Uptake of Organic Contaminants from Soil into Vegetables and Fruits - Dealing with Contaminated Sites: From Theory Towards Practical Application - page 401

plants has been observed (McKone and Maddalena 2007 , Thompson et al. 1998 ).
Inside plants, a reduction of the nitro groups to amino groups is likely and would
lead to an increase of the toxic potential. Furthermore, bound residues may be
formed.
9.8.7 Phenols
Phenol is the common name for a class of contaminants with a phenolic ring. A vari-
ety of chemical groups may be attached to the ring. This leads to contaminants with a
large variety of properties (nitrophenols, anilines, chlorinated phenols). Phenols are
less volatile than the aromatics benzene, toluene, ethylbenzene and xylene (BTEX).
The contaminant phenol as well as monochlorophenol were degraded rapidly in the
root zone (Ucisik and Trapp 2006 , 2008 ), while 2,4-dichlorophenol was taken up
into roots and translocated to stem, and to some extent also to leaves (Ucisik et al.
2007 ).
9.8.8 Cyanides
Cyanides are contaminants with a CN-group. They are often found at (abandoned)
gasworks sites and gold mines. Free cyanide (HCN, CN − ) is rapidly taken up into
roots and metabolized. An accumulation in healthy plants was not observed, because
free CN is highly toxic (Larsen et al. 2004 , 2005 ;Yuetal. 2004 , 2005b ). Iron-
complexed cyanide (ferri- and ferrocyanide) is taken up by plants and translocated
upwards, while slow metabolism was observed (Ebbs et al. 2003 ; Larsen and Trapp
2006 ; Samiotakis and Ebbs 2003 ). Field measurements at a former gas works site
showed no accumulation of total cyanide (sum of free and complexed CN) in leaves
(Trapp and Christiansen 2003 , and own results, unpublished). Surface contamina-
tion of crops by solid iron cyanide (such as Prussian blue) is possible and has been
observed (“blue strawberries”).
9.9 Monitoring of Contaminants in Soils and Shallow Aquifers
with Vegetation
The uptake of soil and groundwater contaminants into plants has also positive
aspects: contaminants such as chlorinated solvents in soils and shallow aquifers can
be monitored using plant samples. In principle, every tree could be considered as
a well, a pump and a passive sampler, all in one. Plant samples can be taken from
stems of trees (Fig. 9.11 ) and analyzed to identify and map subsurface contamina-
tion. The method is rapid and cheap. Screening an area suspect of contamination in
the upper aquifer with the tree core method prior to boring observation wells can
support the determination of optimal location of these wells, instead of arbritrarily
placing wells. This reduces the number of wells necessary for the investigation and
thus reduces overall costs. Besides, tree cores can be sampled at sites which are