contaminated with antifouling paint particles containing Irgarol 1051 on the marine macrophyte Ulva intestinalis. Chemosphere 68, 1519–1524. Turner, A., Fitzer, S., Glegg, G.A., 2008. Impacts of boat paint chips on the distribution and availability of copper in an English ria. Environmental Pollution 151, 176–181. Yebra, D.M., Kiil, S., Dam-Johansen, K., 2004. Antifouling technology – past, present and future steps towards efficient and environmentally friendly antifouling coatings. Progress in Organic Coatings 50, 75–104.
Contents lists available at ScienceDirect
Marine Pollution Bulletin journal homepage: www.elsevier.com/locate/marpolbul
Trace metals in antifouling paint particles and their heterogeneous contamination 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 Keywords: Antifouling paint Leisure boats Copper Zinc Trace metals Organometallics
i n f o
a b s t r a c t Antifouling paint residues collected from the hard-standings of a marine leisure boat facility have been chemically characterised. Scanning electron microscopy revealed distinct layers, many containing oxidic particles of Cu and Zn. Quantitative analysis indicated concentrations of Cu and Zn averaging about 300 and 100 mg g1, respectively, and small proportions of these metals (<2%) in organometallic form as pyrithione compounds. Other trace metals present included Ag, Cd, Cr, Ni, Pb and Sn, with maximum concentrations of about 330, 75, 1200, 780, 1800 and 25,000 lg g1, respectively. Estuarine sediment collected near a boatyard contained concentrations of Cu and Zn an order of magnitude greater than respective concentrations in ‘‘background” sediment, and mass balance calculations suggested that the former sample was contaminated by about 1% by weight of paint particles. Clearly, antifouling residues represent a highly significant, heterogeneous source of metallic contamination in the marine environment where boating activities occur. Ó 2008 Elsevier Ltd. All rights reserved.
1. Introduction Antifouling paints are applied to the hulls of boats and to other submerged structures to prevent the growth of fouling organisms, including algae, barnacles and bivalves. The slow, controlled release of biocides from such applications does, however, have important environmental ramifications, particularly in semi-enclosed environments with a high density of boats. Thus, elevated concentrations of biocidal components, including Cu and Zn and various organic boosters, are frequently reported (Comber et al., 2002; Helland and Bakke, 2002), while concern has been levelled at 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 biological impacts of spent paint particles derived from boat hull cleaning or that flake off structures, including grounded and abandoned vessels, in situ (Tolhurst et al., 2007; Turner et al., 2008). Regulations or codes of practice concerning the removal and subsequent disposal of antifouling residues from commercial and recreational boatyards exist in many countries. For example, with regard to the leisure boat industry in the UK, the British Marine Federation (2005) recommends that tarpaulin is emplaced below boats to collect paint fragments during hull cleaning or maintenance, and/or that debris is carefully vacuumed from the site; hazardous particulates should then be disposed of appropriately. In * Corresponding author. Tel.: +44 1752 584570; fax: +44 1752 584710. E-mail address: [email protected] (A. Turner). 0025-326X/$ - see front matter Ó 2008 Elsevier Ltd. All rights reserved. doi:10.1016/j.marpolbul.2008.11.014
many cases, however, marinas and boaters are unaware of these guidelines (Srinivasan and Swain, 2007). Consequently, paint particles of various sizes and colours are a common sight, both on the hard-standings in an around boat maintenance facilities and on the foreshore in the vicinity of boat moorings. These particles are readily transported into the local aquatic environment with washwater and runoff or as airborne dust. Their potential for long-range transport, coupled with a relatively high surface area and erodibility, suggests that antifouling boat paint particles may pose chemical and biological impacts that are more widespread than is generally acknowledged. In this study, we use qualitative and quantitative methods to chemically characterise individual spent paint particles and a composite of such collected from a marine leisure boat maintenance facility. We focus on the metallic components (organic booster biocides are the subject of a separate research programme) with an overall aim of evaluating the signature of and potential for contamination of the marine coastal environment from contemporary boat cleaning and maintenance activities.
