Environmental Health Impacts of Natural and Man-Made Chemicals

Humans have been exposed to naturally occurring toxic chemicals and materials over the course of their existence as a species. These materials include various metals, the metalloid arsenic, and atmospheric combustion particulates, as well as bacterial, fungal, algal, and plant toxins. They have also consumed plants that contain a host of phytochemicals, many of which are believed to be beneficial, such as plant polyphenols. People are exposed to these various substances from a number of sources. The pathways of exposure include air, water, groundwater, soil (including via plants grown in toxic soils), and various foods, such as vegetables, fruit, fungi, seafood and fish, eggs, wild birds, marine mammals, and farmed animals. An overview of the various health benefits, hazards and risks relating to the risks reveals the very wide variety of chemicals and materials that are present in the natural environment and can interact with human biology, to both its betterment and detriment. The major naturally occurring toxic materials that impact human health include metals, metalloids (e.g., arsenic), and airborne particulates. The Industrial Revolution is a major event that increased ecosystem degradation and the various types and duration of exposure to toxic materials. The explosions in new organic and organometallic products that were and still are produced over the past two centuries have introduced new toxicities and associated pathologies. The prevalence in the environment of harmful particulates from motor-vehicle exhaust emissions, road dust and tire dust, and other combustion processes must also be considered in the broader context of air pollution. Natural products, such as bacterial, fungal, algal, and plant toxins, can also have adverse effects on health. At the same time, plant-derived phytochemicals (i.e., polyphenols, terpenoids, urolithins, and phenolic acids, etc.) also have beneficial and potential beneficial effects, particularly with regard to their anti-inflammatory effects. Because inflammation is associated with most disease processes, phytochemicals that have antioxidant and anti-inflammatory properties are of great interest as potential nutraceuticals. These potentially beneficial compounds may help to combat various cancers; autoimmune conditions; neurodegenerative diseases, including dementias; and psychotic conditions, such as depression, and are also essential micronutrients that promote health and well-being. The cellular and molecular mechanisms in humans that phytochemicals modulate, or otherwise interact with, to improve human health are now known. In the early 21st century, some of the current pollution issues are legacy problems from past industrialization, such as mercury and persistent organic pollutants (POPs). These POPs include many organochlorine compounds (e.g., polychlorinated biphenyls, pesticides, polychlorinated and polybrominated dibenzo-dioxans and -furans), as well as polycyclic aromatic hydrocarbons (PAHs), nitro-PAHs, and others. The toxicity of chemical mixtures is still a largely unknown problem, particularly with regard to possible synergies. The continuing development of new organic chemicals and nanomaterials is an important environmental health issue; and the need for vigilance with respect to their possible health hazards is urgent. Nanomaterials, in particular, pose potential novel problems in the context of their chemical properties; humans have not previously been exposed to these types of materials, which may well be able to exploit gaps in our existing cellular protection mechanisms. Hopefully, future advances in knowledge emerging from combinatorial chemistry, molecular modeling, and predictive quantitative structure-activity relationships (QSARs), will enable improved identification of the potential toxic properties of novel industrial organic chemicals, pharmaceuticals, and nanomaterials before they are released into the natural environment, and thus prevent a repetition of past disastrous events.