Levels of BTEX (benzene, toluene, ethylbenzene, and p-xylene) were determined in ambient air of an urban site located at the center of Mexico (Leon City in Guanajuato State) during two climatic ...seasons of 2018 (summer and autumn). Ethylbenzene (11.86 µg m−3) and toluene (11.85 µg m−3) showed the highest median concentrations during the study period. BTEX concentrations did not show a diurnal pattern but a seasonal trend was observed for benzene and toluene at a significant level of α = 0.05. Bi-variate and multivariate analysis showed significant positive correlations (at α = 0.05) among BTEX (excepting benzene), indicating common sources for toluene, ethylbenzene, and p-xylene and a different origin for benzene. A meteorological study was also conducted in order to determine the origin of air masses that could influence the BTEX concentrations in the study site. Finally, it was found that all BTEX species presented hazard quotient values (HQs) <1, indicating that there is no risk of non-cancer during the studied period. Lifetime cancer risk due to benzene exposure for the adult and child populations studied were estimated to be 7 in 1,000,000 and 1 in 100,000, respectively.
The purpose of this study was to study the spatial and temporal variation of BTEX in the ambient air of Leon, Guanajuato, Mexico, to assess the inhalation health risk to the local population from ...exposure to these compounds. BTEX were monitored using passive samplers during two sampling seasons (rainy 2019 and cold dry 2020), and samples were analyzed by gas chromatography with flame ionization detection. BTEX ratios and meteorological analysis suggested that the concentrations were mainly influenced by vehicular and local sources located to the SE of the study area. The sum of average concentrations of BTEX in rainy and cold dry seasons were of 3.52 ± 0.36 µg m
−3
and 4.11 ± 0.38 µg m
−3
, respectively. Mean concentrations were of 0.74, 1.59, 0.48, and 0.69 µg m
−3
, for benzene, toluene, ethylbenzene, and p-xylene, respectively. The highest levels of BTEX were found in sites with an urban land-use type of medium-intensity industrial zones with high population density. The lower BTEX concentrations found during the rainy season were probably due to higher solar radiation and temperatures that favored their photochemical degradation. Bi-variate and multivariate analysis showed that the BTEX species were strongly correlated with each other and with temperature and solar radiation, indicating that they originated from common sources. Benzene and toluene correlated strongly with CO and SO
2
, indicating that they could originate from vehicular exhaust emissions and high-sulfur fuel combustion sources. The health risk assessment showed that the Leon city adult population is at possible risk of developing cancer in their lifetime due to exposure to the measured benzene levels, but indicated no risk of contracting respiratory and cardiovascular diseases due to inhalation of BTEX. The results suggest the need for BTEX emissions reduction policies in the study area, as well as the establishment of a Mexican standard that regulates the maximum permissible limit of these pollutants in ambient air in order to protect the health of the population.
Benzene, toluene, ethylbenzene, p-xylene, O3, NOx, CO, PM2.5 and meteorological parameters were measured in urban air of two sites in Merida, Yucatan, Mexico during 2016–2017. Samples were collected ...using 1.5 h time intervals at three different sampling periods before being analyzed by gas chromatography with flame ionization detection. The highest concentrations of BTEX occurred during midday and afternoon in spring and summer seasons. Mean concentrations of, BTEX for the Cholul and SEDUMA sites, respectively, were 40.91 μg/m3 and 32.86 μg/m3 for benzene; 6.87 μg/m3 and 3.29 μg/m3 for toluene; 13.87 μg/m3 and 8.29 μg/m3 for p-xylene; and 6.23 μg/m3 and 4.48 μg/m3 for ethylbenzene. The toluene/benzene and xylene/ethylbenzene concentration ratios indicated that BTEX levels at both sites were influenced by local and fresh emissions (vehicular traffic). Bivariate and multivariate analyses were performed in order to correlate BTEX concentrations with criteria air pollutants to infer their possible sources. Health risk assessment revealed that exposure to benzene exceeded the recommended value for the integrated lifetime cancer risk. These results suggest that Merida’s population is exposed to cancer risk, and changes in the existing environmental policies should therefore be applied to improve air quality.
