Chemosphere 119 (2015) 1021–1026
Contents lists available at ScienceDirect
Chemosphere journal homepage: www.elsevier.com/locate/chemosphere
Polyacrylate–water partitioning of biocidal compounds: Enhancing the understanding of biocide partitioning between render and water Ulla E. Bollmann a, Yi Ou b, Philipp Mayer c, Stefan Trapp c, Kai Bester a,⇑ a
Aarhus University, Department of Environmental Science, Frederiksborgvej 399, 4000 Roskilde, Denmark University Duisburg-Essen, Department of Chemistry, Universitätsstraße 5, 45141 Essen, Germany c Technical University of Denmark, Department of Environmental Engineering, Miljøvej B113, 2800 Kgs. Lyngby, Denmark b
h i g h l i g h t s
g r a p h i c a l a b s t r a c t
Render-water distribution of biocides
linearly dependent on polyacrylate– water partitioning. The polymer is the dominant phase for the sorption of biocides in polymer enhanced render. Biocide leaching from render can be estimated from polyacrylate–water partitioning.
a r t i c l e
i n f o
Article history: Received 4 June 2014 Received in revised form 25 August 2014 Accepted 27 August 2014 Available online 7 October 2014 Handling Editor: I. Cousins Keywords: SPME Polyacrylate coated glass fibre filters Polymeric coatings Triazines Phenylureas Isothiazolinones
a b s t r a c t In recent years, the application of polymer-based renders and paints for façade coatings of buildings has risen enormously due to the increased mounting of thermal insulation systems. These materials are commonly equipped with biocides – algaecides, fungicides, and bactericides – to protect the materials from biological deterioration. However, the biocides need to be present in the water phase in order to be active and, hence, they are flushed of the material by rain water. In order to increase the knowledge about the partitioning of biocides from render into the water phase, partition constants between the polymer – in this case polyacrylate – and water were studied using glass fibre filters coated with polyacrylate. The polyacrylate–water partition constants (log KAcW) of ten biocides used in construction material varied between 1.66 (isoproturon) and 3.57 (dichloro-N-octylisothiazolinone). The correlation of the polyacrylate–water partition constants with the octanol–water partition constants is significant, but the polyacrylate–water partition constants were predominantly below octanol–water partition constants (Kow). The comparison with render-water distribution constants showed that estimating the leaching of biocides from render based on polymer–water partitioning is a useful and practical tool. Ó 2014 Elsevier Ltd. All rights reserved.
1. Introduction ⇑ Corresponding author. Tel.: +45 87158552. E-mail address: [email protected] (K. Bester). http://dx.doi.org/10.1016/j.chemosphere.2014.08.074 0045-6535/Ó 2014 Elsevier Ltd. All rights reserved.
Polymer enhanced renders and paints for building façades, using polyacrylate or silicone as organic binder, are usually
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U.E. Bollmann et al. / Chemosphere 119 (2015) 1021–1026
equipped with biocides in order to prevent growth of algae or fungi on the surfaces (Reichel et al., 2004). About 0.1–2 g active ingredient per kg material is used in render or exterior paints and, typically, a mixture of several biocides is used. Hence, the total content of biocides in render and exterior paints ranges from 5 to 10 g kg1 (Burkhardt et al., 2011). Laboratory studies on constantly soaked material, dipping experiments with alternating wet and dry cycles, or forced rain experiments showed that the biocides leach out of the render material in considerable fractions (Schoknecht et al., 2003; Burkhardt et al., 2007; Schoknecht et al., 2009; Burkhardt et al., 2011, 2012; Wangler et al., 2012). The leaching process of biocides from render is assumed to be a multistep process: (1) removal from the surface layer which is itself (2) in equilibrium with the deeper layers of the render, from which (3) the surface layer is constantly refilled. According to Schoknecht et al. (2009), the leaching is a diffusion controlled process that can be related to the octanol–water partition constant as well as the water solubility, and the refill of the surface boundary layer could occur via transport of biocides with the evaporating water through the render. Styszko et al. (2014) determined the equilibrium distribution of biocides between render and water. The determined render-water distribution constants of that study revealed similarities but no significant (a = 0.1) correlation with the octanol–water partition constants. Styszko et al. (2014) identified the influence of the polyacrylate content on the partitioning being important for some biocides (isothiazolinone, carbamates or triazines), while the partitioning of phenylureas seemed not to be influenced that much by the polyacrylate content. Styszko et al. (2014) proposed that polyacrylate is one of the main components of the polymeric render controlling the leaching of biocides. Partitioning can be assessed by solid phase micro extraction (SPME) and other passive sampling techniques, which are well established for lipophilic compounds with polydimethylsiloxane (PDMS) as accumulating (sorption) phase, while for more hydrophilic compounds polyacrylate phases are more successfully used (Pawliszyn, 1997; Górecki and Namies´nik, 2002). Further, a central parameter for these passive sampling techniques is the polymer to water partition constant, which sets the upper limit for analyte enrichment and is also crucial for the calibration of these methods. Therefore, a considerable amount of research has been performed on polymer to water partitioning within an analytical context, whereas studies are more scarce when it comes to the leaching and partitioning of key pollutants from technical polymers contained in for examples buildings and constructions. Specifically, polyacrylate–water partition constants for polar organic chemicals have been studied and quantified using solid phase micro extraction (SPME) fibres coated with polyacrylate (Dean et al., 1996; Vaes et al., 1996; Verbruggen et al., 1999; Ohlenbusch et al., 2000; Haftka et al., 2013), with Endo et al. (2011) providing the most comprehensive data set and evaluation. However, none of them have covered a typical set of biocides such as used in building industries, i.e. isothiazolinones, triazoles, triazines, carbamates, and phenylureas. While in the polyacrylate–water system only two phases are involved in the partitioning, the render-water distribution constant describes the distribution into a complex mixture. Typically, main components of polymer enhanced renders are carbonates (30–60%), polymeric binder (10–15% either polyacrylate or silicone) and sand in different grain sizes. Schwarzenbach et al. (2003) introduced the additivity concept in order to estimate sorption to soils, by assuming that (1) each sorption phase acts independently and comes to equilibrium with all other phases and (2) the total pollutant amount sorbed can be estimated as the sum of the pollutant amount in each phase. Transferring this concept to the render-water system, the render-water distribution constant (Drender, Eq. (1)) can be described as the sum of the
partitioning to polyacrylate, carbonates, sand particles and other render ingredients, where f describes the fraction of each of the different phases (i.e. polyacrylate, calcium carbonate, sand, water) and c the concentration of the biocide in each phase:
Drender ¼
f polyacrylate C polyacrylate þ f CaCO3 C CaCO3 þ f Sand C Sand þ . . . C water ð1Þ
In the present study, glass fibre filters were coated with polyacrylate and then used in order to determine the polyacrylate–water partition constants (log KAcW) of biocides used in building materials. The obtained polyacrylate–water partition constants were studied and related to the leaching of biocides from polyacrylatebased render systems by comparing them to render-water distribution constants. It was thus aim of the study to test whether the hypotheses that polyacrylate is the dominating component controlling the partitioning of biocides in the render-water system and thus influencing the leaching holds true and would allow predictions of the leaching of biocides from polyacrylate-based renders using polyacrylate–water partition constants. 2. Material and methods 2.1. Chemicals The experiments were performed for eleven compounds (Table 1), of which ten are used as biocides in building materials (carbendazim, iodocarb, isoproturon, diuron, terbutryn, cybutryn, N-octylisothiazolinone, dichloro-N-octylisothiazolinone, tebuconazole, and propiconazole). Atrazine was previously used as pesticide and has been added for comparative reasons. Aqueous solutions were prepared from a stock solution (100 lg mL-1 in acetonitrile) of the eleven compounds with Millipore-water at 10 ng mL-1 (0.1% acetonitrile). Surrogate standards (1 lg mL-1 in methanol) were used for mass spectrometric analysis: isoproturon-D6, terbutryn-D5, cybutryn-D9, tebuconazole-D6, and carbendazim-D4. Suppliers and purities of the used standards can be found in supplementary S1; all standards were used directly without any further purification. Acetonitrile and methanol (both gradient grade LiChrosolv) were purchased from Merck (Darmstadt, Germany) while Millipore-water was generated by an in-house apparatus. 2.2. Coating of glass fibre filters As the different producers of polyacrylate containing renders do not disclose the exact identity of the used polyacrylate used in their products, for the partitioning experiments in this study one polyacrylate, i.e., Plextol D498 obtained from Synthomer Deutschland (Marl, Germany) was used. This Polymer is used in industry to produce organically modified renders and paints. Plextol D498 is characterised as thermoplastic methylmethacrylate and n-butylacrylate copolymer dispersion (50% w/w, density: 1.05 g mL-1) (Synthomer Deutschland, 2014). Since the total amount of polyacrylate per filter was aimed to be very low, Plextol D498 was diluted with Millipore-water to 20% w/w. Binder free glass fibre filters (WhatmanÒ GF/A, Ø = 25 mm, GE Healthcare, Little Chalfont, United Kingdom) were cleaned with methanol and Millipore-water before usage. After drying, the filters were coated with polyacrylate by adding a defined amount of diluted polymer dispersion onto the filter. Due to capillary forces the polymer dispersion was distributed over the entire filter surface and air dried at room temperature. Afterwards, the homogenous distribution was controlled by visual inspection and the added amount by weighing. Following this procedure, glass fibre filters were coated with 25, 50, and 80 mg polyacrylate.
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Table 1 Studied biocides with name, acronym, CAS-number, formula, and physical–chemical properties (log KOW: octanol–water partition constant, WS: water solubility, pvap: saturation vapour pressure, pKa: acid dissociation constant). Group Name, Acronym, CAS
Formula
Carbamates Carbendazim CD, 10605-21-7 Iodocarb IPBC, 55406-53-6 Phenylureas Isoproturon IP, 34123-59-6
pKa: 4.5 (base) and 10 (acid)
pKa: 11.8 (acid)
pKa: 0.1 (base) and 14.3 (acid)
Log KOW: 2.61 WS: 35 mg L1 pvap: 3.9 * 107 h Pa
pKa: 1.7 (base)
Terbutryn TB, 886-50-0
Log KOW: 3.74 WS: 25 mg L1 pvap: 2.3 * 106 h Pa
pKa: 4.1 (base)
Cybutryn (Irgarol 1051) IRG, 28159-98-0
Log KOW: 3.95 WS: 7 mg L1 pvap: 8.8 * 107 h Pa
pKa: 4.1 (base)
Log KOW: 2.45 WS: 480 mg L1 pvap: 4.9 * 105 h Pa Log KOW: 4.9 WS: 14 mg L1 pvap: 6.67 h Pa (xylene)
pKa: 0.4 (base)
Log KOW: 3.7 WS: 36 mg L1 pvap: 1.7 * 108 h Pa
pKa: 1.8 (base) and 13.7 (acid)
Log KOW: 3.72 WS: 100 mg L1 pvap: 2.7 * 107 h Pa
pKa: 1.7 (base)
Triazines Atrazine AT, 1912-24-9
Isothiazolinones N-Octylisothiazolinone OIT, 26530-20-1 Dichloro-N-octylisothiazolinone DCOIT, 64359-81-5 Triazoles Tebuconazole TBU, 107534-96-3 Propiconazole PPZ, 60207-90-1
a
Log KOW (pH 7): 1.6 WS: 8 mg L1 pvap: carbendazim > N-octylisothiazolinone > iodocarb > cybutryn > terbutryn > propiconazole > tebuconazole > dichloro-N-octylisothiazolinone. During leaching tests from façade render under natural weather conditions Burkhardt et al. (2012) analysed seven biocides. Based on that study, the leaching ability could be sorted according to isoproturon > diuron > iodocarb > N-octylisothiazolinone > cybutryn > terbutryn >
Fig. 2. Correlation between the polyacrylate–water partition constant log KAcW (pH 5.5) and the octanol–water partition constant log KOW (pH 7) (Paulus, 2005; SRC, 2014); DCOIT: dichloro-N-octylisothiazolinone, IRG: cybutryn, TBU: tebuconazole, DR: diuron, OIT: N-octylisothiazolinone, IPBC: iodocarb, CD: carbendazim. The dotted line is plotted for guidance purposes, it is not mathematically calculated.
4
log DOM log Drender
y=0.55x+1.52 y=0.56x+0.51
3
IRG IPBC
TBU
IRG IPBC
TBU
DR IP LogD
The used render contained mainly polyacrylate (10%), carbonate (66%) and quartz sand. As described in that study, the render-water distribution constant is pH-dependent, hence, for comparison only distribution constants at pH 5.6 were used. Further, Styszko et al. (2014) demonstrated that increasing the fraction of polyacrylate in a polyacrylate-based render reduced the desorption from the render for iodocarb, dichloro-N-octylisothiazolinone, tebuconazole, cybutryn, and carbendazim but not for isoproturon and diuron. Hence, the desorption of iodocarb, dichloro-N-octylisothiazolinone, tebuconazole, cybutryn, and carbendazim seemed to be dependent on the fraction of polyacrylate in the render, while the desorption of diuron and isoproturon was almost not affected by the polyacrylate fraction. According to Eq. (1) the render-water distribution constant would be directly correlated to the polyacrylate–water partitioning. If the render partitioning would be solely dependent on partitioning between polyacrylate and water the normalised render-water distribution constant would equal the polyacrylate–water partition constant. The comparison of the polyacrylate–water partition constant (numerical values from this study, Table 2) and the desorption constant from polyacrylate-based render normalised to the organic matter content (Styszko et al., 2014) showed a positive significant
R2=0.79 R2=0.79
2
DR CD IP 1
CD 0 0
1
2
3
4
LogKAcW Fig. 3. Correlation between the polyacrylate–water partition constant (log KAcW) and the distribution constant to polyacrylate-based render (logDrender) as well as the one normalised to the organic matter content (organic matter content = 10%, logDOM) determined by Styszko et al. (2014); IRG: cybutryn, IPBC: iodocarb, DR: diuron, IP: isoproturon, TBU: tebuconazole, CD: carbendazim (trendline and correlation mathematically established without carbendazim; dotted 1:1-line for guidance purposes, not mathematically calculated).
