Stachybotrys chartarum - Toxic Black Mould

stachybotrys toxic mould

The species of mould that is mostly referred to as the Toxic Black Mould S. chartarum(also known as S. atra) and S. chlorohalonata. These fungi are all frequently associated with poor indoor air quality and feature frequently in medical reports and journals.

Stachybotrys is a genus of moulds reproducing  asexually through releasing large numbers of spores. Stachybotrys is described as hydrophilic “water loving” species with a moisture content optimum aw-0.94. (aw- water availability). For this reason it only grows under conditions of high water availability such as leaks or long term condensation. Stachybotrysis frequently isolated from the wallpaper. Although mould growth may be widespread, it can also be limited to scattered patches. This is usually because there is thermal bridging between inner and outer layers of the building envelope at these sites, and as a consequence there are cold spots and condensation or high aw. Structural members such as metal studs or ties, which have a high thermal conductivity, can act as thermal bridges.

Stachybotrys is considered to be a strongly cellulolytic “cellulose loving” species. It degrades cellulose into sugar with a range of enzymes and absorbs nutrient necessary for grows and reproduction. Another commonly colonised material is gypsum board. Gypsum boards contain an inside layer of plaster sandwiched between layers of paper and/or insulation packing. When thoroughly wetted, gypsum boards are readily colonised by black mould because they contain large amount of cellulose and minerals necessary for growth. When old and new gypsum board was artificially inoculated with this species, there was evidence of production (Nielsen et al. 1998b).

Other Stachybotrys species

Stachybotrys genus  is wide spread and contains more than 50 species from which the most common are : S. albipes, alternans, breviuscula, chlorohalonata, cylindrospora, dichroa,  elegans, eucylindrospora, freycinetiae, kampalensis, kapiti  longispora, mangiferae,  microspora, nephrodes, nephrospora, nilagirica, oenanthes, parvispora, ruwenzoriensis,  sansevieriae, sinuatophora, suthepensis, theobromae and waitakere.

Stachybotrys chartarum toxic spores

toxic black mould spores 1

Stachybotrys chartarum mould spores requires high water activity levels to grow and is considered to be s a slow spore (conidia) producer. It predominantly grows on wet cellulose-containing materials (including drywall, paper, ceiling tiles and wallpaper), which have been moist for an extended period of time. Its optimum temperature range for production of conidia lies between 36°-104°F (of 2°-40°C).

Under the microscope toxic mould spores that are still attached to the fungal colony look similar to a dandelion with clusters of conidia growing at the end of hyphae. Conidia are grouped in slimy masses, smooth to coarsely rough, dark olivaceous to brownish black, obovoid, later becoming ellipsoid with age, 10–13 X 5–7 µm in size.

Encasement in a gelatinous mass prevents the spores to be prematurely released into the air. The conidia can be released though if the toxic mould is disturbed or if it dries out. When sporulating, producing fruits, the slimy gelatinous layer becomes dry and powdery allowing the spores to float free. Changes in environmental conditions can also trigger black toxic mould to sporulate.

Due to the fact that toxic black mould spores are heavier then the conidiums of other common indoor moulds they don't stay airborne for long periods of time. The conidia do not usually spread into houses through the air but are often carried inside instead, especially through flooding or on building materials during construction.

Black mould conidia are allergenic just like the spores from other indoor species. However stachybotrys conidia are also toxic because they carry mycotoxins on them. It has been reported that per spore concentrations of satratoxin H in Stachybotrys conidia is estimated at 0.0004 ng/spore. Using this value, have estimated that 10 billion conidia would be required to reach 1.0 mg of this toxin in a cubic meter of air.

toxic black mould spores 2

Thus, the animal no-effect dose is comparable “to a continuous 24-hour exposure to 2.1 x 106 spores/m3 for infants, 6.6 x 106 conidia/m3 for school-aged children, and 15.3 x 106 conidia/m3 for an adult.”

Animals injected with stachybotrys experienced bleeding in the brain, thymus, spleen, intestine, lung, heart, lymph node, liver and kidney and in some cases death (Aerias, 2001b).

Disturbing toxic black mould can also cause a lot of toxic fungal particles to enter the air. This is why you should never disturb or try to remove contamination you find it in your home. Removing toxic black mould is much more dangerous than removing ordinary mould and it should only be done by a professional.

Morphological Description of Toxic Black Mould

stachybotrys chartarum life circle

Stachybotrys chartarum is a greenish black mould. Although it typically appears wet and slimy, it may appear sooty or may be observed as grey-white strands. The slimy mycelial mats are dark olive-gray with smooth margins and rigged or smooth surfaces.

