The analytical scanning electron microscope (SEM) has been used to determine the presence and distribution of atomic elements in mineralogy. However, the detection of light elements such as carbon is difficult to obtain with standard energy-dispersive X-ray spectrometry (EDS) and usual proceedings for SEM. This study proposes a new protocol to detect calcium carbonate by SEM/EDS using sediments from the Jaguaribe River estuary, NE Brazil, as a model. Handmade gold mounting discs (Au stubs) were used as sample support and samples were adhered with inexpensive glue (Loctite Super_Bonder) or directly disposed on the Au stubs. CaCO(3) and NaCl for chemical analysis were used as control and counterproof to the carbon adhesive tape. Control salts EDS analyses indicate that the method was efficient to detect light elements. Sediments obtained from different depths in the core sampled at the Jaguaribe River estuary consist of particles and aggregates with diverse morphology that covers a wide range of particle or aggregate size. Morphology and dimensions were similar for all core depths. Analysis of samples disposed on gold mounting disc without glue showed that sediment bulk particles usually presented small particles adhering on the surface. Clay minerals were predominant but silica was also often identified. Calcium was a trace element in a small number of sediment bulk particles. Biological and non-biological calcium carbonates, including nanoparticles, were identified in all core depths. X-ray emitted from Au stub did not interfere in the CaCO(3) EDS analysis. Calcium carbonate particles from sediments were identified using this novel approach.
Airborne particulate matter (PM) has been included among the most important air pollutants by governmental environment agencies and academy researchers. The use of terrestrial plants for monitoring PM has been widely accepted, particularly when it is coupled with SEM/EDS. Herein, Tillandsia stricta leaves were used as monitors of PM, focusing on a comparative evaluation of Environmental SEM (ESEM) and High-Pressure SEM (HPSEM). In addition, specimens air-dried at formaldehyde atmosphere (AD/FA) were introduced as an SEM procedure. Hydrated specimen observation by ESEM was the best way to get information from T. stricta leaves. If any artifacts were introduced by AD/FA, they were indiscernible from those caused by CPD. Leaf anatomy was always well preserved. PM density was determined on adaxial and abaxial leaf epidermis for each of the SEM proceedings. When compared with ESEM, particle extraction varied from 0 to 20% in air-dried leaves while 23-78% of particles deposited on leaves surfaces were extracted by CPD procedures. ESEM was obviously the best choice over other methods but morphological artifacts increased in function of operation time while HPSEM operation time was without limit. AD/FA avoided the shrinkage observed in the air-dried leaves and particle extraction was low when compared with CPD. Structural and particle density results suggest AD/FA as an important methodological approach to air pollution biomonitoring that can be widely used in all electron microscopy labs. Otherwise, previous PM assessments using terrestrial plants as biomonitors and performed by conventional SEM could have underestimated airborne particulate matter concentration.
Historically, microscopes were used for descriptions of animals, plants and non-living specimens. In 19 th century, the shape-function relationship marked microscopic studies. The later 20 th century witnessed the nanometric special resolution provided by electron microscopes. As we enter the 21 st century, the analytical electron microscopy promises to change our comprehension about the nano-world. Chemical analyses of the shape will redesign our understanding of the structure and functioning of animals, plants and non-living specimens, including sediments.
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