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:According to Kunito et al. (2004), the biological half-life is rather long for trace-elements with high affinity to SH group in cysteine (Cd,Hg), leading to the age dependent increase in the concentration in toppredators.
Category: