RESUMOLevantamento geoquímico nas sub-bacias Vermelho (SBV) e Sororó (SBS) da bacia do Itacaiúnas no sudeste da região Amazônica revela que parâmetros físicoquímicos da água superficial não mostram variações acentuadas entre as estações chuvosa e seca. Com exceção de Fe e Mn, em geral os demais metais revelam baixas concentrações na água e não foram observadas evidências significativas de contaminação. Conteúdos comparativamente mais elevados foram obtidos principalmente durante a estação chuvosa. Fe e Mn se distribuem regularmente na água na área estudada e o aumento de seu conteúdo foi favorecido pelo desmatamento. A concentração de Mn aumenta durante a estação seca possivelmente devido a processos biogeoquímicos. Altas concentrações de Fe e Mn em águas superficiais são inerentes às condições locais da região Amazônica. Fatores geogênicos influenciam a distribuição na água de Co, Cr, Cu, Ni, Pb, Sn, V e Zn. Efeitos antrópicos são subordinados, exceto para Fe e Mn ou em áreas localizadas. A definição de valores de threshold para As, Co, Cr e Pb, apresentou limitações. Valores de threshold puderam ser definidos em pelo menos uma estação nas duas sub-bacias para Cu, Ni, Sn, V e Zn. No caso de Fe total, foram obtidos valores de threshold de 5 a 6 mg/L e de 2 a 3 mg/L nas estações chuvosa e seca, respectivamente. Os valores de threshold para Mn são de 0,30 a 0,45 mg/L na estação chuvosa e, na estação seca, decrescem para 0,20 a 0,30 mg/L na VSB e aumentam para 1,3 a 1,4 mg/L na SSB. Palavras-chave: Geoquímica de água fluviais; Valores de threshold; Metais pesados; Bacia do rio Itacaiúnas; Amazônia Oriental. ABSTRACTGeochemical survey in the Vermelho (VSB) and Sororó (SSB) sub-basins of the Itacaiúnas basin in southeastern Amazonian region has shown that the physicalchemical parameters of stream water do not display accentuated variations between the rainy and dry seasons. Except for Fe and Mn, in general most metals show low contents in water and evidences of significant contamination were not observed. Higher contents were mostly registered during the rainy season. Fe is regularly distributed in water in the studied area and the increase of its concentration was favored by deforestation. Mn contents increase during the dry season possibly due to biogeochemical processes. High Fe and Mn contents in water are inherent to the specific local conditions prevalent in the Amazonian region. Geogenic influence in metal distribution in water is significant for Co, Cr, Cu, Ni, Pb, Sn, V, and Zn. Anthropic effects are subordinate except for Fe and Mn or in local areas. The definition of threshold values for As, Co, Cr, and Pb, was limited, however, threshold values for Cu, Ni, Sn, V, and Zn were estimated for at least one season in each sub-basin. Threshold values of total iron were obtained (5 to 6 mg/L and 2 to 3 mg/L in the rainy and dry seasons, respectively). Estimated Mn threshold values are 0.30 to 0.45 mg/L in the rainy season and in the dry season they decrease to 0.20 to 0.30 mg/L in VSB and increase to 1.3 to 1.4 mg...

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This paper analyses air quality data from megacity Delhi, India, during different periods related to the COVID-19, including pre-lockdown, lockdown and unlocked (post-lockdown) (2018–2020) to determine what baseline levels of air pollutants might be and the level of impact that could be anticipated under the COVID-19 lockdown emission scenario. The results show that air quality improved significantly during the lockdown phases, with the most significant changes occurring in the transportation and industrially dominated areas. A pronounced decline in PM 2.5 and PM 10 up to 63% and 58%, respectively, was observed during the lockdown compared to the pre-lockdown period in 2020. When compared to 2018 and 2019, they were lower by up to 51% and 61%, respectively, dropping by 56% during unlock. Some pollutants (NOx and CO) dropped significantly during lockdown, while SO 2 and O 3 declined only slightly. Moreover, when compared between the different phases of lockdown, the maximum decline for most of the pollutants and air quality index occurred during the lockdown phase 1; thus, this period was used to report the COVID-19 baseline threshold values (CBT; threshold value is the upper limit of baseline variation). Of the various statistical methods used median + 2 median absolute deviation (mMAD) was most suitable, indicating CBT values of 143 and 75 ug/m 3 for PM 10 and PM 2.5 , respectively. This results although preliminary, but it gives a positive indication that temporary lockdown can be considered as a boon to mitigate the damage we have done to the environment. Also, this baseline levels can be helpful as a first line of information to set future target limits or to develop effiective management policies for achieving better air quality in urban centres like Delhi. Supplementary Information The online version contains supplementary material available at 10.1007/s13762-021-03142-3.

We present this manuscript as a methodological approach and general guidelines for geochemical mapping and background/baseline projects for environmental assessment in tropical areas. A case study was carried out in the Itacaiúnas River watershed (IRW), Eastern Amazon, to fill in a gap in knowledge on the distribution of chemical elements, particularly those potentially toxic, in the near-surface environment of the area. The high-impact results of this research project revealed the need for similar scientific investigation across the globe with the implementation of a systematic methodology. The study shows, for example, the importance of well-planned field activities, multi-medium sampling, analytical methods, laboratory procedures, database construction, and general aspects of data processing and statistical treatment. The importance of this contribution is that it can be used as a reference in support of geospatial analysis in research within the scope of geochemical mapping and background-baseline projects. The database is accessible through a web-based geographic information system front-end; a Geochemical Atlas of the IRW will be available as soon as possible.