Effect of Insecticides on Plankton and Fish of Ignacio Ramirez Reservoir (Mexico): A Biochemical and Biomagnification Study

Studies on the limnology, plankton, and biomagnification of pesticides at Ignacio Ramírez (IR) reservoir (Mexico) were undertaken. The reservoir is located in central Mexico, in an agricultural zone with high soil erosion. Acetylcholinesterase (AchE), γ-glutamyl transpeptidase (GGTP), and lipid peroxidation were assayed in fish. Organochlorines (0.024–0.279 mg/liter) and organophosphates (0.02×10−3–0.21×10−3 mg/liter) were present at high concentrations in water and the biota assayed. In the IR dam the plankton fluctuated depending on the dry and wet seasons. The dominant group of phytoplankton was Bacillariophyta (20–85%) in May, Cyanophyta (22–65%) in September, and Cyanophycean (10–65%), Chlorophycean (10–60%), and Bacyllariophycean (5–80%) species in March. The zooplankton were dominated by cladoceran species (40–70%). Organochlorine and organophosphate insecticides were bioconcentrated (2- to 10-fold) from water to algae, 10- to 25-fold in zooplankton, and 8- to 140-fold in fish. GGTP activity and lipid peroxidation increased and AchE activity in fish decreased in response to the environmental stress caused by the elevated biomagnification of pesticides. The bioaccumulation of these contaminants in fish and the potential for biomagnification in humans are perceived as threats.