However, pesticide residues are found ubiquitously in the environment in ng/liter to low μg/liter concentrations. For instance, surveys of groundwater and not-yet-treated potable water in industrialized countries typically detect 10 to 20 substances in recurrent findings above 0.01 μg/dL (3.6×10−12 lb/cu in) the maximum accepted drinking water concentration for pesticides in many countries. About half of the detected substances are no longer in use and another 10 to 20% are stable transformation products.[1]