bioreceptivity a new concept for building ecology studies

8/17/2019 Bioreceptivity a New Concept for Building Ecology Studies

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Tbtai l wirmment

The Science of the Total Environment 167 (1995) 215-220

Bioreceptivity: a new concept for building ecology studies

0. Guillitte

Unik d’Enseignem ent et de Recherche de Bioiogie Vigt tale, Facultk des Scien ces Agronomiques, Passag e des Dipo&s 2,

B-5030 Gemblowr, B elgium

Abstract

A definition of the concept of bioreceptivity as the ability of a material to be colonised by living organisms is given.

Related terms, such as primary, secondary, tertiary, intrinsic, extrinsic and semi-extrinsic bioreceptivity, and

bioreceptivity index are also expla ined. The usefulness, possible uses and methodological issues arising from this

concept are discussed.

Keywords: Bioreceptivity; Building ecology studies;Building material colonization

1. Introduction

Many building materials are prone to colonisa-

tion by living organisms. This colonisation causes

changes in colour and in the chemical or physical

properties of the materials. Since the late-60s,

these changes have been grouped under the terms

‘biodegradation’ or ‘biodeterioration’. The latter

seems to be used mainly in connection with mate-

rial degradation; it is missing in many specialised

dictionaries in favour of the word ‘biodegrada-

tion’ which applies more widely to the biological

degradation of substances or well-defined chemi-

cal compounds. These terms tend to give ‘col-

onisation’ negative and sometimes entirely sub-

jective connotations. Indeed, the invasion of ma-

terials by living organisms does not necessarily

lead to physical and chemical degradation but

simply to reversible colour changes that are per-

ceived differently according to the type of con-

struction, the location and the person studying

them. On the contrary, some authors consider the

colour changes to be aesthetically pleasing [l],

credit them with a protective role against man- or

weather-induced aggression [2-41 and suggest that

they have a cleansing effect which benefits the

environment [5].

Therefore, if one wishes to study the colonisa-

tion of materials without being biased by its ef-

fects on the materials, one should not limit one-

self to those characteristics affected by the

colonisation but should include those that allow

colonisation to take place. The precise role of the

building material characteristics in the colonisa-

tion process is not fully understood, with the

exception of acidity, whose influence on the tax-

onomic content of colonising organisms is well

known. In a previous work [5] on the kinetics of

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the Total Environment 167 (1995) 215-220

the colonisation of composite building materials

by plants, we have studied these characteristics

but have not been able to identify them all pre-

cisely. Thus, we have grouped them all under the

term ‘bioreceptivity’ as a means of elucidating

the impact of colonisation on the material with-

out having to resort to a full analytical approach.

2. Basic definitions and variants

In the medical field, the term ‘susceptibility” is

used to describe the vulnerability of an organism

to diseases, especially infectious diseases. The

term is also used in veterinary medicine. Toma et

al. [6] define susceptibility as the ‘aptitude of an

organism to harbour a pathogen, to allow its

development or multiplication, without necessar-

ily suffering’.

By extension, we would define the term ‘biore-

ceptivity’2 as the aptitude of a material (or any

other inanimate object) to be colonised by one or

several groups of living organisms without neces-

sarily undergoing any biodeterioration. The word

‘colonise’ is important since it indicates that con-

ditions for harbouring, development and multipli-

cation have to be met and excludes the ability of

a material to receive living organisms in a tran-

sient and fortuitous manner. It implies that there

is an ecological relationship between the material

and the colonising organisms. Thus, for example,

a joint of mortar is not bioreceptive to ants circu-

lating on it, even if it is their favourite trail on the

masonry. On the other hand, it can be highly

bioreceptive to others insects, such as the ichneu-

mons, if they are able to lay their eggs into it.

Seeds that are deposited on a material without

‘In French: r6ceptivi t6; in German: Empfanghchkeit.

*Our choice of the word ‘biorecept ivity’ as an alternative to

‘susceptibil ity’ is justified by an attempt to use a word that

translates in the same way into different languages after

adding the pretix ‘bio’. Furthermore, the word ‘receptivity’ is

used in English to describe the ability of a flower stigma to be

fertihsed by pollen grains through the pollen tube. There is a

clear similari ty with our concept. Therefore, we suggest using

the word ‘bioreceptivite’ in French, ‘Biorezeptivit lt’ in Ger-

man, ‘bioreceptiviteit’ in Dutch, ‘bioreceptividad’ in Spanish,

‘bioreceptividade’ in Portuguese and ‘biorecettivith’ in Italian.

being able to germinate and develop cannot be

related to the bioreceptivity of the material. How-

ever, if they are able to grow into plantlets and

survive for some time, one could probably say

that this material is bioreceptive to higher plants.

