Analysis of quaternary ammonium compounds in urban stormwater samples

Abstract

A method for benzalkonium analysis has been developed to measure benzalkonium concentration in dissolved and particulate fractions from urban runoff samples. The analysis was performed by liquid chromatography coupled with mass spectrometry (LC-MS/MS). The dissolved matrix was extracted by Solid Phase Extraction (SPE), with cationic exchange and the particles by microwave extraction with acidified methanol. Recovery percentages were closed to 100% for benzalkonium C12 and C14. The protocol was applied to roof runoff samples collected after a roof demossing treatment, and to separative stormwater samples from a 200 ha catchment. The results illustrate an important contamination of the roof runoff, with a maximum concentration close to 27 mg/L during the first rain. The benzalkonium concentration (sum of C12 and C14) stayed high (up to 1 mg/L) even 5 months after the treatment. Benzalkonium concentration measured in stormwaters was low (0.2 μg/L) but with contaminated suspended solids (up to 80 μg/g).

Introduction

Alkyldimethylbenzylammonium chloride (usually called benzalkonium chloride) is a group of well-known Quaternary Ammonium Compounds (QACs). Benzalkonium is composed by a positively charged nitrogen atom linked to a long alkyl chain (commonly from 12 to 18 carbon atoms) on one side, and a benzyl group on the other. The two last positions are occupied by methyl groups (Fig. 1). These molecules have a large range of biocidal effects against bacteria (Kummerer et al., 2002, Nalecz-Jawecki et al., 2003, Sutterlin et al., 2008a, Tezel et al., 2008), algae, diatoms and crustaceans (Beveridge et al., 1998, Nalecz-Jawecki et al., 2003). Benzalkonium is particularly used by hospitals (Kummerer et al., 1997) and the food industry (Krockel et al., 2003) for disinfecting surfaces and equipment.

The toxicity of benzalkonium is very high especially to aquatic organisms. The EC50 of respectively fishes and invertebrates are 280 μg/L and 5.9 μg/L (USEPA, 2006). Benzalkonium is less toxic for bacteria with EC50 from 500 to 6000 μg/L (Sutterlin et al., 2008b). It has been established during a toxicity test with sewage sludge that benzalkonium is adsorbed on particulate matter at a ratio of 40% in only 3 h (Kummerer et al., 2002). After adsorption, benzalkonium continues to have a less important but non negligible biocidal effect. Lastly, benzalkonium can have effects on human health. Professional diseases have been reported like asthma, skin allergy or eye irritation (Hemery, 2008, INRS, 2005, Popin et al., 2008, Preller et al., 1996, Sènécal-Fouquoire et al., 2001, Tennstedt, 2008).

Because of the large benzalkonium use and its high toxicity, the presence of the molecule has been studied in sewage system, surface water and also in sediments and sewage sludge, but exclusively during dry weather (Ferrer and Furlong, 2001, Ferrer and Furlong, 2002, Kreuzinger et al., 2007, Kummerer et al., 1997, Li and Brownawell, 2010, Martinez-Carballo et al., 2007a, Martinez-Carballo et al., 2007b, Sutterlin et al., 2007). Concerning hospitals, a 24 h mean effluent concentration of 1900 μg/L has been found (Kummerer et al., 1997). In sewers, depending on the localization of the sampling point (the presence of a hospital, or a laundry can be a local source of benzalkonium), concentrations from 0.03 to 2800 μg/L have been measured (Kreuzinger et al., 2007). In surface water, in Austria, the mean concentration measured was 0.2 μg/L (Kreuzinger et al., 2007, Martinez-Carballo et al., 2007b). The authors also illustrate an increase in the concentration downstream of different wastewater treatment plant (WWTP) discharges. For sediments, concentrations can be high with a maximum of 8.9 μg/g in urban estuarine sediments (Li and Brownawell, 2010). In that case, it is observed that sorbed QACs in sediment might be persistent (Li and Brownawell, 2010). Finally sewage sludge is also an important sink of benzalkonium, with a mean concentration of 8 μg/g reported in Spain (Martinez-Carballo et al., 2007a).

Benzalkonium is also widely used as a de-mossing agent for the cleaning of urban surfaces, especially tile roofs, facades and terraces. This usage possibly leads to important benzalkonium transfer into stormwaters. However, there are no data today concerning the prevalence of benzalkonium in urban runoff and its potential contribution to the contamination of aquatic systems. The aim of this work is to study the leaching of benzalkonium by a treated roof. Indeed the mass of pure benzalkonium spread on a 100 m² roof can reach up to 900 g (Van de Voorde et al., 2009). This represents an important stock which may be mobilized by rain and contaminate rainwater.

The first step of this work was to develop an analytical protocol for benzalkonium analysis in runoff water. This protocol was based on previously published work (Dudkiewicz-Wilczynska et al., 2004, Ferrer and Furlong, 2001, Ferrer and Furlong, 2002, Li and Brownawell, 2009, Martinez-Carballo et al., 2007a, Martinez-Carballo et al., 2007b, Nunez et al., 2004, Sutterlin et al., 2008a, Vincent et al., 2007), but had to be adapted to the specificities of our samples: large range of concentration in a complex matrix and important number of samples to analyze within a short time to avoid benzalkonium degradation. This paper presents the analytical method that was developed and an application on real runoff samples.