1. The Third Polish Congress of Cities Sanitation (1984) Szczecin, Poland
2. Polish Standard BN-89/9103-09
3. Kabata-Pendias A (ed) (1978) Determination of contents of trace elements and sulfur in soils and plants, Prac Wyd Nauk IUNG Pulawy, Poland
4. Ostrowska A et al. (1991) Methods of analysis and evaluation of soils and plants properties, IOS, Warsaw
5. Golimowski J, Cendrowska M (1985) Chem Anal 30:777?782