______________________________________ WELL Study A Review of Policy and Standards for Wastewater Reuse in Agriculture: A Latin American Perspective Task No: 68 Part II Dr Anne Peasey, Dr Ursula Blumenthal, Prof. Duncan Mara and Prof. Guillermo Ruiz-Palacios June 2000 Task Management & Quality Assurance by: Dr Sandy Cairncross London School of Hygiene & Tropical Medicine, UK WEDC, Loughborough University, UK E-mail: [email protected] Internet: http://www.lboro.ac.uk/well/ ______________________________________ Table of Contents Executive Summary… ....................…………………………………………………………...4 1. Introduction ....................................................................................................................6 1.1 Wastewater Reuse ...........................................................................................................6 1.2 Standards for Wastewater Reuse .....................................................................................6 2. Wastewater reuse in Mexico ..........................................................................................8 2.1 Extent of Reuse in Mexico.................................................................................................8 2.2 Wastewater treatment in Mexico .....................................................................................10 3. Current policies for wastewater reuse and treatment in Mexico ...............................12 3.1 Wastewater reuse policy.................................................................................................12 3.2 Wastewater treatment policy...........................................................................................13 3.3 Current policy questions and dilemmas...........................................................................13 4. Evidence of health risks from recent studies in Mexico ............................................15 4.1 Study area .......................................................................Error! Bookmark not defined. 4.2 Risks to farm workers related to restricted irrigation & effect of wastewater treatmentError! Bookmark not defined. 4.2.1 Exposure to raw wastewater ...............................Error! Bookmark not defined. 4.2.2 Exposure to partially treated wastewater.............Error! Bookmark not defined. 4.3 Risks to consumers related to unrestricted irrigation ..........Error! Bookmark not defined. 5. Evidence of health risks from studies in other sites ..................................................15 5.1 Effects on farmworkers or wastewater treatment plant workers.......................................18 5.2 Effects on consumers of vegetable crops........................................................................18 5.2.1 Evidence from microbiological studies of crops irrigated with treated wastewater..............................................................................................................18 5.2.1.1 Studies on bacterial contamination of vegetable crops ................................18 5.2.1.2 Studies on contamination of vegetable crops with nematode eggs ..............20 5.2.2 Evidence from risk assessment studies ...........................................................22 6. Implications for wastewater reuse standards and policies in Mexico .......................23 6.1 Implications for Unrestricted Irrigation Standards............................................................22 6.1.1 Faecal coliform standard for unrestricted irrigation...........................................22 6.1.2 Nematode egg standard for unrestricted irrigation............................................23 6.2 Implications for Restricted Irrigation Standards ...............................................................24 6.2.1 Faecal coliform standard for restricted irrigation...............................................24 6.2.2 Nematode egg standard for restricted irrigation ...............................................24 6.3 Implications for a Disease Control Approach...................................................................25 6.3.1 Unrestricted irrigation.......................................................................................25 6.3.2 Restricted irrigation..........................................................................................25 6.4 Proposed Standards for Mexico ......................................................................................25 6.5 Implications for Health Protection ...................................................................................26 6.5.1 Wastewater treatment......................................................................................26 6.5.2 Crop restriction ................................................................................................28 6.5.3 Irrigation technique ..........................................................................................28 6.5.4 Human Exposure Control.................................................................................29 6.6 Implications for Policy .....................................................................................................30 7. References....................................................................................................................31 2 List of Tables Table 1-1. Health guidelines for the use of wastewater in agriculture and aquaculture (WHO 1989) ........................................................................................................................7 Table 2-1. Wastewater Irrigation Districts in Mexico....................................................................9 Table 2-2. Wastewater treatment plants in Guerrero State .......................................................10 Table 3-1. The Policy Process in Mexico 1971-1996 ..................................................................12 Table 3-2. Mexican Standard NOM-001-ECOL-1996 governing wastewater reuse in agriculture .13 Table 6-1. Proposed changes to Mexican Standard NOM-001-ECOL-1996 ................................26 Table 6-2. Mean annual performance of five waste stabilization ponds in series in northeast Brazil .......................................................................................................................27 List of Annexes Annex A The History of Wastewater Reuse Policy in Mexico...................................................37 Annex B Summary of evidence supporting WHO guidelines for safe use of water in agriculture (1989) ....................................................................................................................41 Annex C Epidemiological studies of wastewater reuse in Hidalgo, Mexico...............................46 Annex D Microbiological studies in Brazil and England............................................................52 Annex E Wastewater treatment...............................................................................................56 Annex F Implications of results for international guidelines and policy concerning wastewater use in agriculture....................................................................................65 Annex G Wastewater reuse guidelines in Andalucia, Spain. ....................................................72 Annex H List of participants at Technical meeting on wastewater reuse in agriculture…………73 List of Figures Figure 1a: Effect of exposure to wastewater on Ascaris infection: effect of raw wastewater……………………………………………..……………………………….17 Figure 1b: Effect of exposure to wastewater on diarrhoeal disease: effect of raw wastewater…………………………………………………………………………...…17 Figure 1c: Effect of exposure to wastewater on Ascaris infection: effect of retention in one reservoir……………………………………………………………………………...18 Figure 1d: Effect of exposure to wastewater on diarrhoeal infection: effect of retention in one reservoir…………………………………………………………………..18 Figure 1e: Effect of exposure to wastewater on Ascaris infection; effect of retention in two reservoirs…………………………………………………………………………….18 Figure 1f: Effect of exposure to wastewater on diarrhoeal disease: effect of retention in two reservoirs………………………………………………………………….18 Figure 2a: Effect of consumption of raw onion (times/month) on diarrhoeal disease……………19 Figure 2b: Effect of consumption (times/fortnight) of raw green tomatoes on seroresponse to Human Norwalk-like virus/MX among 5-14year olds……………….19 Figure 2c: Effect of consumption of raw chillies on diarrhoeal disease………………………… 19 Acknowledgements The authors would like to thank Rebecca Stott for her preparation of Annex D - "Experimental microbiological studies on contamination of wastewater-irrigated crops in Brazil and UK". We would also like to thank the participants of the technical meeting on wastewater reuse held in Mexico City of December 4th 1998 for their invaluable comments; particular thanks go to Gabriella Moeller (Mexican Institute of Water Technology, Juitepec, Mexico), Blanca Jimenez (Faculty of Engineering Faculty, National University of Mexico, Mexico) and Ma.Esperanza Garcia Rodriguez (National Vaccination Council, Mexico). We are also grateful to Humberto Romero Alvarez (National Water Commission, Mexico) for his useful comments and advice prior to the technical meeting, and to Esther Gpe. Vitervo, Roxana Remus and Beatriz Ruiz-Palacios for their assistance in organising the technical meeting. Finally we would like to thank DFID for providing the necessary funds to organise the technical meeting and for the preparation