In the indoor environment, settled dust may contain a number of biogenic and a-biogenic entities. The nature, type, and contents of microbial populations harbored by the “House Dust” may vary depending on the ecological niche and other environmental parameters, such as humidity, temperature etc.
Collection and analysis of nuisance dust from building environments is not an easy task. However, it is essential in order to determine the identity and quantity of microbes and their by-products in an indoor environment. This is not only helpful for understanding the common indoor pollutants/allergens of indoor environments, but it is also essential in reducing measures, remediation, and/or the management of a good indoor environment.
Microbial constituents and their byproducts in house dust can exist in two different phases, i.e. dormant and active/viable, which may or may not influence each other. Mainly, there are two different markers, culture and non-culture, which are used for enumerating dust microbiota of indoor environments. These methods are based on microscopy, biochemical assays, ELISA (Enzyme-linked immunosorbent assay), and PCR (Polymerase Chain Reaction) techniques. Environmental dust sample collection is one of the integral parts of the analysis, in either case. A house dust sample may be collected by vacuuming, swapping, and lifting accumulated dust particles in and around a test site with aseptic techniques.
The most common microbiota of house dust includes, but is not limited to, submicroscopic particles (Viruses and Mycoplasma etc.); Bacteria; Protozoa; Fungi/Mold; Arthropods such as Mites; Myxomycetes; Pollen grains; Cysts; Plant trichomes; Animal hairs; other Plant and Animal borne materials beside other indoor bioallegens typically originated as byproducts/biochemicals from Mites; Cockroach; Cat, Dog; Rat; and Mice etc. Mycotoxin; Endotoxin and Exotoxin can also be reported from “House Dust” samples. Some of the influential factors for the perpetuation of dust-borne particles are identified as: availability of organic and inorganic chemicals, dampness, moisture, temperature, and ventilation etc. in and around close structures.
Several studies in the recent past reveal that the dust microbiota is linked with health and hygiene (Micro-organisms in Home and Indoor Work Environments Diversity, Health Impacts, Investigation and Control: Flanning, Samson and Millar, published by CRC press 2001; Characterization of Microorganisms in Indoor Environments: Ulla Lignell, published by the National Public Health Institute, 2008).
Exposure to these substances, even in small quantities, can trigger allergenic symptoms/disorders and/or other health concerns. Common symptoms of house dust biomass include, but are not limited to, asthma, fever, headache, fatigues, infections, sneezing, itchy or watery eyes, nasal congestion, runny nose, eczema, etc. These signs appear either as acquiring direct infection or as a result of production of immunoglobulin E (IgE) antibodies in a sensitive individual upon the exposure of dust biota. In the case of allergenic disorders, IgE binds to mast cells in the mucosa in eye conjunctiva, nose, throat, and bronchi, and triggering a release of histamine. Histamine causes dilation of vessels in mucosa, and secretion of mucus from mucous glands, resulting in mucosal swelling and mucus secretion, giving rise to allergenic symptoms.
Successful management of house dust related health and hygienic care requires a two-fold approach (i.e. clinical diagnosis of the sufferer and environmental monitoring of the dwelling). The clinical evaluation of a patient includes symptom history, blood tests, IgE levels, and evaluation of suspected allergens (skin prick or patch test), etc. Environmental monitoring divulges the identification and quantification of microbial contents and their byproducts in house dust.
Dr. Rajiv R. Sahay is a Certified Indoor Air Quality Professional (CIAQP) and Laboratory Director at the Environmental Diagnostics Laboratory (EDLab) at Pure Air Control Services Inc. in Clearwater, Florida, USA.