1. Effect of metal toxicity on the size of the soil microbial biomass
2. Brookes, P.C., McGrath, S.P., Klein, D.A. and Elliott, E.T. Environmental Contamination synmp. Proc. Land. CEP Consultants. Edinburgh. pp.574–583.
3. Metal concentrations in sludges and soil from a long-term field trial
4. Paye, A.L. 1984.“Fate and Effects of Trace Elements in Sewage Sludge when Applied to Agricultural Lands. A Literature Review Study”, Report No. EPA 670/2–74–005 97