pathogens and other components such as nutrients (very effective denitrification
processes) and metals. In addition, CWs represent a potential low-cost solution for
the removal of contamination from emerging organic contaminants, including pharmaceutical products in wastewater effluents [63]. In fact, in these natural environments, a multitude of physical, chemical, and biological processes occur
simultaneously, such as adsorption (soil or sediments), photolysis, volatilization,
absorption and accumulation in plants, exudation, and microbial degradation
[86, 87]. CWs allow to treat a high load of wastewater with large quantities of
organic substances and PhACs representing a great potential of use in low-income
countries and in rural areas [88]. The removal efficiency of PhACs in wetlands may
be influenced by numerous design parameters in addition to the presence and type of
vegetation as well as the type of substrate. In addition to the design and operating
factors (area, bed depth, hydraulic loading speed, organic loading speed, and
hydraulic retention time), other variables that could influence the removal efficiency
of the CW are the physical-chemical parameters (dissolved oxygen, temperature, and
pH), the amount of sunlight, the type and composition of microbiota, the age of the
wetland, and the seasonality of the high microbial biomass. The geographic variables
and the temperature together with the type of vegetation affect the microbial activity
and evapotranspiration and consequently the mobility and the degradation of organic
compounds [89]. In fact, seasonality affects the intensity and the cycle of light,
consequently influencing the biological cycle of the plants, microbes, and their
activities. Generally, constructed wetlands consist of a single species, e.g., dense
reed plantations with heights that can reach 2 or 3 meters. These reeds are mainly
formed by marsh straw or rushes (Phragmites australis or Juncus effusus), in areas
with lower water, while in waters of greater depth, mainly by cattails (Typha latifolia
or Typha angustifolia), may be utilized. Plants absorb pollutants through their roots
which can be translocated to non-immersed parts, such as stems and leaves where
they can be accumulated, translocated, metabolized, or degraded by the plant itself or
in cooperation with the endophytic microorganisms inhabiting plant tissues. In fact,
the rhizosphere constitutes the most active reaction zone of the submerged plants of
the wetlands, where physical-chemical and biological processes occur induced by
the interaction of plants, microorganisms, substrate, and pollutants [90, 91]. In most
cases, greatest biodegradation of pharmaceutical products occurs there
[92]. Although CWs are a green and economic alternative to wastewater treatment
especially in rural or economically disadvantaged areas, the biggest problem is the
removal and disposal of the large vegetable biomass produced. A non-careful
management of this biomass, in fact, could recirculate large amounts of toxic organic
substances accumulated in it into the environment.
The Journey of Human Drugs from Their Design at the Bench to Their Fate in Crops
23
processes) and metals. In addition, CWs represent a potential low-cost solution for
the removal of contamination from emerging organic contaminants, including pharmaceutical products in wastewater effluents [63]. In fact, in these natural environments, a multitude of physical, chemical, and biological processes occur
simultaneously, such as adsorption (soil or sediments), photolysis, volatilization,
absorption and accumulation in plants, exudation, and microbial degradation
[86, 87]. CWs allow to treat a high load of wastewater with large quantities of
organic substances and PhACs representing a great potential of use in low-income
countries and in rural areas [88]. The removal efficiency of PhACs in wetlands may
be influenced by numerous design parameters in addition to the presence and type of
vegetation as well as the type of substrate. In addition to the design and operating
factors (area, bed depth, hydraulic loading speed, organic loading speed, and
hydraulic retention time), other variables that could influence the removal efficiency
of the CW are the physical-chemical parameters (dissolved oxygen, temperature, and
pH), the amount of sunlight, the type and composition of microbiota, the age of the
wetland, and the seasonality of the high microbial biomass. The geographic variables
and the temperature together with the type of vegetation affect the microbial activity
and evapotranspiration and consequently the mobility and the degradation of organic
compounds [89]. In fact, seasonality affects the intensity and the cycle of light,
consequently influencing the biological cycle of the plants, microbes, and their
activities. Generally, constructed wetlands consist of a single species, e.g., dense
reed plantations with heights that can reach 2 or 3 meters. These reeds are mainly
formed by marsh straw or rushes (Phragmites australis or Juncus effusus), in areas
with lower water, while in waters of greater depth, mainly by cattails (Typha latifolia
or Typha angustifolia), may be utilized. Plants absorb pollutants through their roots
which can be translocated to non-immersed parts, such as stems and leaves where
they can be accumulated, translocated, metabolized, or degraded by the plant itself or
in cooperation with the endophytic microorganisms inhabiting plant tissues. In fact,
the rhizosphere constitutes the most active reaction zone of the submerged plants of
the wetlands, where physical-chemical and biological processes occur induced by
the interaction of plants, microorganisms, substrate, and pollutants [90, 91]. In most
cases, greatest biodegradation of pharmaceutical products occurs there
[92]. Although CWs are a green and economic alternative to wastewater treatment
especially in rural or economically disadvantaged areas, the biggest problem is the
removal and disposal of the large vegetable biomass produced. A non-careful
management of this biomass, in fact, could recirculate large amounts of toxic organic
substances accumulated in it into the environment.
The Journey of Human Drugs from Their Design at the Bench to Their Fate in Crops
23