1. Bulgarian State Standard, BSS 16714–87
2. S.G. Malachova (Ed.), Vremennie metoditcheskie recomendacii po controlju zagrjasnenija potchv, part II, Gidrometeoizdat, Moskow, 1984, pp. 8.18.24
3. ISO/TR 11046–94/E/
4. B.H. Florovskii, Luminiscentnaja Bituminologia, MGU, Moskow, 1975, p. 192
5. K. Gjurova, M. Zagortcheva, L. Ljubtchev, Third International Symposium on Ekology 94, 8–10 September, Bourgas, Bulgaria, 1994, vol. III, p. 238