Detection of chemical compounds in water for agricultural use in Xochimilco and Tlahuac
Agricultural production is the main source of contamination of water bodies due to the excessive use of agrochemicals and inadequate handling of organic waste from animals. Water used for agricultural irrigation can contain various chemical compounds, such as sulfates [SO42-], phosphates [PO43-], phenols [Ph] and 2-Chlorophenol [ClPh]. Mexican legislation establishes limits of [130 and 250], [0.05 and 5], [0.1 and 0.3], and [0.04] ppm, respectively. A combination of these, especially PO43- (0.5 ppm), causes the mortality of aquatic and terrestrial ecosystems. The municipalities of Xochimilco and Tlahuac, in Mexico City, produce vegetables, among other foods, using water from the canal with residual water for irrigation. Therefore, it is necessary to analyze the presence of these compounds, using sensitive analytical methods for their detection according to the Official Mexican Standards. The objective of this work was to detect the concentrations of SO42-, PO43-, Ph and ClPh, present in the water for agricultural use in the areas of Xochimilco and Tlahuac. A total of 20 samples of water for agricultural use were collected, coming from 20 geographic points of the water bodies of Xochimilco and Tlahuac. The determination of SO42-, PO43- and total phenols was carried out by UV-VIS spectrophotometry, using the methods: molybdenum blue, modified turbidimetric, and direct spectrophotometric, respectively. Ph and ClPh were identified and quantified by a new HPLC method. Water for agricultural use presented maximum levels of SO42-, PO43-, total phenols and ClPh of 277.56 ± 0.3, 4.71 ± 0.004, 1.44 ± 0.01 and 0.965 ± 0.002 ppm, respectively. For water for livestock use, the maximum values were 461.03 ± 3.58, 1.71 ± 0.05, 0.78 ± 0.005 and 0.119 ± 0.004 ppm, respectively. The water for agricultural use in Xochimilco and Tlahuac has concentrations high of SO42-, PO43-, Ph, and ClPh. In some cases, it exceeds the established limits by Mexican regulation. Therefore, it is considered unsuitable for these activities since it represents a risk for the environment, animal health, and human health.
Key words: chlorophenol, phenol, phosphates, sulfates, water for agricultural use.
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