Arsenic (As) can occur in many chemical forms, from harmless to toxic compounds. Its toxicity depends on valence and the chemical environment. Small amounts of toxic forms can even have therapeutic and fortifying effects. The use of As was practiced for hundreds of years, leading to accidental or deliberate poisoning. Waters with high As concentrations (up to 5000 μg/L) adversely affect the drinking water supply of about 200 million people worldwide mainly in Argentina, Chile, Mexico, China, West Bengal (India), Bangladesh, Vietnam and Hungary. In Hungary, the As exposure of the population has been significantly reduced since 2017 by drilling new wells with lower As content and setting up new waterworks in the settlements affected, with financial help from the European Commission. Arsenic possesses a complex water chemistry and occurs in several inorganic and organic species in water depending on pH, salinity, acid dissociation constants of its oxyacids, and the As(V)/As(III) redox potential. The possible technological solution for As removal from water is definitely governed by the species concerned. Chemical oxidation, co-precipitation, adsorption, ion exchange, reverse osmosis and membrane filtration are used to remove As from water. From the technological point of view, As removal processes can be divided into three major groups: i) conventional technologies (coagulation, iron–manganese removal, lime softening); ii) sorption processes (ion exchange, activated aluminum); and iii) membrane technologies (reverse osmosis, nano-, micro- or ultrafiltration). Each of the aforementioned technologies is more efficient for As(V). Therefore, an oxidation step is often needed. Oxidation by simple direct aeration is slow, but there are a number of chemicals that can accelerate the process, such as chlorine gas, sodium hypochlorite, ozone, potassium permanganate, hydrogen peroxide and manganese oxides, and ultraviolet radiation may also be suitable for oxidizing As(III). Given the lack of a definitive solution for As removal from drinking water, it is important to estimate the exposure of the population in large areas affected by As contamination. For estimation of the As(III)/As(V) ratios, conventional As speciation analysis generally consists of on-line hyphenation of a chromatographic separation technique to an atomic spectrometric detector. Replacement of either the high-performance liquid chromatograph or the atomic spectrometer (e.g. inductively coupled plasma mass spectrometer) – or both – may lead to cost-effective solutions enabling extension of our knowledge with respect to As speciation.

Global warming and increasing energy demand characterized by reduced air exchange led to the construction of energy-efficient buildings. Given that the XXI century people spend a significant part of their time in such enclosed spaces, the study of indoor air quality is extremely important in these microenvironments. In the last decade and a half, the number of chemical studies to understand the adverse effects of atmospheric aerosol particles (PM2.5) with aerodynamic diameters less than 2.5 μm has increased significantly. These particles are mainly of primary (eg biomass combustion) and secondary origin of hydrophobic or hydrophilic organic macromolecules (up to 50% by weight of the PM2.5 fraction), carbon black and elemental carbon (EC), sulphate, nitrate and ammonium ions. and metal compounds. It is not known exactly which components of PM2.5 are primarily responsible for adverse health effects. The toxicity of particles is attributed to both their chemical composition and size. The toxicity of PM2.5 is manifested in oxidative stress. Reactive oxygen species (ROS) can enter the human body directly by binding to PM or are formed in vivo in redox reactions in cells catalyzed by the components of inhaled PM. The oxidation potential (OP) of PM can be estimated by acellular and in vitro cellular assays with different sensitivities. Methods based on the determination of antioxidant depletion use antioxidants added to non-biological media (e.g., dithiothreitol, AA, and GSH). In vitro cellular assays determine ROS components in living cells (e.g., macrophages) directly exposed to PM samples by fluorescent probes.