Water Quality Index of Lake Chapala in Mexico and its potential risk to public health
R. Vallejo-Rodríguez, E. León-Becerril, J.J. Díaz-Torres, L. Hernández-Mena, J. Del Real-Olvera, V. Flores-Payán, L.J. Martínez-Mendoza, A. López-López*
Corresponding author: allopez@ciatej.mx
(a) Purpose
Lake Chapala is located in Jalisco, Mexico, and is an important resource for drinking water for the Metropolitan Zone of Guadalajara (MZG), the third economic city in Mexico. Thus, the aim of this work is to evaluate the Water Quality Index (WQI) of Lake Chapala in accordance with the National Sanitation Foundation (NSF) and the Mexican guideline NOM-127-SSA1-1994, and the possible impacts and implications in public health for the use and consumption of water.
(b) Summary of the problem
Lake Chapala receives the discharge from Lerma river that collects the domestic and industrial wastewaters along its route of 708 km from Toluca Valley in the southwest of Mexico City; wastewater without treatment from the villages settled around Lake Chapala; runoff water from agricultural field and discharges from wastewater treatment plants. Lake Chapala provides 62% of water to be treated in the drinking water treatment plants and is distributed to the MZG.
(c) Methodology used
Using Geographic Information Systems (GIS), a water-sampling plan of Lake Chapala with 17 sample sites, including the discharge of Lerma river, a point where Santiago River arises from Lake Chapala, and two effluents from drinking water treatment plants, was implemented. The water-sampling plan was performed in dry and rainy seasons to collect water for physicochemical and biologic analysis. WQI is one of the most effective index to communicate water quality, it includes parameters such as pH, dissolved oxygen, biochemical oxygen demand, fecal coliforms, temperature, total phosphate, nitrate, turbidity, and total solids; also, the presence of metals included in the NOM-127-SSA1-1994 was determined.
(d) Results
In Lake Chapala, average WQI was 55 points, which indicates a water of medium quality; therefore, the direct use of water for drinking purpose is not recommended; also heavy metals were found, however they are under the limit established by the NOM-127-SSA1-1994. Lerma River is one of the principal sources of pollution to Lake Chapala whose WQI is 45 in the site of sampling water, indicating a poor quality. In the site sampling for Santiago river, (downstream, 1.5 km from Lake Chapala), WQI was 41, also indicating poor quality due to the discharges from municipal wastewater without treatment. For the water sample from the drinking water treatment plants, WQI were above 80 points indicating a good water quality.
(e) Implications of the study or its results
WQI lets to define the use and the final disposal of water and gives a research perspective about endocrine disrupting compounds and their possible estrogenicity in the second part of this research.
(f) Science-policy dimension
This study contributes with a preventive plan to reduce the potential risk to public health, that should include a more strict regulation of municipal and industrial wastewaters, and an adequate drinking water treatment to assure the water quality supplied to the population.