1. Department of ToxicologyNational Institute for Occupational Health4788Johannesburg, 2000South Africa
2. Kobus Dekker Occupational Hygiene ConsultancyPO Box 38243, Garsfontein East 0060PretoriaSouth Africa
3. Department of Haematology and Molecular MedicineUniversity of the WitwatersrandPrivate Bag 3, WITS 2050JohannesburgSouth Africa