ContaminYaqui

The Yaqui River (Sonora state, Mexico) is the longest and most important river in the “world belt of deserts” where the hydrographic system is highly sensitive to climatic changes. Anthropogenic activities along the river have induced high levels of contamination of the Yaqui waters due to metals and metalloids, either naturally present or added by mining activities, and pesticides related to agriculture. Chemical contaminants enter in the Yaqui hydrosystem and are transported by the river to a lagoon in the Gulf of California, and then to the Pacific Ocean. This contamination can have harmful effects on biodiversity and human health all along the river.

In the first part of the project, we sought to identify the major pollutants in the Yaqui hydrosystem. We found that the main inorganic pollution is carried by Fe, Mn, Zn, Cu, Cr, and As in the waters, by Cd and Hg in the sediments, and by Fe, Zn, and Cu in biota (clams in Tobari lagoon). We evaluated the mobility of each of these pollutants, focusing on their chemical forms both in water and sediments. One of the main forms of pollution in the water appears to be related to arsenic, in the form of arsenate species, a soluble and highly toxic form that can be transported over long distances. In contrast, the bioaccumulation of As in marine organisms is not very significant (low bioconcentration factors of 1.7-2.5). For the next step, we will examine the chemical forms of pollutants and the physico-chemical conditions in the river to estimate their transport in the Yaqui hydrosystem. Stable isotope measurements in water samples will also be performed to determine the origin of the nitrate contamination (e.g., agriculture).

In the second part of the project, we have developed an innovative sensor to detect and measure arsenic in rivers and ground water at trace concentrations (< 1 µg.L^-1), in a continuous manner, and over large distances (> 100 m). This new sensor is based on optical fibers that are sensitive to arsenate species. The new Optical Fiber Sensor (OFS) will provide instantaneous measurements of As content in water, and hence will greatly assist pollution detection and monitoring.