In large industrialized cities, tons of particles containing heavy metals are released into the environment and accumulate on street surfaces. Such particles cause a potential risk to human health ...due to their composition and size. The heavy metal contamination levels, main emission sources, and human health risks were identified in 482 samples of street dust. Heavy metal concentrations were obtained by microwave-assisted acid digestion and ICP-OES. The results indicated that street dust in Mexico City is contaminated mainly with Pb, Zn, and Cu, according to the contamination factor and the geoaccumulation index. The pollution load index of the street dust was made with the concentrations of Pb, Zn, Cu, Cr, and Ni. The main sources of Pb, Zn, Cu, and Cr are anthropic, probably due to vehicular traffic. The highest levels of Cr and Pb in urban dust represent a health risk for children. Contamination limits were proposed for heavy metals in street dust of Mexico City. These limits might be useful to generate and apply public policies to decrease anthropic emissions of the heavy metals studied, particularly Cr and Pb.
The geomagnetic field variations on the continent of Africa are still largely undeciphered for the past two millennia. In spite of archaeological artefacts being reliable recorders of the ancient ...geomagnetic field strength, only few data have been reported for this continent so far. Here we use the Thellier-Coe and calibrated pseudo-Thellier methods to recover archaeointensity data from Burkina Faso and Ivory Coast (West Africa) from well-dated archaeological artefacts. By combining our 18 new data with previously published data from West Africa, we construct a reference curve for West Africa for the past 2000 years. To obtain a reliable curve of the archaeointensity variation, we evaluate a penalized smoothing spline fit and a stochastic modelling method, both combined with a bootstrap approach. Both intensity curves agree well, supporting the confidence in our proposed intensity variation during this time span, and small differences arise from the different methodologies of treating data and uncertainties. Two prominent peaks at around 740 AD and 1050 AD appear to be common in ours and several reference curves from other locations, indicating a general westward movement from China to Hawaii of a rather stable feature of the geomagnetic field. However, independent smaller peaks that do not correlate in different locations may hint to localized expressions of the geomagnetic field as a result of temporarily varying non-dipole sources.
San Jacinto archaeological site in Northern Colombia hosts America's oldest pottery, radiometrically dated between 5940 ± 60 BP and 5190 ± 40 BP. Eleven ceramic fragments were subjected to detailed ...archaeomagnetic and archaeointensity investigation. Alternating field and thermal demagnetization, as well as magnetic mineralogy experiments, were carried out before double heating paleointensity determination to select the most suitable samples. Magnetic susceptibility vs. temperature curves revealed that magnetite and hematite grains are the main carriers of the thermoremanent magnetization. However, the contribution of hematite in total remanence seems to be negligible. Thirty-six samples corresponding to six pottery fragments were selected for Thellier-type paleointensity determinations. Mean intensity values range from 50.7 ± 4.7 to 65.3 ± 11.9 μT while virtual Axial Dipole Moments vary from 12.6 ± 1.2 to 16.2 ± 2.9 × 1022 Am2, indicating high geomagnetic field strength compared to values predicted by global geomagnetic models. This represents the first evidence of relatively high archaeointesities before 1000 BC. Similar or even higher geomagnetic strengths are observed in the Levant around 1100–800 BC and SW Pacific Region at 1450 AD. The actual cause of such anomalously high intensity, often attributed to the processes in the vicinity of the Core-Mantle Boundary, is still not fully understood.
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•San Jacinto archaeological site in Northern Colombia probably hosts America's oldest pottery.•Available radiocarbon ages range from 5940 ± 60 BP to 5190 ± 40 BP.•Six out of 11 ceramic fragments were subjected to magnetic mineralogy and absolute intensity experiments.•Virtual Axial Dipole Moments indicate high intensity compared to values predicated by global geomagnetic models.•First strong evidence of high geomagnetic intensity before 1000 BC.
Historical documents, archives and old photographic collections allowed to analyze 877 direct geomagnetic measurement data obtained by sailors (including pirates), United States Coast and Geodetic ...Survey and National Astronomical Observatory since 1587. The updated catalogue includes 844 values of magnetic declination, 495 of inclination, 467 of the horizontal intensity component (H) and 455 of the vertical intensity component (Z). All data were relocated to Mexico City through the pole conversion method in order to build a reference secular variation curve for Mexico and surrounding area using bootstrap method to mitigate the effect of outliers and estimate the probability of density functions. The directional variation patterns obtained in this investigation were compared to the curves retrieved from Sha.Dif.14k, GUFM1and IGRF-12 models while VADM fluctuations were confronted to similar quality determinations from other localities worldwide as well as archaeomagnetic curves from Mesoamerica.
•Historical documents allowed to analyze 877 direct geomagnetic measurement data since 1587.•A reference secular variation curve was constructed using bootstrap method.•A potential geomagnetic jerk was detected at about 1850 already reported for Balkan region.
