1. Baker, A.J.M. and Brooks, R.R. (1989) ‘Terrestrial higher plants which hyperaccumulate metallic elements-A review of their distribution ecology and phytochemistry’, Biorecovery 1, 81–126.
2. Brooks, R.R., Morrison, R.S., Reeves R.D., Dudley, T.R. and Akman, (1979) ‘Hyperaccumulation of nickel by Alyssum L., (Cruciferae)’. Proceedings of the Royal Society of London, Series B, 203, 387–403.
3. Commission of the European Community (1986) ‘Council Directive of 12 June 1986 on the protection of the environment, and in particular of the soil, when sewage sludge is used in agriculture’, Official Journal of the European Communities, No L181 (86/278/EEC), pp 6–12.
4. McGrath, S.P. (1987) ‘Long-term studies of metal transfers following applications of sewage sludge’, in P.J. Coughtrey, M.H. Martin and M.H. Unsworth (eds.), Pollutant Transport and Fate in Ecosystems, Blackwell Scientific, Oxford, pp. 301–317.
5. UK Statutory Instruments, (1989) The sludge (Use in agriculture) regulations, SI 1263, HMSO, London.