4 Conclusion
The extensive use of treated wastewater in irrigation can be a significant source of
PhACs into agricultural soils, which can be further accumulated in plants and food.
There were only a few studies reporting their potential accumulation in irrigated
soils. This chapter only analyzed studies conducted under agricultural growing and
irrigation conditions because they enable an appropriate risk assessment of
wastewater-derived contaminants to accumulate in soil as they integrate irrigation,
soil, and plant processes.
The main conclusion highlights the lack of PhAC cumulative pattern in soil
across time under long-term TWW irrigation scenarios. PhAC concentration levels
in the 0.06–200 ng g
À1 range were frequently observed. This lack of accumulation
could be likely related to abiotic and biotic transformation processes and to the
formation of NER. Chronic and repeated application of TWW on agricultural soils
has implication on PhAC degradation because there is a potential for agricultural soil
to develop accelerated biodegradation due to microorganism’s adaptation processes,
similar to what has been observed for pesticides [90].
Soil plays therefore a significant role as regulator of the pharmaceuticals available
for plant uptake. The behavior and fate of PhACs in soil are very complex due to
interconnected processes (e.g., sorption, formation of NER, biodegradation). These
environmental processes were briefly discussed in this chapter.
However, the main challenge is related to the determination of the relative
significance of these different abiotic and biotic processes. Enantiomeric fractionation of chiral PhACs has been discussed as a tool for discriminating abiotic and
biotic degradation processes in field studies where the use of radioactively labelled
compounds is not allowed and consequently when a mass balance is difficult to
achieve. The enantiomeric fractionation of two chiral PhACs, namely, MET and
CLB, has been investigated by using chiral LC-HRMS because the former one
underwent aerobic biodegradation and the latter one under anaerobic conditions,
thus covering different environmental conditions. As enantioselectivity reflects very
predominantly biological processes, a shift in enantiomeric ratio of a chiral PhAC
highlighted biodegradation and allowed for differentiating between
photodegradation and biodegradation processes. This approach might be also quantitative by applying the Rayleigh model allowing for a quantitative assessment of
biodegradation processes without establishing a mass balance. The main scientific
gap remains the quantitative determination of the formation of NER of PhACs in soil
because these studies require the use of isotope-labelled compounds (e.g.,
14 C or
13 C) and are costly and suffer from a lack of standardized procedures in their
implementation.
Soil Sorption and Degradation Studies of Pharmaceutical Compounds Present in. . .
169
The extensive use of treated wastewater in irrigation can be a significant source of
PhACs into agricultural soils, which can be further accumulated in plants and food.
There were only a few studies reporting their potential accumulation in irrigated
soils. This chapter only analyzed studies conducted under agricultural growing and
irrigation conditions because they enable an appropriate risk assessment of
wastewater-derived contaminants to accumulate in soil as they integrate irrigation,
soil, and plant processes.
The main conclusion highlights the lack of PhAC cumulative pattern in soil
across time under long-term TWW irrigation scenarios. PhAC concentration levels
in the 0.06–200 ng g
À1 range were frequently observed. This lack of accumulation
could be likely related to abiotic and biotic transformation processes and to the
formation of NER. Chronic and repeated application of TWW on agricultural soils
has implication on PhAC degradation because there is a potential for agricultural soil
to develop accelerated biodegradation due to microorganism’s adaptation processes,
similar to what has been observed for pesticides [90].
Soil plays therefore a significant role as regulator of the pharmaceuticals available
for plant uptake. The behavior and fate of PhACs in soil are very complex due to
interconnected processes (e.g., sorption, formation of NER, biodegradation). These
environmental processes were briefly discussed in this chapter.
However, the main challenge is related to the determination of the relative
significance of these different abiotic and biotic processes. Enantiomeric fractionation of chiral PhACs has been discussed as a tool for discriminating abiotic and
biotic degradation processes in field studies where the use of radioactively labelled
compounds is not allowed and consequently when a mass balance is difficult to
achieve. The enantiomeric fractionation of two chiral PhACs, namely, MET and
CLB, has been investigated by using chiral LC-HRMS because the former one
underwent aerobic biodegradation and the latter one under anaerobic conditions,
thus covering different environmental conditions. As enantioselectivity reflects very
predominantly biological processes, a shift in enantiomeric ratio of a chiral PhAC
highlighted biodegradation and allowed for differentiating between
photodegradation and biodegradation processes. This approach might be also quantitative by applying the Rayleigh model allowing for a quantitative assessment of
biodegradation processes without establishing a mass balance. The main scientific
gap remains the quantitative determination of the formation of NER of PhACs in soil
because these studies require the use of isotope-labelled compounds (e.g.,
14 C or
13 C) and are costly and suffer from a lack of standardized procedures in their
implementation.
Soil Sorption and Degradation Studies of Pharmaceutical Compounds Present in. . .
169