2016). Besides their hydrophobicity, organic contaminants possess other specific
characteristics than can also help them bioaccumulate. For instance, the highest BCF
values were observed for halogenated contaminants such as hexachlorobenzenes
(BCF up to 147,000 L g
À1 ), PCBs (BCF up to 56,000 L g
À1 ), or per- and
polyfluoroalkylated substances (BCF up to 10,000 L g
À1 ) (Fig. 5, Table S1),
suggesting that the compounds’ high electron affinity with living cells is also
strongly involved in its accumulation. Nevertheless, validation of this hypothesis
remains bottlenecked by technical limitations, as the quantification of intracellular
organic contaminants in microbial biofilms is not yet possible (Sect. 2.2).
Non-organochlorine pesticides and pharmaceuticals measured in periphytic biofilms
generally show lower BCFs (BCF < 3.6 L g
À1 ) than metals and fluorinated or
organochlorine contaminants (e.g., DDT, dichlorodiphenyltrichloroethane; BCF up
to 78,550 L g
À1 ). The lower concentration of these contaminants in periphytic
biofilms could also be explained by different biodegradation processes for different
substances. For instance, studies have shown that periphytic microbial communities
can partially transform and/or mineralize pesticides (e.g., the phenylurea herbicide
diuron (Pesce et al. 2009) and glyphosate (Carles et al. 2019)) and antibiotics (e.g.,
the sulfonamide antibiotics sulfamethazine and sulfamethoxazole (Vila-Costa et al.
2017)). Metabolites are thus sometimes found in biofilms (e.g., atrazine metabolites
(Lawrence et al. 2001) or glyphosate metabolites such as aminomethylphosphonic
acid (Carles et al. 2019)), but it is not always possible to discriminate those produced
through biodegradation by the biofilm itself from those that were already present
in the water column before being bioaccumulated. Additionally, the lower BCFs
observed for the non-organochlorine pesticides (i.e., glyphosate, diuron, and its
metabolites) could also be explained by higher exposure concentrations since
those values were applied in laboratory experiments (contrary to BCF values for
pharmaceuticals obtained in the field); further field study investigating pesticides
bioaccumulation in natural periphytic biofilms is therefore required to confirm those
first observations.
Each step of the bioaccumulation process is influenced by a number of factors
such as exposure duration and concentration, physical-chemical conditions, and
biofilm composition. Hydrology and geomorphology are also likely to influence
bioaccumulation especially by driving contaminants repartition between aquatic
compartments (surface water, particulate matter, sediment, periphytic biofilm).
In the dataset analyzed, exposure duration was not significantly correlated with
metal BCFs, which argues for fast adsorption of metals in the biofilm matrix. Among
the metals considered, aluminum had the highest uptake efficiency even at low
exposure concentrations (BCF up to 31,800 L g
À1 ), irrespective of exposure duration
(1–35 days). Corcoll et al. (2012) hypothesized that the amount of Al accumulated
was thus “background” content for the biofilms studied. In contrast, Pb accumulation
above a certain exposure concentration (exceeding more than ten times the criteria
for chronic exposure concentration as defined by the US Environmental Protection
Agency) dropped strongly with log BCF < À1. Exposure concentrations influence
metal bioaccumulation; thus a positive correlation (Pearson correlation coefficient;
n ¼ 238; r
2
¼ 0.28, p < 0.05) was found between metal concentration in biofilm and
130
C. Bonnineau et al.
characteristics than can also help them bioaccumulate. For instance, the highest BCF
values were observed for halogenated contaminants such as hexachlorobenzenes
(BCF up to 147,000 L g
À1 ), PCBs (BCF up to 56,000 L g
À1 ), or per- and
polyfluoroalkylated substances (BCF up to 10,000 L g
À1 ) (Fig. 5, Table S1),
suggesting that the compounds’ high electron affinity with living cells is also
strongly involved in its accumulation. Nevertheless, validation of this hypothesis
remains bottlenecked by technical limitations, as the quantification of intracellular
organic contaminants in microbial biofilms is not yet possible (Sect. 2.2).
Non-organochlorine pesticides and pharmaceuticals measured in periphytic biofilms
generally show lower BCFs (BCF < 3.6 L g
À1 ) than metals and fluorinated or
organochlorine contaminants (e.g., DDT, dichlorodiphenyltrichloroethane; BCF up
to 78,550 L g
À1 ). The lower concentration of these contaminants in periphytic
biofilms could also be explained by different biodegradation processes for different
substances. For instance, studies have shown that periphytic microbial communities
can partially transform and/or mineralize pesticides (e.g., the phenylurea herbicide
diuron (Pesce et al. 2009) and glyphosate (Carles et al. 2019)) and antibiotics (e.g.,
the sulfonamide antibiotics sulfamethazine and sulfamethoxazole (Vila-Costa et al.
2017)). Metabolites are thus sometimes found in biofilms (e.g., atrazine metabolites
(Lawrence et al. 2001) or glyphosate metabolites such as aminomethylphosphonic
acid (Carles et al. 2019)), but it is not always possible to discriminate those produced
through biodegradation by the biofilm itself from those that were already present
in the water column before being bioaccumulated. Additionally, the lower BCFs
observed for the non-organochlorine pesticides (i.e., glyphosate, diuron, and its
metabolites) could also be explained by higher exposure concentrations since
those values were applied in laboratory experiments (contrary to BCF values for
pharmaceuticals obtained in the field); further field study investigating pesticides
bioaccumulation in natural periphytic biofilms is therefore required to confirm those
first observations.
Each step of the bioaccumulation process is influenced by a number of factors
such as exposure duration and concentration, physical-chemical conditions, and
biofilm composition. Hydrology and geomorphology are also likely to influence
bioaccumulation especially by driving contaminants repartition between aquatic
compartments (surface water, particulate matter, sediment, periphytic biofilm).
In the dataset analyzed, exposure duration was not significantly correlated with
metal BCFs, which argues for fast adsorption of metals in the biofilm matrix. Among
the metals considered, aluminum had the highest uptake efficiency even at low
exposure concentrations (BCF up to 31,800 L g
À1 ), irrespective of exposure duration
(1–35 days). Corcoll et al. (2012) hypothesized that the amount of Al accumulated
was thus “background” content for the biofilms studied. In contrast, Pb accumulation
above a certain exposure concentration (exceeding more than ten times the criteria
for chronic exposure concentration as defined by the US Environmental Protection
Agency) dropped strongly with log BCF < À1. Exposure concentrations influence
metal bioaccumulation; thus a positive correlation (Pearson correlation coefficient;
n ¼ 238; r
2
¼ 0.28, p < 0.05) was found between metal concentration in biofilm and
130
C. Bonnineau et al.