imbalances and phytotoxicity [26]. Each cultivated species is characterised by
specific nutrient requirements depending on the phenological phase. Excesses or
deficiencies in some mineral elements can significantly affect crop production, both
in quantitative and qualitative terms [27].
2.2 Heavy Metal Accumulation in Soil and Crops
Another possible outcome of wastewater reuse for cultivated species is the accumulation of heavy metals in the irrigated soil. The presence of heavy metals in the soil at
very low concentrations is necessary for the growth plants, but at high concentrations, they can be toxic and harmful [12, 28]. Although the heavy metal content in
wastewater used for irrigation is subject to legal limits, continuous use of wastewater
can lead to their buildup in the soil [29]; this can cause stress to plants due to
interference with the metabolic activities and physiological functions in the
plants [30].
Excessive levels of metals can also degrade soil quality, reduce marketable crop
yields, and reduce the quality of marketable agricultural products; these effects can
also pose significant hazards to the health of humans and the surrounding ecosystem
[12, 31].
The leaves and vegetative tissues of cultivated plants tend to accumulate higher
amounts of heavy metals than the fruits [32]. Studies have shown that heavy metals
taken up through plant roots can be transported to the shoots through the xylem
vessels [33] but have poor mobility in the phloem [34]. Crop storage organs
(primarily fruits and seeds) are characterised by low transpiration rates and do not
accumulate heavy metals because they are largely phloem-loaded. Harmful effects
on human health from soil and vegetables contaminated with heavy metals have,
however, been widely reported [12, 35].
Heavy metal activity in the soil is highly influenced by chemical and physical soil
characteristics (pH, texture, and organic matter content) and the effect of heavy
metals on plants varies by crop. It is therefore challenging to set precise limits and
thresholds of tolerance and/or hazard deriving from the presence of heavy metals.
The risk to human health related to the uptake of heavy metals by food crops
depends more on the increase in their available fraction than on their total concentration in the soil [36]; moreover, it is dependent on the heavy metal speciation and
solubility and on the crops cultivated in contaminated soil [37].
High contents of heavy metals are normally found in industrial wastewater,
whereas the concentrations of these metals in domestic wastewater are generally
low due to the settling of solids during treatment [29, 38].
Generally speaking, the use of treated municipal wastewater in agriculture may
result in heavy metal accumulation in the surface layers of the soil [1, 39, 40]
following very long periods (decades) of application, after which concentrations
that can cause adverse effects on crop growth are possible [41–43]. However,
regardless of the heavy metal content of the wastewater, the metals are only taken
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G. Gatta et al.
specific nutrient requirements depending on the phenological phase. Excesses or
deficiencies in some mineral elements can significantly affect crop production, both
in quantitative and qualitative terms [27].
2.2 Heavy Metal Accumulation in Soil and Crops
Another possible outcome of wastewater reuse for cultivated species is the accumulation of heavy metals in the irrigated soil. The presence of heavy metals in the soil at
very low concentrations is necessary for the growth plants, but at high concentrations, they can be toxic and harmful [12, 28]. Although the heavy metal content in
wastewater used for irrigation is subject to legal limits, continuous use of wastewater
can lead to their buildup in the soil [29]; this can cause stress to plants due to
interference with the metabolic activities and physiological functions in the
plants [30].
Excessive levels of metals can also degrade soil quality, reduce marketable crop
yields, and reduce the quality of marketable agricultural products; these effects can
also pose significant hazards to the health of humans and the surrounding ecosystem
[12, 31].
The leaves and vegetative tissues of cultivated plants tend to accumulate higher
amounts of heavy metals than the fruits [32]. Studies have shown that heavy metals
taken up through plant roots can be transported to the shoots through the xylem
vessels [33] but have poor mobility in the phloem [34]. Crop storage organs
(primarily fruits and seeds) are characterised by low transpiration rates and do not
accumulate heavy metals because they are largely phloem-loaded. Harmful effects
on human health from soil and vegetables contaminated with heavy metals have,
however, been widely reported [12, 35].
Heavy metal activity in the soil is highly influenced by chemical and physical soil
characteristics (pH, texture, and organic matter content) and the effect of heavy
metals on plants varies by crop. It is therefore challenging to set precise limits and
thresholds of tolerance and/or hazard deriving from the presence of heavy metals.
The risk to human health related to the uptake of heavy metals by food crops
depends more on the increase in their available fraction than on their total concentration in the soil [36]; moreover, it is dependent on the heavy metal speciation and
solubility and on the crops cultivated in contaminated soil [37].
High contents of heavy metals are normally found in industrial wastewater,
whereas the concentrations of these metals in domestic wastewater are generally
low due to the settling of solids during treatment [29, 38].
Generally speaking, the use of treated municipal wastewater in agriculture may
result in heavy metal accumulation in the surface layers of the soil [1, 39, 40]
following very long periods (decades) of application, after which concentrations
that can cause adverse effects on crop growth are possible [41–43]. However,
regardless of the heavy metal content of the wastewater, the metals are only taken
84
G. Gatta et al.