Spores (conidia) are brownish, and the colony may have powdery surface during sporulation.

Conidiophores are determinate, macrocematous, solitary or in groups, erect, irregularly branched or simple, septate and dark olivaceous; the upper parts are often rough walled. 120-180 µm tall, 3.5-4.5 µm wide near the base, 2.5-3.2 µm wide and pale olive in the upper part.

Phialides 6-7 in whorl, 10-13 x 5.5-6.5 µm, pale olive, ellipsoid occur in whorls, often have conspicuos collarettes and produce conidia singly or successively into a slime droplet that covers the phialides.

Conidia elliptical, 8-10 x 5-5.5 µm., dark fuligineous, rough-walled.

A cosmopolitan cellulolytic species isolated from soil and mouldering plant matter, e.g. damp straw. Commonly on very wet gypsum board/walls and wallpaper, and on cotton fabrics/textiles such as canvas. Also isolated from asbestos building substitute, UFFI; HVAC humidifier water and fan; hospital/factory air.

Distinguishing characteristics from other fungi include moderately rapid growth (colonies measure up to 3 cm within 4 days), colour pattern (both surface and reverse of colonies are black) and the slimy conidial (spore) masses.

In indoor environments also other species of Stachybotrys occur, which are recognized by a different conidium size and ornamentation.

Life cycle of toxic black mould

stachybotrys toxic mould

Typically moulds growing indoors have four stages in their life circle:

Mould releases millions of spores into the indoor air which are then transported around by air currents and finally settle on all surfaces. If there is sufficient moisture and some nutrients present at the surface the mould spores starts to germinate.

Once the spores have germinated, the resulting germ tube is ready to grow into hyphae, then a cluster mycelium.  In this growth stage, fungi produce microscopic, cylindrical filaments, the thread-like cellular strands called hyphae, into the food sources (material). These hyphae produce and excrete digestive enzymes in the food and take up nutrients in watery form, and transport them to the growing hyphal tips. The hyphae grow by extending itself on the tip or by branching out new threads at the tip and in the older parts. The total quantities of hyphae produced by a fungus are collectively termed as a mycelium.

The mycelium grows into the material (wall paper, plasterboard, wool, silicon seals etc), consumes its organic components in the process, weakens the structure of the material, and eventually destroys the structure and renders the material incapable to fulfil its function.

In the last stage of the life circle the fruiting bodies of mould produce spores which are then released back into the indoor air.

Clasification

DOMAIN : EUKARYOTA

They are organisms such as plants, animals and fungi which possesses eukaryotic cells. The word eukaryote means "true nucleus".

KINGDOM: FUNGI

Fungi are a common name for mushrooms, yeast, mould, and mildew. There are approximately 100 000 species of fungi which have managed to colonize almost every possible environment including human bodies.Fungi include mushrooms rusts, smuts, puffballs, truffles, morels, moulds and yeasts. Almost all fungi are heterotrophic, deriving their energy from other organisms. The free living saprobes and saprophytes, producing enzymes that degrade biopolymers , use carbon fixed b other organisms; they live and grow on woody substances and in soil, leaf litter, dead animals and others. Some fungi are biotrophs, form symbiotic associations with plants, animals and prokaryotes, Fungi are the most important plant pathogens, and some are fungal parasites of humans and other animals. Currently approximately 300 fungal species have been identified as human pathogens.

One distinguishing characteristic of fungi is the presence of chitin in the cell walls. Fungi also do not perform photosynthesis, but rather are heterotrophs, depending on other sources for their food.

CLASS: SORDARIOMYCETES

Are a class of several thousand species of sac fungi in the kingdom Fungi characterized by a flask-shaped fruiting body that bears saclike structures and usually has a pore through which ascospores are discharged.

ORDER: HYPOCREALES

This order consists of 7 fungal  families, 237 genera, and 2647 species. Species of Hypocreales are usually recognized by their brightly coloured, perithecial ascomata, or spore-producing structures. These are often yellow, orange or red.

FAMILY: DEMATIACEAE

A family of soil-inhabiting, brown or black melanin-producing fungi found in decaying vegetables, rotting wood, and forest carpets, and including several of the dark-coloured genera that cause chromoblastomycosis in man, such as Phialophora, Fonsecaea, and Cladosporium.

GENUS: STACHYBOTRYS

A genus of mould that grows on water damaged materials such as ceiling tiles, insulation, wallpaper, wood, sheet rock, and can be found in dust from contaminated building materials.

SPECIES: STACHYBOTRYS CHARTARUM

Toxic Black Mould