Formaldehyde is classified as a carcinogen by the International
Agency for Research on Cancer [1]. The oral reference
dose (RfD) suggested by the US Environmental Protection
Agency (EPA) is 0.2 mg/kg [2]. Formaldehyde occurs endogenously
in many foods. According to a study by the World
Health Organization, formaldehyde content ranges from
3.3 mg/kg to 60 mg/kg in fruits and vegetables, 8e20 mg/kg in
meats, 1e3.3 mg/kg in milk and 1e98 mg/kg in fish [3]. In 2001,
the Rapid Alert System for Food and Feed from the European
Commission made an alert notification after finding that
shiitake mushrooms from China contained 300 mg/kg of
formaldehyde [4] and suggested the possibility that the
formaldehyde had been added deliberately. After the incident,
the French food safety agency Agence Franc¸aise de Se´curite´
Sanitaire des Aliments required that the level of formaldehyde
cannot exceed 63 mg/kg for fresh mushrooms [5]. In response
to this alert, the China Quality Inspection Administration set a
tentative maximum limit standard of 63 mg/kg in fresh mushrooms and 300 mg/kg in dry mushrooms [6]. However,
the Center for Food Safety of Hong Kong revealed that
100e320 mg/kg of formaldehyde occurs naturally in dry
mushrooms [7] and 6e54.5 mg/kg of formaldehyde occurs
endogenously in fresh mushrooms. Mason et al from the
Central Science Laboratory of the UK Government commissioned
a survey of formaldehyde content in shiitake mushrooms
using liquid chromatographyemass spectrometry
(LCeMS) [8]. The concentrations of formaldehyde found were
100e320 mg/kg. Mason et al stated that under the harsh conditions
of steam distillation with acid, the formaldehyde
released was the sum of free and reversibly bound formaldehyde.
Therefore, the measured formaldehyde concentrations
were relatively high. They suggested that the method used for
formaldehyde analysis should only determine free
formaldehyde.