The study of the triacylglycerols (TAG) by gas chromatography (GC) using capillary columns is an efficient technique for the determination of some characteristics of quality of fats and oils. The objective of the present study was to determine by GC the content of TAG present in fat of cow and goat milk produced in four zones of Mexico. According to criteria established in Mexican Standardization, 25 samples were obtained of 1 L of ultra-pasteurized cow milk (UHT) and 27 and 48 of raw cow and goat milk, respectively. The fat was extracted from all of the milk samples by detergent solution, and was stored at −20˚C until its analysis. The chromatographic conditions made it possible to identify and quantify TAG of 28 to 54 numbers of carbons, which were analyzed under descriptive and inferential statistical techniques. For the cow milk fat, the statistical analyses indicated significant difference (p < 0.05) in the TAG C34, C50 and C52, and for the goat milk fat in the TAG of C36 to C52. No equality of means was found among the TAG of the cow and goat milk fat. This study offers an advance in the characterization of the TAG present in the cow and goat milk fat produced in Mexico.

2,4-Dichlorophenoxyacetic acid (2,4-D) is used for commercial herbicides preparation. In Ecatepec, Mexico, there is an industrial plant that manufactures 2,4-D and other herbicides that discharges a low pH, high salinity and 2,4-D rich effluent: a very aggressive and toxic wastewater. This research aimed at acclimating a 2,4-D degrading culture from wild inocula, and implementing and determining the performance of an extractive membrane bioreactor (EMB) for 2,4-D removal from an effluent similar to that industrial wastewater. The experimental work consisted of two phases. In the first phase a mixed, aerobic microbial culture was acclimated to 2,4-D in submerged culture. In the second phase, a lab scale EMB was implemented. The acclimated culture was able to use 2,4-D as the sole source of carbon and energy with an optimum at pH = 8. Gram negative microorganisms predominated in the consortium. The culture growth in 2,4-D followed an Andrews-like substrate inhibition kinetic model with μmax = 0.06 1/h, Ks = 17 mg/L, Ki = 128 mg/L. The hydrophobic membrane had a partition coefficient membrane/water of 131 Laq/Lmembr, which suggested an important adsorption effect/solution in the membrane. The permeability coefficient determined at pH 0, 1 and 4 was practically independent of pH with an average value of 3.2=10-8 m/s. After inoculation, continuous, steady-state experiments were also run at influent 2,4-D concentration of 300 mg/L. The reactor showed 2,4-D unit reductions in the range of 110 to 120 mg 2,4-D/L lumen.h (32 to 34 mg/h.m2) at lumen retention times of 4.1 to 15 min. The unit surface removal rate values in this work compared favourably with literature data for EMB degrading other xenobiotics (for instance, phenol, retention time 353 min, removal rate 94.1 mg/h.m2). Studies are underway to determine 2,4-D removals at longer retention times. Overall, the EMB seems to be an effective configuration for removing 2,4-D while at the same time avoiding the active biomass exposure to the low pH and high salinity concentration of the influent.

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This paper describes PAH concentrations in apple crops that are growing in rural terrains in Mexico City. The concentrations of individual PAHs showed great variability, there being low and high molecular weight compounds in dry (high molecular weight for Tlahuac 7.06 microg/g and Milpa Alta 3.96 microg/g) and wet months (high molecular weight for Tlahuac 11.25 microg/g and Milpa Alta 12.05 microg/g). Some PAHs indicators and cross plot ratios Ant/(Ant + Phe) and Flu/(Flu + Pyr) define fossil fuels and vegetation combustion as the source of contamination over the cuticle of the apples. It is likely that deposition (dry and wet) is the principal source o f contamination over the apple surface. This study reveals the presence of PAHs in apples due to the high air contamination of Mexico City.

The nature of organochlorine pesticides (OCP) and their physical-chemical properties exert immediate action of control on live systems, which has justified their use in agricultural practices. Their long life makes them a persistent ecological aggressor and biomagnifier. They reach foods by biotic and abiotic means, and are absorbed and accumulate in adipose tissue. In lactation processes, they are excreted in milk through the mobilization of fats. Diverse studies have identified them as neurotoxic, affecting reproductive processes, altering the immunological response and act as endocrine disruptors. An analysis was made of the content of organochlorine pesticides in twenty-one samples of infant milk formulas marketed in the south of Mexico City in 2010. The determinations were made following the protocols of the International Dairy Federation, by means of gas chromatography with electron capture detector, and the majority presence was found of α-HCH (100%), β-HCH (95.2%), γ-HCH (90.5%), aldrin (85.7%), heptachlor (80.9%) and heptachlor epoxide (80.9%) with mean values of 0.24, 0.13, 0.32, 0.62, 0.92 and 0.18 μg/kg of fat, respectively; all below the limits permitted by the Codex Alimentarius. With null or lower recurrence and in lower quantities, the family of DDT, endrin, endrin aldehyde and the endosulphanes were quantified.