Human Exposure to Pollutants via Dermal Absorption and Inhalation

One of the most important environmental concerns of today is the negative impact of pollution on human health. The air we breathe and the water we drink are essential ingredients for a healthy life. Unfortunately polluted water and air are common throughout the world. Over a day a healthy adult will consume between 2 and 3 l of fluid and inhale around 11 m³ of air. While exposure to pollutants in air is via inhalation that for water may occur via the ingestion, dermal absorption and inhalation routes. In this chapter we review the sources and concentrations of various air pollutants before considering drinking water quality. For the latter we concentrate on the potentially harmful disinfection by-products.

Population exposure to various air pollutants is likely to be higher in the indoor micro-environment than outdoors due to the amount of time people spend there. Consequently, indoor air quality has drawn considerable attention in recent years. There are noticeable differences in the types and strength of air pollution sources across the globe and they are closely linked to socio-economic developments. Typically higher indoor concentrations occur in developing rather than developed countries. The types, concentration, and sources of indoor air pollutants vary considerably from one micro-environment to another. Hence, an understanding of the concentration of pollutants in different micro-environments is of great importance for improving exposure estimates and, in turn, for developing efficient control strategies to reduce human exposure and health risk.

Chemistry takes place all around us, regulating the intensity and nature of our exposure to pollutants in water, air and soil. In indoor environments, chemistry can significantly alter the composition of the air we breathe. Transformations reduce our exposure to reactants and increase our exposure to products. If this reaction takes place on or in a surface, the relative exposure depends on the nature of the species; exposure to reactants and products may depend not only on rates and mechanisms but also on volatility.

Human exposure to air pollutants is ubiquitous. Once a pollutant has been discharged into or has been formed in the air, exposure to this pollutant can hardly be avoided as people have to breathe continuously. Because people move, commute, and frequently change their positions, they can be exposed daily to various kinds and mixtures of gases and airborne particles. In addition to the diversity of the environments where exposure may occur, the many different activities and the potential number of chemicals present all pose a challenge in investigating the health risks posed by air pollutants. Not only do the daily activities and social behaviour of modern humans vary substantially. Air chemistry (species, ions, elements, mixtures), physics (temperature, pressure, radiation) and biology (fungal spores, viruses, bacteria, mites) all change in space and time as well. The air also changes dynamically in connection with differences in the meteorological, microclimatic, and other environmental characteristics.

Although air quality in large cities and industrial areas of Western Europe was deteriorating since the beginning of the industrial revolution in nineteenth century, it was not until the first half of the twentieth century that the adverse health effects of air pollution started attracting scientific attention. Two widely quoted air pollution episodes, the Great London Smog of 1952 and the Meuse Valley (Belgium) episode of 1930, raised public awareness of the potential health effects of air pollution. The London Smog, attributed to the widespread use of coal for domestic heating in London and the stagnant atmospheric conditions prevailing in the capital in December 1952, caused approximately 4,000 premature deaths in a period of around 1 week (representing a 200–300% increase in mortality), with mortality remaining above normal levels for several months after the smog episode. Although air quality has improved a lot since the 1950s due to cleaner fuels, better industrial processes and control technologies, road traffic has emerged as the dominant source of air pollution in developed countries. In December 1991, another winter smog episode induced by similar weather conditions as in 1952 occurred in London causing a 10–25% increase in mortality. In this event, road transport and to a lesser extent domestic heating were the main sources of air pollution. In this Chapter, the health effects of a wide range of outdoor and indoor air pollutants are reviewed based on current toxicological and epidemiological evidence.

The estimation of deposition of inhaled aerosol particles in the respiratory tract during breathing is of importance in environmental health and occupational hygiene assessments. Respiratory deposition and subsequent clearance of the deposited amounts determine the effective doses delivered to the lungs. Realistic inhalation dosimetry modeling provides valuable information on the complete exposure-dose-response relationship, as required in environmental pollutant health effects analyses.

The focus of this chapter is on modeling the absorption of chemical pollutants into and across human skin. The skin is a primary route of systemic exposure to a number of environmental pollutants either directly as neat chemicals, in aqueous solution when exposure is to polluted water, or in complex solvents when exposure occurs secondary to contact at industrial waste sites. These differences in exposure modalities may significantly modulate the extent of dermal absorption seen and thus should be factored into any risk assessment.

“Indoor air quality” is a wide subject with different social, economic, and health aspects. In developed countries, people spend more than 80% of their time indoors where they are exposed to many kinds of air pollutants either from outdoor origin or produced indoors. An air pollutant can be a gas or an aerosol particle (solid, liquid, radioactive, bio-aerosols, etc.). Indoor air pollutants are transported from the outdoor air by means of mechanical ventilation systems or across the building shell as a result of natural ventilation. In many aspects, the indoor-to-outdoor relationship of air pollutants, as well as, the dynamic behavior of air pollutants can be addressed and investigated by means of mathematical models. However, the accuracy of such mathematical models depends on many factors including, most importantly, the confidence in the input parameters, validity of the assumptions, description of the processes, and user influence.

Atmospheric pollution occurs on different spatial and temporal scales. On the macro scale, global problems of importance are the depletion of the stratospheric ozone layer and global warming, which is caused by the emission and accumulation of greenhouse gases in the atmosphere. On a regional scale, the transboundary transport of pollutants can be responsible for acid deposition or the formation of photochemical smog. Air quality on a local and urban scale is closely related to emissions arising from almost all human activities, and to local characteristics such as topography, climate and also economy. Aspects of air quality investigated on a micro-scale include studies on emissions from a single point source, indoor pollution from oil or wood burning stoves, or the dispersion of pollutants in a street canyon.