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Pollution, water and metals: no easy measure value to check against

by Xavier in Paris Thu Apr 23rd, 2009 at 07:01:23 AM EST

A friend of mine is a researcher in pollution by metals components such the ones you can find in mine wastes.

He's just started to write a few texts to explain how you really have to study these phenomenae, the need for complex methods, and some traps to avoid when interpreting data.
I think the part on interpreting data is particularly interesting, because we usually have a lot of data in medias on hot issues, you can find information on the exact values, but the meaning of these is almost never challenged.

So, if you care to read further, I'll try to extract the best parts, to illustrate how complex it may be to study a physical phenomenon before being able to decide about it.

promoted by whataboutbob


Pour le dire vite, il n'est pas essentiel de connaître les quantités totales de polluants sauf pour dimensionner un risque ; par exemple, il y a mille tonnes de tel polluant à tel endroit.Pour le dire autrement si les décharges d'ordures étaient confinées (pas d'eau qui en sort, pas d'odeur, pas de vue ...) elles ne poseraient aucun problème d'environnement. To put it quickly, it is not essential to know the total quantity of pollutants except for evaluating a global risk.
For example, to say there is a thousand ton of pollutants in a particular place gives no information on immediate risk. To say it otherwise, if determined loads of rubbish were completely confined (no water coming out, no smell, no sight ...) they would pose no threat for the environment.

How and where the polluting species will find themselves?

In front of pollution, you need to look for a serie of basic questions:

Si je plante du blé sur un site riche en arsenic (en plomb etc.) est-ce qu'il poussera, s'il pousse est-ce qu'il sera contaminé, si oui quelles sont les parties de la plante qui accumuleront le polluant (les racines, la tige ou les grains), ensuite est-ce que je pourrai manger le pain qui en est issu, combien pourrai-je en manger, au bout de combien de temps serai-je malade et ma voisine (ou mon voisin) qui mange exactement les mêmes quantités que moi sera-t-elle malade en même temps que moi ? Même raisonnement pour l'eau du puits voisin. Et dans le cas de polluants multiples y a-t-il des interactions entre eux ?If I plant wheat on a site rich in arsenic (lead etc..), does it grow?
If it does it will be contaminated, if so, which parts of the plant will accumulate the pollutant (roots, stems or seeds)? Would I be able to eat the bread that comes from? how much can I eat, how long before I become sick? And will my neighbor ( who eats exactly the same quantity as I do) become ill at the same time? Same reasoning to the water in nearby wells. And in the case of multiple pollutants are there any interactions between them?

These impacts on human being are strongly dependent on pollutant form: is it oxydised? hydrated? cristallized? amorphous?
 a gold mine waste heap in Limousin - France

Connaître la forme (solide ou liquide) sous laquelle se trouve un élément (c'est à dire s'il est lié à l'oxygène, au soufre ou à n'importe quelle autre molécule) est très important car ses propriétés diffèrent selon qu'il est associé à tel ou tel autre atome.De plus pour un même élément certaines formes sont plus toxiques que d'autres.To know the form (solid or liquid) in which the element is found (ie if it is linked to oxygen, sulfur or any other molecule) is very important because its properties differ according to the associated species.
For the same element, some forms are more toxic than others .
Par exemple lorsque l'arsenic est réduit c'est à dire développé dans un milieu où il y a peu d'oxygène et donc lorsqu'il est sous forme As3+, il est plus toxique que sous sa forme oxydée (As5+). Un traitement possible pour l'eau arseniée peut donc être de l'oxyder. For example, when arsenic is reduced ie in an environment where there is little oxygen and therefore finds itself as AS3+ ion, it is more toxic than in its oxide (AS5+).
A possible treatment for arsenied water can therefore consist in an oxidization.
Toujours pour l'arsenic, lorsqu'il est associé à des molécules organiques, il est moins toxique que lorsqu'il est associé à des molécules non organiques. For arsenic when associated to organic molecules it gets less toxic than when it is associated to non-organic molecules.
Pour l'étain par exemple, c'est le contraire. Tin, on the contrary, works the opposite way.

and on its physical form: is it in a bulf form? reduced to powder?

Pour récupérer les métaux dans un minerai brut, on le broie puis on fait passer la poudre dans des bains dont la composition et les autres caractéristiques sont calculées de manière à séparer le métal intéressant. Le résidu est mis en décharge ou ailleurs et il faut à tout prix éviter que les circulations d'eau n'y percolent. Dans les terrils, l'eau se charge en éléments polluants bien plus facilement que si le minerai n'était pas broyé. To extract metals from a crude ore, it is crushed and then put the powder in different baths, the composition of which are calculated so asto separate the mineral of interest. The rest is going to waste in a landfill or elsewhere.
It is necessary to avoid, at all costs, the circulation of water seeping there.
In waste heaps, the water loads itself in pollutants more readily than if the ore had never been crushed.

In a gold mine waste study, sample were taken every 15 days during a year in different sampling points.

# Les concentrations en arsenic sur le site sont très importantes. Hors du site (dans la rivière, dans les puits) elles sont importantes, parfois au delà de ce qui est toléré pour les rejets ;
# les concentrations en arsenic sont très variables pour un même point de prélèvement : ces variations sont de 10 fois 100 fois ou plus entre les différents jours de l'année ;
# Concentrations of arsenic on the site are very important. Off-site (in the rivers, wells) are important, sometimes beyond what is tolerated for discharges;
# arsenic concentrations are very variable for the same sample point: these variations are 10 times 100 times or more between the different days of the year.

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This is lazy recycling, but I hope you get some information in it.
by Xavier in Paris on Wed Apr 22nd, 2009 at 08:52:57 AM EST
to the world of geochemistry.
by Nomad on Wed Apr 22nd, 2009 at 01:31:10 PM EST
[ Parent ]
Hello Xavier, you may have been around awhile at ET, but this is the first time I have read an article of yours. Cool! Thanks!! Up it goes on the front page. Welcome to ET, and look forward to more of your articles!

Cheers!

"Once in awhile we get shown the light, in the strangest of places, if we look at it right" - Hunter/Garcia

by whataboutbob on Thu Apr 23rd, 2009 at 07:02:58 AM EST
Thanks a lot. I'm just not sure I can compete with all our usual experts. ;-)
by Xavier in Paris on Thu Apr 23rd, 2009 at 08:50:04 AM EST
[ Parent ]
just to dedicate about landfills of Johannesburg, about their history and their current management. Part of the reason why southern Johannesburg is so gritty and messy is in part because of the landfills that dot the city landscape. Never mind about their cyanide contents that still blow across the city during strong gales...

http://maps.google.nl/maps?f=q&source=s_q&hl=nl&geocode=&q=Johannesburg&sll=52.4 69397,5.509644&sspn=2.938099,9.887695&ie=UTF8&ll=-26.216439,28.095217&spn=0.067607,0 .154495&t=h&z=13

Particularly the landfills around west Soweto are gargantuan in size and the impact of gold mining has been disastrous for the wetlands south of Johannesburg...

by Nomad on Thu Apr 23rd, 2009 at 07:26:16 AM EST


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