[Indoor air guide values for monocyclic monoterpenes (limonene)]

The German Working Group on Indoor Air Guidelines of the Federal Environment Agency and the States' Health Authorities is issuing indoor air guide values to protect public health. For health evaluation of monocyclic monoterpenes in indoor air valid inhalation studies are missing. Therefore, indoor air guide values have to be derived from animal feeding studies with limonene and chronic exposure (feeding: 5 days per week over two years). The Lowest Adverse Effect Level based on histological lesions of liver tissue was observed with 500 mg limonene/kg bw x day. The extrapolation to continuous exposure (7 days/week) corresponds to a dose of 357 mg/kg x d (LOAEL). The indoor air guide values are calculated using 20 m³ as rate of inhalation per day, a standard body weight of 70 kg for man, the standard factors of 10 x 10 for interspecies and interindividual variability, a factor of two for the specific physiology of children (higher breathing rate compared to adults) and an absorption factor of 63% for inhalative incorporation of limonene. A health hazard guide value (RW II) of 10 mg limonene/m³ in indoor air and a health precaution guide value (RW I) of 1 mg limonene/m³ are derived. The precaution guide value of 1 mg/m³ coincidences with the lower range of reported odour thresholds of limonene.