Sediments are also recognized as an important sink of metals in freshwater
environments. Indeed, numerous studies have reported the accumulation of metal
contaminants in sediments from various kinds of ecosystems including streams (e.g.,
Rodrigues and Formoso 2006), estuaries, and large rivers (e.g., Hamzeh et al. 2016),
artificial reservoirs (e.g., García-Ordiales et al. 2016), and natural lakes (e.g., Gascón
Díez et al. 2017) all over the world, from Europe (e.g., Thevenon et al. 2011) to the
USA (e.g., Garvin et al. 2017), South America (e.g., Smolders et al. 2003), Asia
(e.g., Liao et al. 2017), and Africa (e.g., Kilunga et al. 2017). While anthropogenic
activities can explain part of this contamination, metals are also naturally present in
sediments as geogenic particulate components (Ho et al. 2013). The ubiquity of
metal contamination in freshwater sediments is illustrated in a report summarizing
the results of an extensive chemical survey (567 sampling stations) designed to
measure metal concentrations in sediments from various fluvial ecosystems dotted
across France (INERIS 2010). The reported median, average, and maximum concentrations (in mg kg
À1 dry weight sediment) were, respectively, 7.3, 12.4, and
1,005 for As; 0.7, 10.2, and 7,285 for Cd; 36.0, 52.1, and 5,300 for Cr; 21.7, 48.5,
and 4,330 for Cu; 0.1, 1.2, and 200 for Hg; 19.0, 26.8, and 2,380 for Ni; 32.6, 122.0,
and 50,420 for Pb; and 130.0, 446.0, and 142,500 for Zn (INERIS 2010).
Comparatively, there has been less effort to investigate organic and inorganic
contaminant accumulation in submerged leaf litter. This could be explained by the
ephemeral presence of the substratum in the ecosystem but also by the fact that
studies addressing contamination gradients are mostly focused on downstream
contaminated sections where riparian vegetation is often poor. However, leaf litter
has been proven to adsorb metals (Sridhar et al. 2001) and a range of herbicide and
fungicide molecules (Passeport et al. 2013; Vallée et al. 2014; Rossi et al. 2018). The
sorption potential of these contaminants on leaf substrates may depend on their stage
of decomposition (e.g., Dimitrov et al. 2014 for the fungicide tebuconazole). Leaf
litter accumulated in rivers has comparatively similar (and/or greater) pesticide
adsorption capacities to sediments (Margoum et al. 2006; Passeport et al. 2011).
Vallée et al. (2014) revealed that straw has greater retention potential than sediments
and soils for three herbicides and three fungicides in constructed wetlands. These
results show the importance of organic carbon content and nature in the pesticides
sorption process. A tracer injection experiment was conducted in the field in a “wet”
forest buffer zone to test its potential for reducing loads of glyphosate, isoproturon,
metazachlor, azoxystrobin, epoxiconazole, and cyproconazole (Passeport et al.
2014). Results confirmed that leaf litter layer thickness was a key parameter that
influences the potential for delaying and reducing pesticide transfers and increasing
their degradation.
As observed for periphytic biofilms and discussed above, bioaccumulation of
organic contaminants in sediments, leaves, or drift particulate matter can be
influenced by substratum characteristics and/or environmental factors. A field
study in the Pearl River Estuary (South China) found that sediment total organic
carbon and water pH were the most important factors influencing the dynamics of
distribution of the antibiotics norfloxacin and erythromycin between water and
sediments, respectively (Liang et al. 2013). Different environmental parameters,
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C. Bonnineau et al.
environments. Indeed, numerous studies have reported the accumulation of metal
contaminants in sediments from various kinds of ecosystems including streams (e.g.,
Rodrigues and Formoso 2006), estuaries, and large rivers (e.g., Hamzeh et al. 2016),
artificial reservoirs (e.g., García-Ordiales et al. 2016), and natural lakes (e.g., Gascón
Díez et al. 2017) all over the world, from Europe (e.g., Thevenon et al. 2011) to the
USA (e.g., Garvin et al. 2017), South America (e.g., Smolders et al. 2003), Asia
(e.g., Liao et al. 2017), and Africa (e.g., Kilunga et al. 2017). While anthropogenic
activities can explain part of this contamination, metals are also naturally present in
sediments as geogenic particulate components (Ho et al. 2013). The ubiquity of
metal contamination in freshwater sediments is illustrated in a report summarizing
the results of an extensive chemical survey (567 sampling stations) designed to
measure metal concentrations in sediments from various fluvial ecosystems dotted
across France (INERIS 2010). The reported median, average, and maximum concentrations (in mg kg
À1 dry weight sediment) were, respectively, 7.3, 12.4, and
1,005 for As; 0.7, 10.2, and 7,285 for Cd; 36.0, 52.1, and 5,300 for Cr; 21.7, 48.5,
and 4,330 for Cu; 0.1, 1.2, and 200 for Hg; 19.0, 26.8, and 2,380 for Ni; 32.6, 122.0,
and 50,420 for Pb; and 130.0, 446.0, and 142,500 for Zn (INERIS 2010).
Comparatively, there has been less effort to investigate organic and inorganic
contaminant accumulation in submerged leaf litter. This could be explained by the
ephemeral presence of the substratum in the ecosystem but also by the fact that
studies addressing contamination gradients are mostly focused on downstream
contaminated sections where riparian vegetation is often poor. However, leaf litter
has been proven to adsorb metals (Sridhar et al. 2001) and a range of herbicide and
fungicide molecules (Passeport et al. 2013; Vallée et al. 2014; Rossi et al. 2018). The
sorption potential of these contaminants on leaf substrates may depend on their stage
of decomposition (e.g., Dimitrov et al. 2014 for the fungicide tebuconazole). Leaf
litter accumulated in rivers has comparatively similar (and/or greater) pesticide
adsorption capacities to sediments (Margoum et al. 2006; Passeport et al. 2011).
Vallée et al. (2014) revealed that straw has greater retention potential than sediments
and soils for three herbicides and three fungicides in constructed wetlands. These
results show the importance of organic carbon content and nature in the pesticides
sorption process. A tracer injection experiment was conducted in the field in a “wet”
forest buffer zone to test its potential for reducing loads of glyphosate, isoproturon,
metazachlor, azoxystrobin, epoxiconazole, and cyproconazole (Passeport et al.
2014). Results confirmed that leaf litter layer thickness was a key parameter that
influences the potential for delaying and reducing pesticide transfers and increasing
their degradation.
As observed for periphytic biofilms and discussed above, bioaccumulation of
organic contaminants in sediments, leaves, or drift particulate matter can be
influenced by substratum characteristics and/or environmental factors. A field
study in the Pearl River Estuary (South China) found that sediment total organic
carbon and water pH were the most important factors influencing the dynamics of
distribution of the antibiotics norfloxacin and erythromycin between water and
sediments, respectively (Liang et al. 2013). Different environmental parameters,
134
C. Bonnineau et al.