Study Notes on Aeropalynology | Palynology

The below mentioned article provides a study note on aeropalynology.

Erdtman (1969) defines aeropalynology as the study of palynomorphs found in the atmosphere. The term palynomorph encompasses pollen grains, spores and other bioparticles that cannot be dissolved in hydrofluoric acid. Aeropalynology is a branch of palynology and related to the study of pollen and spores that are dispersed in the atmosphere. The study also includes their eventual dissemination, deposition and impact on human systems.

Pollen grains are dispersed more than 400 miles away from the source plants. They can be found more than two miles above the surface. The airborne pollen grains originate from anemophilous plants and so they are small, light, smooth walled, colourless, produced in large numbers, dry and lack nectar.

In other words they are custom made for wind transport. The first and foremost requirement in the study of airspora is to identify and detect the airborne palynomorphs and sporomorphs. A sound knowledge of ground flora is essential for this purpose. The study of ground flora of a particular area will reveal the genera and species present in that locality and their flowering season.

Pollen grains from each species are to be studied and the slides of them are to be deposited in herbarium for future references.

The airborne pollen are trapped for sampling by two major principles:

(1) Simple gravimetric method where pollen and spores are deposited by normal gravitational force on slides, and

(2) Suction method where the atmospheric air is sucked in with the help of instruments called sampler.

There are many types of sampler that can suck certain volume of air according to a known velocity for a definite time. Along with the air pollen and spore are sucked in and they get stuck either on a plastic band or sticky cello-tape (fitted according to sampler), which were previously placed there for the purpose of trapping pollen. Mention may be made of Burkard seven days sampler, Burkard personal slide sampler, Burkard petriplate sampler, Anderson sampler and Hirst spore trap.

The next task is to analyze the trapped grains. Analysis includes identification and quantification of sporomorph and palynomorphs. Microscopic identification is dependable in most cases. Certain fungal spores cannot be identified under the microscope. If the spores are culturable, they are isolated and cultured in cultural media. Colonies are formed and thus they are identified.

Pollen and spores are identified on the basis of sporoderm stratification, shape, size and apertural characters. The morphological characters of trapped pollen and spore are compared with those of ground flora and thus the airborne grains get identified. The frequency of the identified grains is also calculated.

Trapping, identification and quantification are carried out throughout the year and the results are recorded. The data help to prepare the pollen calendar of a particular locality. A pollen calendar reveals the name of plant species that release pollen and spore in particular month(s). It also reveals the approximate amount of grains released in that season.

The term ‘pollen count’ is frequently used to represent the concentration of pollen in atmosphere. It is a measure of how much amount of pollen and spore is present in the atmosphere in a particular area at specific time. The count may consist of a particular type of pollen or spore, or all the pollen grains and spores present in the air.

Pollen count is expressed as the number of pollen present in a cubic metre or other standard volume of air over a twenty-four hour period at a particular place. The samplers collect pollen grains.

A sampler has a drum or rod coated with silicone grease or sticky cello-tape. During trapping the rod/drum is rotated one turn only in an entire 24 hours of a day with the help of a motor fitted with the sampler. The trapped pollen grains are then analyzed for identification and quantification.

Anemophilous plants of local vegetation determine the frequency of airspora and so the pollen counts. Meteorological factors also influence the pollen count. The change in climatic condition has a profound effect on the concentration of air spora.

Pollen count increases in dry, warm and breezy days. It decreases in chilly with high humidity and rainy days. Moreover pollen count can be changed due to pollution, industrialization, population growth, tree plantings and cuttings, land use etc.

Singh et al. (2004) published a detailed list of airspora of the various parts of India along with their sources in literature. Chanda and Sarkar (1972) reported the existence of the following pollen at the atmosphere of greater Kolkata. The grass pollen contributed 39% to the total pollen present in air.

The dominant pollen types are from Amaranthns, Argemone, Azadirachta indica, Caesalpinia, Carica papaya, Chenopodium, Mangifera indica, Xanthium strumarium etc. In West Bengal 59 types of pollen in air were reported. In the month of May the concentration of pollen was maximum. The maximum concentration of pollen grains belonging to the family Asteraceae and Chenopodiaceae was found in the month of June.