Environmental pollution is a negative externality of urbanization and is of great concern due to the fact that it poses serious problems to human health. Pollutants, such as heavy metals, have been ...found in urban road dust; however, it is unclear whether the urban form has a role in its accumulation, mainly in cases where there is no dominant unique source. We collected 482 samples of road dust, we determined the concentrations of five heavy metals (Cr, Cu, Pb, Zn, and Ni) using inductively coupled plasma optical emission spectrometry (ICP-OES), and then we derived the pollution load index (PLI). After estimating the mostly anthropogenic origin of these pollutants based on global levels of reference, there were two main aims of this study. Firstly, to analyze the spatial correlation of heavy metals, and secondly, to identify the main factors that influenced the heavy metal concentrations in the road dust of Mexico City. We did this by using a spatial autocorrelation indicator (Global Moran’s I) and applying ordinary least squares (OLS) and spatial regression models. The results indicated low levels of positive spatial autocorrelation for all heavy metals. Most variables failed to detect any relationship with heavy metals. The median strip area in the roads had a weak (significance level of 90%) but consistent positive relationship with Cr, Cu, Ni, Pb, and the PLI. The distance to the airport had a weak (significance level of 90%) and inverse relationship with Pb. Manufacturing units were associated with an increase in Cu (significance level of 95%), while the entropy index was associated with an increase in Ni (significance level of 95%).
A detailed magnetic mineralogy and archaeomagnetic investigation was performed on thirty-two red mural painting samples belonging to the colonial Santo Domingo Convent in Oaxaca (Southern ...Mesoamerica). Systematic magnetic experiments included continuous thermomagnetic curves, hysteresis cycles, acquisition of isothermal remanence and step-wise alternating field demagnetization of the pictorial remanent magnetization (PiRM). Titanium-poor titanomagnetite seems to act as responsible for major part of pictorial remanent magnetization while heating and cooling curves show marked irreversibility and high thermal instability. Although all samples were demagnetized by means of alternating fields up to 90 mT, only seven of them provided reasonably well-grouped paleodirections yielding following mean values: Inclination = 35.2°, Declination = 2.3°, α95 = 4.8° and k = 161. According to the probability density function obtained by means of the global geomagnetic model SHA.DIF.14 K, the possible elaboration date of the painting layer under study is estimated between 1684 CE and 1744 in accordance with historical documents. Despite low success rate, the described methodology deserves to be considered for dating of wide range of red mural paintings worldwide.
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•A detailed magnetic mineralogy and archaeomagnetic investigation was performed on thirty-two red mural painting samples.•Titanium-poor titanomagnetite seems to act as responsible for major part of pictorial remanent magnetization.•The possible elaboration date of the painting layer under study is estimated between AD 1684 and 1744.•Despite low success rate, the described methodology deserves to be considered for dating of wide range of wall paintings.
We report a detailed rock-magnetic, archaeomagnetic and absolute intensity investigation on burned in situ remains of the Plazuelas archaeological site (Northern Border of Mesoamerica). Fifty-six ...specimens were subjected to step-wise alternating field demagnetizations to retrieve characteristic remanence directions. All samples yielded evidence of stable, single-component magnetization carried by magnetite or Ti-poor titanomagnetite. Sixty-four specimens were selected for paleointensity experiments following the Thellier double heating technique, including remanence anisotropy correction. The archaeomagnetic dating, based on full geomagnetic vectors, was performed using the global geomagnetic models and the regional Paleosecular Variation Curves available for Mesoamerica. The most probable age intervals obtained for the burned floor of Site 1 (Casas Tapadas North) are within the interval 972AD – 744 AD. In the case of the burned floor of Site 2 (Casas Tapadas West), the ages obtained fall within 971 AD - 752 AD. In the case of the burned floor of Site 3 (South Sector), the ages obtained fall within the interval 752 AD – 969 AD. The calculation of the most probable age intervals, carried out using the Bootstrap resampling method, provided the dates of 940 ± 6 AD, 896 ± 14 AD and 883 ± 14 AD, respectively. These ages agree well with various archaeological hypotheses on the sudden collapse of Plazuelas as a result of intentional destruction, mutilation and generalized firing due to the local war and/or social unrest.
Modeling of the recent geomagnetic secular variation in terms of both directions and intensity is commonly based on observatory data, available for the last four centuries in Europe but less than 100 ...years in most part of our planet. Geomagnetic Repeat Stations provide invaluable supplementary data for such purpose allowing largely extend the magnetic record. Here, we compile database retrieved from 32 localities in Mexico providing 257 values of magnetic declinations, 239 inclinations, 236 data for the horizontal component and other 233 for the vertical component of intensity. The selected dataset consists of twenty-six repeat stations providing 216 declinations, 234 inclinations, 140 intensities, 213 values for horizontal and 209 vertical components. An agglomerative hierarchical grouping tree method and Chebyshev metrics were used to mitigate the measurement errors while the relocation error exercise was also implemented. The Bootstrap method and penalized cubic splines were used to build the secular variation curve which show rather similar trends comparing to the global model data for the most time interval involved. Several potential geomagnetic jerks are observed for 1958, 1969 and 1978 most likely corresponding with those detected in French observatories in Chambon la Forêt and in Tucson in North America.
•Twenty-two Geomagnetic Repeat Stations provided robust dataset for the geomagnetic field modeling in Mexico.•The database consists of 257 magnetic declinations and 239 inclinations.•The relocation error exercise was carried out using the GUFM1 and IGRF-12 models.•Bootstrap methodology allowed to generate 500 synthetic curves.•Several potential geomagnetic jerks are observed.
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