MadSci Network: Environment & Ecology

Re: what is a biomarker? Insects as drosophila can be used as biomarkers?

Date: Thu Aug 19 00:38:51 1999
Posted By: Richard Kingsley, Science teacher
Area of science: Environment & Ecology
ID: 933074545.En

Dear Fouad, (Un version en Français est en-bas)

I think a better term for you to use in this context is "Pollution Indicator". Any organism can be used as some sort of pollution indicator with varying degrees of effectiveness provided you know what environmental limits that insect can tolerate. However, animals that fly may not be great indicators because they can move from clean areas to polluted areas and back with great speed. Thus, insect larvae and nymphs are usually better indicators than their adult counterparts.

Insects and other macroinvertebrates are excellent pollution indicators in running water and have been used extensively. In the United Kingdom a scoring system called the BMWP score was devised to allow quick qualitative assessments of streams and rivers. Biologists would take a sample of macroinvertebrates from a stream and identify all the different groups of insects present. If a particular family of dragonflies was present then 10 points was added. If a chironomid larva was present then only two points were added. This is because chironomid larvae can tolerate heavily polluted water while dragonflies need clean water. In this way, a score can be built up from all the groups present in the sample and a high score indicated clean water. This scoring system was designed for organic pollution, but I also found a good correlation between the scoring system and inorganic pollution when I carried out a study of this and other systems at university.

This system is effective because the effects of one pollution event on the animals may last for months in flowing water while a chemical analysis would only reveal a pollution event occurring at that very moment. Chemical analysis involves using specialised equipment in a lab whilst biological analysis using pollution indicators can be done quickly in the field. Chemical analysis is still useful because it provides quantitative evidence of pollution.

If a biologist working in the field identified a problem, that biologist could move upstream to every junction of the river and determine where the source of pollution lies. This can be done within hours. The BMWP score is not the only system that can use insects to measure stream pollution. There are several others which work well. Click here to visit a page showing the results of a sample taken from a British river using BMWP score.

Whilst Drosophilla itself might not be useful, other insects definitely can be used effectively to indicate pollution.

Richard Kingsley

As you are from Morocco I offer you a French version of my answer.

Je prefère la terme "l'indicateur de pollution" dans ce contexte. On peut utiliser n'importe quelle insecte pourvu qu'on sache leur limites environmentales de tolérance. Mais quelques animaux sont plus valable comme autres. Par exemple, les animaux qui voles peut bouger tres vite de zones pollueés aux zones parfaites. Donc, les larves et les nymphes sont plus valable que les adultes.

En Royaume-Uni il ya un système de points qu'on utilise pour juger le niveau de pollution dan les rivières et les fleuvres. Dan ce système, on utilise les insectes et autres groupes de macroinvertébrés. Le biologiste prend une section représentative de macroinvertébrés dans une rivière et identifie tous les groupes présentes. Si on trouve une groupe de libellules, le biologistes adjoute dix points. Si on trouve une larve chironomide on n'adjoute que deux points parce-que le larve chironomide peut survivre dans l'eau pollueé, mais la libellule dois avoir de l'eau de bonne qualité. Comme ça, on obtien un marque pour la qualité de l'eau dans la rivière.

Ce système de points (Le BMWP) etait fait pour trouver le pollution organique et c'est efficace, mais j'ai trouvé qu'on peut l'utiliser pour le pollution inorganique ausssi. Un biologiste qui travail sur le terrain peut trouver la source de pollution très facilement sans d'équipement lourd . On n'a besoin que quelques heures. Aussi, la biologiste peut remarquer un événement de pollution passé parce-que les effets sur les macroinvertébrés durent pendant quelques mois. Un chimiste ne peut remarquer que le pollution qui est là en même temps de l'essai. et il a besoin d'équipement specialisé qu'on ne peut pas porter sur le terrain. Une analyse chimique est encore utile parce-que on peut mesurer exactement le niveau de pollution. Ici on trouve un lien pour montrer le BMWP système de points.. Peut-être le drosophila n'est pas utile comme un indicateur de pollution mais beaucoup d'insectes sont très valables.

Richard Kingsley

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