Abstract

Exposure to airborne fungi is being proposed as a cause of adverse health effects. The study was undertaken to examine the concentrations of airborne fungal spores in eight suburban areas which are strategically located near industries in North Chennai, India. N - 6 Andersen single stage sampler was used to collect the air with Potato Dextrose Agar (PDA) at a flow rate of 25 l/min. A total of 25 species belonging to 13 genera of fungi were recorded. Total concentration of airborne fungi in each area ranged from 266.00 – 441.76 CFU/m³ of air. Major prevalent airborne fungi belong to Aspergillus and Penicillium. This study provides a useful index for relative risk exposure of airborne fungi in the suburban areas of North Chennai.

Keywords: Industry, Airborne fungi; Bioaerosol; Fungal spores

Introduction

Bioaerosols are natural or artificial particles of microbial, plant or animal origin suspended in air and may be called as organic dust. It includes live or dead bacteria, fungi, viruses, allergens, bacterial endotoxins (compounds of cell membranes of Gram - negative bacteria), antigens (molecules that can induce an immune response), toxins (toxins produced by microorganisms), mycotoxins (toxins produced by fungi), glucans (components of cell walls of many molds), pollen, plant fibers, etc. Microorganisms are frequently absorbed onto dust particles and transported along with the dust. Many bioaerosols are known to cause symptoms and/or illness, including a wide range of adverse health effects and infection. Individuals may become increasingly sensitized to some bioaerosols through repeated exposure.

Several epidemiological studies in several countries have indicated an association between human exposure to fungal spores in indoor air and adverse respiratory symptoms. More than 80 genus of fungi have been associated with symptoms of respiratory tract allergies (Horner et al., 1995). Cladosporium, Alternaria, Aspergillus and Fusarium are amongst the most common allergenic genera. Airborne fungi are among the most common organisms in nature. They were considered to be correlated with air pollution and were proposed as a cause of adverse health effects on humans, animals and plants (Shelton et al., 2002). It was reported that the dominant fungi were Cladosporium, Alternaria, Penicillium, and Aspergillus in the atmosphere (Adhikari et al., 2004).

Chennai, one of the major metropolitan cities in India, was chosen for the present study due to its dense population and industrialization. Emission of air pollutants and dust particles (including organic dust) from industries are continuous, and seems to affect the normal life style of the residents of nearby areas. However, no studies on airborne fungal molds in heavily industrialized part of Chennai city were performed so far. Therefore the objectives of this study were to reveal the distribution characteristics and nature of airborne fungal spores in such areas.

Materials and methods

Sampling site

Eight suburban areas in North Chennai viz; Thiruvottiyur, Manali, Andarkuppam, Manali New Town (NT) , Ernavur, Kathivakkam, Ennore, and Mathur were selected which are immediate surroundings of industries. The study was carried out from the period of January 2008 to July 2008. Almost 5 different sampling locations were selected randomly in each area.

Sampling method and Mold identification

N - 6 Andersen single stage sampler was used to isolate fungal molds from the open environment at a suction rate of 25 l/ min. Samples were collected for 3 minutes between 10.00 am to 12.00 pm. For each sampling the sampler was loaded with 9.0 cm petri dishes containing Sterile Potato Dextrose Agar (PDA) with streptomycin to inhibit bacterial growth. Exposed petri dishes were incubated for 72 h at 27 ± 2^oC. Few colonies did not generate spores even after incubation upto 7 days and were classified as “non-sporing colonies” group. After incubation, fungal colonies growing on each dish were counted and sub cultured for species identification. The number of colonies recorded is expressed as colony forming unit per cubic meter of air [CFU/m³] and calculated as follow.

  No. of Colonies  obtained
CFU/m³  =  ×1000
Sampling time  ×
Suction rate of the sampler

 

Isolation frequency of a fungi is denoted by the number of sampling in which a fungi is recorded against the total number of samplings. On the basis of percent isolation frequency the molds are grouped into Most common (>80 %), Common (60 - 80 %), Frequent (40 - 60 %), Occasional (20 - 40 %) and  Sporadic (< 20 %).

Results

Considering all sampling sites, concentration (Mean CFU/m³ of five locations in each area) of airborne fungi in 8 suburban areas are represented in Table 1. Higher fungal concentrations of 441.76 and 441.56 CFU/m³ were found in Thiruvottiyur and Mathur respectively. Minimal level of 266 CFU/m³ was recorded in Manali New town. The concentration of fungi in other areas ranges from 316 CFU/m³ to 423 CFU/m³. Concerning non-spore formers, the highest concentration of 29.26 CFU/m³ was observed in Thiruvottiyur, while in other areas it ranges from 2.66 CFU/m³ to 23.94 CFU/m³ except Mathur.

Fungal diversity

Thirteen genera, including 25 species of culturable fungi, were identified. The genus of Aspergillus with 9 species occupied more than 32 % of the total number of isolated fungal species. The genus of Penicillium only had five species and all other genera were represented by single species. A maximum number of eleven genera and 19 species were identified in the area of Mathur and a minimum of six genera and 12 species were identified in Manali New Town. The fungal species isolated from all the suburban areas and its isolation frequency are given in Table 1.

Table 1. Prevalence of airborne fungi (Mean CFU/m³)  in eight suburban  areas  of  North Chennai

S. No.	Species	Thiru-vottiyur	Manali	Andar-kuppam	Manali NT	Ernavur	Kathi-vakkam	Ennore	Mathur	Isolation Frequency
1	Rhizopus stolonifer	-	-	5.32	15.96	-	-	-	-	S
2	Syncephalastrum racemosum	-	5.32	-	-	2.66	2.66	-	2.66	S
3	Aspergillus flavipes	-	5.32	-	2.66	-	-	-	2.66	S
4	Aspergillus flavus	42.56	18.62	39.9	45.22	90.44	26.6	61.18	37.24	C
5	Aspergillus fumigatus	10.64	21.28	5.32	-	37.24	7.98	2.66	2.66	O
6	Aspergillus japonicus	101.08	26.6	29.26	26.6	45.22	77.14	53.2	82.46	C
7	Aspergillus nidulans	29.26	10.64	13.3	10.64	18.62	34.58	15.96	29.26	F
8	Aspergillus niger	117.24	135.66	125.02	114.39	82.46	82.46	77.14	103.74	MC
9	Aspergillus ochraceus	2.66	2.66	10.64	5.32	15.96	5.32	-	-	S
10	Aspergillus tamarii	21.28	7.98	13.3	2.66	13.3	-	18.62	21.28	O
11	Aspergillus terreus	7.98	18.62	5.32	-	-	-	-	2.66	S
12	Aureobasidium pullulans	-	-	-	-	-	-	2.66	-	S
13	Chrysoporium pannorum	7.98	7.98	-	-	-	5.32	-	2.66	S
14	Cladosporium cladosporioides	5.32	-	5.32	-	-	18.62	2.66	5.32	S
15	Curuvalaria lunata	-	5.32	5.32	-	-	-	-	15.96	S
16	Drechslera australiensis	5.32	-	2.66	7.98	29.26	2.66	13.3	7.98	O
17	Fusarium oxysporum	-	-	-	-	-	13.3	-	2.66	S
18	Monilia sitophila	7.98	2.66	18.62	2.66	23.94	7.98	23.94	15.96	O
19	Paecilomyces variotii	-	2.66	5.32	2.66	-	-	7.98	5.32	S
20	Penicillium citrinum	-	21.28	-	-	-	2.66	-	-	S
21	Penicillium frequentans	18.62	-	-	-	-	37.24	21.28	-	O
22	Penicillium funiculosum	-	-	-		-	-	2.66	5.32	S
23	Penicillium oxalicum	15.96	15.96	18.62	21.28	34.58	15.96	71.82	90.44	F
24	Penicillium restrictum	-	7.98	-	-	18.62	-	-	-	S
25	Trichoderma viride	18.62	-	2.66	-	2.66	-	5.32	5.32	S
	Non spore formers	29.26	23.94	10.64	7.98	7.98	5.32	2.66	-	O
	Total	441.76	340.48	316.54	266.00	422.94	351.12	383.04	441.56

S - Sporadic; C - Common; F - Frequent; O - Occasional; MC - Most Common

The most dominant group was found to be Aspergillus and the maximum frequency of isolation varied from 10 to 95 % followed by Penicillium with a range from 5 to 47.5 %. Within the group of Aspergillus, Aspergillus niger had the highest isolation frequency (95%). Other fungal groups varied from 2.5 % to 35 %. The Isolation frequency of non spore formers was 35%. Aspergillus niger was recorded as Most Common (MC) in its occurrence. Aspergillus flavus and Aspergillus japonicus were recorded as Common (C) in their occurrence. Of the remaining, 2 species were recorded as Frequent (F), 5 as Occasional (O) and 15 as Sporadic (S). Non-spore formers were recorded as Occasional (O) in their occurrence.

Conclusion

The present study has clearly demonstrated the prevalence of airborne molds especially Aspergillus and Penicillium. Among the several species of Aspergillus isolated, the level of Aspergillus niger, A. flavus, and A. japonicus was relatively high, posing greater risk to population residing in these industry oriented suburban areas. The presence of Penicillium species like Penicillium oxalicum, P. restrictum, and P. citrinum are of great concern as they are considered to be potential toxin producers.

Many organic materials expelled from different industries are found to be dispersed in the environment. This is due to the excessive production of wastewater, dumping of waste and emission of air pollutants in the atmosphere.  This may favor the growth and survival of many fungal spores within the environment. The difference in the nature of organic materials expelled may be the cause of abundance of certain species in certain areas. Many reports are also available for the prevalence of fungal spores in outdoor environments very close to industries.  Although, the study was carried over in few areas, it clearly revealed the concentration and multiple fungal species present in the environment. Hence, few recommendations have to be carried out to minimize /control the airborne spore levels in these areas, otherwise they may pose a serious potential health risk to nearby populations.

References

Adhikari, A., Sen,  M. M., Gupta - Bhattacharya, S. and Chanda, S. (2004) Airborne viable, non-viable and allergenic fungi in a rural agricultural area of India: a 2- year study at five outdoor sampling stations. Sci. Total Environ. 326, 123 - 141.

Horner, W. E., Helbling, A., Salvaggio, J. E. and Lehrer, S. B. (1995) Fungal allergens . Clin. Microbiol. Rev. 8, 161 -179.

Shelton, B. G., Kirkland, K. H., Flanders, W. D. and Morris, G. K. (2002) Profiles of airborne fungi in buildings and outdoor environments in the United States. Appl.   Environ. Microbiol. 68(4), 1743 - 1753.