Dear Colleagues,

Toxic inhalants can disrupt the respiratory and immune systems after exposure to the human body. Inhaled particles may have outdoor or indoor origins and both environments contain substances with potential harmful health effects.

Air pollutants comprise particulate matter (PM) and gases that derive from anthropogenic activities and natural events, whereas biological pollutants are made up of bacteria, virus, cell debris and several types of pollen and fungal spores, whose allergens can affect susceptible individuals.

When inhaled particles enter the respiratory tract, they reach different anatomical sites depending on, among other properties, their size. Pollen grains were found to be associated with PM, with these particles being efficient carriers of secondary allergens or proinflammatory compounds in lower airways. There is evidence that PM can diffuse into the systemic circulation via the blood–air barrier, reaching the heart, liver, spleen or brain. In the airways, pollutants will first interact with the bronchial epithelium, triggering both innate and adaptive immune responses. Secondly, innate immune players, such as the alveolar macrophages, can contribute to the clearance of particles via phagocytosis. Both pathways eventually lead to the induction of oxidative stress and inflammatory responses in the airways, causing damage to the lungs or even cancer.

The inhaled biological components present in PM may stimulate alveolar macrophages and respiratory epithelial tissue to release proinflammatory cytokines and chemokines. Additionally, the biological components may have synergetic effects on other components of the PM, such as diesel exhaust, enhancing IgE production and thus facilitating allergic sensitization. In addition, clinically relevant microbial allergens (e.g., endotoxins) can enrich the PM-borne components and trigger toxicological outcomes.

Large segments of the world’s population inhale many of the above-mentioned substances on a daily basis. Still, there is limited information regarding new inhaled toxicants that the human body can be exposed to, particularly under the current geoclimatic and social context. The human population is facing unprecedented invisible threats such as toxic gases and particles derived from natural sources (e.g., volcanic eruptions), conflict scenarios, migrations or even biological particles from invasive plants whose respiratory and immunological effects are not well-known. On the other hand, there are novel inhalable substances of technological origin of which toxicological effects in the respiratory and immune systems are unreported yet. The ability of emerging chemical pollutants to have harmful effects on human health and the environment is becoming evident, specially by the increasing trade of chemical products at a global scale.

The purpose of this Special Issue of Toxics is to increase the insight on underexplored air pollutants that are affecting human heath, either in indoor or outdoor environments.

We are pleased to invite you to submit original research articles, reviews, and short communications that focus on single or complex air pollutants, of natural or anthropogenic origins and their impact on respiratory and immune systems. The articles may span from molecular to epidemiological aspects of the main theme and propose exposure threshold limits for health surveillance purposes.

Research areas related to novel air pollutants may include (but are not limited to) the following:

• Exposome
• Susceptibility profiles
• Mechanisms of toxic action
• In vivo, in vitro and in silico studies
• Field and laboratory approaches
• Emerging toxicity models
• Health impact assessments
• Short- and long-term effects
• Biomarkers of exposure/effects
• Preventive/mitigation strategies for air pollutants exposure

I look forward to receiving your contributions,

Dr. Irene Gomes Câmara Camacho
Guest Editor

Manuscript Submission Information

Manuscripts should be submitted online at www.mdpi.com by registering and logging in to this website. Once you are registered, click here to go to the submission form. Manuscripts can be submitted until the deadline. All submissions that pass pre-check are peer-reviewed. Accepted papers will be published continuously in the journal (as soon as accepted) and will be listed together on the special issue website. Research articles, review articles as well as short communications are invited. For planned papers, a title and short abstract (about 100 words) can be sent to the Editorial Office for announcement on this website.

Submitted manuscripts should not have been published previously, nor be under consideration for publication elsewhere (except conference proceedings papers). All manuscripts are thoroughly refereed through a single-blind peer-review process. A guide for authors and other relevant information for submission of manuscripts is available on the Instructions for Authors page. Toxics is an international peer-reviewed open access monthly journal published by MDPI.

Please visit the Instructions for Authors page before submitting a manuscript. The Article Processing Charge (APC) for publication in this open access journal is 2600 CHF (Swiss Francs). Submitted papers should be well formatted and use good English. Authors may use MDPI's English editing service prior to publication or during author revisions.

• aerosols
• aeroallergens
• air pollution
• immune system
• public health
• respiratory system
• toxicology