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dichloro-N-octylisothiazolinone. Schoknecht et al. (2013) achieved similar results using short term immersion tests according to EN 16105:2011: diuron N-octylisothiazolinone > iodocarb > terbutryn carbendazim > dichloro-N-octylisothiazolinone. The comparison of the results from the artificial walls as well as the laboratory studies with the estimated ones based on polyacrylate-water partition constants indicates that polyacrylate indeed is the dominant phase for the partitioning of most biocides in the render-water system. Therefore, even though several processes might influence the desorption of biocides from polymer-based render into water, the concept of estimating the desorption behaviour based on the partition constants from the pure polymer (e.g. polyacrylate or polydimethylsiloxane) seems to be a useful tool, based on a rapid and easy method. 4. Conclusions In this study polyacrylate–water partition constants (log KAcW) were determined for biocides used in building material to range between 1.66 (isoproturon) and 3.57 (DCOIT). It was shown that the partitioning of the biocides in the render-water system for most compounds is dependent on the polyacrylate–water partitioning and the polyacrylate fraction in the render. Basically, the distribution constant to polyacrylate-based render (logDrender) as well as the one normalised to the organic matter content (logDOM) can be predicted linearly from the polyacrylate–water partition constants. However, the reader should be aware that outliers as carbendazim can occur and thus make a refined assessment necessary. Such assessments are crucial for the dossiers for the biocide regulation, but are probably also important for the development of performance criteria of new renders and paints. Acknowledgements The authors acknowledge the financial support of U.E. Bollmann’s PhD-stipend by the Danish EPA through the project Methods for the improvement of scenarios concerning the emission of biocides from buildings, 667-00065 & 667-00066 as well as the project Transport and transformation of biocides (667-00178 & 66700179) and the AUFF grant: Advanced water purification using bio-inorganic nanocatalysts and soil filters (waterpurification.au.dk). The authors acknowledge Synthomer Deutschland (Marl, Germany) for providing Plextol D498. Appendix A. Supplementary material Supplementary data associated with this article can be found, in the online version, at http://dx.doi.org/10.1016/j.chemosphere. 2014.08.074. References Benhabib, K., Mimanne, G., 2014. Optimized parameters of SPME analysis for atrazine and its application to measure speciation. Appl. Clay Sci. 87, 260–264. Bollmann, U.E., Vollertsen, J., Carmeliet, J., Bester, K., 2014. Dynamics of biocide emissions from buildings in a suburban stormwater catchment – concentrations, mass loads and emission processes. Water Res. 56, 66–76.
Burkhardt, M., Kupper, T., Hean, S., Haag, R., Schmid, P., Kohler, M., Boller, M., 2007. Biocides used in building materials and their leaching behavior to sewer systems. Water Sci. Technol. 56, 63–67. Burkhardt, M., Zuleeg, S., Vonbank, R., Schmid, P., Hean, S., Lamani, X., Bester, K., Boller, M., 2011. Leaching of additives from construction materials to urban storm water runoff. Water Sci. Technol. 63, 1974–1982. Burkhardt, M., Zuleeg, S., Vonbank, R., Bester, K., Carmeliet, J., Boller, M., Wangler, T., 2012. Leaching of biocides from facades under natural weather conditions. Environ. Sci. Technol. 46, 5497–5503. Dean, J.R., Tomlinson, W.R., Makovskaya, V., Cumming, R., Hetheridge, M., Comber, M., 1996. Solid-phase microextraction as a method for estimating the octanolwater partition coefficient. Anal. Chem. 68, 130–133. Endo, S., Droge, S.T.J., Goss, K.U., 2011. Polyparameter linear free energy models for polyacrylate fiber–water partition coefficients to evaluate the efficiency of solid-phase microextractions. Anal. Chem. 83, 1394–1400. Górecki, T., Namies´nik, J., 2002. Passive sampling. TrAC, Trends Anal. Chem. 21, 276–291. Haftka, J.J.H., Scherpenisse, P., Jonker, M.T.O., Hermens, J.L.M., 2013. Using polyacrylate-coated SPME fibers to quantify sorption of polar and ionic organic contaminants to dissolved organic carbon. Environ. Sci. Technol. 47, 4455–4462. Lambropoulou, D.A., Sakkas, V.A., Albanis, T.A., 2002. Analysis of antifouling biocides Irgarol 1051 and Sea Nine 211 in environmental water samples using solid-phase microextraction and gas chromatography. J. Chromatogr. A 952, 215–227. Mayer, P., Vaes, W.H.J., Hermens, J.L.M., 2000. Absorption of hydrophobic compounds into the poly(dimethylsiloxane) coating of solid-phase microextraction fibers: High partition coefficients and fluorescence microscopy images. Anal. Chem. 72, 459–464. Mayer, P., Tolls, J., Hermens, J.L.M., Mackay, D., 2003. Equilibrium sampling devices. Environ. Sci. Technol. 37, 184A–191A. Ohlenbusch, G., Kumke, M.U., Frimmel, F.H., 2000. Sorption of phenols to dissolved organic matter investigated by solid phase microextraction. Sci. Total Environ. 