Heavy metals in the sediments of urban sinkholes in Cancun, Quintana Roo.

Soils in urban areas can accumulate heavy metals as a result of anthropogenic inputs. This research focuses on a young coastal tourist city that has been urbanized over the last 52 years and shows accelerated demographic growth and urban development. Deposition of heavy metals in soils is caused by human economic activities, which has significant implications for the environment. We evaluated heavy metal concentrations in urban sinkholes, which are sites for the natural accumulation of water and sediments. These locations also receive rainfall runoff or have been used as unregulated dumps. By performing a multistage extraction to address availability and risk, we found that Zn, Fe and Al were the predominant metals; Cu, Pb and Ni were only detected in some sinkholes. The contamination factor was high for Zn and moderate for Pb. The geoaccumulation index showed that Zn is the most abundant and available metal in urban sinkholes and the metal with the highest potential ecological risk. Between 12 and 50% of the total concentration of all metals was extracted from the organic matter phase. Correlations were found between the degree of urbanization of the city and the degree of pollution, and the trends were stronger in older sections of the city. Zn is the most prevalent element and has high concentrations. The metal concentrations in the sediments can be used as warning signs for their potential risk to environmental and human health, and these results can be compared with those of other tourist cities in karstic environments around the world.

Distribution and ecological risk of metals in an urban natural protected area in the Riviera Maya, Mexico.

Urbanization can negatively impact natural protected areas near or surrounded by cities, and such impacts include untreated wastewater discharge, leachates from dumpsters, e-waste, and road dust. In this research, we show that not only large cities with industry are prone to be polluted, but also young touristic cities with high population increase rate can suffer from urban contamination. We evaluated metal pollution in a natural protected area within a 50-year-old city without conventional industry that was likely contaminated by the urban sprawl around the protected area. We tested water, zooplankton, sediment and plant samples for metallic elements to evaluate their bioaccumulation in zooplankton, enrichment factors and geoaccumulation index values in sediments, and translocation factors in plants. Finally, we evaluated the ecological risk due to metal contamination. Metals at levels above our detection limit (20 µg/L) were not found in the water and zooplankton samples. The sediments and plants in the storm drain section of the protected area had a greater concentration of metals and wastewater indicators (coliforms) than those in the rest of the lagoon. Moreover, signs of Al, Cu, Ni, Zn, Cr, Pb, and Ti contamination were found in the plant tissues. We estimated that the ecological risk of this natural protected area surrounded by the city of Cancun (Mexico) ranged from mild to strong, with Zn being the metal of most concern. The results highlight that young touristic cities around the world will endure contamination from urban sources; signs or early warnings of contamination must be identified to prevent and resolve such issues.

A multi-approach assessment of land use effects on groundwater quality in a karstic aquifer.

Groundwater represents almost half of the drinking water worldwide and more than one third of water used for irrigation. Agro-industrial activities affect water resources in several manners; one of the most important is leaching of agrochemical residues. This research identifies the major contributors of changes in groundwater quality comparing two contrasting land uses in a karstic area of the Yucatan peninsula as case study. Using a multiple approach, we assess the impact of land use with physicochemical data, multivariate analyses, hydrogeochemistry and nitrate isotopic composition. We confirmed that agricultural land use has a greater impact on groundwater quality, observed in higher concentration of nitrates, ammonium, potassium and electrical conductivity. Seasonality has an influence on phosphates and the chemical composition of the groundwater, increasing the concentration of dissolved substances in the rainy season. There was a clear effect of manure application in the agricultural zone and the nitrate isotopic composition of groundwater points toward recharge in certain areas. We consider that seasonality and land use effects are intertwined and sometimes difficult to separate, likely because of land use intensity and hydrogeochemical process at a local scale. Finally, we observed poor groundwater quality in the agricultural area during the wet season; thus, it is desirable to maintain non-agricultural areas that provide groundwater of appropriate quality.

Nitrogen isotope fractionation factors (α) measured and estimated from the volatilisation of ammonia from water at pH 9.2 and pH 8.5.

This paper examines the nitrogen isotope fractionation factors (α) associated with the volatilisation of ammonia from water under controlled conditions at two pH values (8.5 and 9.2). This experiment assumed the continuous removal of ammonia at a single purge rate of 10 mL air min-1. The fractionation resulting from the removal of total ammonia from the water into an acid trap was named the observed isotope fractionation factor (αobs), and it was measured as 1.019 (±0.0025) at pH 8.5 and 1.030 (±0.0025) at pH 9.2. The observed isotope fractionation factor includes the equilibrium isotope fractionation factor (αeq) and the kinetic isotope fractionation factor (αkin), each one mathematically derived from the experimental data. The equilibrium and kinetic isotope fractionation factors were estimated as αeq = 1.036 (±0.0014) and αkin = 1.050 (±0.003), respectively. Our results are compared to other previously measured and estimated fractionation factors.

Wastewater effluent impacts ammonia-oxidizing prokaryotes of the Grand River, Canada.

The Grand River (Ontario, Canada) is impacted by wastewater treatment plants (WWTPs) that release ammonia (NH3 and NH4+) into the river. In-river microbial communities help transform this ammonia into more oxidized compounds (e.g., NO3- or N2), although the spatial distribution and relative abundance of freshwater autotrophic ammonia-oxidizing prokaryotes (AOP) are not well characterized. This study investigated freshwater N cycling within the Grand River, focusing on sediment and water columns, both inside and outside a WWTP effluent plume. The diversity, relative abundance, and nitrification activity of AOP were investigated by denaturing gradient gel electrophoresis (DGGE), quantitative real-time PCR (qPCR), and reverse transcriptase qPCR (RT-qPCR), targeting both 16S rRNA and functional genes, together with activity assays. The analysis of bacterial 16S rRNA gene fingerprints showed that the WWTP effluent strongly affected autochthonous bacterial patterns in the water column but not those associated with sediment nucleic acids. Molecular and activity data demonstrated that ammonia-oxidizing archaea (AOA) were numerically and metabolically dominant in samples taken from outside the WWTP plume, whereas ammonia-oxidizing bacteria (AOB) dominated numerically within the WWTP effluent plume. Potential nitrification rate measurements supported the dominance of AOB activity in downstream sediment. Anaerobic ammonia-oxidizing (anammox) bacteria were detected primarily in sediment nucleic acids. In-river AOA patterns were completely distinct from effluent AOA patterns. This study demonstrates the importance of combined molecular and activity-based studies for disentangling molecular signatures of wastewater effluent from autochthonous prokaryotic communities.