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Methods for Aeroallergen Sampling Estelle Levetin, Phd

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Methods for Aeroallergen Sampling Estelle Levetin, Phd Methods for Aeroallergen Sampling Estelle Levetin, PhD Address for all applications. In addition, no standard protocols are Faculty of Biological Science, The University of Tulsa, available for many investigations. In this review, we describe 600 S. College, Tulsa, OK 74104, USA. several widely used samplers along with some new instru- E-mail: [email protected] ments and the analytical techniques used to study aeroaller- Current Allergy and Asthma Reports 2004, 4:376–383 gens in both outdoor and indoor environments. Current Science Inc. ISSN 1529-7322 Copyright © 2004 by Current Science Inc. Principal Collection Methods Air sampling provides information about the bioaerosol Airborne particles can be collected passively by gravity as composition of the atmosphere. Principal methods of well as with specific instruments that actively sample the volumetric sample collection include impaction, impingement, atmosphere through impaction, impingement, filtration, or and filtration. Many instruments have been developed based other methods that provide volumetric samples [2,6,7•,8– on these collection methods. The most widely used devices 11]. The simplest, least expensive, but least accurate method are slit impactors, rotating arm impactors, and sieve of collecting airborne biological samples is through the use impactors. Samples can be analyzed by various methods, with of gravity. This method often consists of exposing a coated microscopy and culturing the most important approaches; microscope slide or open Petri dish containing agar (often however, immunoassays, molecular methods such as called a settle plate) to the outdoor atmosphere or indoor polymerase chain reaction, and other new techniques are air for a set period of time. Gravity sampling is nonquantita- becoming more widely used to analyze samples. tive for atmospheric concentrations of aeroallergens and is affected by particle size and shape and also by air move- ment. Gravity samples are biased toward larger and, there- Introduction fore, heavier pollen and spore types. Consequently, small Air sampling has been used since the 19th century to examine pollen, such as Morus and Urtica, and small spores, such as the bioaerosol composition of the atmosphere. The early his- Penicillium and Aspergillus, will be underrepresented in the tory of aerobiology and the development of air samplers have sample, although these four taxa are important allergens. been thoroughly reviewed in several publications [1–5]. Aero- This bias is well recognized, and gravity sampling is not rec- biological data have been used by physicians as well as scien- ommended. Nevertheless, a mold test kit using a settle plate tists in many disciplines. Allergists have used aeroallergen is sold commercially at home-improvement stores around information to aid in the diagnosis and treatment of patients the country. In addition, similar services are offered on the and to determine pollen calendars for their geographic areas. Internet by dozens of vendors. The air sampling data have also been used in the medical The most widely used instruments for air sampling are community to determine the effects of allergen exposure on impaction samplers. These samplers separate particles from patient symptoms and to evaluate clinical trials. Plant pathol- the air stream by using the inertia of the particles; this causes ogists utilize air sampling to study the dispersal of agricultur- deposition of the particles onto a solid or agar surface as the ally important pathogens, and epidemiologists study human air stream bends to bypass the surface. The deflection of the or animal pathogens. Air sampling is used to monitor the air stream is achieved in both suction impactors and rotat- spread of genetically engineered microbes and pollen from ing arm impactors. A wide variety of impaction samplers are genetically engineered crops in the natural environment. available for both outdoor and indoor sampling, including Paleoecologists, geologists, and archeologists use air sampling slit samplers for total spores and pollen, rotating arm impac- to understand the relationship between modern pollen depo- tors for total spores and pollen, and sieve samplers for cul- sition and modern plant communities as a guide to interpret- turable fungi (Table 1). Several of these are discussed in ing former plant communities using fossil pollen records. detail later. Analysis of the samples is generally done by Recently, mycologists, industrial hygienists, and other indoor microscopy or culturing. investigators have used air sampling data to evaluate exposure Like impactors, impingement samplers separate particles where indoor fungal amplification is