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:Interest in the use of CWs for remediation of runoff from agricultural irrigation and agro-industrial production has become increasingly popular over the last decades, due to their low capital and operational cost, low energy consumption, and environmental friendliness (Huett et al., 2005; Scholz, 2007; Carty et al., 2008).
Category: