[34, 35]. Nitrogen is the second compound present at relatively high concentrations
(2–8% of DM). It is found in organic form (63%: proteins, amino acids, and urea)
and ionic (37%: nitrates and nitrites) [23, 24, 26, 28, 29, 36, 37]. Phosphorus is also
an important fertilizer in sludge (2–8% of dry matter). It results from exogenous
contributions of detergents, pesticides, agricultural fertilizers, or microorganisms’
storage (polyphosphates) [35, 38]. Sludge also contains other macro-elements such
as K, Ca, Mg, and Na that result from urban activities [38, 39] (Table 1).
3.2 Metal Trace Elements (MTE) and Nanomaterials
Heavy metals found in WW or its sludge are associated with various products of
domestic, industrial, or agricultural use or come from road leaching. The most
frequently found MTEs are Zn, Cu, Ni, Pb, Cd, Hg, and Cr [42]. The concentrations
of the MTEs, which are often important, depend on the countries and the type of
effluents discharged into the urban network (Table. 2). They are characterized by
their persistence, their bioaccumulation, and their toxicity vis-à-vis the soil and the
environment (Fig. 2). Ferreiro-Domínguez et al. showed that land spreading of
sewage sludge increases copper content of plants grown in agronomic and forest
soils; this effect is more pronounced in unseeded areas of forest soils [42]. Their
accumulation in the soil known as “terraccumulation” is defined as the concentration
of pollutants in soils from land application of contaminated biosolids generated by
agricultural practices, water, and WW facilities. It occurs when the soil ecosystem
becomes unable to metabolize contaminants supplied by biosolids or water
[45]. This may cause toxicity effect on plant and may disturb the autochthonous
microbial communities (e.g., reduction of microbial biomass or alteration of the
community structure).
Due to their widespread use in commercial products, nanomaterial (NM) research
continues to expand, and their impacts on the environment are documented by
numerous reviews and papers, describing new methods of detection, environmental
occurrence and fate, as well as toxicity. Using wetland mesocosms with aquatic
plants, Colman et al. published an interesting study on the impact of silver
nanoparticles on ecosystems. They investigated two diameters of nanosilver
(12 and 49 nm) compared to ionic silver (Ag
+
) in 19 wetland mesocosms. Over
30 days of exposure, they concluded that all three silver treatments were toxic to the
aquatic plants, leading to a significant release of dissolved organic carbon and
chloride following exposure. Despite widely different toxicities observed in controlled laboratory tests, toxicities in the outdoor mesocosms were very similar [36].
56
E. Ammar et al.
(2–8% of DM). It is found in organic form (63%: proteins, amino acids, and urea)
and ionic (37%: nitrates and nitrites) [23, 24, 26, 28, 29, 36, 37]. Phosphorus is also
an important fertilizer in sludge (2–8% of dry matter). It results from exogenous
contributions of detergents, pesticides, agricultural fertilizers, or microorganisms’
storage (polyphosphates) [35, 38]. Sludge also contains other macro-elements such
as K, Ca, Mg, and Na that result from urban activities [38, 39] (Table 1).
3.2 Metal Trace Elements (MTE) and Nanomaterials
Heavy metals found in WW or its sludge are associated with various products of
domestic, industrial, or agricultural use or come from road leaching. The most
frequently found MTEs are Zn, Cu, Ni, Pb, Cd, Hg, and Cr [42]. The concentrations
of the MTEs, which are often important, depend on the countries and the type of
effluents discharged into the urban network (Table. 2). They are characterized by
their persistence, their bioaccumulation, and their toxicity vis-à-vis the soil and the
environment (Fig. 2). Ferreiro-Domínguez et al. showed that land spreading of
sewage sludge increases copper content of plants grown in agronomic and forest
soils; this effect is more pronounced in unseeded areas of forest soils [42]. Their
accumulation in the soil known as “terraccumulation” is defined as the concentration
of pollutants in soils from land application of contaminated biosolids generated by
agricultural practices, water, and WW facilities. It occurs when the soil ecosystem
becomes unable to metabolize contaminants supplied by biosolids or water
[45]. This may cause toxicity effect on plant and may disturb the autochthonous
microbial communities (e.g., reduction of microbial biomass or alteration of the
community structure).
Due to their widespread use in commercial products, nanomaterial (NM) research
continues to expand, and their impacts on the environment are documented by
numerous reviews and papers, describing new methods of detection, environmental
occurrence and fate, as well as toxicity. Using wetland mesocosms with aquatic
plants, Colman et al. published an interesting study on the impact of silver
nanoparticles on ecosystems. They investigated two diameters of nanosilver
(12 and 49 nm) compared to ionic silver (Ag
+
) in 19 wetland mesocosms. Over
30 days of exposure, they concluded that all three silver treatments were toxic to the
aquatic plants, leading to a significant release of dissolved organic carbon and
chloride following exposure. Despite widely different toxicities observed in controlled laboratory tests, toxicities in the outdoor mesocosms were very similar [36].
56
E. Ammar et al.