Short-term effects of air pollution on the number of hospital admissions in eight municipalities of the Metropolitan Area of Monterrey, Mexico, were assessed from 2016 to 2019 using a time-series ...approach. Air quality data were obtained from the Atmospheric Monitoring System of Nuevo Leon State (SIMA) which belongs to SINAICA (National System of Air Quality Information), providing validated data for this study. Epidemiological data were provided by SINAIS (National System of Health Information), considering admission by all causes and specific causes, gender and different age groups. Guadalupe had the highest mean concentrations for SO2, CO and O3; whereas Santa Catarina showed the highest NO2 concentrations. Escobedo and Garcia registered the highest levels for PM10. Only PM10 and O3 exceeded the permissible maximum values established in Mexican official standards. A basal Poisson model was constructed to assess the association between daily morbidity and air pollutants, from this, a second scenario in which daily mean concentrations of air pollutant criteria increase by 10% was considered. Most of pollutants and municipalities studied showed a great number of associations between an increase of 10% in their current concentrations and morbidity, especially for the age group between 5 and 59 years during cold months, excepting ozone which showed a strongest correlation during summer. Results were comparable to those reported by other authors around the world, however, in spite of relative risk index (RRI) values being low, they are of public concern. This study demonstrated that considering the nature of their activities, economically active population and students, they could be more vulnerable to air pollution effects. Results found in this study can be used by decision makers to develop public policies focused on protecting this specific group of the population in metropolitan areas in Mexico.
Atmospheric concentrations of BTEX were measured in an urban site located in the vicinity of an oil storage-distribution facility in Paraiso, Tabasco, Mexico. Samples were collected during two ...seasons (nortes 2018 and dry 2019). The relative abundance of BTEX mean concentrations was: toluene (5.24 µg m
−3
) > ethylbenzene (3.92 µg m
−3
) > m, p-xylene (3.89 µg m
−3
) > benzene (2.43 µg m
−3
). BTEX concentrations had a clear diurnal and seasonal pattern, showing higher levels during the dry season due to differences in wind conditions, rainfall patterns and temperature. Statistical analysis showed significant positive correlations among BTEX, indicating that these compounds had common sources. Interspecies ratios revealed that BTEX were originated from sources beyond vehicular traffic and that they were influenced by the transport of local air masses. The assessment of lifetime cancer risk showed that the population in the study area is at possible risk of developing cancer.
Zooplankton biomass is recognized as an important indicator of secondary production, its spatial and temporal variation in neritic zones is particularly affected by discharges of the rivers, and the ...spatial-temporal effect of continental water discharges on the distribution of zooplankton biomass in the southern Gulf of Mexico was analyzed for 5 areas off the coasts of Veracruz, Tabasco and Campeche. The analyzed material was obtained from 534 samples collected during different climatic seasons from 1984 to 2001. The discharge volumes of 5 hydrological regions were obtained from the government’s data base. The results obtained indicated that biomass variation throughout the seasons in the different areas was very similar to the pattern of discharges. The greater biomass values were recorded off Tabasco and the lower values off Veracruz, where the greater and lower continental water discharges were recorded respectively. Biomass variation depended on the discharges, not only in terms of an annual cycle, but was also directly related to the volumes discharged into the ocean. A Tree analysis made it possible to conclude that biomass is always low on the outer shelf and oceanic region of the southern Gulf of Mexico, independently of the season of the year or of a particular area. A greater biomass was recorded on the shallow shelf, with a magnitude that varied in relation to the area and season. The biomass off Campeche did not depend on the continental water discharges, but was generated on the Yucatán shelf.
Short-term effects of air pollution on the health of residents in the Metropolitan Area of Monterrey, Mexico were assessed from 2012-2015 using a time-series approach. Guadalupe had the highest mean ...concentrations for SO
, CO and O
; whereas Santa Catarina showed the highest NO
concentrations. Escobedo and Garcia registered the highest levels for PM
. Only PM
and O
exceeded the maximum permissible values established in the Mexican official standards. Most of pollutants and municipalities showed a great number of associations between an increase of 10% in their current concentrations and mortality, especially for people >60 years. Different scenarios resulting from climatic change were built (increases of 5-25% in daily mean temperature), but only the increase of 25% (5 °C) showed a significant association with air pollutant concentrations and mortality. All pollutants and municipalities showed significant increases in relative risk indexes (RRI) resulting from an increase of 5 °C when people >60 years was considered. Results were comparable to those reported by other authors around the world. The RRI were low but significant, and thus are of public concern. This study demonstrated that the elderly is strongly threatened not only by atmospheric pollution but also by climatic change scenarios in warm and semiarid places.
