Vegetation

Pollution by heavy elements is a serious environmental problem

Its resolution usually requires heavy investments that are often delayed. However, non-assisted plant activity can be part of cheap interventions through which it is possible to effectively remove these pollutants in reasonable time frames.

Plants absorb soluble elements so that they become part of their tissues. 

It is the accumulation of plant debris what forms organic soil. Through it  these elements return back to the mineral substrate. Heavy elements participate in this cycle, but their relative abundance in living vegetables and organic soils does not always correspond to what we usually observe in the solid mineral substrate, waters and in possible contributions from atmospheric dust. This is because many plant species manage them selectively. Even within environmental settings that are rich in contaminants of this type, only very low proportions of heavy elements are found in most of edible fleshy fruits. (Remember:  plants encourage animals to disperse their seeds by making fruit an attractive food). On the contrary, in many other cases the proportions of heavy elements in plant tissues significantly exceed those in the inorganic frame of reference. This accumulation of materials are harmful to animal health but current theories state it functions as a vegetal chemical defense mechanism. And this is advantageous for the plant species that adopt it as it spares them from having to manufacture  expensive toxic compounds. Thus, some plants just take advantage of resources that are already available in the environment for their defense. In support of this idea is the fact that the accumulation of heavy elements happens mostly in nitrophyllic plant species, with a high protein content, and in halophiles, which are very rich in salts. Both products are usually scarce resources in ecosystems and highly demanded by animals. 

It seems that the selective accumulation of heavy elements brings important competitive advantages to this type of plants, since it has developed in different taxonomic groups through parallel and convergent evolutionary processes.

In the Iberian Southeast there are many suitable plant communities to carry out heavy element extraction functions in places where they are creating problems.

The phytosociological classes of interest are Kakiletea, Chenopodienea, Salicornietea, Juncetea, Saginetea, Artemisietea, Pegano-salsoltea, Tamaricetea and Secalienea, among others, with a wide range of adaptation to various environmental frameworks and conjunctural situations.

As usual it is a priority to withdraw harmful or excessively available products, meaning that these would have to be productive ecosystems that should not stabilize to the point that their cycles close. To achieve this goal a periodic harvest of biomass would have to be carried out, extracted and exported. The destinations for this biomass could be diverse, but in all cases it will have to have as a final product either the heavy elements themselves, as soon as they are there, or in byproducts where they are trapped in a stable way. In any case, the risk of returning to the ecosystem cycles should be minimal.

Weighing multiple environmental and economic factors in the corresponding decisions becomes necessary.