1. Arshad, M. A., & Martin, S. (2002). Identifying critical limits for soil quality indicators in agro-systems. Agriculture, Ecosystems & Environment, 88, 153–160.
2. Brinton, F.W. (2000). Compost quality standards and guidelines. Woods End research Laboratory, Inc., New York State Association of Recyclers
3. Council Directive 86/278/EC on the protection of the Environment and in particular soil when sewage sludge is used in agriculture.
4. Council Directive 91/689/EEC of 12 December 1991 on hazardous waste.
5. Council Directive 91/271/EEC concerning urban wastewater treatment. Adopted on 21 May 1991 to protect the water environment from the adverse effects of discharges of urban waste water and from certain industrial discharges.