Therefore, bioreceptivity can also be defined as

the totality of material properties that contribute

to the establishment, anchorage and development

of fauna and/or flora. In stony materials, for

instance, it relates mainly to properties of the

area exposed to climatic elements, such as rough-

ness, porosity, moisture and the chemical compo-

sition of the surface layer. The capillary porosity

is a property of the core of the material that can

also affect colonisation.

When a material has not yet been exposed to

colonisation, the bioreceptivity wil l be expressed

only during the appearance of the first colonising

organisms. As long as the properties of the mate-

rial remain very similar or identical to those of its

initial state, we propose using the term ‘primary

bioreceptivity’ to indicate the initial potential of

colonisation. Characteristics of these properties

can evolve over time under the action of colonis-

ing organisms or other factors causing change,

and result in a new type of bioreceptivity, which

we call ‘secondary bioreceptivity’ (Fig. 1). For

practical purposes, secondary bioreceptivity is of-

ten more important than primary bioreceptivity.

Any human activity affecting the material - con-

solidation, coating with a biocide or surface

polishing - also modifies the initial or secondary

characteristics of the properties of the material,

inducing ‘tertiary bioreceptivity’. In principle,

efficient treatments should make this tertiary

bioreceptivity less important than primary and

secondary bioreceptivity.

Particles or substances that are not part of the

material, such as soil, dust or organic particles,

can deposit and accumulate on the material.

These exogenous deposits modify the initial con-

ditions of bioreceptivity. If they are substantial,

they can result in a type of colonisation which no

longer relates directly to the properties of the

material, i.e. those properties that allowed de-

posits to accumulate (Fig. 2). We suggest using

the word ‘extrinsic bioreceptivity’ to describe such


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Fig. 1. Primary, secondary and tertiary biorecept ivity in a stony material. White arrows, black arrows and discontinuous lines

represent the colonisation, physico-chemical deterioration and biodeterioration mechanisms, respectively.

a situation. Some elements of the colonising vege-

tation can, in turn, be colonised by epiphytes or

parasitised by other organisms. Thus, the vegeta-

tion can also be responsible for some extrinsic

bioreceptivity. In other cases, colonisation de-

pends directly and simultaneously on the proper-

ties of the material and on the deposits of ex-

ogenous substances (Fig. 3). We suggest using the

word ‘semi-extrinsic bioreceptivity’ to refer to this

phenomenon. Finally, when colonisation depends

mainly on the properties of the material, irrespec-

tive of exogenous contributions, one could use

the phrase ‘intrinsic bioreceptivity’. In fact, the

three types of bioreceptivity and their intermedi-

ate stages can occur on the same material.

3. Usefulness of the concept

The first advantage of the bioreceptivity con-

cept is that it completes the accessibility concept

developed by Heimans [7] to explain the colonisa-

tion process of materials involving other environ-

mental factors. Accessibility can be defined as the

characteristics of the environment that determine

the abundance of diaspore sources, proximity and

transport capabilities (anemochoria, myrmo-


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218 0. Guillitte /Science of the Total Environment 167 (1995) 215-220

Fig. 2. Extrinsic biorecept ivity in a stony material (in the case

of primary biorecept ivity). The white arrow represents the

colonisation mechanism.

choria, avichoria, etc.), including the exposure of

the material to these sources and vectors.

Whereas this concept relates to the colonisation

potential of the environment, the bioreceptivity

concept expresses the colonisation potential as

defined by the characteristics of the material. It is

the combination of these potentials and particu-

lar environmental conditions, such as water, tem-

perature and light, that allows colonisation to

occur. Colonisation cannot occur in the absence

of one group of factors. Therefore, bioreceptivity

is the missing link that was required in the adop-

Fig. 3. Semi-extrinsic bioreceptivity in a stony material (in the

case of secondary biorecept ivity). White and black arrows

represent the colonisation and physico-chemical deterioration,

respectively.

tion o f an integrated approach to the colonisation

of materials. The bioreceptivity of a material will

be best expressed under maximum accessibility

and environmental conditions that are optimal for

the development of organisms.


