Ecological Engineering 37 (2011) 955–962 Contents lists available at ScienceDirect Ecological Engineering journal homepage: www.elsevier.com/locate/ecoleng Assessing the influence of vegetation on reduction of pesticide concentration in experimental surface flow constructed wetlands: Application of the toxic units approach David Elsaesser a,∗ , Anne-Grete Buseth Blankenberg b , Anna Geist a , Trond Mæhlum b , Ralf Schulz a a Institute for Environmental Sciences – University of Koblenz-Landau, Fortstr. 7, Landau 76829, Germany b Bioforsk Soil and Environment Division, Frederik A. Dahlsvei 20, Ås, 1432, Norway article info Article history: Received 20 May 2010 Received in revised form 27 January 2011 Accepted 15 February 2011 Available online 17 March 2011 Keywords: Constructed wetland Pesticide Mitigation Nonpoint-source pollution Toxic units abstract In summer 2008, an experiment on retention of a mixture of five pesticides in the Lier experimental wet- land site (Norway) was performed. Two vegetated cells with hydraulic retention times (HRT) of 280 min and 330 min and one cell without vegetation (HRT of 132 min) of 120 m 2 surface area each were inves- tigated regarding their ability to reduce peak concentrations, pesticide masses and predicted adverse effects. Discrete water, plant and sediment samples were taken and analysed. The inlet peak concentra- tions of the pesticides dimethoate, dicamba, trifloxystrobin and tebuconazole ranged from 18 ng/L up to 5904 ng/L. The mean reduction of peak concentration was 72% in the non-vegetated cell and up to 91% in the vegetated cells. Less than 5% of the masses were retained within the wetlands. Uptake and sorption by plants was low (up to 4%), however, higher for the vegetated cell dominated by Phalaris arundinacea L. than for the one with Typha latifolia L. as dominant plant. The toxic units (TU) approach was used to describe the potential reduction of toxicity within the wetland cells. Calculated toxicity of the substances decreased by 79% in the non-vegetated cell and by 95% in the two vegetated cells. Despite the low mass retention, the vegetated wetland system reduced the toxic effects, expressed as toxic units from values of 0.24 to 0.01, i.e. a concentration two orders of magnitude below the acute toxicity threshold, within a distance of 40 m while the non vegetated would need to be about 64 m long for the same efficiency. © 2011 Elsevier B.V. All rights reserved. 1. Introduction Pesticides are widely used in agriculture, but adverse effects may be observed when the substances are transferred to natu- ral ecosystems (Schulz, 2004). Nonpoint-source pollution through runoff, drainage and spray drift accounts for a majority of all sur- face water pollution (Zaring, 1996). Constructed wetlands have the ability to mitigate pesticide pollution deriving from various agricul- tural nonpoint sources (Baker, 1992; Schulz and Liess, 2001; Schulz and Peall, 2001; Schulz et al., 2001a). Dense vegetation increases the effectiveness in remediating pesticide pollution (Susarla et al., 2002; Braskerud and Haarstad, 2003; Imfeld et al., 2009; Moore et al., 2002, 2006, 2009b; Rogers and Stringfellow, 2009). Retention of pesticide loads is driven by physico-chemical characteristics of the substances, inserted masses and the hydraulic retention time as well as physical properties of the wetland filter (Baker, 1992; Gregoire et al., 2009; Schulz, 2004). Nonetheless, our knowledge ∗ Corresponding author. Tel.: +49 634128031330; fax: +49 634128031326. E-mail address: elsaesser@uni-landau.de (D. Elsaesser). about the processes which lead to decreasing concentrations in those systems is limited (Gregoire et al., 2009; Schulz, 2004). During peak application of pesticides in a watershed, a mixture of numerous substances may be transported to the waterbodies (Battaglin and Goolsby, 1999; Schulz, 2004; Thomas et al., 2001). Adverse effects are driven by exposure time and concentration levels of the substances. High peak concentrations in water and suspended solids may occur during exposure events (Schulz, 2004). Even if there is low risk of adverse effects with low concentrations of the single substances, the mixture may lead to severe impacts in the receiving waterbody. Junghans et al. (2006) proposed to sum up the toxicity of the single substances as toxic units to describe the effects of pesticide mixtures within the recieving ecosystem. The toxic units (TU) approach is a feasible method to predict adverse effects of complex chemical mixtures on the structure and functioning of aquatic ecosystems (Junghans et al., 2006; Peterson, 1994; Sprague, 1970). However, this approach so far was never used to assess the potential positive effects artificial wetlands may have on aquatic surface water quality. As an integrated part of the EU Life project ArtWET (Gregoire et al., 2009) we focus on the role of vegetation in optimising the 0925-8574/$ – see front matter © 2011 Elsevier B.V. All rights reserved. doi:10.1016/j.ecoleng.2011.02.003