253, 63–74. Paulus, W., 2005. Directory of Microbicides for the Protection of Materials: A Handbook. Springer, Dordrecht, Netherlands. Pawliszyn, J., 1997. Solid Phase Microextraction. Theory and Practice. Wiley-VCH, New York. Reichel, A., Hochberg, A., Köpke, C., 2004. Plaster, Render, Paint and Coatings: Details, Products, Case Studies. Birkhäuser, Basel, Switzerland. Schoknecht, U., Wegner, R., Horn, W., Jann, O., 2003. Emission of biocides from treated materials – test procedures for water and air. Environ. Sci. Pollut. Res. 10, 154–161. Schoknecht, U., Gruycheva, J., Mathies, H., Bergmann, H., Burkhardt, M., 2009. Leaching of biocides used in facade coatings under laboratory test conditions. Environ. Sci. Technol. 43, 9321–9328. Schoknecht, U., Sommerfeld, T., Borho, N., Bagda, E., 2013. Interlaboratory comparison for a laboratory leaching test procedure with façade coatings. Prog. Org. Coat. 76, 351–359. Schwarzenbach, R.P., Gschwend, P.M., Imboden, D.M., 2003. Environmental Organic Chemistry, second ed. Wiley-Interscience, Hoboken, New Jersey. SRC, 2014. PhysProp Database (assessed 25.02.14). Styszko, K., Bollmann, U.E., Wangler, T.P., Bester, K., 2014. Desorption of biocides from renders modified with acrylate and silicone. Chemosphere 95, 188– 192. Synthomer Deutschland, 2014. Technical Data Sheet PLEXTOL D 498. Marl, Germany. Vaes, W.H.J., Hamwijk, C., Urrestarazu Ramos, E., Verhaar, H.J.M., Hermens, J.L.M., 1996. Partitioning of organic chemicals to polyacrylate-coated solid phase microextraction fibers: kinetic behavior and quantitative structure-property relationships. Anal. Chem. 68, 4458–4462. Verbruggen, E.M.J., Vaes, W.H.J., Parkerton, T.F., Hermens, J.L.M., 1999. Polyacrylatecoated SPME fibers as a tool to simulate body residues and target concentrations of complex organic mixtures for estimation of baseline toxicity. Environ. Sci. Technol. 34, 324–331. Wangler, T.P., Zuleeg, S., Vonbank, R., Bester, K., Boller, M., Carmeliet, J., Burkhardt, M., 2012. Laboratory scale studies of biocide leaching from facade coatings. Build. Environ. 54, 168–173. Zambonin, C.G., Palmisano, F., 2000. Determination of triazines in soil leachates by solid-phase microextraction coupled to gas chromatography–mass spectrometry. J. Chromatogr. A 874, 247–255.
Contents lists available at ScienceDirect
Chemosphere journal homepage: www.elsevier.com/locate/chemosphere
Polyacrylate–water partitioning of biocidal compounds: Enhancing the understanding of biocide partitioning between render and water Ulla E. Bollmann a, Yi Ou b, Philipp Mayer c, Stefan Trapp c, Kai Bester a,⇑ a
Aarhus University, Department of Environmental Science, Frederiksborgvej 399, 4000 Roskilde, Denmark University Duisburg-Essen, Department of Chemistry, Universitätsstraße 5, 45141 Essen, Germany c Technical University of Denmark, Department of Environmental Engineering, Miljøvej B113, 2800 Kgs. Lyngby, Denmark b
h i g h l i g h t s
g r a p h i c a l a b s t r a c t
Render-water distribution of biocides
linearly dependent on polyacrylate– water partitioning. The polymer is the dominant phase for the sorption of biocides in polymer enhanced render. Biocide leaching from render can be estimated from polyacrylate–water partitioning.
a r t i c l e
i n f o
Article history: Received 4 June 2014 Received in revised form 25 August 2014 Accepted 27 August 2014 Available online 7 October 2014 Handling Editor: I. Cousins Keywords: SPME Polyacrylate coated glass fibre filters Polymeric coatings Triazines Phenylureas Isothiazolinones
a b s t r a c t In recent years, the application of polymer-based renders and paints for façade coatings of buildings has risen enormously due to the increased mounting of thermal insulation systems. These materials are commonly equipped with biocides – algaecides, fungicides, and bactericides – to protect the materials from biological deterioration. However, the biocides need to be present in the water phase in order to be active and, hence, they are flushed of the material by rain water. In order to increase the knowledge about the partitioning of biocides from render into the water phase, partition constants between the polymer – in this case polyacrylate – and water were studied using glass fibre filters coated with polyacrylate. The polyacrylate–water partition constants (log KAcW) of ten biocides used in construction material varied between 1.66 (isoproturon) and 3.57 (dichloro-N-octylisothiazolinone). The correlation of the polyacrylate–water partition constants with the octanol–water partition constants is significant, but the polyacrylate–water partition constants were predominantly below octanol–water partition constants (Kow). The comparison with render-water distribution constants showed that estimating the leaching of biocides from render based on polymer–water partitioning is a useful and practical tool. Ó 2014 Elsevier Ltd. All rights reserved.