evident or suspect. from the air stream using inertia; however, the particles are A wide variety of sampling devices are in use today, and deposited into a liquid collecting medium. Air is drawn in new methods and instruments are continually being devel- by a vacuum pump and bubbles through water or a dilute oped. No single method is appropriate for all bioaerosols or buffer. Particles from the air stream are dispersed into the Methods for Aeroallergen Sampling • Levetin 377 Table 1. Characteristics of commonly used impaction samplers Collection d50 method Sampler (µm) Comments Slit impaction Burkard spore traps (Burkard 3.7 One-day and 7-day sampling heads available. Manufacturing, Ltd, Rickmansworth, UK) Collects pollen and total spores. Lanzoni VPPS 2000 Wind oriented and allows time- (Lanzoni, S.r.L., Bologna, Italy) discriminate sampling. Kraemer-Collins sampler (G R Electric, Manhattan , KS) Burkard continuous recording sampler 5 Allows for time discrimination. Not wind (Burkard Manufacturing, Ltd, oriented, so more suitable for indoor use. Rickmansworth, UK) Allergenco MK-3 (Environmental 2 Not wind oriented, so more suitable for Monitoring Systems, Charleston, SC) indoor use. Programmable sampling and small particle efficiency. Burkard personal sampler 2.5 Single-grab sample for total spores and pollen. (Burkard Manufacturing, Ltd, Battery operated. Rickmansworth, UK) Air-O-Cell cassette 2.6 Single-grab sample for total spores and pollen. (Zefon, St. Petersburg, FL) Easy to sample and analyze. Cyclex-d (Environmental Monitoring 2 Single-grab sample for total spores and pollen. Systems, Charleston, SC) Rotating-arm Rotorod sampler (Sampling Technologies/ 10 Independent of wind speed and direction. impaction Multidata, St. Louis Park, MN) Easy to use and efficient for pollen sampling. Culture plate Andersen 6 stage 7.0 for Sieve impactor. Only for culturable fungi able to impaction (Thermo Andersen, Franklin, MA) stage 1 grow on medium used. Biocassette sampler is Andersen 2 stage to disposable N-6 sampler. (Thermo Andersen, Franklin, MA) 0.65 for Andersen 1 stage (N-6) stage 6 (Thermo Andersen, Franklin, MA) Aerotech 6 (Aerotech Laboratories, Phoenix, AZ) Biocassette (Environmental Microbiology Labs, San Bruno, CA) Burkard sampler for agar plates (Burkard 4 Sieve impactor. Only for culturable fungi able to Manufacturing, Rickmansworth, UK) grow on the medium used. Battery operated. SAS (Biotest Diagnostic Corp, 1.5 to 2.0 Sieve impactor. Only for culturable fungi able to Denville, NJ) grow on medium used. Biotest RCS (Bioscience International, 7.5 Centrifugal sampler with collection onto agar Rockville, MD) strips. Only for culturable fungi able to grow on medium used. collecting fluid. Because the liquid will evaporate during trapped and the type of analysis desired. Collection efficiency is prolonged sampling, and thus reduce sampling efficiency, generally high but depends on filter pore size and flow rate. most impingement samplers, such as the AGI-30, are only Also, loss of viability may occur during sampling due to dehy- useful for short sampling periods of 1 hour or less [12]. dration [7•]. Like impingement samples, several analytical However, the BioSampler (SKC, Eighty Four, PA) permits methods can be used for samples collected by filtration. sampling for longer periods into nonevaporating fluids. Other collection methods include electrostatic precipita- Samples collected by impingers can be analyzed by a variety tion, thermal precipitation, and cyclone sampling [10], of methods, including microscopy, culture, biochemistry, although these are not widely used compared with the meth- immunochemistry, and molecular biology. ods previously described. In electrostatic precipitators or ion- Filtration separates particles from the air stream by trapping izers, particles are first charged and then attracted to an them in a fibrous or porous substrate. Filtration samplers range opposite charge on a collector plate in the sampler. This from small, personal-cassette samplers worn by individuals to device is best suited for small particles. In a recent study, an determine personal exposure to large, high-volume samplers ionizer was used for monitoring Fel d 1 cat allergen in homes that can process thousands of liters of air per hour [9]. Most and daycare centers [13]. The drawback pointed out by the applications use disposable plastic cassettes that hold filters authors of this study was the inability to quantify the amount from 25 to 47 mm in diameter. A wide range of filter material is of allergen per volume of air; results were expressed as aller- available for use, depending on the type of bioaerosol to be gen collected per 24 hours. 378 Allergens Sampler Performance the 7-day lid, a metal drum is mounted on a clock attached Sampler efficiency is based on the ability to capture the
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