Characterization of Biological Particulate Loads in Metropolitan Air
نویسندگان
چکیده
-The atmospheric particulate load includes a wide range of naturally occurring particles of biological origin that serve as a reservoir of allergenic agents in respiratory disease. Improved knowledge of potential aeroallergens is needed by medical clinicians. Aims are to better characterize air spora, qualitatively and quantitatively, and determine daily (by hour) periodicities of occurrence and prevalence of different kinds of spores, and seasonal variations. Main emphasis is on fungus spores about which least is known though they occur in considerable numbers. Efficient volumetric samplers provide time-related deposits of air spora at three sites in Pennsylvania. I NCLUDED IN T H E ATMOSPHERIC load of particulates is a wide range of naturally occurring particles of biological origin, such as microorganisms, pollens and other plant spores, fragments of plants and insect parts, etc. This diverse a i r spora of natural origin also serves as a reservoir of allergenic agents in respiratory disease. Improved knowledge of potential aeroallergens is much needed by medical clinicians. Characterization of airborne biological particulates is the first phase of a study of aeroallergens being carried out a t the Center for Air Environment Studies a t The Pennsylvania State University. Aeroallergens a re defined as substances encountered in the a i r which can incite allergic responses. Generally, these a re inhalant allergens, and the major responses are allergic rhinitis, including seasonal hay fever, and bronchial asthma. Primary aims of this phase of the project are to apply modern techniques of a i r spora study to : (1) characterize qualitatively the potential aeroallergens, mainly fungus spores and pollens, of major regions of Pennsylvania; (2) to provide quantitative volumetric data on a i r spora; and (3) to determine circadian (daily, time-related) and seasonal periodicity of occurrence and prevalence of different kinds of spores. We also a re beginning to relate spore data to appropriate meteorological variables where possible. The econornic impact of aeroallergens can be assessed in only general terms. Of the United States population, about 15 percent may be sensitized easily to many allergenic materials and another 25-30 percent a re considered somewhat sensitive (Kern 1962). Approximately 15 million persons in the U.S. suffer effects of hay fever and/or asthma. More than $70 million are spent on prescription medications related to allergic response each year. About 25 million work days a re lost per year due to hay fever. Further, lowered work efficiency due to symptoms and sedative effects of some medications is probable. Allergic rhinitis also often increases susceptibility to infections of the respiratory tract. Asthma incidence leads to an estimated $260 million a year in resource costs, including premature deaths, medical treatments and absenteeism (Finkelstein 1969). Almost any organic material, from plant or animal sources, may be a potential allergen. Among the more common known aeroallergens are pollens, fungus spores, danders (animal hairs, feathers, flakes of epidermis, etc.) ; house dust (heterogenous mixture) ; insect parts ; algae ; certain cosmetics ; and products containing linseed oil, organic solvents, etc. The two most important groups of naturally occurring aeroallergens are the pollens and fungus spores. Pollens a re usually considered to cause the most problems, and ragweed is believed to account for some 90 percent of pollenosis in the U.S. (Hewson 1967). POLLENS IN THE ATMOSPHERE Pollens are produced in great numbers throughout the world. Of the approximately 100,000 known species of flowering plants, about 10 percent are adapted to wind pollination (Gregory 1973). Most pollen grains range in size from 15 to 50 pm, and most species have distinctive features and characteristic size. Gravitational fall rates range from about 1 to 10 cm/sec. In general in the temperature zone, the tree-pollen season is in the spring, the grass season from late spring through summer, and the weed season mostly in late summer and fall. There are of course variations and overlappings depending on species and climate as well as more local meteorological conditions. The members of the ragweed group (Ambrosia sp.) are prolific pollen producers, and the pollen grains are exceptionally well suited to aerial dissemination. The plants may grow in abundance where soil and cover vegetation have been disturbed as in housing developments, along highways, railroads, etc., as well as on agricultural land. Millions of acres in the U.S. are infested by ragweeds to some extent. Surveys have revealed as many as 170,000 plants/acre (about 42/m2) in some fields when no cover crops were grown after winter cereal grains were harvested. About 56,000 plants/acre ( l l /m2) were found in a subdivision area under construction (Hewson 1967). An estimated 50 pounds (22 kg) of pollen could be produced by an acre of giant ragweed plants in a season (Finkelstein 1969) ; a t 200 million grains/gram of pollen, this means 4.5 x 1012 pollen grains could be produced per acre over an 8-week pollen production period. About 5 to 10 percent of the pollen can be expected to become airborne. The distance traveled depends on many factors, and i t should be noted that airborne particles are being deposited continuously on surfaces near the ground. Despite deposition, the proportion escaping to be transported some distance from the source places considerable numbers in the air to be dispersed over large areas. Concentrations of several hundred ragweed pollen grains/m3 of a i r are not uncommon over much of the central and eastern U.S. during the ragweed season each year (Hewson 1967). Peak concentrations over cities some distance from major sources may reach several hundred per m3 in some areas. Cities often have local sources of ragweed as well. The relationship of concentration of pollen in the a i r to production of symptoms is not well known. Individuals may differ greatly in their sensitivity to dosage. However, i t has been reported that as few as 100 pollen grains inhaled over a 1-hour period often caused symptoms, and in one individual as few as 30 incited hay fever (Connell 1968). Since the volume of air inhaled approximates 1 m3/hr for an adult engaged in light activity, i t is apparent that exposure levels commonly encountered could readily incite allergic responses in susceptible individuals. It is also known that being sensitized to one pollen or substance can increase sensitivity to certain other allergens (Connell 1969). Ragweed pollen fall rate in a i r due to gravity is about lcm/sec, thus convection currents can readily carry them aloft. Most ragweed pollen is released in the morning hours, but concentration peaks may occur also later in the day or a t night due to pollen descending from high altitudes. In general there is a decrease in concentration with height, though greater numbers may occur a t 1 or 2 km altitude than a t ground level, due to various atmospheric factors and source locations (Gregory 1973). FUNGI IN THE ATMOSPHERE Fungus spores, which are usually more prevalent in a i r than pollens (often >75 to 1) also can act as potent allergens (Hamilton 1959). Fungi grow on organic matter and some parasitize living plants, insects, and animals. Most spores occurring commonly in outside a i r originate from fungi growing on plant debris or on surfaces of living plants, trees, etc., rather than from soil as sometimes inferred. Air in buildings may in addition to spores from outside a i r also contain spores from moldy surfaces and mildewed materials within the building. Fungus spores are usually smaller than pollens. Most range in size from 3 to 30 pm (the size range of water droplets in clouds). Gravitational settling rates are 0.05-2 cm/sec, and thus most fungus spores become airborne and remain suspended longer than pollens. Viable fungi have been recovered a t altitudes of 17 miles (27 km), and over oceans thousands of miles from land as well as over the North Pole (Ingold
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