Pollen grains have impact on human systems. The air, without which life cannot exist, contains an array of bioparticles among which pollen grains form one of the dominant concentrations. People inhale the free-floating pollen grains and spores without knowing them. Pollen enter and move through nasal passages to the throat. People, who are not sensitive to pollen, swallow or cough out the grains.

But different conditions arise in pollen sensitive individuals. These people manifest hypersensitive reactions that are called allergy, von Pirquet in 1906 introduced the term allergy. The term allergy is defined as “an altered or accelerated reaction of a person to a second or subsequent exposures to a substance, usually harmless to the general population, to which he/she has been sensitized during the first exposure” — Shivanna and Agarwal et al.

The sensitizing agents are known as allergens and it is defined as a substance to which a person is allergic (e.g. pollen and spores, food protein, house dust mites, furry animals etc.). Sometimes the term allergen is used as a synonym for antigen or immunogen. It is protein in nature.

The symptoms of pollen allergy are as follows: in case of asthma coughing, wheezing and difficulty in breathing due to narrowing of the bronchial passages and excess mucous production; in case of eczema rash and itchy skin; in case of hay fever also known as seasonal rhinitis sneezing accompanied by a runny or clogged nose, itching nose, throat and eye, persistent upward rubbing of nose by a child, conjunctivitis, watering eyes; the lips and mouth show symptoms in case of gastrointestinal allergy.

The upper tract respiratory allergy, naso-bronchial allergy and seasonal rhinitis are very common. The symptoms are manifested after respiratory tract infection. If asthma symptoms accompany the symptoms of hay fever, it indicates that the bronchial tubes have become involved indicating the need for immediate medical attention.

Hay fever or allergic rhinitis also called pollenosis (also spelt as pollinosis) is the best-known allergy of all. Ambrosia pollen grain is the dominant pollen type to cause allergic rhinitis and pollen asthma in North America. The allergy problems are caused by A. artemisiifolia and A. trifida although 21 species of Ambrosia occur in North America. Ambrosia pollen grain is also reported from the atmosphere of Tulsa, Oklahoma.

The other pollen types that cause hay fever throughout the world are Alnus, Betula, Chrysanthemum, Populus, and Salix etc. In India Singh et al. (2000) published a detailed list of allergenic species during spring, autumn and winter.

Mention may be made of grasses (Cynodon dactylon, Eragrostris tenella, Poa annua etc.), weeds (Cannabis sativa, Amaranthus spinosa, Chenopodium album, C. murale, Cassia occidentalis, Xanthium strumarium, Ricinus communis, Suaedafruticulosa etc.) and trees (Alnus nitida, Cedrus deodar a, Eucalyptus sp., Putranjiva roxburghii etc.).

Free-floating allergenic pollen grains enter in the human system through nostrils during inhalation. Most of them are swallowed and others are either coughed off or remain in the nose. Within a few minutes after entrance a chain of reactions occur that leads to the release of chemical mediator like histamine.

Histamine induces allergic symptoms in pollen sensitive individuals. When pollen and spore come in contact with the mucous membranes present in nose, respiratory tracts, stomach, oral cavity and eyes, the mucous secretion hydrates them. The mucous liquid helps to dissolve the pollen allergens.

The allergens then diffuse out of pollen and penetrate the mucous tissue. The mucous tissue contains mast cells that are present in the upper respiratory tract, intestinal tract, lungs and skin. The allergens induce the formation of antibodies. The antibodies are largely of Immunoglobulin E class or in short IgE.

It is glycoprotein in nature. The mast cells of allergic person have a high concentration of IgE. IgE occurs on the surface of mast cells. As more and more pollen allergens are released they bind and cross-link with specific IgE. Thus a complex is formed between antigen, e.g. pollen allergen and IgE antibody.

