afforded a relatively precise mapping of metals in periphyton, which can be found in
different microenvironments of periphytic biofilms depending on the metal form/
speciation and the characteristics of the microenvironment. Precipitates can be found
in the biofilm matrix at the cell surfaces (Brown et al. 1998), while positively
charged metal ions can accumulate in negatively charged cell walls and EPS.
Metal speciation is also reported to influence the site of metal bioaccumulation
(bound to membrane vs. EPS; Hunter et al. 2008). Biofilms have also evolved
enzymatic mechanisms of metals reduction (Lloyd 2003) or metal sequestration
via thiol-rich polypeptides known as phytochelatins able to sequester excess intracellular metals in a stable, detoxified form (e.g., Lavoie et al. 2012). Depending on
the metal and environmental conditions, they are able to store and concentrate large
amounts of metals that are potentially transferable to higher trophic levels.
As stated earlier, there is less data available on the bioaccumulation of organic
contaminants in periphytic biofilms. However, the pattern seems to be that these
contaminants tend to accumulate at lower final concentrations (Fig. 4), but some
more efficiently (i.e., with higher BCFs), than metals (Fig. 5, Table S1). These
Fig. 5 Bioconcentration factor, expressed as log(BCF), for periphytic biofilms (n ¼ 304), data from
22 published studies. Plain circles stand for observations from the field, stars for observations from
laboratory experiments. PAHs polycyclic aromatic hydrocarbons, PCBs polychlorinated biphenyls,
HCH hexachlorocyclohexane, TBEP tris(butoxyethyl)phosphate, DCPU N-(3,4-dichlorophenyl)
urea, DCPMU N-(3,4-dichlorophenyl)-N-(methyl) urea, DDTs dichlorodiphenyltrichloroethane
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C. Bonnineau et al.
different microenvironments of periphytic biofilms depending on the metal form/
speciation and the characteristics of the microenvironment. Precipitates can be found
in the biofilm matrix at the cell surfaces (Brown et al. 1998), while positively
charged metal ions can accumulate in negatively charged cell walls and EPS.
Metal speciation is also reported to influence the site of metal bioaccumulation
(bound to membrane vs. EPS; Hunter et al. 2008). Biofilms have also evolved
enzymatic mechanisms of metals reduction (Lloyd 2003) or metal sequestration
via thiol-rich polypeptides known as phytochelatins able to sequester excess intracellular metals in a stable, detoxified form (e.g., Lavoie et al. 2012). Depending on
the metal and environmental conditions, they are able to store and concentrate large
amounts of metals that are potentially transferable to higher trophic levels.
As stated earlier, there is less data available on the bioaccumulation of organic
contaminants in periphytic biofilms. However, the pattern seems to be that these
contaminants tend to accumulate at lower final concentrations (Fig. 4), but some
more efficiently (i.e., with higher BCFs), than metals (Fig. 5, Table S1). These
Fig. 5 Bioconcentration factor, expressed as log(BCF), for periphytic biofilms (n ¼ 304), data from
22 published studies. Plain circles stand for observations from the field, stars for observations from
laboratory experiments. PAHs polycyclic aromatic hydrocarbons, PCBs polychlorinated biphenyls,
HCH hexachlorocyclohexane, TBEP tris(butoxyethyl)phosphate, DCPU N-(3,4-dichlorophenyl)
urea, DCPMU N-(3,4-dichlorophenyl)-N-(methyl) urea, DDTs dichlorodiphenyltrichloroethane
128
C. Bonnineau et al.