2. Materials and methods Before use, all equipment for sampling, sample processing and sample storage was soaked in 10% HCl for at least 24 h and subsequently rinsed in distilled water. Reagents employed throughout were of analytical grade or better, and were purchased from Fluka, VWR or Fisher Scientific.
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2.1. Sample collection and processing Fragments of boat paint, of between about 5 and 50 mm in length, were collected by hand from the hard-standings and slipways of a large (>100 berth) marine boat maintenance facility, catering for mainly (but not exclusively) leisure craft, in Plymouth during April 2007. Although we implicitly refer to the sample and fragments thereof as antifouling in nature, it is important to appreciate that some paint particles may have been derived from parts of the boat not associated with the hull (e.g. decking and cabin) but undergoing general maintenance. These particles have a different chemical makeup to antifouling fragments, but the net sample is representative of the signature of particulate contamination derived from the general, contemporary practice of marine leisure boat maintenance. In the laboratory, visible extraneous particulates (e.g. grit and macroalgae) were removed and the fragments pooled in two 150 ml screw-capped polyethylene canisters. The contents of one canister were ground with a pestle and mortar, a process aided by the occasional addition of a few ml of liquid nitrogen. The ground sample was then sieved through a 63 lm nylon mesh and the fine fraction stored in a polyethylene bottle. On the basis of colour and texture, a variety of paint fragments (n = 25) was selected from the second canister and stored individually in polyethylene tubes. Inter-tidal sediment was collected during December 2007 from two sites on the Plym Estuary, SW England; specifically, about 10 m from the foot of a hard-standing of a leisure boatyard, and at a location remote from significant boating activity. Surface, oxic scrapes were obtained using a polyethylene spatula and transferred to zip-locked plastic bags. In the laboratory, the contents of the samples were sieved through a 63 lm nylon mesh with the aid of a few ml of estuarine water. The fine fractions were freeze-dried and subsequently stored in polyethylene canisters under desiccation. 2.2. Sample digestion–extraction and metal analysis Three aliquots of both fractionated sediment samples, three subsamples of the fractionated paint composite and clippings taken from individual fragments (including replicates of some fragments) were chemically characterised. For the complete digestion of metals (and phosphorus), about 100 mg of sediment or 5– 10 mg of paint powder (composite) or paint clipping were accurately weighed into a 50 ml Pyrex beaker. Five millilitres of aqua regia (three parts HCl to one part HNO3) were added to each beaker, and after about 1 h the contents were covered with watch glasses and heated on a hot plate to about 75 °C for a further 2 h. The cooled contents and Milli-Q water rinsings were transferred to individual 25 ml Pyrex volumetric flasks and diluted to mark with 0.1 M HNO3. Digestions were undertaken in batches of ten, and procedural blanks, performed likewise but in the absence of solids, were undertaken in triplicate for each batch. To evaluate the contribution of organometallic compounds to the total metal content of the paint composite, triplicate subsamples were subject to solvent extraction according to the method outlined in Thomas et al. (2000) after some minor modifications. Thus, about 50 mg were weighed into a Pyrex beaker to which 30 ml of a 1:1 mixture of dichloromethane–ethylacetate were added. The beaker was covered with Al foil and agitated on a lateral shaker at about 100 rpm at room temperature for about 2 h. The contents were subsequently sonicated for 10 min and centrifuged at 2100g for 15 min. Ten millilitres of supernatant were pipetted into a clean beaker and the contents evaporated to dryness in a flow hood for about 24 h. The remaining, dried contents were redissolved in 5 ml of 0.1 M HNO3 and transferred to a 10 ml volumetric flask where they were diluted to mark with Milli-Q water.
Procedural blanks were undertaken likewise but in the absence of paint particles. Digests and extracts were analysed for Ca, Ba, Cu, Fe, Mn, P, Sr, Ti and Zn by inductively coupled plasma–optical emission spectrometry (ICP–OES) using a Varian 725 ES (Mulgrave, Australia), and for Ag, Cd, Co, Cr, Ni, Sn and Pb by inductively coupled plasma–mass spectrometry (ICP–MS) using a Plasma Quad PQ2+ (Thermoelemental, Winsford, UK). Both instruments were calibrated using mixed, acidified standards, and internal standardisation was achieved by the addition of either yttrium (ICP–OES) or indium and iridium (ICP–MS). Metals were detectable (greater than three standard deviations of concentrations determined in the corresponding procedural controls) in all cases with the exception of Ag, Cr, Mn, Ni and Sr in a few fragments and Ag in the composite. Accuracy, evaluated from triplicate digestions of a river sediment sample certified for metal concentrations available to aqua regia (LGC 6187; Laboratory of the Government Chemist, Teddington, UK) was better than 90% for all elements where certified concentrations were available. 2.3. CHN analysis Total concentrations of C, H and N were determined in 2 mg aliquots (as a powder or clipping) of each sample by flash combustion using a Carlo Erba EA 1110 elemental analyser calibrated with EDTA standards. Accuracy, based on analysis of C in a variety of certified soils and sediments, was better than 95%. 2.4. Scanning electron microscopy The bulk physico-chemical characteristics of selected paint fragments (n = 20) were examined by scanning electron microscopy coupled with energy dispersive X-ray spectrometry (SEM–EDX). Between six and eight fragments were glued, vertically, to the bottom of a 20 ml plastic mould which was then filled with resin and cured for 24 h in a fume cupboard. After removing the mould, the resin was polished with a series of sand papers of successively finer grain size (grit 400–1200) until paint layers were exposed and a smooth surface attained. Embedded samples were then sputter-coated with a thin film in an EMITECH K 450 high vacuum carbon-coating unit. Individual fragments were labelled using conducting ink before the resin was attached to the SEM with adhesive tape. Samples were photographed using a JEOL JSM-6100 operated at 20 kV and at a working distance of 15 mm. Qualitative elemental analysis was performed using an Oxford Instruments Inca 200 system. 2.5. Fourier transform infrared analysis In order to evaluate the nature of any organometallic compounds present, Fourier transform infrared (FTIR) spectra arising from the analysis of selected paint fragments were recorded using a Bruker IFS 66 spectrometer attached to a Hyperion 1000 IR microscope with a liquid nitrogen cooled mercury–cadmium–telluride (MCT) detector. Fragments were compressed between the windows of a Specac diamond compression cell until an appropriate thickness was attained. Transmission spectra were acquired by averaging 100 scans at a resolution of 4 cm1 over the range 4000– 400 cm1. Compounds were identified by comparing peaks obtained 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 individual paint fragments. Concentrations do not, necessarily, reflect
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N. Singh, A. Turner / Marine Pollution Bulletin 58 (2009) 559–564 Table 1 Elemental concentrations in the boat paint composite and individual paint fragments. Concentrations are in lg g1 and results are shown in descending order of mean metal (and non-metal) concentration in the composite. AM, SD and GM denote arithmetic mean, standard deviation and geometric mean, respectively.
10000
Minimum
Maximum
40,490 16,660 20,480 8300 3720 152 353 163 271 213 776 350 79.5 5.74 11.9 34.0
956 1180 2390 1420 195 5.9 31.0 13.8 10.3 25.9 27.4 81.6 12.5 1.11 0.77 3.45
402,100 261,200 341,900 34,740 13,300 29,200 24,890 1780 4030 777 6470 1025 1240 74.5 917 333
C H N P
179,700 ± 2300 22,000 ± 300 7200 ± 300 3800 ± 330
331,500 38,080 8880 1860
123,200 13,000 900 17.5
577,900 58,600 18,700 30,920
Total (%)
65.68 ± 3.27
60.53
39.57
93.14
n < 25 for Ag, Cr, Mn, Ni and Sr. Not detected in the composite.
-1
GM
311,200 ± 20,600 114,100 ± 7660 6770 ± 401 6380 ± 562 2870 ± 185 1050 ± 89 550 ± 27.0 525 ± 33.9 234 ± 18.5 149 ± 3.9 75.1 ± 7.3 43.5 ± 3.6 34.0 ± 1.5 7.56 ± 1.02 5.49 ± 0.34 ndb
1000
µg g
AM ± SD Cu Zn Fe Ca Al Ba Sn Pb Ti Ni Mn Sr Cr Cd Co Ag
100 Cd-Co Al-Ca
10
Ti-Zn Pb-Sn Cd-Cu
1
Zn-Co Fe-Cu P-Ba
0.1 0
1
10
100
1000
10000
100000 1000000
-1
µg g 7 6 5
H, %
Composite (n = 3)
a
100000
Fragments (n = 25)a
Element
b
1000000
C:H = 9.13
4 3 2
concentrations in the corresponding original applications because of the differential leaching rates of the various components, especially in non-self-polishing formulations (Fay et al., 2005). Of the metals analysed, Cu and Zn are most abundant in many of the fragments, consistent with their use in the principal pigments (cuprous oxide, cuprous thiocyanate and zinc oxide) of contemporary antifouling formulations (Comber et al., 2002; Yebra et al., 2004). Aside the polymeric constituents, carbon and hydrogen, other components of antifouling paints (and topside paints and primers) that are reflected in the results of our chemical analysis include extenders (e.g. barium sulphate and calcium carbonate), additional pigments (e.g. anatase titanium, barium metaborate, chromium oxide, iron oxide, tin oxide, various cadmium and lead compounds) and corrosion inhibitors (e.g. zinc phosphate and strontium chromate). The presence of metals such as Mn and Ni in many samples may also reflect components of metallic base materials which, in some cases, were visibly attached to paint fragments, or to non-silica-based particles of spent abrasives. Concentrations of a given metal (and P) are highly variable among the fragments, with a range spanning orders of magnitude and, in most cases, a standard deviation in excess of the arithmetic mean. Variability was also evident within duplicate digestions/ analyses of the same sample (results not shown); for Cu, Zn, Fe and Al, duplicate concentrations sometimes differed by an order of magnitude. Inter-fragment variability may be largely attributed to an inherent variation in the chemical composition of individual formulations (including non-antifouling paints), although heterogeneous contamination by small adherent particulates or components of the base matrix (e.g. hull) may also be significant in some cases. Heterogeneous, extraneous contamination may also be responsible for intra-fragment variability of some chemical components, although we suspect that layering and the inconsistent subsampling of these layers in duplicate clippings is a more important factor. The chemical heterogeneity of the paint fragments was reflected by the lack of correlations among the elements analysed,
1 0 0
10
20
30
40
50
60
70
C, % Fig. 1. Scatter plots of (a) different metal (and P) concentrations and (b) H versus C in individual paint fragments.
and as exemplified by the composite of scatter plots shown in Fig. 1. The only chemical pair that was significantly (p < 0.05) correlated was carbon and hydrogen, also shown in Fig. 1, with an average C:H ratio of about nine. Lack of dispersion in these data reflects the narrow range of C–H among different polymers and resins and other (extraneous) source materials. Table 1 also shows the elemental composition of the fine fraction of the composite sample of boat paint fragments. Replicate digestions–analyses indicate a relative standard deviation of below 15% for all elements, suggesting that grinding and fractionation provides a good means of sample homogenisation. In total, around 65% of the paint composite mass was accounted for from our quantitative analysis. Given the chemical makeup of most paints and results of our SEM analysis described below, we surmise that the principal remaining elements of the sample were Si, Cl, O, Mg and S. 3.2. Physico-chemical forms of Cu and Zn Information on the physico-chemical forms and speciation of the metallic biocidal components was gained by further quantitative and qualitative analysis of individual paint fragments and the ground composite. The electron micrograph of the cross section of a paint fragment shown in Fig. 2 is typical of the many obtained
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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 respectively numbered boxes. The upper layer contains granular Cu as cuprous oxide (white grains) and cuprous thiocyanate (darker grains) embedded in an inert matrix. The middle layer illustrates finer granules of Zn oxide and the presence of pores in the matrix. The lower layer contains grains of silica and Zn phosphate.
in this study. Thus, most fragments consisted of distinct layers, presumably reflecting multiple applications removed concurrently during boat hull maintenance. Pits and holes of various dimensions in 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 containing any combination of Si, Ca, Mg, Al, Fe and Ti; and (iii) a matrix containing, additionally, Cu or Zn. Copper mainly occurred in the form of particles of various shapes and sizes, but generally between about 5 and 20 lm in diameter, and spectra indicated that the metal existed largely as cuprous oxide or, given its coincidence with S, as cuprous thiocyanate. Zinc occurred as oxidic grains ranging from about 0.1–5 lm in diameter and, in some layers, as less well dispersed grains of Zn phosphate. A measure of organometallics in the paint composite was obtained 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/w concentration and as a percentage of the respective total metal content. Although organometallic forms represent only a few per-
cent or less of total metal, with respect to Cu and Zn this is equivalent to considerable absolute concentrations. The identity of the organometallic compounds was inferred from FTIR analysis of selected individual fragments of paint. Results suggested the presence of the booster biocide, zinc pyrithione (peak band = 821.5 cm1), in most samples, and the presence of copper pyrithione (peak band = 831.5 cm1) in some fragments. Zinc pyrithione is employed as a booster biocide in many antifouling formulations (Maraldo and Dahllöf, 2004) and, although Cu pyrithione is sometimes employed, this compound may also form in situ by the transchelation of Zn pyrithione (Grunnet and Dahllöf, 2005). The Sn–C bond, with a spectral peak in the region 590–520 cm1 (Rehman et al., 2005), was not, however, observed in the samples. It is possible that any organotin present was heterogeneously dispersed within a few fragments and not, therefore, detected from our limited number of FTIR scans. Alternatively, given the small concentrations of Sn extracted by the solvent (Table 2), the majority of organotin originally present in older formulations may have undergone degradation.
N. Singh, A. Turner / Marine Pollution Bulletin 58 (2009) 559–564 Table 2 Concentrations of solvent-extractable (organometallic) compounds in the boat paint composite and the percentage contribution of these compounds to total metal concentrations. The arithmetic mean ± one standard deviation of three independent determinations is given. Concentration (lg g1)
%
Cu Zn Sn
463 ± 60.9 1310 ± 73.1 16.4 ± 2.6
0.15 ± 0.02 1.15 ± 0.11 3.07 ± 0.63
Table 3 Elemental concentrations in fractionated (<63 lm) Plym estuarine sediment collected from the vicinity of a leisure boatyard (BY) and remote from any boating activity (ES). Concentrations are in lg g1, and the arithmetic mean ± one standard deviation of three independent determinations is given. EF represents the enrichment factor of a trace metal as calculated using Eq. (1). BY
ES
21,600 ± 1800 19,500 ± 940 30,000 ± 2000
18,600 ± 2100 17,400 ± 950 29,000 ± 5000
Cu Zn Ni Cr Co Pb Cd Sn
2230 ± 1900 916 ± 600 31.1 ± 6.1 34.8 ± 3.8 11.2 ± 0.7 163 ± 16.3 0.97 ± 0.25 12.3 ± 0.9
EF
98.5 ± 9.3 129 ± 15.0 11.1 ± 1.2 18.0 ± 1.7 5.9 ± 0.3 85.9 ± 11.8 0.57 ± 0.03 8.2 ± 2.5
19.49 6.09 2.41 1.67 1.64 1.63 1.46 1.30
3.3. Contribution of antifouling paint particles to metal concentrations in sediment Elemental contents of size fractionated (<63 lm) inter-tidal particles collected from the Plym Estuary, SW England, both in the vicinity of a boatyard (BY) and remote from any obvious boating activity (ES), are shown in Table 3. Given that concentrations of Al, Fe and C are similar in both samples, it is reasonable to assume that the particles are geochemically consistent. Enrichment factors (EF) for trace metals in the vicinity of the boatyard, also shown in Table 3, were computed from arithmetic mean metal concentrations, [Me], after normalisation with respect to Al as follows:
