ID:DA04658917
Helmer, Richard, Dr.-Ing
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edited by Richard Helmer and Ivanildo Hespanhol
E & FN Spon 1997
Available at 6 libraries
Barry Lloyd, Richard Helmer
Longman Scientific & Technical , Wiley 1991
Available at 3 libraries
edited by Michel Meybeck, Deborah V. Chapman, Richard Helmer
Published on behalf of the World Health Organization and the United Nations Environment Programme by Blackwell Reference 1990