Forests embedded in an urban matrix are an important site to investigate the effects of multiple anthropogenic influences that can lead to the modification of biogeochemical cycles and, consequently, ...of the ecosystem services they provide. In this study, the main soil properties, exchangeable cations, and heavy metal concentrations were measured to assess soil quality and fertility, as well as soil carbon stock (SCS) and CO2 effluxes (Rs) at the Natural Protected Area Bosque de Tlalpan (BT). Four study zones were considered: strict protection zone (Z1), restricted use protection zone (Z2), extensive public use zone (Z3), and intensive public use zone (Z4) during three climatic seasons (rainy, dry-cold, and dry-warm seasons). The concentration of heavy metals in the BT soil showed that these elements are within the reference limits accepted by Mexican standards and are not considered toxic to the environment, except for mercury, which exceeded the standard with double the concentration. The results revealed significant variations in the SCS and soil organic matter (SOM) among the different sites. The highest mean values of SCS (3.01 ± 0.63 and 4.96 ± 0.19 kg m−2) and SOM (7.5 ± 1.01% and 8.7 ± 0.93%) were observed in areas of high protection and extensive public use. CO2 effluxes showed significant differences between sampling seasons, with fluxes being highest during the rainy season (3.14 ± 1.01 µmol∙m−2∙s−1). The results suggest that the level of conservation and effective management of the sites played an important role in the carbon storage capacity and in the physicochemical properties of the soil. This not only provided insights into the current state of an urban forest within a large urban area but also emphasized the significance of conserving such ecosystems.
Trace metal concentrations in PM10 were measured in an urban–industrial site in León, Mexico in three different seasons. PM10 were collected in quartz fiber filters of 47 mm diameter using low volume ...equipment operating with a controlled flow of 5 L min−1 over 24 h. Mass concentrations were gravimetrically determined and it was found that PM10 samples showed values in excess of the Mexican standard and the established values by WHO during cold dry and warm dry seasons. Morphology of selected particles was studied by SEM-EDS analysis, and the elemental composition was determined. Collected samples were analyzed by atomic absorption spectrometry in order to quantify ambient air concentrations of some trace metals (Cu, Co, Zn, Cd, Fe, Mg, and Mn). Median concentrations of trace metals showed the maximum value for iron (3.079 μgm−3) and the minimum value for Cd (0.050 μgm−3) over the entire period. From the meteorological analysis, it was found that sources located SW and ESE of the sampling site contributed to the levels of trace metals in PM10 in the studied site. The health risk assessment found that the population of León is at increased lifetime risk of experiencing cancer because of exposure to these concentrations of PM10 and their trace metal content.
Changes in the composition and abundance of fish larvae in the water column were analyzed throughout an annual cycle (1994-1995) in the southern Gulf of Mexico, in order to establish the difference ...between the habitat of the larvae and the effect of oceanographic events on larval vertical distribution. The study area comprised the continental shelf off Tabasco and Campeche in the southern Gulf of Mexico. Samples were collected at five water column levels: 0-6, 6-12, 12-18, 45-55 and 95-105 m. A total of 118 taxa were identified, 52 were dominant species, 33 were larvae of neritic parents and 19 were larvae of mesopelagic parents. The results indicate that the water column presented two layers above the 105 m depth: a surface layer (0-18 m) and a deep layer (45-105 m). The greatest density of larval species that inhabit neritic areas as adults was recorded in the surface layer (0-18 m), while larvae of which the parents inhabit mesopelagic areas were found in the deep layer (45-105 m). The mixing of the water column was the most important physical factor regarding the variation in the vertical distribution of the larvae of both groups, particularly in winter. However, the biology of each species and the habit to occupy a particular depth were the most important factors that determined their distribution in the water column.
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