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Based on this principle, one could consider the

possibility of assessing the bioreceptivity of a ma-

terial to an organism by artificially inoculating the

material with the diaspores of the organism and

placing them under optimal environmental condi-

tions (e.g. a growth chamber). A specific biorecep-

tivity index could thus be determined and in-

cluded in a bioreceptivity scale similar to biotic

indices. These indices would be complementary,

as biotic indices determined on similar substrates

allow a quality assessment of environmental con-

ditions. In this instance, the absence of colonising

cryptogams on the material would reflect a high

level of air pollution, whereas the same absence

in an experiment like that mentioned above would

mean that the material is not bioreceptive to

these cryptogams. A practical application of the

bioreceptivity index would be to provide weighted

biotic indices whenever they are determined from

different materials. For example, Seaward [8] has

shown that asbestos-cement slates are more likely

to be colonised by Lecanora muralis a lichen,

than natural slates or tiles, particularly in pol-

luted areas. Therefore, in spite of its ubiquity, this

lichen cannot be used as a pollution bioindicator,

unless the same roofing materials are found in

the areas under study. However, this exercise

could be carried out - if the bioreceptivity could

be determined accurately for each material - by

dividing the measurement data (number of occur-

rences, average size of the thallus, etc.) by the

bioreceptivity index.

The bioreceptivity index of a material would

also provide users with information on the coloni-

sation risk and help them choose an alternative

material or another use for the same material,

depending on whether or not colonisation is de-

sirable. It could also give information on the

effectiveness of various types of treatments of the

materials. Similarly, the influence of individual

properties or their synergetic effect on the coloni-

sation process could be assessed by measuring

bioreceptivity after a gradual change has occurred

in some of those properties.

Finally, the various types of bioreceptivity de-

fined above could be used to establish the se-

quence of events that lead to a potential or

observed colonisation. It also forces the observer

to conduct an analytical study of the pheno-

menon, thereby fostering a better understanding

of the factors involved in the colonisation process

and ways to prevent or enhance it. Among other

things, the distinction between primary and sec-

ondary bioreceptivity allows one the possibility to

assess the impact of biodeterioration.

4. Methodological problems arising from the

concept

The bioreceptivity of a given material can be

expressed only by subjecting it to various groups

of organisms under environmental conditions that

are optimal and specific for each group. The first

problem that needs to be overcome lies in the

lack of information on these conditions. The sec-

ond issue is how to get a material to be colonised

faster by colonising organisms such as lichens.

Finally, because many types of colonisation are

part of a synecological mechanism, colonisation

by a single type of organism can become either

impossible or completely atypical. In this case, it

is difficult to assess the respective contribution of

intrinsic and extrinsic bioreceptivity.

These problems in growing the colonising or-

ganisms are compounded by the selection of

parameters for measuring bioreceptivity or biore-

ceptivity indices (number of occurrences, biomass,

colonised area, appearance and growth rate of

colonising organisms, fertility, etc.). A practical

approach of these difficulties was illustrated by

the author [9]. At the current stage of concept

definition, it is interesting to note that the biore-

ceptivity of materials can be determined from a

set of relatively cosmopolitan species belonging to

the following major biological groups: autotrophic

bacteria, heterotrophic bacteria, microfungi,

macromycetes, cyanobacteria, green algae,

chrysophytes, endolithic lichens, epilithic lichens,

bryophytes, ferns and flowering plants.

5. Conclusion

Although the concept of bioreceptivity is at-

tractive, it requires additional methodological

studies before it can be used outside the area of

building materials. Multidisciplinary teams con-

sisting of biologists and building material special-

ists have to be set up to conduct integrated stud-


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ies under experimental conditions that are as

standard as possible to remove any subjectivity

attached to the concept. Specialised laboratories

will then be able to design bioreceptivity tests

similar to those used to determine the susceptibil-

ity to frost, and the hardness and the mechanical

strength of materials. These tests will provide an

additional tool for the selection of materials by all

users, including architects and those involved in

restoring buildings.

Acknowledgement

This paper was initiated with the financial sup-

port of the European Commission under the re-

search entitled ‘Interactive physical weathering

and bioreceptivity studies on building stones,

monitored by computerized X-ray tomography

(CT) as a potential non-destructive research tool’.

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bioreceptivity a new concept for building ecology studies

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