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Lake Yuriria, located in the heavily populated and polluted Mexican Central Plateau, receives domestic sewage, industrial effluents, and municipal wastewaters that are still directly discharged without treatment into the tributaries and the lake. Pollutants in water and sediments include heavy metals, aromatic hydrocarbons, and organochlorine pesticides. Activities of the antioxidant enzymes superoxide dismutase (SOD), catalase (CAT), glutathione peroxidase (GPx), as well as Na/K-adenosine triphosphatase (Na/K-ATPase) activity, and lipid peroxidation (LPO) were evaluated in the livers of the fish Goodea atripinnis after 96 h of exposure to water collected in March and June 2005 from three sites: Y (limnetic zone), L (Lerma tributary), and C (la Cinta tributary). Physical and chemical parameters of the lake water were also analyzed. Increases in CAT activity and LPO levels at all three sites were detected compared with control fish ( P < 0.05), while GPx and SOD activities decreased significantly ( P < 0.05). Na/K-ATPase activities were similar to the control in fish exposed to limnetic water from both March and June but were higher than control at the two tributary sites in March ( P < 0.05); fish exposed to water from the Lerma tributary in June exhibited lower Na/K-ATPase than the control ( P < 0.05). During March, CAT and Na/K-ATPase activities were increasing more than in June in Y and L, respectively, while in June, SOD and GPx were depleted more than March in L and Y and L, respectively. Despite the antioxidant defenses of the fish liver, exposure to all water samples from Lake Yuriria exerted alterations in hepatic LPO levels, antioxidant enzymes, and Na/K-ATPase activities that could substantially impair the mechanisms of fish defenses against oxidative stress. [ABSTRACT FROM AUTHOR]

The article deals with the process of helminths and lipid peroxidation (LPO) in Astyanax aeneus from a subtropical river in Mexico. Researchers were able to identify the trematodes Uvulifer ambloplitis and Clinostomum, the nematodes Contracaecum species and Spiroxys species, and the acanthocephalan Polymorphus species. It was found that the richness of helminth species rose along a gradient from the headwaters to the middle reaches of the river. Another discovery was a direct correlation between fill and muscle LPO and mean abundance of Clinostomum complanatum, contracaecum species, and orthophosphate values as well as between liver LPO and mean abundance of Polymorphus species.

Madin Reservoir (MR), located in the State of Mexico, is fed mainly by the Rio Tlalnepantla. MR supplies potable water to the municipalities of Naucalpan and Atizapan, and various recreational activities take place in its vicinity, such as sailing and the fishing of diverse species including the common carp Cyprinus carpio. The purpose of this study was to determine the toxic effects of contaminants present in MR water and sediment on C. carpio. Five sampling stations were selected (those considered to have the most problems due to discharges). Water and sediment samples were taken and toxicity studies were performed, including acute toxicity (lethality) and subacute toxicity assays. The biomarkers used in the subacute assays were lipid peroxidation (LPX) and activity of the antioxidant enzymes superoxide dismutase (SOD), catalase (CAT) and glutathione peroxidase (GPX) in the liver and brain of test organisms. These biomarkers were also evaluated in local carp, i.e. carp with chronic exposure in situ to reservoir contaminants. Results show that contaminants in the water and sediment of the different sampling stations induce oxidative stress, this toxicity being more evident in samples from stations near the entry point of the Rio Tlalnepantla tributary and in local carp. This may be due to high contaminant levels as well as the fact that the physicochemical characteristics of the matrices might favor their bioavailability. Thus, both the water and sediment of this reservoir are contaminated with xenobiotics hazardous to C. carpio, a species consumed by the local human population. [ABSTRACT FROM AUTHOR]

The black chocolate clam Megapitaria squalida is a commercially important bivalve along the Pacific coast of Mexico and is used as a bioindicator in environmental health studies. Previous studies of Bahía de La Paz indicated significant differences in heavy metal content among localities in this clam. To identify areas affected by heavy metal pollution, lipid peroxidation (TBARS) levels and activity of superoxide dismutase (SOD) and glutathione S-transferase (GST) were measured in muscle, gonad, and digestive gland tissue and correlated with heavy metal levels of clams from six localities along the shore of the bay. Significant differences in TBARS levels and antioxidant enzyme activity were found among these tissues at all localities. Such differences are ascribed to the physiology of each organ. Higher levels of TBARS were found in areas with higher cadmium content. SOD activity in muscle correlated positively with cadmium, lead, and iron in areas with a higher content of those elements. This study suggests that TBARS levels and SOD and GST activity are affected by biotic and abiotic factors and have potential as indicators of heavy metal contamination. [ABSTRACT FROM AUTHOR]

Lake Xochimilco has been the receiver of untreated domestic wastewater, agricultural run off and secondary effluent of a treatment facility, thus becoming the receptor of a mixture of pollutants and their metabolites. Major zones in Lake Xochimilco are urban, agricultural and tourist; all of them exert environmental pressure to the Lake, that has been associated with the extinction of two fish species, and the limited presence of another, Girardinichthys viviparous . Early warning biomarkers of G. viviparous were analyzed after its reintroduction to waters of Lake Xochimilco, in order to evaluate the responses of the fish in the case of their repopulation in their ancient habitat. We examine some indicators of the water quality, the level of lipid peroxidation and the acetylcholinesterase activity in brain, gill, liver and muscle of G. viviparous after exposure to waters of each zone of Lake Xochimilco. The results show that the urban area presents an enrichment of ammonium, related to the sewage; the agricultural zone apparently had the highest concentrations of phosphorous, perhaps derived from the use of fertilizers; and the tourist zone reached elevated values in chlorophyll a and turbidity. Differences were detected in lipid peroxidation and the acetylcholinesterase among the sites and tissues tested. The urban and agricultural zones, produced increases in the lipid peroxidation in muscle, brain, liver and gills. Acetylcholinesterase shows an inhibition in the function of the brain, liver and gills of fish exposed to agricultural waters; however, the muscle shows an increase in all the sites. The observed effects might have health implications for the species studied, although further research would be required. [ABSTRACT FROM AUTHOR]

The article reports on hazard assessment of a mixture of pollutants from a sugar industry to three fish species of western Mexico by the responses of enzymes and lipid peroxidation. The discharge of pollutants by several industries represents a serious water pollution problem due to the toxic properties of these contaminants and the adverse effects on the biota. Among the pollutants of the sugar industry are pressed pulp, lignin and phenol, molasses, vinasses, sulfur, organochiorines, organophosphates, herbicides and fungicides that may produce multiple damages in fish.