The antigen-antibody complex activates the enzyme that causes the release of chemical mediator like histamine. Histamine induces edema of the mucous membrane thus causing narrowing of nasal or bronchial passages, contraction of nasal or bronchial muscles, the dilation of blood capillaries, excess mucous production and secretion of watery nasal fluid, sneezing and itching.

People with hay fever may at first suspect that they have a summer cold. It is important to consult doctor if the allergic symptoms persist more than a week or two. Doctor will study the medical history of the patient. If it is noted that the symptoms recur at the same time each year, the doctor will proceed to diagnose the causative agent of allergy under the hypothesis that a seasonal allergen is involved.

Respiratory allergy is a seasonal and local problem. It is related to the appearance and the concentration of specific airborne allergens in that particular area. It is to correlate among the presence and abundance of airspora type, meteorological conditions and respiratory symptom incidence.

Blood and skin test are performed to detect the causative agents of respiratory allergy. Among the blood tests mention may be made of Enzyme Linked Immuno Sorbent Assay (ELISA), Paper Radio Immuno Sorbent Test (PRIST) and Radio Allergo Sorbent Test (RAST). These tests indicate the amount of IgE present in the serum of patients. Consult Shivanna (2003) and Bhattacharya et al. (2006) for details of these tests.

Although these tests offer advantages over skin test, they are time consuming, expensive and somewhat less sensitive. These tests become compulsory for those patients who have certain disorders in the skin. The skin test is most commonly employed as it is simple, convenient, and highly specific and less expensive.

To perform the test the antigenic extract of each type of pollen found in the local area of the patient is applied to a scratch made on the arm of patient or injected under the patients’ skin. In positive reaction at the test site of skin (scratch/prick) an elevated reddened area with a surrounding flush, called wheal appears. The size of the wheal provides the diagnostic clue.

Medication is the best treatment to relieve symptoms of allergy due to pollen and spore. Though antihistamine and corticosteroids are very effective in controlling allergic disorders, they have serious side effects after prolonged usage. Avoidance of allergen as a primary mode of therapy might give relief to some extent.

Avoidance includes the followings:

(1) Reduction in exposure to the particular species, in which a patient is allergic.

(2) Moving to a place where the allergenic plant does not grow. Allergy specialists strongly discourage this approach because patient may develop allergies to other plants.

(3) It is advisable to remain in indoors when the pollen count is highest especially in the early morning and late afternoon.

(4) To wear Face Mask, which is designed to filter pollen out of the air during inhalation.

(5) After returning from outdoors it is recommended to take bath and use fresh cloth.

(6) Use of air cleaners like air conditioners and air purifiers inside the rooms can reduce pollen level inside.

(7) To dry wet clothes in dryer instead of hanging outside, where pollen may get trapped on the wet clothes.

(8) Pollen grains generally settle down in the evening and so it is advisable to close all windows in the evening.

(9) To avoid planting the allergenic plants around house.

(10) The house compound must be free from weeds and grasses.

(11) To install Electronic/electrostatic precipitator.

Respiratory allergy is a very common disease among all populations all over the world. In India 20 to 30% of the population suffer from allergic rhinitis and 15% suffer from asthma. So it is necessary to develop a network of centres in various biozones of India to collect data of the dispersed palynomorphs and sporomorphs.

These centres will prepare pollen calendars from the collected data and broadcast the pollen count. This will be very useful for clinicians and as well as patients. The centres will also perform the clinical and immunological tests based on local allergens to local patients. In this respect some work has been done. Singh et al (1992) published the pollen calendars of 12 different states of India.

In conclusion it is to mention that aeropalynology comes under the purview of Aerobiology. Aerobiology includes the study of bioparticles present in the atmosphere in addition to pollen and spores. These bioparticles might affect human and animal health, crops etc. Aerobiology also includes the identification of bioparticles and their geographical origin.

The study of morphology, physiology, concentration, dispersion and seasonal patterns of bioparticles are also included in the study of aerobiology. In aerobiological research palynologists in collaboration with clinicians search the causative agents present in the atmosphere that have impact on human health.