Planning for controlling the quality of irrigation water destined for vegetable production in Chile
The outbreak of cholera in Chile in April of 1991 made it urgently necessary to control the use of contaminated irrigation water used on vegetable crops that are normally eaten raw. The Ministry of Health began a major programme to restrict such production in heavily contaminated areas. This increased the urgency for the Servicio Agrícola y Ganadero (SAG) of the Ministry of Agriculture to evaluate the extent of irrigation water contamination and to develop methods to promote production in safe areas.
FAO together with SAG developed a one-year international project (Oct 1992 - Sept 1993) to evaluate the impact of microbial contamination in irrigation water. The project counterpart was the Department of Natural Resource Protection (DEPROREN) of SAG. The principal objectives of the project were to evaluate the existing levels of contamination, develop a database that could be used as a basis to control contaminated water use in vegetable production and to propose a certification system that could be used to promote safe production areas for both internal and international markets.
The project was operated in three distinctly different phases:
Phase 1 (Water Quality Monitoring Phase)
In developing and conducting the water quality monitoring, the project reviewed whether the procedures had national and international recognition, formed a legal basis for follow-up actions and whether SAG could use the procedure and results to promote safe production. Monitoring was conducted in only two pilot areas; the Metropolitan and V Regions of Chile. These areas represented 50 percent of the population and 49 percent of the total vegetable production in the country. In addition, the two Regions contain 80 percent of the production of the 14 crops identified by the Ministry of Health as high-risk crops.
The project used faecal coliform count as the contamination indicator. This indicator is recognized internationally by WHO, PAHO and other organizations in Latin America. Faecal coliform count is also used in regulations in Chile that deal with wastewater and how it can be used on crops (NCh 1333/1978) and is within the capability of all public and private laboratories in Chile to determine on a routine basis. The project recommended the continued use of this indicator until changed by the Ministry of Health.
TABLE 14: Distribution of faecal contamination in irrigated areas of the Metropolitan and V Regions, Chile
|
|
Faecal contamination level (Faecal coliforms/100 ml) |
|||
|
<103 |
103 - 104 |
104 - 105 |
>105 |
|
|
% of the 120 000 ha sampled in the Metropolitan Region |
8 |
25 |
41 |
26 |
|
% of the 80 000 ha sampled in the V Region |
27 |
65 |
8 |
0 |
The analytical method used by the project was the multiple-tube fermentation technique. This method was recommended for future programmes within Chile but the project felt strongly that SAG, the Ministry of Health and the University of Chile should attempt to adapt the membrane filtration method to use with Chilean irrigation waters. This would give SAG and others much more flexibility in sampling in remote rural areas and responding to emergency situations throughout the other regions.
The project used the University and Public Health Institute (ISP) laboratories for analytical work. The main reason for using these laboratories was the lack of capabilities within SAG laboratories and the need to demonstrate a high level of credibility during the monitoring programme. The project recommended that SAG continue to strengthen its ties with the ISP laboratories until capabilities within SAG laboratories could be established.
Two contamination sources were considered in setting the water quality monitoring sites: primary contamination that occurred in the rivers before the water is diverted into the irrigation system and secondary contamination that occurred within the irrigation system. The project developed guidelines for selecting monitoring sites based on these two contamination sources and complying with existing regulations as defined in NCh 1333/1978. The guidelines emphasized only monitoring potentially clean areas to promote safe production. This approach avoided using financial resources to monitor heavily contaminated areas that have little potential for future production of vegetables.
The monitoring network set out by the project divided the Metropolitan Region into five irrigated zones. From December 1992 to March 1993, a total of 604 samples were collected from 120 sites within these five zones which cover approximately 120 000 hectares. The V Region was divided into seven irrigated zones. From January to April 1993, over 750 samples were collected from 150 sampling sites within the seven zones that cover approximately 80 000 hectares.
Phase 2 (Data Analysis Phase)
Based on the monitoring results, the project was able to make the estimates shown in Table 14.
In order to evaluate the project results, the project assessed primary contamination. This contamination was generally due to discharges of untreated urban wastewater in amounts that were so large that often there was not sufficient natural river water to dilute the discharge to bring the faecal coliform levels below the 103 FC/100 ml standard designated in NCh 1333/1978.
