Analysis of long-term average pollination periods of birch and cereal grass

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Introduction

Pollinosis is one of the most common allergic diseases, with prevalence in Russia ranging from 12.7% to 24.3%, and in some regions, up to 38.1% [1], confirming the medical relevance of pollen allergy. Birch pollen grains are the main cause of pollinosis in central Russia [2]. Their very high concentration at the beginning of the pollen season causes sudden allergic symptoms in people sensitive to this allergen [3]. Fluctuations in the concentration of pollen grains in the air significantly affect the symptoms of allergy sufferers, which is why aeropallinological monitoring is so important. The medical literature does not clearly define a clinically significant and scientifically substantiated threshold for exposure to pollen allergens (the minimum number of airborne pollen grains sufficient to trigger an allergic reaction) [4–6]. According to O. Pfaar et al. (2011), the threshold for the effect of pollen grains on symptoms in people with allergies can vary widely [7]. The study by D. Caillaud et al. (2014) showed that thresholds for the effect of pollen allergens are usually in the relatively low range of measured concentrations between 0and 100 pollen grains per cubic meter (p.g./m³) of air [8]. It was found that at a concentration of more than 30 p.g./m³ per day, the first symptoms may already appear in individual patients, and at a value of more than 80 p.g./m³ of air per day, 90% of those suffering from hay fever have clinical manifestations [9].

Various researchers [7; 10] have developed various methods for describing the duration of the pollen season and determining the beginning and end of pollen periods. A task force of experts from the European Academy of Allergy & Clinical Immunology (EAACI), consisting of both aerobiologists and physicians, in the EAACI position paper [11] provided recommendations for calculating the characteristics of the pollen season for the most allergenic plants (birch, cereal grasses, cypress, olive, ragweed), developed for the application of unified approaches in analyzing the results of the effectiveness of allergen-specific therapy (ASIT). ASIT is the only pathogenetic treatment method that modifies the immune response to a causative allergen [12]. It is the high significance of the ASIT method that served as the basis for standardizing approaches to assessing its effectiveness in patients with pollinosis, taking into account the actual characteristics of the pollen spectrum. In the study by O. Pfaar et al. (2020), the pollen season calculated using the new evaluation criteria corresponded well to the dynamics of changes in specific symptoms of pollen allergy to birch (to a greater extent) and cereals [13].

In the central part of Russia, birch pollen grains dominate the pollen spectrum of trees [14; 15] and are one of the most significant allergens of the pollen group [16]. Cereal grasses are among the leading families of the flora of Russia and individual regions, and their pollen has pronounced allergenic activity [17]. Therefore, the interest of researchers in the characteristics of the season of allergenic pollen release has practical and scientific significance.

The aim of the study is to analyze the average long-term values ​​of the pollination periods of birch and cereal grasses.

Materials and Methods

Aeropallinological monitoring was carried out annually from April 1 to September 30 from 2010 to 2019 and in 2023 (from 2020 to 2022 it was not carried out for technical reasons) using volumetric Burkard and Lanzoni pollen traps installed at a height of about 20 m. The operating principle of the pollen traps is based on the forced supply of 14.4 m³/day of air volume. The pollen trap's collecting surface is made of transparent, non-adhesive tape coated with a mixture that promotes the settling of pollen grains and other airborne particles. Each specimen was examined using an OLYMPUS BX 51 light microscope with a DP51 imaging system and CELL B software. To identify the pollen grains, atlases, palynological manuals, and materials from the international palynological database (Pollen Databases) were used. The pollen grain concentration was recorded as the number of p.g./m³ of air per day.

The seasons of birch and grass pollen release were described using two methods. In one case (method I), the main pollen period (MPP) was determined by the time interval during which the pollen grain content in the atmosphere was 98% of the total annual amount of pollen grains of this species (MPP 98): the start date of the season was determined when the total amount of birch pollen grains reached 1%, and the end date was determined when 99% of the total annual concentration of pollen grains was reached [18]. In another case (method II), when determining the pollination season (PS) using the EAACI method, the start of the PS for birch was considered to be the first day of a series of five days (out of seven consecutive days) in which the pollen grain concentration was at least 10p.g./m³, and the total pollen grain concentration for these 5 days was at least 100 p.g./m³, the end date of the birch PS was the last day of a series of 5 days (out of 7 consecutive days) with a pollen grain concentration of at least 10p.g./m³ and a total concentration for these 5 days of at least 100 p.g./m³. For the grass pollen season, according to the EAACI methodology, the start date of the PS was determined as the first day of a series of five days (out of seven consecutive days) in which the pollen concentration was at least 3 p.g./m³, and the total pollen grain concentration for these 5 days was at least 30 p.g./m³, the end date of the PS was the last day of a series of 5 days (out of 7consecutive days) with a pollen grain concentration of at least 3 p.g./m³ and a total concentration for these 5 days of at least 30p.g./m³ [11].

