Elsevier

Water Research

Volume 56, 1 June 2014, Pages 66-76
Water Research

Dynamics of biocide emissions from buildings in a suburban stormwater catchment – Concentrations, mass loads and emission processes

https://doi.org/10.1016/j.watres.2014.02.033Get rights and content

Highlights

  • Biocide emissions from buildings are also important in Northern Europe.

  • Constant, rather than first flush emissions during rain events on catchment scale.

  • Biocide emissions from buildings correlate with driving rain.

Abstract

Biocides such as isothiazolinones, carbamates, triazines, phenylureas, azoles and others are used to protect the surfaces of buildings, e.g. painted or unpainted render or wood. These biocides can be mobilized from the materials if rainwater gets into contact with these buildings. Hence, these biocides will be found in rainwater runoff (stormwater) from buildings that is traditionally managed as “clean water” in stormwater sewer systems and often directly discharged into surface waters without further treatment. By means of a 9 month event-based high resolution sampling campaign the biocide emissions in a small suburban stormwater catchment were analysed and the emission dynamics throughout the single rain events were investigated. Five out of twelve of the rain events (peak events) proved significantly higher concentrations than the rest (average) for at least one compound. Highest median concentrations of 0.045 and 0.052 μg L−1 were found for terbutryn and carbendazim, while the concentrations for isoproturon, diuron, N-octylisothiazolinone, benzoisothiazolinone, cybutryn, propiconazole, tebuconazole, and mecoprop were one order of magnitude lower. However, during the peak events the concentrations reached up to 1.8 and 0.3 μg L−1 for terbutryn and carbendazim, respectively. Emissions of an averaged single family house into the stormwater sewer turned out to be 59 and 50 μg event−1 house−1 terbutryn and carbendazim, respectively. Emissions for the other biocides ranged from 0.1 to 11 μg event−1 house−1. Mass load analysis revealed that peak events contributed in single events as much to the emissions as 11 average events. However, the mass loads were highly dependent on the amounts of rainwater, i.e. the hydraulic flow in the receiving sewer pipe.

The analysis of the emission dynamics showed first flush emissions only for single parameters in three events out of twelve. Generally biocides seemed to be introduced into the stormwater system rather continuously during the respective events than in the beginning of them. Mass flows during the events did correlate to driving rain, whereas mass loads neither correlated to the length or the intensity of rainfall nor the length of dry period.

Introduction

Building façades are exposed to wet conditions such as driving rain and undercooling condensation, and, hence, susceptible to growth of algae, fungi and bacteria. For preservative reasons, polymeric based coatings as renders and paints, which are very susceptible for microbial attack, are equipped with biocides (Reichel et al., 2004). These polymeric based renders and paints are commonly used as finishing coating on top of thermal insulation systems. Also other façade materials, such as polymer based paints for wooden surfaces, are preserved by biocides (Schoknecht and Bergmann, 2000). Biocides are regulated in the EU and defined in the European biocidal product directive (BPD) (European Parliament and Council, 2012) as substances designed “to destroy, deter, render harmless, prevent action of, or otherwise exert a controlling effect on any harmful organism by chemical or biological means.”

Both renders and exterior paints can be equipped with film preserving compounds. It is known that triazines and phenylureas are used as algaecides and carbamates as fungicides, while isothiazolinones are used as bactericides for such purposes. Besides the use as film preservatives some of the biocides, primarily the ones with high water solubility, are only added to the products to increase shelf life of the formulated products until they are used (in-can preservatives) (European Commission (EC), 2013a, European Commission (EC), 2013b). The concentration per single biocide is about 0.1–2 g kg−1 in render, which corresponds to 0.3–4 g m−2 wall area (Burkhardt et al., 2011). In-can and film preservatives consist of mixtures of about one to eight different biocides, leading to a total content of biocides in render and exterior paints from 0.5% to 1% (Burkhardt et al., 2011). Additionally to the previous named biocides, triazoles are used for the preservation of wood, as they are very effective fungicides (Schultz et al., 2007). Besides usage in buildings also private gardening is a potential source for urban pollution (Fig. 1). Only use, (European) laws and regulations but not effects discriminate between biocides and pesticides. However, for most compounds it is quite clear for which purpose they are used in Denmark (Table 1).

The current literature that focuses on biocide leaching from materials relies on equilibrium partitioning and forced weathering. Schoknecht et al., 2003, Schoknecht et al., 2009) and Styszko et al. (2014) demonstrated that triazine, phenylurea and isothiazolinone biocides can be washed off from construction material surfaces (paints and renders) in idealized laboratory experiments, in which materials were constantly soaked with water. Under forced rain in combination with drying periods (Burkhardt et al., 2009, Burkhardt et al., 2011, Schoknecht et al., 2003, Schoknecht et al., 2009) the biocides leach in considerable fractions from the respective materials (paints and renders). However, significantly higher amounts of rain were applied in these experiments than naturally occurring. The authors intended these experiments as first guidance and not as sound basis for massive assessment/modelling. In additional projects it has been found out, that the delivery rate of the biocides through the materials is diverse, even though the used renders are very similar, i.e. it depends on the exposure to weather (Burkhardt et al., 2012, Wangler et al., 2012).