The project also assessed secondary contamination. Some of the causes of secondary contamination have been identified as discharges directly to the irrigation canals of domestic household wastewater and from animal confinement facilities. The choice of monitoring sites focused on detecting the presence of secondary contamination in channels that initially showed low levels of contamination at the river intakes. The selection of sites followed the guidelines shown in Figure 7.
As shown in Table 14, the Metropolitan Region had the highest level of bacterial contamination. The main cause was the direct discharge of untreated urban wastewater to natural waterways before the water was diverted for irrigation (primary contamination) but secondary contamination sources did play a role. This results in only 8 percent of the irrigated area with a high potential to participate directly in a programme of water certification for safe vegetable production. Because of the extent of the primary contamination from discharges to the river, it is unlikely that the area available for vegetable production could increase significantly until the treatment works are in place for the urban wastewater. Because of the high initial levels of contamination, secondary contamination in such channels did not appear to be a significant factor with the exception of zones irrigated with well water or in areas not affected by large urban discharges.
It can be seen in Figure 8 that 37 percent of the irrigated area of the Metropolitan Region initially was below the maximum defined in NCh 1333/1978 but this dropped to only 8 percent after secondary sources of contamination were examined. This decrease was followed by a rise in the percentage of area found in the intermediate range (103-104). The increase in percentage of the area contaminated was due to discharges directly to the canal system downstream of the intake.
Figure 8 also shows that the percentage of area affected in the heavily contaminated areas (>104) did not vary significantly. These areas are affected by heavily contaminated discharges that were external to the irrigation system (primary contamination) and these high levels did not drop significantly as the water passed through the irrigation channels.
In the V Region, almost 1/3 of the irrigated area tested had a high probability for direct participation in a certification programme for safe production areas. The most important cause of contamination in the V Region was secondary contamination. An additional 63 percent of the irrigated area tested could participate in a certification programme if the direct discharges to the canals were eliminated (Figure 16).
Secondary contamination discharges were found to prevent a significant amount of the total irrigated area from immediately participating in a water certification programme. The sampling points for this programme were chosen to represent a large irrigated area and, as such, samples were often taken at intermediate points in the irrigation system. The extent of irrigated area that moves from the low (<103) to the intermediate range (103-104) or higher is likely to increase as water samples are collected closer to the individual fields. Thus solving the secondary contamination problem should not be overlooked as it may be a major constraint in developing safe (clean) production areas.
(Source: FAO, 1993)
The project recommended that SAG work with the Ministries of Health and Public Works to seek international assistance in developing and implementing methods to reduce or eliminate secondary contamination from areas showing high potential for safe vegetable production (areas <5000 faecal coliforms/100 ml).
Phase 3 (Crop Certification Phase)
The water quality data from Phase 1 and 2 were used to develop the concepts of a crop certification programme. The strong cholera eradication programme already instituted resulted in a heightened awareness of product quality by the consumer. The result was a number of labels used by producers that emphasize to the consumer the safety of the water used in production.
In order to implement this programme, SAG needed to be prepared to develop and operate a nation-wide water quality monitoring programme to assess the extent of irrigation water contamination. To carry out this programme, it was recommended that SAG develop a staff who can plan, execute and interpret a water quality monitoring programme. The procedures used in this project were recommended for use as the guidelines for conducting such a programme.
The project developed a five-step process for certifying clean production areas. The first three steps focus on water certification. The final two steps shift the focus of SAG to developing and applying a SAG label to vegetable production originating in safe production areas. The procedure for controlling the labelling of safe vegetable production was reviewed. It was recommended that, if resources are available, the certification of the water and the application of a SAG label should be controlled by direct contact with each producer. Control at this level ensures that certified water and safe production practices are used. Alternative and less intensive approaches considered were issuing labels on an area-wide basis or allowing groups of producers to control the labelling in SAG certified areas.
The project also recommended that SAG and the Ministry of Health strengthen the role of the certification programme by using public education techniques to emphasize to consumers the need to buy only SAG certified produce.
The scheme laid out by the project was considered a concept. The actual certification programme must consider several factors. There are four factors the project felt were extremely important to the success of any programme:
that all public agencies agree that only one label is recognized as certifying production in safe areas. The use of alternative labels must be dealt with decisively and quickly;
