bioavailability for primary consumers and thus trophic transfers within the food web.
Lundqvist et al. (2012) showed that increasing DOM concentrations in water led to
increasing sorption of chlorpyrifos in biofilms. However, despite the resulting high
concentrations in biofilms, dietary uptake of chlorpyrifos by snails remained relatively low, and the results showed that the combined presence of biofilms and of
medium- and high-DOM concentrations reduced the share of chlorpyrifos bioavailable for snails. Testing two other insecticides (carbofuran and lindane) exhibiting
lower hydrophobicity levels than chlorpyrifos on a low-to-high-DOM concentration
gradient, Lundqvist et al. (2012) also demonstrated that the accumulation of pesticides by the snails was influenced by both DOM concentrations and pesticide
hydrophobicity.
Microbial biofilms are an important food resource in freshwater ecosystems,
and our literature analysis highlights their potential to accumulate contaminants
and modify their bioavailability, thus influencing their transfers through food
webs. However, the role of biofilms in dietary contaminant exposure has been
neglected for a long time, and the importance of biofilms in trophic transfers of
those potentially toxic substances is still understudied, leaving a critical lack of
knowledge, especially but not exclusively concerning biofilms attached to sediments
or organic substrates such as leaf litter.
5 Conclusions and Future Challenges
This literature review, which illustrates the dynamic interactions between contaminants and biofilms in aquatic ecosystems, underscores widely different levels of
knowledge according to the kind of substrate where the biofilm grows and the food
web pathway(s) to which it contributes. Accordingly, while studies on periphyton
show that biofilms are able to accumulate a wide range of metals and organic
contaminants, the role of biofilms in the distribution of contaminants among different aquatic compartments (surface water, periphyton, sediments, leaf litter) and the
associated biota remains unclear and has not, to our knowledge, been quantified.
This is mainly due to the fact that we still lack methods to specifically assess and
measure contaminants in microbial communities of complex solid matrices such as
sediment or leaf litter. Moreover, even though several studies have attempted to
investigate chemical concentrations simultaneously in different aquatic compartments (sediment, surface water, and biofilm; Kohušová et al. 2011), there is still a
lack of data on the role of microbial communities in contaminant accumulation
(or release) processes in sediments and organic substrates. This issue remains a
bottleneck, given the abovementioned methodological limitations. Field or microcosm surveys including systematic characterization of the contamination in these
different aquatic compartments combined with laboratory experiments quantifying
sorption/desorption rates under various controlled conditions are now needed to
better estimate the role played by biofilms in contaminant fluxes within the aquatic
ecosystem and their food webs.
Role of Biofilms in Contaminant Bioaccumulation and Trophic Transfer in Aquatic. . .
141
Lundqvist et al. (2012) showed that increasing DOM concentrations in water led to
increasing sorption of chlorpyrifos in biofilms. However, despite the resulting high
concentrations in biofilms, dietary uptake of chlorpyrifos by snails remained relatively low, and the results showed that the combined presence of biofilms and of
medium- and high-DOM concentrations reduced the share of chlorpyrifos bioavailable for snails. Testing two other insecticides (carbofuran and lindane) exhibiting
lower hydrophobicity levels than chlorpyrifos on a low-to-high-DOM concentration
gradient, Lundqvist et al. (2012) also demonstrated that the accumulation of pesticides by the snails was influenced by both DOM concentrations and pesticide
hydrophobicity.
Microbial biofilms are an important food resource in freshwater ecosystems,
and our literature analysis highlights their potential to accumulate contaminants
and modify their bioavailability, thus influencing their transfers through food
webs. However, the role of biofilms in dietary contaminant exposure has been
neglected for a long time, and the importance of biofilms in trophic transfers of
those potentially toxic substances is still understudied, leaving a critical lack of
knowledge, especially but not exclusively concerning biofilms attached to sediments
or organic substrates such as leaf litter.
5 Conclusions and Future Challenges
This literature review, which illustrates the dynamic interactions between contaminants and biofilms in aquatic ecosystems, underscores widely different levels of
knowledge according to the kind of substrate where the biofilm grows and the food
web pathway(s) to which it contributes. Accordingly, while studies on periphyton
show that biofilms are able to accumulate a wide range of metals and organic
contaminants, the role of biofilms in the distribution of contaminants among different aquatic compartments (surface water, periphyton, sediments, leaf litter) and the
associated biota remains unclear and has not, to our knowledge, been quantified.
This is mainly due to the fact that we still lack methods to specifically assess and
measure contaminants in microbial communities of complex solid matrices such as
sediment or leaf litter. Moreover, even though several studies have attempted to
investigate chemical concentrations simultaneously in different aquatic compartments (sediment, surface water, and biofilm; Kohušová et al. 2011), there is still a
lack of data on the role of microbial communities in contaminant accumulation
(or release) processes in sediments and organic substrates. This issue remains a
bottleneck, given the abovementioned methodological limitations. Field or microcosm surveys including systematic characterization of the contamination in these
different aquatic compartments combined with laboratory experiments quantifying
sorption/desorption rates under various controlled conditions are now needed to
better estimate the role played by biofilms in contaminant fluxes within the aquatic
ecosystem and their food webs.
Role of Biofilms in Contaminant Bioaccumulation and Trophic Transfer in Aquatic. . .
141