For descriptive statistics, the median (Me) and interquartile range [25Q; 75Q] were used. Differences between median values were determined using the Mann–Whitney U test. Statistical processing of the obtained data was performed using Microsoft Excel® 2016 and Statistica 6software.

Results and Discussion

Analysis of overall pollen productivity showed that the total concentration of birch pollen grains during the observation period ranged from 1,057 to 37,541 p.g./m³. The years with the highest productivity (more than 30,000 p.g./m³) were 2014, 2016, and 2019, while the years with the lowest productivity (less than 10,000 p.g./m³) were 2012, 2013, 2017, 2018, and 2023 (Table 1).

 

Table 1. Main characteristics of birch pollen seasons

Year of observation	Total pollen grain concentration per year, p.g./m3	Method I (MPP 98)			Method II (PS)
		Beginning *	End*	Duration, days	Beginning *	End*	Duration, days
2010	19478	114	141	27	110	142	32
2011	19764	119	141	22	117	147	30
2012	4483	107	188	81	112	143	31
2013	1057	107	126	19	119	127	8
2014	37541	122	149	27	119	155	36
2015	20314	120	142	22	119	143	24
2016	37487	113	150	37	106	154	48
2017	3024	122	162	40	122	162	40
2018	5784	119	169	50	136	142	6
2019	32094	121	152	31	120	152	32
2020	-	-	-	-	-	-	-
2021	-	-	-	-	-	-	-
2022	-	-	-	-	-	-	-
2023	2688	114	177	63	114	136	22
Me [25Q; 75Q]	19478 [3024; 32094]	119 [113; 121]	150 [141; 169]	31 [22; 50]	119 [112; 120]	143 [142; 154]	31 [22; 36]

Note: * – day from January 1.

 

The median values for the start of birch pollen season in different years fell in the third ten days of April to the first ten days of May, and the end of the season fell in the third ten days of May or the first ten days of June. In 2023, the birch pollen season lasted 22 days, beginning in the third decade of April (April24) and ending in the second decade of May (May 16), calculated using method II. However, the duration of the main pollen period, calculated using method I, was 63 days due to low pollen grain counts at the end of pollination. No statistically significant differences were found between the characteristics of birch pollen seasons calculated using methods I and II: date of pollen season start (p = 0.9), date of pollen season end (p = 0.88), pollen season duration (p = 0.82).

The total concentration of cereal pollen during the observation period ranged from 50 to 2147 p.g./m³. The years with the highest productivity (over 1000 p.g./m³) were 2012 and 2015, and those with the lowest (less than 500 p.g./m³) were 2010, 2013, 2014, 2016, and 2023 (Table 2).

 

Table 2. Main characteristics of cereals pollen seasons

Year of observation	Total pollen grain concentration per year, p.g./m3	Method I (MPP 98)			Method II (PS)
		Beginning*	End*	Duration, days	Beginning*	End*	Duration, days
2010	446	157	215	58	171	202	31
2011	861	162	234	72	167	235	68
2012	1100	153	239	86	162	199	37
2013	180	183	229	46	183	194	11
2014	391	152	236	84	165	197	32
2015	2147	152	214	62	152	201	49
2016	238	140	191	51	155	186	31
2017	766	160	226	66	169	202	33
2018	916	169	235	66	169	211	42
2019	522	162	235	73	143	235	92
2020	-	-	-	-	-	-	-
2021	-	-	-	-	-	-	-
2022	-	-	-	-	-	-	-
2023	50	157	201	44	-	-	-
Me [25Q; 75Q]	522 [238; 916]	158 [152; 162]	231,5 [215; 235]	66 [58; 73]	166 [155; 169]	201 [197; 211]	35 [31; 49]

Note: * – day from January 1.

 

The median values for the start of cereal pollination fell in the first to second ten days of June, and the end of pollination in the second to third ten days of July, when calculated using method II.

We have established statistically significant differences between the duration of pollination when calculating with methods I and II: the period of pollination of cereals according to method I is longer (p = 0.01), reaching the second ten days of August, since the days of the end of pollination for the observed period were recorded later (р=0.02).

In 2023, the cereal pollination period lasted 44 days (calculated using Method I), beginning in the first ten days of June (June 6) and ending in the second ten days of July (July 20). Cereal pollen counting using Method II was not possible due to low pollen concentrations.

