1. Clinical and Histological Study of Coal Tar Phototoxicity in Humans
2. Hazardous Substances Data Bank (HSDB) http://toxnet.nlm.nih.gov/
3. National Toxicology Program (NTP) 11th and 12th Annual Report on Carcinogens http://ntp.niehs.nih.gov/?objectid=72016262-BDB7-CEBA-FA60E922B18C2540
4. GESTIS International Limit Values 2011 http://bgia-online.hvbg.de/LIMITVALUE/WebForm_gw.aspx