Figure 2
From: Caffeine in surface and wastewaters in Barbados, West Indies
Selected average concentrations of caffeine in surface waters collected worldwide. Letters in italics represent locations proximal to wastewater plants: a downstream, b upstream. Numbers in parentheses are the following references: 01 Bahlmann et al. 2012, 02 Tewari et al. 2013, 03 Wu et al. 2010, 04 Siegener and Chen 2002, 05 Knee et al. 2010, 06 Yargeau et al. 2007, 07 Benotti and Brownawell 2007, 08 Comeau et al. 2008, 09 Verenitch and Mazumder 2008, 10 Ferreira 2005, 11 Rodriguez del Rey et al. 2012, 12 Singh et al. 2010.