EF ¼
½MeBY =½AlBY ½MeES =½AlES
½MeBY ½MeES ½MePC ½MeES
The elemental content of the composite of paint fragments collected from a leisure boat maintenance facility is consistent with what is known about the composition of the most popular contemporary antifouling formulations (Comber et al., 2002; Yebra et al., 2004). Clearly, paint residues represent an important local source of particulate metallic contamination to the coastal marine environment through the cleaning, maintenance, grounding and abandonment of boats, and the flaking from a variety of underwater structures in situ. Given the compositional variation observed among the individual paint fragments collected from the leisure boat industry, this source is likely to be highly heterogeneous, exhibiting both temporal and geographical variation that is dependent on the precise formulations applied and removed. The magnitude of contamination from boatyards will depend on additional factors such as the size and layout (e.g. enclosure and drainage) of the facility, the time of year, and whether safe disposal of particulates is enforced or practiced. Copper and Zn exhibit greatest enrichment in the paint composite compared with estuarine sediment uncontaminated by boating activity but, because of the range in metal concentrations encountered in individual fragments, other metals such as Ag, Cd, Cr and Pb could pose more local or transient threats to the benthic community. Ultimately, the risk and impacts arising from spent paint particulates will be dependent on the solubility or rate of geochemical and biological mobilisation of toxic metals (and additional organic boosters) from the paint matrix. Accordingly, we are currently investigating the release of metals from paint particles suspended in sea water under different environmental conditions, along with in vitro measures of metal bioaccessibility to suspension-feeding and deposit-feeding invertebrates using digestive enzymes and proteins. Regardless of the precise outcome of ongoing experiments, stricter enforcement of the safe disposal of antifouling paint particles from the leisure boating industry is recommended.
Acknowledgements
ð1Þ
Values are greater than unity for all trace metals analysed and greatest enrichment is exhibited by the two metals that are most abundant in the paint composite. Clearly, therefore, metal contamination of this sample is attributable to local leisure boating activity. Moreover, substantial variability among the replicate analyses of Cu and Zn (rsd > 50%) and visible paint fragments remaining on the sieve used to fractionate the sediment strongly suggest that paint particles are responsible. Contamination may arise directly, from spent fragments themselves, and indirectly, through leaching of metals into interstitial waters and subsequent readsorption to sediment particles. Neglecting small granular and textural differences between the estuarine samples, the following mass balance equation may be used to evaluate the fractional, mass contribution of paint particles to the contaminated sediment, fPC, as follows (Turner et al., 2008):
fPC ¼
by around seven parts per 1000 of antifouling paint particles is required to attain the concentrations measured in the sediment sample near to the boatyard. 3.4. Nature and impacts of antifouling paint particle contamination
Metal
Al Fe C
563
ð2Þ
where [Me]PC denotes the concentration of a metal in the paint composite. Using the arithmetic mean data for Cu and Zn reported in Tables 1 and 3, contamination of background estuarine sediment
We are grateful to Dr. Andy Fisher, Dr. Roy Moate and Mr. Andrew Tonkin (UoP) for assistance with sample analysis. NS was supported by an Erasmus Mundus studentship to undertake a Joint European Masters in Water and Coastal Management. This study was funded, in part, by the Green Blue initiative of the Royal Yachting Association/British Marine Federation.
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