Caffeine has alsobeen used as a che

Caffeine has also
been used as a chemical marker for faecal source tracking (Field and
Samadpour, 2007; Scott et al., 2002). Its definite advantage is that it
is almost entirely a human-specific pollutant; natural sources of
caffeine in the environment (e.g. guarana, coffee plants) are so few
and generate such low background levels that they can be neglected,
especially in the Northern hemisphere