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Direct use of wastewater in Mexico

Organisation. Ministry of Agriculture and Water Resources runs irrigation districtsInfrastructure material humanPayment for wastewaterPolicy - Untreated wastewater plus crop restrictionsEnforcement - fines and confiscation crops. Crop restrictions. Depends on water qualityUntreated: cereal

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Direct use of wastewater in Mexico

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    1. Direct use of wastewater in Mexico Dr Ursula Blumenthal, LSHTM

    2. Organisation Ministry of Agriculture and Water Resources runs irrigation districts Infrastructure – material + human Payment for wastewater Policy - Untreated wastewater plus crop restrictions Enforcement - fines and confiscation crops

    3. Crop restrictions Depends on water quality Untreated: cereal (maize, wheat), fodder (alfalfa), chillies Improved (dilution, ‘treatment’): some vegetable crops River water with effluent – not controlled, vegetables eaten raw grown

    4. How well does it work? Agriculture; Allows for cash crops not just subsistence farming Farmers prefer to grow vegetables Many plots are small – leased, p/t work Management issues – water demand varies, storage issues, XS to river Water table rising; run-off issues; salinity

    5. Health effects ? Studies in Irrigation Districts 03 and 100 ‘Evaluate’ policy Reservoirs used to store water ref irrigation demand ? water quality improvements Studies to find out risks of untreated wastewater use and improvements necessary

    9. Implications Restricted irrigation - workers’ health:- (a) Nematode egg guideline ? 1 egg/litre ? 0.1 egg/litre as children of farmworkers have increased prevalence and intensity of Ascaris infection at ? 1 egg/litre - little excess at 0 egg/litre (Cifuentes, 1998 Blumenthal 2000, Peasey 2000)

    11. Implications (b) Faecal coliform guideline Need to add FC guideline of (ii) 103 FC/100ml where use flood/furrow irrigation and/or children exposed - as 2x increase in diarrhoea and 4x inc. in Norwalk-like virus in children 5-14 yrs at 104 FC/100ml (Blumenthal et al, 2000)

    12. Indirect use of wastewater Part flow from one reservoir diverted to river; authorities ‘lose control’ of it Unrestricted irrigation - Used to irrigate large area of vegetable and salad crops including tomato, onion, lettuce, cucumber, parsley, cauliflower etc Sold in local wholesale and retail markets Studied isolated population eating vegetables originating in wholesale market

    16. Implications – international Faecal coliform guideline for unrestricted increase in diarrhoeal disease when guideline exceeded by factor of 10 (10,000 FC/100ml) (Blumenthal et al, 2000) so guideline needs to be below 104 FC/100ml ? 1000 FC/100ml adequate in endemic area

    17. Mexico guidelines 1996 Unrestricted irrigation – 103 FC/100ml (monthly mean) and ? 1 egg/litre Restricted irrigation - 103 FC/100ml and 5 eggs/litre (1998 internal 105 FC only; semi-restricted 103 – 105 FC only ?!) Achievable by secondary treatment and chlorination; added filtration too costly ref restricted irrigation

    18. Reality Most STP’s inefficient due to operation and maintenance problems – much wastewater not treated Time limits for compliance yr 2000-2010 – but who pays ? Public health – anthelminthic campaigns in areas high helminths – also w/w areas? Keep restricted irrigation where possible

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