1. Introduction ⇑ Corresponding author. Tel.: +45 87158552. E-mail address: [email protected] (K. Bester). http://dx.doi.org/10.1016/j.chemosphere.2014.08.074 0045-6535/Ó 2014 Elsevier Ltd. All rights reserved.
Polymer enhanced renders and paints for building façades, using polyacrylate or silicone as organic binder, are usually
1022
U.E. Bollmann et al. / Chemosphere 119 (2015) 1021–1026
equipped with biocides in order to prevent growth of algae or fungi on the surfaces (Reichel et al., 2004). About 0.1–2 g active ingredient per kg material is used in render or exterior paints and, typically, a mixture of several biocides is used. Hence, the total content of biocides in render and exterior paints ranges from 5 to 10 g kg1 (Burkhardt et al., 2011). Laboratory studies on constantly soaked material, dipping experiments with alternating wet and dry cycles, or forced rain experiments showed that the biocides leach out of the render material in considerable fractions (Schoknecht et al., 2003; Burkhardt et al., 2007; Schoknecht et al., 2009; Burkhardt et al., 2011, 2012; Wangler et al., 2012). The leaching process of biocides from render is assumed to be a multistep process: (1) removal from the surface layer which is itself (2) in equilibrium with the deeper layers of the render, from which (3) the surface layer is constantly refilled. According to Schoknecht et al. (2009), the leaching is a diffusion controlled process that can be related to the octanol–water partition constant as well as the water solubility, and the refill of the surface boundary layer could occur via transport of biocides with the evaporating water through the render. Styszko et al. (2014) determined the equilibrium distribution of biocides between render and water. The determined render-water distribution constants of that study revealed similarities but no significant (a = 0.1) correlation with the octanol–water partition constants. Styszko et al. (2014) identified the influence of the polyacrylate content on the partitioning being important for some biocides (isothiazolinone, carbamates or triazines), while the partitioning of phenylureas seemed not to be influenced that much by the polyacrylate content. Styszko et al. (2014) proposed that polyacrylate is one of the main components of the polymeric render controlling the leaching of biocides. Partitioning can be assessed by solid phase micro extraction (SPME) and other passive sampling techniques, which are well established for lipophilic compounds with polydimethylsiloxane (PDMS) as accumulating (sorption) phase, while for more hydrophilic compounds polyacrylate phases are more successfully used (Pawliszyn, 1997; Górecki and Namies´nik, 2002). Further, a central parameter for these passive sampling techniques is the polymer to water partition constant, which sets the upper limit for analyte enrichment and is also crucial for the calibration of these methods. Therefore, a considerable amount of research has been performed on polymer to water partitioning within an analytical context, whereas studies are more scarce when it comes to the leaching and partitioning of key pollutants from technical polymers contained in for examples buildings and constructions. Specifically, polyacrylate–water partition constants for polar organic chemicals have been studied and quantified using solid phase micro extraction (SPME) fibres coated with polyacrylate (Dean et al., 1996; Vaes et al., 1996; Verbruggen et al., 1999; Ohlenbusch et al., 2000; Haftka et al., 2013), with Endo et al. (2011) providing the most comprehensive data set and evaluation. However, none of them have covered a typical set of biocides such as used in building industries, i.e. isothiazolinones, triazoles, triazines, carbamates, and phenylureas. While in the polyacrylate–water system only two phases are involved in the partitioning, the render-water distribution constant describes the distribution into a complex mixture. Typically, main components of polymer enhanced renders are carbonates (30–60%), polymeric binder (10–15% either polyacrylate or silicone) and sand in different grain sizes. Schwarzenbach et al. (2003) introduced the additivity concept in order to estimate sorption to soils, by assuming that (1) each sorption phase acts independently and comes to equilibrium with all other phases and (2) the total pollutant amount sorbed can be estimated as the sum of the pollutant amount in each phase. Transferring this concept to the render-water system, the render-water distribution constant (Drender, Eq. (1)) can be described as the sum of the
partitioning to polyacrylate, carbonates, sand particles and other render ingredients, where f describes the fraction of each of the different phases (i.e. polyacrylate, calcium carbonate, sand, water) and c the concentration of the biocide in each phase:
Drender ¼
f polyacrylate C polyacrylate þ f CaCO3 C CaCO3 þ f Sand C Sand þ . . . C water ð1Þ
