metallic
forms of the metal despite their high toxicity (Hedegaard and
Sloth, 2011). However, results suggest that there is accumulation of
OrgHg in roots (BAFs N 1) which results from both root uptake and
plant enhanced methylation of IHg in surrounding rhizosphere
(Sun et al., 2011). It has also been suggested that there is no barrier
to the translocation of OrgHg from roots to shoots as in the case of
IHg. These processes result in accumulation of OrgHg also in shoots,
relatively to soil concentrations (BAFs N 1). Such BAFs for OrgHg in
shoots increase with increasing BAFs for roots. But since no limits
for OrgHg concentrations in animal feed were found in Portuguese
or European legislation (European Commission, 2002) it is not possible
to effectively evaluate potential risks of exposure for livestock
associated with dietary intake of feed at these OrgHg levels. Also,
without such limits it is not possible to back-calculate threshold concentrations
for OrgHg in soils, using soil-to-plant transfer relationships
for OrgHg which could be derived from experimental data as
described by Rodrigues et al. (2012a,b). Such site-specific thresholds
for OrgHg in soils could then be used as amost robust way to identify
those fields which in fact should not be used for raising cattle or for
the production of food and fodder products.
Finally, since the toxicokinetics of Hg in animals depends on the
chemical form of the metal, in order to properly ensure food safety it
is necessary to further understand transfer and potential bioaccumulation
of OrgHg in animal organs since currently no BAFfeed-animal are available
from literature.