Raúl Belmont

Carbonyl levels in indoor and outdoor air in Mexico City and Xalapa, Mexico.

Carbonyl compounds in air were measured at two houses, three museums, and two offices. All sites lacked air-conditioning systems. Although indoor and outdoor air was measured simultaneously at each site, the sites themselves were sampled in different dates. Mean concentrations were higher in indoor air. Outdoor means concentrations of acetone were the highest in all sites, ranging from 12 to 60 microg m(-3). In general, formaldehyde and acetaldehyde had similar mean concentrations, ranging from 4 to 32 and 6 to 28 microg m(-3), respectively. Formaldehyde and acetone mean indoor concentrations were the highest, ranging from 11 to 97 and 17 to 89 microg m(-3), respectively, followed by acetaldehyde with 5 to 47 microg m(-3). Formaldehyde and acetaldehyde had the highest mean concentration in the offices where there were smokers. Propionaldehyde and butyraldehyde concentrations did not show definite differences between indoor and outdoor air. In general, the highest outdoor and indoor hourly concentrations were observed from 10:00 to 15:00 h. Mean indoor/outdoor ratios of carbonyls exceeded 1. Formaldehyde and acetaldehyde risks were higher in smoking environments.

Measurements of formaldehyde and acetaldehyde in the atmosphere of Mexico City.

Ambient levels of carbonyls were measured at the University of Mexico campus, Mexico City. Only formaldehyde and acetaldehyde were measured, since aldehydes with higher molecular weight were not detected. The most abundant aldehyde was formaldehyde, with an overall ratio CH3CHO/H2CO of 0.43. Maximum concentrations occurred for formaldehyde at 10:00 h while for acetaldehyde at 8:00 h. Comparing the concentration measured in this work with those in urban areas it was found that the formaldehyde and acetaldehyde levels in Mexico City are among the highest reported in the literature.

Arsenic concentrations in water, soil, milk and forage in Comarca Lagunera, Mexico.

Arsenic levels were determined in seventy three samples of well water, and in fifty samples of soil, forage and cows milk collected at the most important dairy farms of the Comarca Lagunera located in Coahuila and Durango, Mexico, region naturally rich in As. The total inorganic arsenic concentration in well water ranged from 7 to 740 μg L-1 and about ninety percent of the total arsenic was found as As(V). The agricultural soil texture of the sampled area was sandy clay loam type with total arsenic levels up to 30 μg g-1, however, the extractable arsenic was not higher than 12% of the total and it was higher in the 0–30 cm depth horizon. In alfalfa, the most important crop, the total aresenic ranged from 0.24 to 3.16 μg g-1, with 40% of it accumulated at the root level. Significant correlations (p=0.05) were obtained between arsenic (III), (V) and total inorganic arsenic in groundwater with arsenic in soil (0–30 cm depth), and with arsenic in alfalfa (leaves and roots). It was also found a good correlation between extractable arsenic in soil with As concentrations in alfalfa (roots). Arsenic concentrations found in milk ranged from <0.9 to 27.4 ng g-1. The cows milk biotransfer factor for arsenic was up to 6 × 10-4, applying a pharmacokinetic approach. It was associated with the exposure not only to food but also to water arsenic.

Cytogenetic effects of cadmium accumulation on water hyacinth (Eichhornia crassipes).

Cadmium was bioassayed to observe cytogenetic effects in the water hyacinth (Eichhornia crassipes). Plants were exposed for 96 hr to freshwater containing 0.01, 0.05, 0.10, 1.5, and 10 mg/liter of cadmium. Metal concentrations in tissues were determined by atomic absorption spectrophotometry. The highest level was found in roots, thus root-tip cells were used for cytogenetic studies; after 24 hr of exposure, micronuclei, c-mitotic effects, and pycnosis were detected and after 48 hr polyploidy was observed. A linear relationship between frequencies of micronuclei and cadmium concentrations was found: at 1.5, and 10 mg/liter micronuclei numbers were always the lowest. The inhibition of cell proliferation. shown by the low mitotic index, was proportional to the concentration and time of exposure. From the results presented in this paper it may be concluded that water hyacinth is a good sensor, due to its fast rate of metal accumulation, which allows an easy way to determine the presence of potential mutagenic compounds in water.

The algal community as an indicator of the trophic status of lake Patzcuaro, Mexico

An evaluation of water quality and phytoplankton composition position was carried out in order to determine the trophic conditions of Lake Patzcuaro (2035 m above sea level), a high altitude tropical lake. Temperatures ranged from 15 to 23 degrees C. Total phosphorus and inorganic nitrogen showed a seasonal variation; highest values coincided with the rainy season (0.48 and 2.1 mg litre(-1), respectively). Dissolved oxygen ranged from 2 to 7.9 mg litre(-1) at the surface and from 0.6 to 7.3 mg litre(-1) on the bottom, the lowest values being found in shallow zones. Average transparency varied from 0.62 to 1.4 m Secchi depth. Rainfall was a primary factor in seasonal variability as it influenced both physical and biological conditions by contributing to the transport and deposition of silt, which mixed with sinking algal cells. The composition of the surface phytoplankton segregated along five major divisions comprising a total of 49 species. General seasonal patterns of dominance alternated in a sequence beginning with Bacillariophyta, through Chlorophyta to Cyanophyta. Diatoms, the dominant group from February to early June, included Melosira granulata, Stephanodiscus sp., Synedra sp. and Fragilaria sp. During the rainy season (late June to September), Microcystis aeruginosa, Oscillatoria sp., Anabaena sp., Merismopedia sp., Crucigenia cuadrata, Oocystis lacustris, Selenastrum gracile, Mallomonas sp. and Tetraediella sp. were important. Melosira granulata was present throughout the period of study. Spatial and temporal variability in both physical and biological conditions make it difficult to assign a specific trophic state to Lake Patzcuaro. Nevertheless, analysis of the algal community indicates a generally mesotrophic condition.

