Patterns in utilization of carbon sources in soil microbial communities contaminated with mine solid wastes from San Luis Potosi, Mexico.

In San Luis Potosí, Mexico, the exploitation of minerals has historically been carried out as an activity that has left in its path environmental liabilities, with high concentrations of heavy metals. These metals have undergone weathering by rain and wind and have moved closer to inhabited locations as is the case of Cerro de San Pedro (CSP) and Villa de la Paz (VDP). The objective of this study is to show the biological alteration of soils due to the presence of heavy metals and metalloids like Cadmium (Cd), Copper (Cu), Lead (Pb) and Arsenic (As) and to find the relationship between contamination and risk indexes. Soil samples were obtained from sites with historical records of mining activity and their surroundings. Several analyses were performed, such as pH levels, organic matter, electrical conductivity, clays, heavy metals and As. Moreover, Community Level Physiological profiling (CLPP) were conducted. The obtained evidence showed high levels of contamination by As and heavy metals in both sites (CSP: 6485.1 mg/Kg of Pb and pH of 4.4; VDP: 7188.2 mg/Kg of As and pH of 7.8). According to the Metal Pollution Index (MPI), 607.0 in CSP and 1050.5 in VDP, presented a high environmental risk, apart from, risk to human health (SQGQI) 35.8 in CSP and 131.5 in VDP. At the same time, CLPPs showed that microbiological communities were selective in taking up substrate groups, in the following order: Carbohydrates > Polymers > Carboxylic acids > Amino acids > Amines/Amides. However, a positive correlation in CSP was only found between both indexes and Amines/Amides (r = 0.46, p < 0.05), and in VDP the D-Galactonic acid-γ-Lactone with the MPI (r = 0.49, p < 0.05), and with the SQGQI (r = 0.45, p < 0.05). Although this behavior was not homogeneous, it was possible to find negative correlations between both indexes and the AWCD with other substrates, influenced by the physicochemical characteristics presented in each studied site. Consequently, according to our findings, a combined effect between the physicochemical characteristics, As, and heavy metals took place, on the metabolic activity, causing alterations to soil functions.

Levels of organochlorine pesticides in blood plasma from residents of malaria-endemic communities in Chiapas, Mexico.

Organochlorine (OC) pesticides have been extensively used for pest control in agriculture and against malaria vectors in the region of Soconusco, Chiapas, in southern Mexico. Our study aimed to identify whether the inhabitants of four Soconusco communities at different locations (i.e., altitudes) and with different history of use of OC pesticides, have been similarly exposed to residues of these pesticides. In particular, we analyzed the potential relationship between levels of OC pesticides in plasma and the age, gender, and residence of the study population (n = 60). We detected seven pesticides in total (γ-HCH, ß-HCH, heptachlor, p,p'-DDE, p,p'-DDT, ß-endosulfan, endrin aldehyde). Of these, p,p'-DDE and ß-endosulfan were the most frequently found (in 98% and 38% of the samples, respectively). The low-altitude (<20 m above sea level; masl) and mid-altitude (520 masl) locations had the highest levels of p,p'-DDE, with geometric means of 50.6 µg/L and 44.46 µg/L, respectively. The oldest subjects (>60 years) had the highest p,p'-DDE level (56.94 ± 57.81 µg/L) of all age groups, while men had higher p,p'-DDE (34.00 ± 46.76 µg/L) than women. Our results demonstrate that residents of the Soconusco region are exposed to p,p'-DDE because of high exposure to DDT in the past and current environmental exposure to this DDT-breakdown product.

DDT and DDE concentrations in the blood of Mexican children residing in the southeastern region of Mexico.

The aim of this study was to assess the levels of dichlorodiphenyltrichloroethane (DDT) and dichlorodiphenyldichloroethylene (DDE) in the blood of children living in the southeastern region of Mexico. In this study, we found high levels of DDT and its principal metabolite (DDE) in the blood of children residing in the communities studied. The levels of total DDT found in our study ranged from 4,676.4 ng/g lipid to 64,245.2 ng/g lipid. All of the children in the study had detectable levels of DDT and/or DDE. In conclusion, our data indicate that children living within the study areas are exposed to high levels of DDT and DDE. Moreover, these results can be used as a trigger to revisit local policies on environmental exposures.

DDT, DDE, and 1-hydroxypyrene levels in children (in blood and urine samples) from Chiapas and Oaxaca, Mexico.

The aim of this study was to evaluate the DDT, DDE, and 1-hydroxypyrene exposure levels of children living in communities located in southeastern Mexico. The study communities were Lacanja and Victoria in Chiapas state and Ventanilla in Oaxaca state. Children living in Lacanja had total blood DDT levels (mean ± SD, 29,039.6 ± 11,261.4 ng/g lipid) that were significantly higher than those of children in Victoria (10,220.5 ± 7,893.1 ng/g lipid) and Ventanilla (11,659.7 ± 6,683.7 ng/g lipid). With respect to the 1-hydroxypyrene levels in urine samples, the levels in Lacanja (4.8 ± 4.1 µg/L or 4.5 ± 3.9 µmol/mol creatinine) and Victoria (4.6 ± 3.8 µg/L or 3.9 ± 3.0 µmol/mol Cr) were significantly higher than levels found in Ventanilla (3.6 ± 1.4 µg/L or 2.5 ± 0.5 µmol/mol Cr). In conclusion, our data indicate high levels of exposure in children living in the communities studied in this work. The evidence found in this study could be further used as a trigger to revisit local policies on environmental exposures.

