## 1 Introduction  
Water is a very complex and dynamic resource and although the estimated amount of the available water on the planet is 140 billion km\({}^{3}\), only 3% is fresh water [1]. Due to the distribution of fresh water resources around the globe, less than 1% of these resources are available for human use. This, in turn, leads to water shortage problems in many regions of the world, particularly developing countries. Water scarcity combined with poverty is forcing the reuse of untreated or partially-treated wastewater for irrigation in order to cope with the high food demands of growing populations [2]. Consequently, the risk of bacterial infections, roundworms and diarr diseases are much greater [3]. A recent survey revealed that the 46 countries, representing 75% of the world's irrigated land, use polluted water for irrigation [4]. Globally, an estimated 20 million ha of land are irrigated with wastewater, and this area is expected to markedly increase in the next few years [5]. Wastewater, originating from the discharge of municipal and industrial effluents, contains a number of inorganic and organic substances. Among organic contaminants of wastewater and sludge, surfactants are often detected at the highest concentrations [6; 7; 8]. Non-ionic surfactants concentrations ranging from 10\({}^{2}\) to 10\({}^{3}\) mg L\({}^{-1}\) have been detected in wastewater [9]. Non-ionic surfactants such as alcohol ethoxylates (AEs), alkylphenol ethoxylates (APE) are used extensively as leather degreasing agents and in other textile industry applications. Consequently, non-ionic surfactants have been identified as major contaminants in untreated wastewater from such industries [10; 11]. Owing a non-dissociable hydrophilic group (e.g., alcohol, phenol, ether, ester, or amide), non-ionic surfactants do not ionize in water. Although in the wastewater treatment plants, APEs degrade into metabolites such as nonylphenol ethoxylates (NPEs), treatment plants are not adequately efficient to remove the metabolites such as environmentally damaging nonylphenols (NPs) [12; 13]. Consequently, nonylphenols (NPs) were detected at high concentrations ranging from 1.8 to 25 g L\({}^{-1}\) in two rivers in Switzerland [14]. Further, studies showed that the continuous use of household products containing AEs, contributes to NPE and NP loads in urban sewer waters [13; 15]. Certain AEs are now used as an alternative to alkyl polyphenol ethoxylates (APEOs), as they are safer as result of their rapid breakdown to less toxic, less persistent and less estrogenic compounds. Generally, the presence of nonionic surfactants in irrigation water leads to two major concerns: (1) The degradation products of non-ionic surfactants such as nonylohenol ethoxylates (NPEO) and NP act as estrogen mimicking compounds, leading to symptoms like change in sex ratio, decrease in fish population and malformations in some aquatic animals [16]. In terms of the estrogenic effects, a study in US raised a great concern of potable water contamination by NPs which have been detected in some wells. The authors reported that the source of these compounds is the continuous infiltration disposal of wastewater treatment plant effluents [17]. (2) Non-ionic surfactants in the irrigation water may have an impact on the mobility of chemicals in soil and cause contamination of groundwater [18; 19; 20; 21]. [PERSON] (2008) [22] reported that the downward movement of pesticides in soil was enhanced by the presence of high non-ionic surfactant concentrations in leaching water. However, the effect may depend on the surfactant concentration. Similarly, [PERSON] _et al._ (2006) [23] indicated that, at low concentrations 0-20 mg L\({}^{-1}\), surfactants have the potential to decrease sorption and thus mobilize herbicides such as atrazine. For example, at low concentrations (0.04 g kg\({}^{-1}\)), non-ionic surfactants decreased the mobility of the herbicide metabolchlor in soil; however, at high concentrations (5-50 g kg\({}^{-1}\)),the mobility increased [24].