In the present study, glass fibre filters were coated with polyacrylate and then used in order to determine the polyacrylate–water partition constants (log KAcW) of biocides used in building materials. The obtained polyacrylate–water partition constants were studied and related to the leaching of biocides from polyacrylatebased render systems by comparing them to render-water distribution constants. It was thus aim of the study to test whether the hypotheses that polyacrylate is the dominating component controlling the partitioning of biocides in the render-water system and thus influencing the leaching holds true and would allow predictions of the leaching of biocides from polyacrylate-based renders using polyacrylate–water partition constants. 2. Material and methods 2.1. Chemicals The experiments were performed for eleven compounds (Table 1), of which ten are used as biocides in building materials (carbendazim, iodocarb, isoproturon, diuron, terbutryn, cybutryn, N-octylisothiazolinone, dichloro-N-octylisothiazolinone, tebuconazole, and propiconazole). Atrazine was previously used as pesticide and has been added for comparative reasons. Aqueous solutions were prepared from a stock solution (100 lg mL-1 in acetonitrile) of the eleven compounds with Millipore-water at 10 ng mL-1 (0.1% acetonitrile). Surrogate standards (1 lg mL-1 in methanol) were used for mass spectrometric analysis: isoproturon-D6, terbutryn-D5, cybutryn-D9, tebuconazole-D6, and carbendazim-D4. Suppliers and purities of the used standards can be found in supplementary S1; all standards were used directly without any further purification. Acetonitrile and methanol (both gradient grade LiChrosolv) were purchased from Merck (Darmstadt, Germany) while Millipore-water was generated by an in-house apparatus. 2.2. Coating of glass fibre filters As the different producers of polyacrylate containing renders do not disclose the exact identity of the used polyacrylate used in their products, for the partitioning experiments in this study one polyacrylate, i.e., Plextol D498 obtained from Synthomer Deutschland (Marl, Germany) was used. This Polymer is used in industry to produce organically modified renders and paints. Plextol D498 is characterised as thermoplastic methylmethacrylate and n-butylacrylate copolymer dispersion (50% w/w, density: 1.05 g mL-1) (Synthomer Deutschland, 2014). Since the total amount of polyacrylate per filter was aimed to be very low, Plextol D498 was diluted with Millipore-water to 20% w/w. Binder free glass fibre filters (WhatmanÒ GF/A, Ø = 25 mm, GE Healthcare, Little Chalfont, United Kingdom) were cleaned with methanol and Millipore-water before usage. After drying, the filters were coated with polyacrylate by adding a defined amount of diluted polymer dispersion onto the filter. Due to capillary forces the polymer dispersion was distributed over the entire filter surface and air dried at room temperature. Afterwards, the homogenous distribution was controlled by visual inspection and the added amount by weighing. Following this procedure, glass fibre filters were coated with 25, 50, and 80 mg polyacrylate.
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Table 1 Studied biocides with name, acronym, CAS-number, formula, and physical–chemical properties (log KOW: octanol–water partition constant, WS: water solubility, pvap: saturation vapour pressure, pKa: acid dissociation constant). Group Name, Acronym, CAS
Formula
Carbamates Carbendazim CD, 10605-21-7 Iodocarb IPBC, 55406-53-6 Phenylureas Isoproturon IP, 34123-59-6
pKa: 4.5 (base) and 10 (acid)
pKa: 11.8 (acid)
pKa: 0.1 (base) and 14.3 (acid)
Log KOW: 2.61 WS: 35 mg L1 pvap: 3.9 * 107 h Pa
pKa: 1.7 (base)
Terbutryn TB, 886-50-0
Log KOW: 3.74 WS: 25 mg L1 pvap: 2.3 * 106 h Pa
pKa: 4.1 (base)
Cybutryn (Irgarol 1051) IRG, 28159-98-0
Log KOW: 3.95 WS: 7 mg L1 pvap: 8.8 * 107 h Pa
pKa: 4.1 (base)
Log KOW: 2.45 WS: 480 mg L1 pvap: 4.9 * 105 h Pa Log KOW: 4.9 WS: 14 mg L1 pvap: 6.67 h Pa (xylene)
pKa: 0.4 (base)
Log KOW: 3.7 WS: 36 mg L1 pvap: 1.7 * 108 h Pa
pKa: 1.8 (base) and 13.7 (acid)
Log KOW: 3.72 WS: 100 mg L1 pvap: 2.7 * 107 h Pa
pKa: 1.7 (base)
Triazines Atrazine AT, 1912-24-9
Isothiazolinones N-Octylisothiazolinone OIT, 26530-20-1 Dichloro-N-octylisothiazolinone DCOIT, 64359-81-5 Triazoles Tebuconazole TBU, 107534-96-3 Propiconazole PPZ, 60207-90-1
a
Log KOW (pH 7): 1.6 WS: 8 mg L1 pvap: carbendazim > N-octylisothiazolinone > iodocarb > cybutryn > terbutryn > propiconazole > tebuconazole > dichloro-N-octylisothiazolinone. During leaching tests from façade render under natural weather conditions Burkhardt et al. (2012) analysed seven biocides. Based on that study, the leaching ability could be sorted according to isoproturon > diuron > iodocarb > N-octylisothiazolinone > cybutryn > terbutryn >
Fig. 2. Correlation between the polyacrylate–water partition constant log KAcW (pH 5.5) and the octanol–water partition constant log KOW (pH 7) (Paulus, 2005; SRC, 2014); DCOIT: dichloro-N-octylisothiazolinone, IRG: cybutryn, TBU: tebuconazole, DR: diuron, OIT: N-octylisothiazolinone, IPBC: iodocarb, CD: carbendazim. The dotted line is plotted for guidance purposes, it is not mathematically calculated.