Assessment of the levels of hexachlorocyclohexane in blood samples from Mexico.

The aim of this study was to evaluate hexachlorocyclohexane (HCH) exposure in children living in nine hot spots in four Mexican states. We analyzed HCH (α, ß, and γ-isomers) in blood using gas chromatography/mass spectrometry. HCH exposure level in 261 children was assessed and approximately 75 % of the children studied had detectable levels of HCH. These levels ranged from 188 to 40,096.7 ng/g lipid. The highest mean levels were found in Lacanja (5,446.9 ng/g lipid), an indigenous community in Chiapas, Mexico. Our data indicate high exposure to HCH in children living in these communities.

Assessment of the levels of persistent organic pollutants and 1-hydroxypyrene in blood and urine samples from Mexican children living in an endemic malaria area in Mexico.

The aim of this study was to evaluate the exposure levels to persistent organic pollutants and 1-hydroxypyrene in children living in an endemic malaria zone in Mexico. The blood levels for 1,1,1-trichloro-2,2-bis(p-chlorophenyl)ethane (DDT), 1,1-dichloro-2,2-bis(p-chlorophenyl)ethylene (DDE) and lindane ranged from 15.4 to 17,886.5 ng/g lipid, 6,624.3 to 100,119.0 ng/g lipid, and 351.1 to 6,153.8 ng/g lipid, respectively. For total polychlorinated biphenyls the blood levels ranged from 2,584.9 to 14,547.9 ng/g lipid. Regarding urinary 1-hydroxypyrene levels, the mean level was 2.9 ± 3.1 µmol/mol creatinine. In conclusion, the children in our study are exposed to levels higher than normal to mixtures of environmental contaminants.

Assessment of DDT and DDE levels in soil, dust, and blood samples from Chihuahua, Mexico.

The aim of this study was to assess levels of DDT and DDE in two environmental matrices (soil and dust) and to investigate the blood levels of these insecticides in exposed children living in a north Mexican state (Chihuahua) where DDT was sprayed several years ago during (1) health campaigns for the control of malaria and (2) agricultural activities. DDT and DDE were analyzed by gas chromatography/mass spectrometry. In general, lower levels were found in household outdoor samples. The levels in outdoor samples ranged from 0.001 to 0.788 mg/kg for DDT and from 0.001 to 0.642 mg/kg for DDE. The levels in indoor samples ranged from 0.001 to 15.47 mg/kg for DDT and from 0.001 to 1.063 mg/kg for DDE. Similar results to those found in indoor soil were found in dust, in which the levels ranged from 0.001 to 95.87 mg/kg for DDT and from 0.001 to 0.797 mg/kg for DDE. Moreover, blood levels showed that all of the communities studied had been exposed to DDT and/or DDE, indicating a general past or present exposure to DDT. It is important to note that the quotient DDT/DDE in all matrices was always >1. Whether the people living in our study area are at risk is an issue that deserves further analysis. However, applying precautionary principles, it is important to initiate a risk-reduction program to decrease exposure to DDT and its metabolites in people living in this area.

Assessment of polychlorinated biphenyls and mercury levels in soil and biological samples from San Felipe, Nuevo Mercurio, Zacatecas, Mexico.

The aim of this work was to evaluate contamination by polychlorinated biphenyls and mercury in soil, and to assess exposure level to both contaminants in children living in San Felipe, Nuevo Mercurio, Zacatecas, Mexico. We found soil levels of total polychlorinated biphenyls ranging from non detectable (nd) to 190 µg/kg. Mercury soil levels ranged from 8.9 to 10215.0 mg/kg. Exposure levels of total polychlorinated biphenyls assessed in blood and urinary mercury in children living in the studied community were 1,600 ± 8,800 ng/g lipid and 4.2 ± 7.1 µg/g creatinine, respectively.

Exposure assessment of persistent organic pollutants and metals in Mexican children.

Environmental policies in Mexico have contributed to the reduction in the production or use of some persistent organic pollutants (POPs) and metals. However, monitoring of POPs concentrations in humans living in hot spots is lacking. Therefore, the objective of this study was to conduct a screening for POPs and metals first in Mexican children living in high-risk areas. During the year 2004, we analyzed a total of 229 healthy children (aged 6-12 years old) who resided in communities located in nine Mexican states. Organochlorine insecticides, PCBs and metals were quantified in plasma and urine samples. We detected p'p-DDE in all the children; moreover, p'p-DDT, lindane and hexachlorobenzene were detected respectively in 14%, 85% and 10% of the children studied. Measurable levels of PCBs were recorded in only one community, where six of 14 PCB congeners assayed were detected (numbers 52, 118, 138, 153, 170 and 180). All the children had detectable levels of lead in their blood (mean level, 4.6 microg dL(-1)); furthermore, 57% of the children studied had levels higher than 5.0 microg/dL. The mean level of urinary arsenic (UAs) for all the children was 22.35 microg g(-1) creatinine and 15% of those children had concentrations of UAs above 50 microg g(-1) creatinine. For cadmium, the mean urinary level was 0.78 microg g(-1) creatinine, and only one percent of the children had values above 2.0 microg g(-1) creatinine. The results cannot be generalized since the communities selected are not representative of the Mexican population; however, they indicate that Mexican children are exposed to chemicals and some at risk levels.