Previous studies showed that leaching from building materials is a major source of biocide pollution concerning urban waters (Burkhardt et al., 2007). Driven by rain, the biocides enter surface waters and soil, where they might undergo degradation processes. As rainwater runoff (stormwater) is often collected in separated sewer systems and either directly discharged into surface waters or infiltrated into groundwater, the contamination of stormwater is of special concern. Burkhardt et al. (2007) expected that urban biocide emissions lead to concentrations exceeding the European drinking water quality standard for pesticides (100 ng L−1 for single pesticide and 500 ng L−1 for total pesticide concentration (European Parliament and Council, 1998)) up to ten fold in the first flush of stormwater runoff. However, these values are only relevant for those biocides that are registered as pesticides as well, for all others no threshold value for drinking water exists and, hence, also substances, forbidden in agricultural usage, are still used as biocides without any regulation in respect to drinking water in Europe. Nevertheless, the presence of biocides exceeding effect levels in surface water would be in conflict with the European water framework directive (WFD) (European Parliament and Council, 2000). A new directive on priority substances under the WFD recommends annual average environmental quality standard (AA-EQS) for inland waters of 2.5 and 64 ng L−1 for cybutryn and terbutryn, and 200 and 300 ng L−1 for diuron and isoproturon, respectively (European Parliament and Council, 2013). The other biocides are not regulated under the WFD. Furthermore, the used biocides are toxic to aquatic organisms and may cause long-term adverse effects in the aquatic environment already at low concentrations. For example the effect concentration of cybutryn, which causes an effect in 10% of the test organisms (EC10), is 10 ng L−1 (Mohr et al., 2008). Additionally, the predicted no effect concentrations (PNEC) of biocides are in the low ng L−1 range, e.g. terbutryn and carbendazim 34 ng L−1 or octylisothiazolinone 13 ng L−1 (Burkhardt et al., 2009).

In this study the stormwater in a suburban catchment was sampled with high temporal resolution and analysed with respect to biocide concentrations and mass loads to study the emission dynamics and detect first flush events. The temporal resolution was used to study whether a treatment of only a fraction of the runoff water for instance the first flush (which we take as the first 30% or less) would make sense. The study covered substances (Table 1) that are known to be used on the Danish building market (N-octylisothiazolinone (OIT), terbutryn (TB), diuron (DR)), as well as those that were analysed in previous studies (cybutryn (IRG), isoproturon (IP), benzoisothiazolinone (BIT), carbendazim (CD), methylisothiazolinone (MI)). Furthermore, tebuconazole (TBU) and propiconazole (PPZ) were added to this study, as they are predominantly used in wood preservation (Schoknecht and Bergmann, 2000), while mecoprop (MCPP) is mainly used in roof protection (Bucheli et al., 1998), and is no longer sold for agricultural or gardening purposes in Denmark (Danish Environmental Protection Agency DEPA, 2011a, Danish Environmental Protection Agency DEPA, 2011b). Among the analysed biocides only propiconazole and tebuconazole are currently used in Danish agriculture (DEPA, 2011a); tebuconazole is used in urban gardening as well (DEPA, 2011b). The occurrence of some compounds analysed in the present study (carbendazim, triazines and phenylureas), has been reported for urban stormwater (Burkhardt et al., 2012, Quednow and Püttmann, 2007, Quednow and Püttmann, 2009, Wittmer et al., 2010), whereas, the isothiazolinones and triazoles have, to the author's knowledge, never been reported in urban waters. The study was undertaken, first, to demonstrate the importance of biocide emission into rainwater catchments in Northern Europe, second, to test whether the assumption that no biocides will be emitted from suburban catchments into surface waters holds true, third, to study the dynamics of biocide emissions in rainwater catchments, and fourth, to study the influence of weather to the respective emissions.

Section snippets

Catchment

The stormwater runoff was collected in a catchment in Silkeborg (Denmark), which is a typical example of a Northern European suburban area. The catchment had previously been hydraulically analysed in detail as its stormwater management system was constructed in connection with an EU LIFE project (Silkeborg Municipality, 2009). The catchment is residential and covers in total 21.5 ha with 140 single family houses. Applying a calibrated runoff model the impervious area was determined to 7.1 ha,

Concentrations

The median and average concentrations of the analysed biocides for all 191 analysed stormwater samples are shown in Fig. 2. The box plot shows concentrations for all biocides, focussing around a median. However, also some outliers, which usually originated from a few events with concentrations exceeding the median by one or two orders of magnitude (peak events), were detected as well. A more detailed discussion about frequency and possible causes for occurrence of these peak events is given in

Conclusions

The different concentration profiles in the stormwater runoff events can be ascribed to different emission pathways and application forms of the biocides (Fig. 1). First of all, the constantly emitted biocides as terbutryn, carbendazim, isoproturon, diuron, tebuconazole, propiconazole, and mecoprop were detected in most of the samples. These compounds are used as film preservatives (European Commission (EC), 2013a, European Commission (EC), 2013b) and slowly released to the environment (

Acknowledgement

The authors acknowledge the financial support of Miljøstyrelsen (Danish EPA) through the project Methods for the improvement of scenarios concerning the emission of biocides from buildings, 667-00065 & 667-00066 and the AUFF grant: Advanced water purification using bio-inorganic nanocatalysts and soil filters. Rossana Bossi provided access to precipitation samples, Birgit Groth and several other technicians and student helpers provided help in respect to sampling and sample preparation and are

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