uptake varies among species. For example, leucaena (Leucaena leucocephala),
annual meadow grass (Poa annua), and indigofera (Indigofera amblyantha) are
known to have high translocation capacity for some metals, such as lead (Pb) and
cadmium (Cd), but limited translocation of heavy metals from the roots to the
aboveground tissues (Chen et al. 2014a, b), while others show the opposite trend
(Ge et al. 2003).
High concentration levels of heavy metals are often found in the vicinity of
railways. Wiłkomirski et al. (2011) reported the same concentration of molybdenum
(Mo) close to and approximately 2 km from the railways in Poland. For instance,
the concentration of nickel, cadmium, cobalt, and lead in the moss (Pleurozium
schreberi) was the same 30 m from the railway as it was at points near the railways
(Mazur et al. 2013). In addition, high concentrations of PAHs were found in the
aerial parts of plant species near the railway and up to distances of 30 m from the
railway (Malawaka and Wilkomirski 2001; Wiłkomirski et al. 2011). On railways,
in particular, the biodegradation of PAHs and herbicides is extremely low and can
persist over decades (Wilkomirski et al. 2012).
Water Pollution
Infrastructures associated with railways (e.g., leakages of petroleum products from
fuel storage tanks) contribute, together with pollutants, to aquatic ecosystems
(Schweinsberg et al. 1999; Vo et al. 2015). Levengood et al. (2015) documented
high concentrations of PAHs and heavy metals in waterways bisected or bordered
by railways. They showed that the PAH concentration was higher downstream than
upstream of the railway (Levengood et al. 2015). They also found that phenanthrene and dibenzo (a, h) anthracene (a PAH element) concentrations at some sites
represented a risk to aquatic life, whereas the chromium (Cr) values were still below
the levels of concern for aquatic life (Levengood et al. 2015).
Herbicides and pesticides are other sources of water pollution. For herbicides,
Schweinsberg et al. (1999) discovered that in Germany before the 1990s, a much
higher total amount of these compounds were applied on railway tracks than in
agriculture. Recently, Vo et al. (2015) showed that many herbicides applied during
the operation of the railway are at concentrations that are lethal to most of the
aquatic fauna, particularly fish populations; they indicate that compounds such as
Imazapyr or Diuron concentrations can take 6 and 48 months, respectively, to drop
below 50% of their original levels.
Soil Erosion and Changes in Hydrology
The abrupt change of soil required to establish the railway embankment leads to
vegetation loss, compresses the soil, and compromises water drainage (Ferrell and
84
P.S. Lucas et al.
annual meadow grass (Poa annua), and indigofera (Indigofera amblyantha) are
known to have high translocation capacity for some metals, such as lead (Pb) and
cadmium (Cd), but limited translocation of heavy metals from the roots to the
aboveground tissues (Chen et al. 2014a, b), while others show the opposite trend
(Ge et al. 2003).
High concentration levels of heavy metals are often found in the vicinity of
railways. Wiłkomirski et al. (2011) reported the same concentration of molybdenum
(Mo) close to and approximately 2 km from the railways in Poland. For instance,
the concentration of nickel, cadmium, cobalt, and lead in the moss (Pleurozium
schreberi) was the same 30 m from the railway as it was at points near the railways
(Mazur et al. 2013). In addition, high concentrations of PAHs were found in the
aerial parts of plant species near the railway and up to distances of 30 m from the
railway (Malawaka and Wilkomirski 2001; Wiłkomirski et al. 2011). On railways,
in particular, the biodegradation of PAHs and herbicides is extremely low and can
persist over decades (Wilkomirski et al. 2012).
Water Pollution
Infrastructures associated with railways (e.g., leakages of petroleum products from
fuel storage tanks) contribute, together with pollutants, to aquatic ecosystems
(Schweinsberg et al. 1999; Vo et al. 2015). Levengood et al. (2015) documented
high concentrations of PAHs and heavy metals in waterways bisected or bordered
by railways. They showed that the PAH concentration was higher downstream than
upstream of the railway (Levengood et al. 2015). They also found that phenanthrene and dibenzo (a, h) anthracene (a PAH element) concentrations at some sites
represented a risk to aquatic life, whereas the chromium (Cr) values were still below
the levels of concern for aquatic life (Levengood et al. 2015).
Herbicides and pesticides are other sources of water pollution. For herbicides,
Schweinsberg et al. (1999) discovered that in Germany before the 1990s, a much
higher total amount of these compounds were applied on railway tracks than in
agriculture. Recently, Vo et al. (2015) showed that many herbicides applied during
the operation of the railway are at concentrations that are lethal to most of the
aquatic fauna, particularly fish populations; they indicate that compounds such as
Imazapyr or Diuron concentrations can take 6 and 48 months, respectively, to drop
below 50% of their original levels.
Soil Erosion and Changes in Hydrology
The abrupt change of soil required to establish the railway embankment leads to
vegetation loss, compresses the soil, and compromises water drainage (Ferrell and
84
P.S. Lucas et al.