Evaluate the collective function of references cited together in a given text segment.
Classify their combined role into one of the following categories: 'method', 'background', or 'result'.

Text:…wastewater treatments (Patrolecco et al., 2015; Santos et al., 2009; Salgado et al., 2010) leading to contamination of surface waters, seawaters, groundwater and in some cases also drinking waters (Salgado et al., 2012; Pereira et al., 2015; de Jesus Gaffney et al., 2015; Lolić et al., 2015).
Category: