No abstract

No abstract

The fate of most of the Hg used to obtain Ag through amalgamation in colonial America is uncertain. Residues of this process are often unsecured, and the environmental risk they pose is frequently unknown. The aim of this study is to assess the exposure of the children population of the town of Cedral in North Central Mexico to Hg associated with uncontrolled historical amalgamation residues (tailings). Tailings were partially reprocessed in the twentieth century to obtain the remaining Ag and Hg, modifying the chemical forms of Hg in the residue and producing inorganic Hg compounds. Earlier reports show high concentrations of Hg in the soils and in the two main deposits of metallurgical waste in Cedral. A moderate level of exposure to Hg (geometric mean 3.5 µg L −1 ) was identified in blood samples from school-age children. A result assessment shows the importance of inhalation as a significant exposure route as well as the bioavailability of the Hg chemical form. Hg 0 content in gaseous elemental mercury (GEM) reaches concentrations of up to 1793 ng m −3 in the atmosphere and, due to a low bioavailability, probably contributes only in small proportion to human exposure. Inorganic Hg compounds in the tailings generated during the reprocessing procedure are contained in the particulate fraction in the atmosphere (PM2.5; mean concentration 23.6 ng m −3 ) and may contribute in a higher proportion than GEM to human exposure, due to its higher bioavailability.

This paper presents atmospheric gaseous elemental mercury (GEM) data recorded during two short-term monitoring surveys in the Mexico City Metropolitan Area (MCMA) at 12th May 2019 and at 22nd May 2020, during conditions of low and high human activity respectively. Results, although they are limited, can be considered as the representative range of exposure to GEM of the inhabitants of MCMA; differences in results reveal the impact of human activities on GEM background levels (2.53 and 3.76 ng m −3 , respectively). GEM concentrations and their spatial distribution does not allow for the identification of important industrial sources and do not reach intervention pollution levels. The activity of the Popocatépetl volcano is not likely to have an effect on GEM in the MCMA. In spite the evident decrease in GEM concentrations compared with data previously reported, monitoring must be carried out routinely given Mexico's participation in the Minamata Convention on Mercury.

Emissions of gaseous elemental mercury (GEM or Hg 0 ) from different sources in urban areas are important subjects for environmental investigations. In this study, atmospheric Hg measurements were conducted to investigate air pollution in the urban environment by carrying out several mobile surveys in Mexico City. This work presents atmospheric concentrations of GEM in terms of diurnal variation trends and comparisons with criteria for pollutant concentrations such as CO, SO 2 , NO 2 , PM 2.5 , and PM 10 . The concentration of GEM was measured during the pre-rainy period by using a high-resolution active air sampler, the Lumex RA 915 M mercury analyzer. In comparison with those for other cities worldwide, the GEM concentrations were similar or slightly elevated, and they ranged from 0.20 to 30.23 ng m −3 . However, the GEM concentration was significantly lower than those in contaminated areas, such as fluorescent lamp factory locations and gold mining zones. The GEM concentrations recorded in Mexico City did not exceed the WHO atmospheric limit of 200 ng m −3 . We performed statistical correlation analysis which suggests equivalent sources between Hg and other atmospheric pollutants, mainly NO 2 and SO 2 , emitted from urban combustion and industrial plants. The atmospheric Hg emissions are basically controlled by sunlight radiation, as well as having a direct relationship with meteorological parameters. The area of the city studied herein is characterized by high traffic density, cement production, and municipal solid waste (MSW) treatment, which constantly release GEM into the atmosphere. In this study, we included the simulation with the HYSPLIT dispersion model from three potential areas of GEM release. Emissions from industrial corridors and volcanic plumes localized outside the urban area contribute to the pollution of Mexico City and mainly affect the northern area during specific periods and climate conditions. Using the USEPA model, we assessed the human health risk resulting from exposure to inhaled GEM among residents of Mexico City. The results of the health risk assessment indicated no significant noncarcinogenic risk (hazard quotient (HQ) < 1) or consequent adverse effects for children and adults living in the sampling area over the study period. GEM emissions inventory data is necessary to improve our knowledge about the Hg contribution and effect in urban megacity areas with the objective to develop public safe policy and implementing the Minamata Convention. Supplementary information The online version contains supplementary material available at 10.1007/s10661-022-10107-7.