Enquirer

From: John Roy
Date: 13th May 1999
Subject: UK native trees cleaning up a heavily contaminated site

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Dear Micky,

Many thanks

John Roy

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Dear Jon

There is quite alot of information about Phytoremediation on the site, have a look at these links :-

1. BIORENEW Phytoremediation project
2. Phytoremediation
3. Phytoremediation - MSc project
4. Phytoremediation project - collaborators/funds sought
5. Phytoremediation - information needed

There have also been two recent articles in Nature biotechnology May 1999 (vol 17 Number 5), which dealt with the use of Transgenic tobacco plants to phytoremediate sites contaminated with TNT (and you thought it was only the nicotine in fags that was dangerous!).

The articles are :-

1. Transgenic phytoremediation blasts onto the scene ( and [both at Pacific Northwest National Laboratory]) - page 428.
2. Biodegradation of explosives by transgenic plants expressing pentaerythritol tetranitrate reductase (Christopher E French [DERA], Susan J Rosser + Gareth J Stephens + Stephen Nicklin + [University of Cambridge]) - pages 491 - 494.

Basically it seems that TNT degredation by wild-plants leads to the build up of another toxin - aminonitrotoluene. However by expressing the bacterial pentaerythritol tetranitrate gene (PETN) reductase gene in tobacco, it is possible to create strains that are resistant to high concentrations of explosives such as GTN and TNT. The bacterial enzyme then is capable of completely denitrifying TNT and trinitroglycerin (GTN)

These strains of tobacco then have the potential to remove nitrate completely and degrade nitrate ester and nitroaromatic explosives, both of which are toxic compounds.

Phytoremediation of Heavy metals has also benefited from genetic engineering. Yellow poplar saplings, expressed with the bacterial mercuric reductase gene, also take up mercury from the soil (Rugh C.L et al. Development of a transgenic yellow poplar for mercury phytoremediation. Nat Biotechnol 16, 925-928, 1998)

However this attempt was not so successful, as the mercury was not destroyed or locked-up in the tree, instead it was transformed into airborne elemental mercury - somewhat more dangerous than leaving it in the ground!

I suppose this just goes to show that Prince Charles might be onto something. One thing is for sure if you are planning to try out phytoremediation in the UK, and plan to use genetically modified plants, you will eventually be smoked out and will not be very poplar !

cheers

Micky

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Dear Jon

There's been loads of work on using trees, going back 30 years or more. However, a lot of it was looking at which trees survived on these sites rather than bioremediated it!

But I would imagine the bioremediation angle is something that has now been looked at in more depth in recent years.

It is usually the pioneer species which survive best on contaminated sites:

• Willows (e.g. Salix caprea, Salix cinerea)
• Birch (Betula pendula + pubscens)
• Aspen (Populus tremula)

These are also native species which have fast rates of growth. Alder used to be a favourite as its N-fixing properties gave it advantages on sites with poor fertility, such as old coal slag heaps. Hawthorn (Crataegus monogyna) is another pioneer which I have seen colonising our own local disused refuse tip (where there was hardly any superficial capping but some heavy metal contamination).

It might be of value to consider tree and shrub seed collections from existing contaminated sites like this which have been naturally colonised by trees and shrubs, as the plants growing in these places must be pretty well adapted to difficult situations and may show some localised adaptation (possibly). THere are people who do such seed collections to contract.

Indeed it would be of some value to establish some specialised nurseries of native trees and shrubs that have colonised these types of sites, to provide a supply of planting material that may be better adapted than a lot of the imported material (trees and shrubs) that is mostly planted these days - ie native species but of foreign origin (which may be climatically maladapted apart from anything else).

I don't know how these species deal with contaminants but this must be documented somewhere? Do they store it in their tissues, or emit some toxic compounds in gaseous form, or are some contaminants not taken up at all?

The ability of trees to assist the development of soil and associated microbes will be an obvious and important aspect of using trees to ameliorate sites. Presumably a combination of tree planting plus the addition of microbes is something that has been looked at?

By the way am an ecologist with knowledge of native trees, but only limited and ancient knowledge of using trees on contaminated land. I am also interested in utilising the genetic diversity of native trees, shrubs and other native plants found in the UK, for biodiversity and ecological restoration. I head up an initiative called Flora locale, which aims to promote the use and propagation of native-origin plants. At the moment, the vast majority of trees and shrubs planted are not of UK native-origin.

Tony Bradshaw, ex. Liverpool University, is an expert in this area. Try looking at references by Bradshaw, A.D. There was a unit at Liverpool dedicated to the ecological aspects of contaminated land restoration - I presume that it still exists.

Tel: (01635) 860 478