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River Atoyac is considered to be one of the most polluted rivers in Mexico due to the discharges of untreated or partially treated wastewater from industrial and municipal activities. In order to improve the river water quality, it is obligatory to identify the possible contaminant sources for upholding a well-balanced ecosystem. Henceforth, the present study incorporates the application of a continuous real-time monitoring system to identify the provenance of pollutants of the river mainly from anomaly events. Four monitoring stations were installed all along the River Atoyac in the State of Puebla, Central Mexico. The real-time monitoring systems have an ability to measure various water quality parameters for every 15 minutes such as Temperature (T), pH, Conductivity (EC), turbidity (TURB), Dissolved Oxygen (DO), Oxidation Reduction Potential (ORP) and Spectral Absorption Coefficient (SAC). In total, eight water samples of anomaly events (i.e.) 2 per monitoring station during rainy (August–September) and winter seasons (November–December), that were detected using the parameters previously mentioned were procured and also analyzed in the laboratory for evaluating almost 54 physicochemical, inorganic and organic characteristics. Statistical results of factorial analysis explained that 30% of the total variance corresponded to textile effluents, 23% related to discharges produced by automobile and petrochemical industries, and 18% of the total variance defined the agricultural activities. Additionally, indices like Overall Index Pollution, Heavy Metal Evaluation Index, Screening Quick Reference Table and Molecular ratios of hydrocarbons for PAH sources was also calculated to estimate the grade of pollution and associated ecotoxicological risks. The present study also enlightens the fact that the assessed results will definitely provide valuable information for the management of river water quality by developing stringent public policies by governmental agencies for the sustainable conservation of Atoyac River.

Microplastics (MPs) are contaminants of emerging concern in aquatic environments. The abundance, distribution and characteristics (color, morphology, texture) of MPs from Atoyac River basin, a highly urbanized river system located in Central Mexico were investigated in this study. The sediment samples were collected from 29 different sites along the Atoyac River basin in four different zones: Zahuapan River, Atoyac River, Confluence zone and Valsequillo dam and processed for MPs extraction using ZnCl2 density separation method. The total number of MPs in Zahuapan River, Atoyac River, Confluence zone and Valsequillo dam was 1633.34 ± 202.56, 1133.33 ± 72.76, 833.33 ± 80.79 and 900 ± 346.12 items kg−1 respectively. It was found that the concentration of MPs is higher in the downstream section of the river (confluence zone: 833.33 ± 80.79 & Valsequillo dam: 900 ± 346.12 items kg−1), revealing significant impacts of dense population and industrial complex of Puebla City. Colored MPs were predominant accounting for 51% and white MPs for 49% of the total MPs. Films (25.9%) and fragments (22.2%) were the most abundant type followed by fibers (14.8%). Scanning electron microscope images revealed varying disintegration features and energy-dispersive X-ray spectra demonstrated the presence of different metal elements on the surface of MPs. The results highlighted the widespread distribution of MPs in the sediments of Atoyac River basin, Mexico.

Mercury and Selenium concentrations were determined in the muscle and liver tissues of Silky shark (Carcharhinus falciformis) and Smooth Hammerhead shark (Sphyrna zygaena) caught off Todos Santos, Southern Baja California, Mexico during August–December 2014. The average mercury concentrations in C. falciformis [(mg/kg) muscle: 3.04; liver: 3.95] and S. zygaena (muscle: 5.23; liver: 3.39) exceeded the permissible limit of 1.0 mg/kg established by the Mexican government. Biomagnification Factors (BMF) to understand the prey-predator relations were also calculated and it was observed that all BMFs were >1 indicating absolute biomagnification of Hg. Additional Se concentrations were found in C. falciformis: 5.34 mg/kg and S. zygaena: 3.29 mg/kg resulting in a molar excess of Se over Hg. Thus, our results prove to offer the basic strategies of Hg-Se biogeochemical processes in marine sharks.