Bioaccumulation of Metals Arsenic, Cadmium, and Lead in Zooplankton and Fishes from the Tula River Watershed, Mexico

The Tula River watershed is a water flow system that runs from the State of Mexico to the south-central part of Hidalgo State in Mexico that includes the Mezquital Valley which was originally a semiarid zone and now is an important agricultural region. We studied the River Tula watershed regarding biological, chemical, and physical parameters, describing the zooplankton species list, and the levels of five metals: arsenic, cadmium, copper, lead, and zinc, in sediments, elutriates, water column, and bioaccumulation in tilapia (Oreochromis nilotica), and some zooplanktonic species using atomic absorption. Arsenic, cadmium, and lead are present in the water column in small concentrations of different reservoirs of the Tula River watershed. Concentration of these three metals in elutriates and sediments are higher than levels in water column. The effects of the presence of these three metals in the water column, elutriates, and sediments include the following: (a) Levels of lead in muscles of tilapia make this species unsafe for human consumption, and (b) arsenic, cadmium, and lead are bioaccumulated in several zooplanktonic species. We discuss these results in the context of (a) bioaccumulation through trophic levels and (b) international and Mexican national standards regarding safe levels of contaminants in fish tissues for human consumption.