4
log DOM log Drender
y=0.55x+1.52 y=0.56x+0.51
3
IRG IPBC
TBU
IRG IPBC
TBU
DR IP LogD
The used render contained mainly polyacrylate (10%), carbonate (66%) and quartz sand. As described in that study, the render-water distribution constant is pH-dependent, hence, for comparison only distribution constants at pH 5.6 were used. Further, Styszko et al. (2014) demonstrated that increasing the fraction of polyacrylate in a polyacrylate-based render reduced the desorption from the render for iodocarb, dichloro-N-octylisothiazolinone, tebuconazole, cybutryn, and carbendazim but not for isoproturon and diuron. Hence, the desorption of iodocarb, dichloro-N-octylisothiazolinone, tebuconazole, cybutryn, and carbendazim seemed to be dependent on the fraction of polyacrylate in the render, while the desorption of diuron and isoproturon was almost not affected by the polyacrylate fraction. According to Eq. (1) the render-water distribution constant would be directly correlated to the polyacrylate–water partitioning. If the render partitioning would be solely dependent on partitioning between polyacrylate and water the normalised render-water distribution constant would equal the polyacrylate–water partition constant. The comparison of the polyacrylate–water partition constant (numerical values from this study, Table 2) and the desorption constant from polyacrylate-based render normalised to the organic matter content (Styszko et al., 2014) showed a positive significant
R2=0.79 R2=0.79
2
DR CD IP 1
CD 0 0
1
2
3
4
LogKAcW Fig. 3. Correlation between the polyacrylate–water partition constant (log KAcW) and the distribution constant to polyacrylate-based render (logDrender) as well as the one normalised to the organic matter content (organic matter content = 10%, logDOM) determined by Styszko et al. (2014); IRG: cybutryn, IPBC: iodocarb, DR: diuron, IP: isoproturon, TBU: tebuconazole, CD: carbendazim (trendline and correlation mathematically established without carbendazim; dotted 1:1-line for guidance purposes, not mathematically calculated).
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dichloro-N-octylisothiazolinone. Schoknecht et al. (2013) achieved similar results using short term immersion tests according to EN 16105:2011: diuron N-octylisothiazolinone > iodocarb > terbutryn carbendazim > dichloro-N-octylisothiazolinone. The comparison of the results from the artificial walls as well as the laboratory studies with the estimated ones based on polyacrylate-water partition constants indicates that polyacrylate indeed is the dominant phase for the partitioning of most biocides in the render-water system. Therefore, even though several processes might influence the desorption of biocides from polymer-based render into water, the concept of estimating the desorption behaviour based on the partition constants from the pure polymer (e.g. polyacrylate or polydimethylsiloxane) seems to be a useful tool, based on a rapid and easy method. 4. Conclusions In this study polyacrylate–water partition constants (log KAcW) were determined for biocides used in building material to range between 1.66 (isoproturon) and 3.57 (DCOIT). It was shown that the partitioning of the biocides in the render-water system for most compounds is dependent on the polyacrylate–water partitioning and the polyacrylate fraction in the render. Basically, the distribution constant to polyacrylate-based render (logDrender) as well as the one normalised to the organic matter content (logDOM) can be predicted linearly from the polyacrylate–water partition constants. However, the reader should be aware that outliers as carbendazim can occur and thus make a refined assessment necessary. Such assessments are crucial for the dossiers for the biocide regulation, but are probably also important for the development of performance criteria of new renders and paints. Acknowledgements The authors acknowledge the financial support of U.E. Bollmann’s PhD-stipend by the Danish EPA through the project Methods for the improvement of scenarios concerning the emission of biocides from buildings, 667-00065 & 667-00066 as well as the project Transport and transformation of biocides (667-00178 & 66700179) and the AUFF grant: Advanced water purification using bio-inorganic nanocatalysts and soil filters (waterpurification.au.dk). The authors acknowledge Synthomer Deutschland (Marl, Germany) for providing Plextol D498. Appendix A. Supplementary material Supplementary data associated with this article can be found, in the online version, at http://dx.doi.org/10.1016/j.chemosphere. 2014.08.074. References Benhabib, K., Mimanne, G., 2014. Optimized parameters of SPME analysis for atrazine and its application to measure speciation. Appl. Clay Sci. 87, 260–264. Bollmann, U.E., Vollertsen, J., Carmeliet, J., Bester, K., 2014. Dynamics of biocide emissions from buildings in a suburban stormwater catchment – concentrations, mass loads and emission processes. Water Res. 56, 66–76.
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