Evaluation of the impact of domestic and semi-industrial wastewater on the physical-chemical quality of the Chiquito River, León from May 2016 - January 2017

Abstract

The present study evaluated the impact of wastewater on the physical-chemical quality of two sampling sites, upstream and downstream, in a selected transect of the Chiquito River in the city of León. Samples were taken during four sampling campaigns, two in the rainy season and two in the dry season. Fifteen physical-chemical parameters and twelve metals, metalloids and nonmetals were compared with national (NTON) and international guidelines (U.S. EPA, CCME, NOM, INEN, and FAO). Canadian Software WQI 1.2 was used to comprehensively assess water quality based on a quality index (CWQI), for different uses of water: protection for aquatic life, and irrigation. High levels of contamination excelled by suspended solids, organic matter (oils and fats, BOD and COD, turbidity), nutrients (ammonium, iron) and metals such as Al, Cr³⁺, Cu, Mn, Se, V, and Zn. The water quality index categorized the site upstream as marginal to regular and poor for downstream, which implies that it was almost always threatened and in most cases departed from desirable levels for the specific uses to which it was submitted. According to CONAGUA, water quality was deteriorated by classifying it from Contaminated to Heavily Contaminated for both sites, with organic matter prevailing implying contamination by discharges of municipal wastewater and tanneries. Hexavalent chromium was detected in May at the upstream site which makes the water in this area more toxic, and the majority of chromium present is in a reduced state.