Oyster (Crassostrea virginica) as indicator of heavy metal pollution in some lagoons of the Gulf of Mexico

The littoral lagoons of the Gulf of Mexico have been investigated to determine the amount of heavy metal pollution. Some lagoons have been contaminated by liquid wastes mainly originating from sugar refining and petrochemical industries, as well as petroleum exploitation and refining. Since mollusks concentrate trace elements, determination of levels of Cd, Cr, Hg, and Pb in oysters (Crassostrea virginica) were measured in some of these lagoons. The results have shown that the concentrations of these metals in lagoon water were below the recommended levels to protect aquatic life, and it was found that oysters are able to concentrate metals, mainly Cd and Pb above the maximum permissible limits for edible consumption.

Some aspects of the environmental exposure to chromium residues in Mexico

Research was conducted to determine the environmental effects of Cr residues from a chromite-ore processing plant (Cromatos de México) on the human population living in the surrounding area. The results of this study provided the first quantitative evidence of the transfer of Cr to the atmosphere, soil and subsequently to ground water. The atmospheric concentration of Cr ranged from 0.25 to 0.39 μg m−3, seven times higher than the level found in the control area. Most of the well water samples (90%) had a higher Cr concentration than the threshold limit value for drinking water of 0.05 mg L−1. The high Cr concentration in the environment may be responsible for the high concentration of this metal in urine (18.6 ng mL−1) and hair (4.3 μg g−1) found in the residents of this polluted area. These results were compared with those of people living in a Cr free zone through statistical analysis (Wilcoxons signed-ranks test). A significant difference of p<0.01 was found between these two populations. In relation to the average concentrations in hair (1.4 μg g−1) and urine (2.0 to 6.0 ng mL−1) considered as normal for a non exposed population in the USA, 70 to 80% of the residents in the Mexican urban-industrial area registered higher values. The high Cr concentration in urine found in workers from the chromite-ore processing plant show the lack of an efficient pollution control system. Therefore the Cr levels found in urine and hair can be used as indicators of environmental exposure.

Chemical composition of precipitation at two sampling sites in Mexico: A 7-year study

Abstract This paper describes the results of a study of the chemical composition of bulk and wet precipitation, collected for 7 years in a large urban area and a forested rural site in Central Mexico. In rain samples from both sites, sulfate was the most abundant ion followed by ammonium. Seasonal patterns of monthly volume-weighted concentration show that the highest values of SO2−4 NO3−, Ca2+ and NH4+were measured in May, the beginning of the rainy season in Central Mexico. The lowest values were observed from July to September, the months when most thunderstorms occurred. Multiple regression correlation analysis was applied to all data and a hierarchical model was used to select the variables included in the final model. In Rancho Viejo the model showed that SO2−4 contributed with 41% in the H+ concentration prediction. In Mexico City, despite the high SO42− concentration in rain water, this ion only contributed 0.46% whereas Ca2+ contributed in wet and bulk precipitation, 61 and 41%, respectively. Finally no long-term trends were noticed.

Scavenging of atmospheric formaldehyde by wet precipitation.

Despite the great importance that formaldehyde has in atmospheric photochemistry, few studies have been reported on rain water. In this paper, concentrations of HCHO in rain fractions within rain events are presented. Two sampling sites were chosen: one at Mexico City, a great polluted urban area, and the second at Rancho Viejo, a forested area under the meteorological influence of the city. The results show a general decrease during the early portion of the rain event. This seems to indicate that below-cloud scavenging is the most important mechanism while, from the small variations observed in the latter portion of the rainfall, it is possible to assume within-cloud scavenging as the predominant mechanism. Using the HCHO concentrations in rain water, the mixing ratios were estimated for the two sampling sites. The values were 0.68 ppb and 0.44 ppb at Mexico City and Rancho Viejo, respectively. Measurements at ground level in Mexico City gave a mean HCHO concentration in air of 24 ppb, much higher than the estimated mixing ratio. The high levels of HCHO found in ambient air and in rain water reflect anthropogenic emissions as the potential atmospheric sources.

Trace metals and inorganic ion measurements in rain from Mexico City and a nearby rural area

Rain is a main source of water for the ecosystem in Mexico. Emitted particulate matter and gases enter the ecosystem by rain scavenging. Although the chemistry of rainwater has been the subject of a number of studies, the insoluble fraction has been virtually ignored. This fraction is made up of particulate material, and can be significant, particularly in rural forest regions. Average aluminium weights were the highest of all elements, in both the soluble and insoluble fractions. Ions with the highest concentrations were and , followed by , Na+, Cl−, Ca2+, Mg2+ and K+. The Spearman rho correlation showed that the acidity was caused by and , and the most important neutralising ion was . High crustal enrichment factors (EFcrusts) suggested that Mexico City in general was richer in Cd, Cr, Mn, Pb, and V than Rancho Viejo. The enrichment factors support the idea that the metals observed in rainwater have an anthropogenic origin. Air mass back trajectories were associated with the concentrations of trace metals and of , Ca2+, Mg2+, and observed during each rainy day.