Pollen characteristics provide important information for patients with pollen allergies, helping them assess the risk of exacerbation, determine treatment strategies for pollen allergies, and evaluate their effectiveness. Pollinosis symptoms in patients can depend not only on the intensity and effectiveness of treatment, but also on seasonal pollen characteristics, given significant inter-seasonal differences. The intensity of the birch pollen season varies significantly from year to year, and differences between successive years can be very significant. The intensity of the birch pollen season varies significantly from year to year, and the differences between successive years can be very high [19]. The birch pollen intensity recorded by us in terms of the total concentration of pollen grains per season in 2013 and 2014 differed by 35times (see Table 1). Inter-seasonal differences in seasonal cereal pollination productivity were less pronounced and did not exceed 9-fold differences over two consecutive years, as in 2015 and 2016 (see Table 2).

According to pollen monitoring data in Perm, the birch pollen count significantly exceeds that of other species. The MPP 98 method was previously used to characterize birch pollen production [20]. Applying the new pollen season characterization method recommended by EAACI (2017) yields comparable results, albeit with some differences. For example, in our study, it was not possible to calculate the duration of cereals pollen season for 2023 using the EAACI methodology due to extremely low seasonal pollen productivity values ​​(see Table 2). It should be noted that seasonal productivity values ​​for that year were the lowest for the given observation period.

Conclusions

Thus, high inter-seasonal variability in the total concentration of pollen grains of allergenic plants was established. The birch pollen intensity during the 2013 and 2014 seasons varied by 35 times, while that of cereals in 2015 and 2016 varied by 9 times. The onset, end, and duration of the birch and cereals pollen seasons are described in accordance with current international recommendations. It is important for physicians to consider the inter-seasonal variability of tree and cereals pollen seasons, as the type of pollen may impact the patient’s diagnosis and treatment.

Funding. The study had no external funding.

Conflict of interest. The authors declare no conflict of interest.

Author contributions:

Devyatkova E.A., Minaeva N.V., Novoselova L.V., Bankovskaya L.A., Devyatkova G.I. – research concept.

Devyatkova E.A. – literature review.

Novoselova L.V. – collection of materials.

Devyatkova E.A. – statistical processing of materials.

Devyatkova E.A., Minaeva N.V., Tarasova M.V., Devyatkova G.I. – analysis of the data obtained.

Devyatkova E.A., Minaeva N.V. – preparation and writing of the article.

Novoselova L.V., Bankovskaya L.A., Tarasova M.V., Devyatkova G.I. – editing of the article.

All authors reviewed the results of the work and approved the final version of the article.

Study limitations. The study complies with the standards of the Declaration of Helsinki and has been approved by the Ethics Committee of the Ye.A. Vagner Perm State Medical University, protocol No. 7 dated September 22, 2025.

About the authors

E. A. Devyatkova

Ye.A. Vagner Perm State Medical University

Author for correspondence.
Email: lizadev94@gmail.com
ORCID iD: 0000-0003-4754-2862

Lecturer of the Department of Public Health and Healthcare with a Course in Healthcare Informatization

Russian Federation, Perm

N. V. Minaeva

Ye.A. Vagner Perm State Medical University

Email: lizadev94@gmail.com
ORCID iD: 0000-0002-2573-9173

DSc (Medicine), Professor, Head of the Department of Pediatrics with a Course in Outpatient Pediatrics

Russian Federation, Perm

L. V. Novoselova

Perm State National Research University

Email: lizadev94@gmail.com
ORCID iD: 0000-0001-9470-4065

DSc (Biology), Professor of the Department of Botany and Plant Genetics

Russian Federation, Perm

L. A. Bankovskaya

Ye.A. Vagner Perm State Medical University

Email: lizadev94@gmail.com
ORCID iD: 0000-0003-4267-8031

DSc (Medicine), Professor, Head of the Department of Public Health and Healthcare with a Course in Healthcare Informatization

Russian Federation, Perm

M. V. Tarasova

Perm Regional Clinical Hospital

Email: lizadev94@gmail.com
ORCID iD: 0000-0002-5237-9863

PhD (Medicine), Head of the Department of Allergology and Immunology

Russian Federation, Perm

G. I. Devyatkova

Ye.A. Vagner Perm State Medical University

Email: lizadev94@gmail.com
ORCID iD: 0000-0002-2318-9390

DSc (Medicine), Professor of the Department of Public Health and Healthcare with a Course in Healthcare Informatization

Russian Federation, Perm

References

Supplementary files