groundwater with secondary and tertiary treated municipal wastewater to irrigate a
succession of tomato and broccoli crops and found that the soil irrigated with
secondary treated wastewater resulted in a significant increase of pH and NH 4 -N,
as well as of Na
+
, SAR, and EC, although these were below the threshold value used
to define the soil as saline. According to the authors, the EC increase due to salt
accumulation was particularly evident during the cultivation of tomatoes, while this
condition changed completely during the cultivation of the broccoli due to the
leaching effect of the autumn and winter rains.
However, other researchers have noted that use of low-quality irrigation water
requires the addition of a leaching fraction to avoid salt accumulation in the root
zone. Basic recommendations to appropriately manage low-quality water and avoid
salinity hazards and soil degradation have been provided by Ayers and Westcot [69]
and Rhoades and Loveday [70]. Moreover, numerous studies reported the impacts of
salinity control measures in irrigated agriculture [60, 71–73].
In terms of the accumulation of heavy metals in soil, Campi et al. [74] carried out
a 3-year field study within the In.Te.R.R.A. project in which annual energy crops
were irrigated with secondary and tertiary treated municipal wastewater and compared with crops irrigated with conventional water. The results showed that the
concentrations of heavy metals in the soil were characterised by negligible mean
variations and no significant differences were found among the experimental
treatments.
These results confirm those reported by other authors in studies conducted over
middle-term time scales. Surdyk et al. [75] in the European FP6 SAFIR project
examined heavy metal comportment in soils irrigated by treated wastewater over
3 years in Serbia, Crete, Italy, and China. The authors reported that, when properly
treated, wastewater influent with higher heavy metal contents can be used over the
middle-term (about 3 years) without visible degradation of the soil, even if long-term
cumulative effects cannot be excluded. To this note, some long-term studies have
reported significant increases in heavy metal concentrations in soil surface layers,
although these were below the critical thresholds established by the international
guidelines [62, 76, 77].
Other authors define the effect of wastewater in the long term. Dere et al. [78] and
Lucho-Constantino et al. [79] evaluated the effects of heavy metal concentrations in
soils irrigated over several decades (up to 100 years) with the low-quality wastewaters (raw sewage) of two cities (Paris and Mexico City). They found significant
heavy metal accumulation, especially in wastewater-irrigated soil zone.
Similar research conducted in three different areas of Zimbabwe [34] has demonstrated that the concentrations of the analysed heavy metals (i.e. Cu, Zn, Cd, Cr,
Pb, and Ni) in the wastewater-irrigated soils were significantly higher respect to the
concentrations found in the non-irrigated soils. These results highlighted that the
application of wastewater had enriched the soils with heavy metals, and the authors
concluded that soil contamination by wastewater use presents long-term environmental and health risks.
The effect of wastewater on the accumulation of heavy metals in soil profiles and
groundwater was examined by monitoring zones irrigated with wastewater for
92
G. Gatta et al.
succession of tomato and broccoli crops and found that the soil irrigated with
secondary treated wastewater resulted in a significant increase of pH and NH 4 -N,
as well as of Na
+
, SAR, and EC, although these were below the threshold value used
to define the soil as saline. According to the authors, the EC increase due to salt
accumulation was particularly evident during the cultivation of tomatoes, while this
condition changed completely during the cultivation of the broccoli due to the
leaching effect of the autumn and winter rains.
However, other researchers have noted that use of low-quality irrigation water
requires the addition of a leaching fraction to avoid salt accumulation in the root
zone. Basic recommendations to appropriately manage low-quality water and avoid
salinity hazards and soil degradation have been provided by Ayers and Westcot [69]
and Rhoades and Loveday [70]. Moreover, numerous studies reported the impacts of
salinity control measures in irrigated agriculture [60, 71–73].
In terms of the accumulation of heavy metals in soil, Campi et al. [74] carried out
a 3-year field study within the In.Te.R.R.A. project in which annual energy crops
were irrigated with secondary and tertiary treated municipal wastewater and compared with crops irrigated with conventional water. The results showed that the
concentrations of heavy metals in the soil were characterised by negligible mean
variations and no significant differences were found among the experimental
treatments.
These results confirm those reported by other authors in studies conducted over
middle-term time scales. Surdyk et al. [75] in the European FP6 SAFIR project
examined heavy metal comportment in soils irrigated by treated wastewater over
3 years in Serbia, Crete, Italy, and China. The authors reported that, when properly
treated, wastewater influent with higher heavy metal contents can be used over the
middle-term (about 3 years) without visible degradation of the soil, even if long-term
cumulative effects cannot be excluded. To this note, some long-term studies have
reported significant increases in heavy metal concentrations in soil surface layers,
although these were below the critical thresholds established by the international
guidelines [62, 76, 77].
Other authors define the effect of wastewater in the long term. Dere et al. [78] and
Lucho-Constantino et al. [79] evaluated the effects of heavy metal concentrations in
soils irrigated over several decades (up to 100 years) with the low-quality wastewaters (raw sewage) of two cities (Paris and Mexico City). They found significant
heavy metal accumulation, especially in wastewater-irrigated soil zone.
Similar research conducted in three different areas of Zimbabwe [34] has demonstrated that the concentrations of the analysed heavy metals (i.e. Cu, Zn, Cd, Cr,
Pb, and Ni) in the wastewater-irrigated soils were significantly higher respect to the
concentrations found in the non-irrigated soils. These results highlighted that the
application of wastewater had enriched the soils with heavy metals, and the authors
concluded that soil contamination by wastewater use presents long-term environmental and health risks.
The effect of wastewater on the accumulation of heavy metals in soil profiles and
groundwater was examined by monitoring zones irrigated with wastewater for
92
G. Gatta et al.