Transfer of glyphosate and its degradate AMPA to surface waters through urban sewerage systems

Abstract

A study of glyphosate and aminomethyl phosphonic acid (AMPA) transfer in the Orge watershed (France) was carried out during 2007 and 2008. Water samples were collected in surface water, wastewater sewer, storm sewer and wastewater treatment plant (WWTP). These two molecules appeared to be the most frequently detected ones in the rivers and usually exceeded the European quality standard concentrations of 0.1 μg L⁻¹ for drinking water. The annual glyphosate estimated load was 1.9 kg year⁻¹ upstream (agricultural zone) and 179.5 kg year⁻¹ at the catchment outlet (urban zone). This result suggests that the contamination of this basin by glyphosate is essentially from urban origin (road and railway applications). Glyphosate reached surface water prevalently through storm sewer during rainfall event. Maximum concentrations were detected in storm sewer just after a rainfall event (75–90 μg L⁻¹). High concentrations of glyphosate in surface water during rainfall events reflected urban runoff impact. AMPA was always detected in the sewerage system. This molecule reached surface water mainly via WWTP effluent and also through storm sewer. Variations in concentrations of AMPA during hydrological episodes were minor compared to glyphosate variations. Our study highlights that AMPA and glyphosate origins in urban area are different. During dry period, detergent degradation seemed to be the major AMPA source in wastewater.

Introduction

Some herbicides, such as glyphosate, AMPA (degradation product of glyphosate), diuron and isoproturon were frequently detected in the last few years in French streams (Legrand et al., 1991, Tisseau et al., 1996, Garmouma et al., 1998, Blanchoud et al., 2004, IFEN, 2007). Since 2003 in the Ile-de-France region including Paris and its conurbation area (2740 km²), the pesticides monitoring programme (Phyt’Eaux Propres) observed a significant increase of glyphosate and AMPA concentrations in surface waters (DIREN Ile de France, 2006, Botta et al., 2008). In particular, the Orge River frequently exceeds the European quality standard for drinking water (0.1 μg L⁻¹ for pesticides) (European Community Council, 1998). This is a serious problem because surface waters constitute 60% of the drinking water resource in the Paris urban area.

Pesticides are used prevalently in agricultural zones but in the last years a lot of studies have shown the impact of urban uses which is important at the local scale due to application on impervious surfaces like roads, sidewalks and lawns (Blanchoud et al., 2004, Skark et al., 2004). Glyphosate is the most widely used pesticide in the world for weed control and also in new agricultural systems, notably glyphosate-tolerant crops (Baylis, 2000, Kannan et al., 2006). In the Orge Basin, considerable applications of glyphosate were registered in particular by railways maintenance (from 60 kg to 280 kg) in 2006 (Hamelet, 2007). A recent study showed that the urban use of glyphosate contributes to glyphosate and AMPA contamination of streams (Kolpin et al., 2006). Consequently to this glyphosate application, its degradation product AMPA (aminomethylphosphonic acid) is frequently detected in surface waters and partially in groundwater (Rueppel et al., 1977). AMPA is the primary glyphosate degradation product due to microbial activity in soils (Forlani et al., 1999) but also a degradation product of some detergents (Skark et al., 1998). In the Orge River basin, AMPA is frequently detected in higher concentrations than glyphosate (Fauchon and Lecomte, 2007).

Surface runoff is known to be the primary way of transfer from agricultural fields to surface waters (Wauchope, 1978). In some areas, like in the Lake Erie Basin, the highest herbicide concentrations typically coincided with the first runoff after application and then steadily decreased to pre application values (Kannan et al., 2006). In urban sectors, concrete and asphalt have been designed to facilitate the rapid transport of runoff to sewers that are commonly networked to feed into surface water bodies (Blanchoud et al., 2007). The glyphosate is very sensitive to surface runoff while it hardly leaches to groundwater (Beltman et al., 2001, Ramwell and Hollis, 2003). This is due to its high solubility in water (10.1 g L⁻¹ at 20 °C) and high sorption (>1.000 L kg⁻¹) to soil particles (Rubio et al., 2003). Rainfall events of high intensity increase glyphosate transfer by runoff on hard surfaces (Luijendijk et al., 2003). But glyphosate transfer quantity is also dependent on the time interval between applications and rainfall (Luijendijk et al., 2005). All these factors suggest that storm sewers and wastewater treatment plant (WWTP) effluents can be a major pathway of glyphosate towards surface waters in urban areas.

Pesticides contamination of sewers is not well described in the literature. Sewers were identified as a point-source of pesticide contamination in some catchments (Müller et al., 2002, Blanchoud et al., 2007, Eriksson et al., 2007). In case of combined sewer system, the relevant use of pesticides in urban areas leads to a universal input of these molecules thought WWTPs in surface waters (Nitschke and Schussler, 1998, Gerecke et al., 2002). Glyphosate and AMPA with urban origins were often detected in WWTP effluent and in streams as well (Kolpin et al., 2006). However, the AMPA origin is actually not determined, as it comes from the degradation of other molecules than glyphosate. Detergents phosphoric acids, the ethylene diamine tetramethylene phosphonate (EDTMP) or diethylenetriamine–penta-methylene phosphonic acid (DTPMP) can also be degraded in AMPA and found in the environment (Nowack, 1997). In the specific case of the Orge River, the downstream part of the catchment presents a separated sewer system. It means that household and stormwater discharges are not mixed. However, during rainfall events, overflows between separated sewers can occur, with untreated wastewater mixing with surface runoff water (Lee and Bang, 2000). In this case, it is possible to find pesticides in both sewers.

Important water supply treatment plants are situated in the Seine River downstream the confluence with the Orge River. This stream is supposed to be the major source of the increasing of pesticides concentrations at this point of the Seine River. Consequently, two programmes started in 2007 to identify the relation between applications, transfers on urban areas and surface water contamination. The programme “Phyt’Eaux Cités” was promoted by a regional water supply agency (SEDIF). The aim of this programme is to reduce the quantities of urban pesticides that reach the rivers, by education of users to the best practices. Another programme “PIREN-Seine” concerns the ecological functioning and pesticides transfer processes of the Seine River system in relation to land use and environmental management. Glyphosate transfer to surface waters was studied in the urban sectors.

The main objectives of this study were to estimate the annual glyphosate and AMPA loads in surface water for the Orge River and to identify urban origins. Following this large scale study, the investigations were carried out in a small urban catchment. Glyphosate and AMPA input pathways to the surface waters were studied and dynamic of transfer were described through urban sewers system, storm sewer, wastewater sewer and WWTP. Another purpose of this study is to provide information about possible AMPA origins in urban area and to investigate its probably domestic origin.