in various countries, depending on income status. For example, whilst 70% of
wastewater produced from municipal and industrial sources is treated in highincome countries (HIC), this value falls to between 28 and 38% in middle-income
countries (MIC), whilst less than 10% of wastewater is treated in low-income
countries (LIC) [146]. Furthermore, even where sewerage networks or on-site
wastewater systems are available, a high proportion of wastewater that is collected
for treatment is not adequately treated, if at all. Treatment of wastewater is a mean of
significantly reducing not only the burden of pathogens and excess nutrients but also
contaminants such as pharmaceuticals. Whilst deliberate (or direct) reuse of highly
treated wastewater for agricultural applications is increasingly seen as a valuable
commodity in HICs, wastewater treated to a considerably lower degree can also be
reused directly or through contamination of surface and groundwater with wastewater (indirectly) in LMICs [146].
Of the 2.75 million km
2 of agricultural land that requires irrigation, up to 7%
(or 200,000 km
2 ) of this total has been estimated to be irrigated with wastewater, at
varying degrees of treatment, with around 1 billion people estimated to be consuming agricultural products irrigated in such a manner [147]. Aside from the potential
risks this entails for exposure to pathogens and nutrient pollution, this also represents
a scenario where minimal mitigation of pharmaceuticals present in wastewater
occurs. For example, biodegradation and sorption of pharmaceuticals, without the
conditions to support enhanced biological removal of pharmaceuticals found in a
WWTP, will be substantially reduced for many pharmaceuticals commonly found in
wastewater [148]. As discussed previously, biosolids, generated during effective
biological wastewater treatment, can accumulate many pharmaceuticals through
hydrophobic and ionic interactions but can also play a protective role in uptake of
pharmaceuticals in plants and terrestrial organisms. Additional treatments, including
filtration, reverse osmosis and disinfection, are also effective in removing pharmaceuticals from wastewater, but these are more commonly used in HICs because of
the initial and ongoing maintenance and cost requirements for their use.
It should be noted, however, that concentrations of pharmaceuticals measured in
wastewater produced in HICs are not necessarily representative of wastewater in
LMICs. For example, the use of pharmaceuticals in HICs is more prevalent due to
the ability to access healthcare and also the higher proportion of chronic diseases that
require long-term pharmaceutical therapy [149]. Conversely, the use of pharmaceuticals in human health and agricultural applications (e.g. aquaculture and livestock)
is typically poorly regulated or used contrary to regulations in LMICs and pharmaceuticals [149, 150]. The direct and indirect use of wastewater from these agricultural applications can also therefore contribute to pharmaceutical loads in irrigation
water for crops [146]. In addition to this, manufacturing of pharmaceuticals is
increasing significantly in LMICs (e.g. China and India), especially for generic
pharmaceuticals. This has led to additional burdens of pharmaceuticals in wastewater being released by these manufacturing facilities, which in some instances can be
substantial [151, 152]. These sources of wastewater are likely to contribute to
indirect wastewater irrigation of crops, albeit at potential high concentrations
[153]. Furthermore, as shown in Fig. 1, few studies have investigated uptake from
210
L. J. Carter et al.
wastewater produced from municipal and industrial sources is treated in highincome countries (HIC), this value falls to between 28 and 38% in middle-income
countries (MIC), whilst less than 10% of wastewater is treated in low-income
countries (LIC) [146]. Furthermore, even where sewerage networks or on-site
wastewater systems are available, a high proportion of wastewater that is collected
for treatment is not adequately treated, if at all. Treatment of wastewater is a mean of
significantly reducing not only the burden of pathogens and excess nutrients but also
contaminants such as pharmaceuticals. Whilst deliberate (or direct) reuse of highly
treated wastewater for agricultural applications is increasingly seen as a valuable
commodity in HICs, wastewater treated to a considerably lower degree can also be
reused directly or through contamination of surface and groundwater with wastewater (indirectly) in LMICs [146].
Of the 2.75 million km
2 of agricultural land that requires irrigation, up to 7%
(or 200,000 km
2 ) of this total has been estimated to be irrigated with wastewater, at
varying degrees of treatment, with around 1 billion people estimated to be consuming agricultural products irrigated in such a manner [147]. Aside from the potential
risks this entails for exposure to pathogens and nutrient pollution, this also represents
a scenario where minimal mitigation of pharmaceuticals present in wastewater
occurs. For example, biodegradation and sorption of pharmaceuticals, without the
conditions to support enhanced biological removal of pharmaceuticals found in a
WWTP, will be substantially reduced for many pharmaceuticals commonly found in
wastewater [148]. As discussed previously, biosolids, generated during effective
biological wastewater treatment, can accumulate many pharmaceuticals through
hydrophobic and ionic interactions but can also play a protective role in uptake of
pharmaceuticals in plants and terrestrial organisms. Additional treatments, including
filtration, reverse osmosis and disinfection, are also effective in removing pharmaceuticals from wastewater, but these are more commonly used in HICs because of
the initial and ongoing maintenance and cost requirements for their use.
It should be noted, however, that concentrations of pharmaceuticals measured in
wastewater produced in HICs are not necessarily representative of wastewater in
LMICs. For example, the use of pharmaceuticals in HICs is more prevalent due to
the ability to access healthcare and also the higher proportion of chronic diseases that
require long-term pharmaceutical therapy [149]. Conversely, the use of pharmaceuticals in human health and agricultural applications (e.g. aquaculture and livestock)
is typically poorly regulated or used contrary to regulations in LMICs and pharmaceuticals [149, 150]. The direct and indirect use of wastewater from these agricultural applications can also therefore contribute to pharmaceutical loads in irrigation
water for crops [146]. In addition to this, manufacturing of pharmaceuticals is
increasing significantly in LMICs (e.g. China and India), especially for generic
pharmaceuticals. This has led to additional burdens of pharmaceuticals in wastewater being released by these manufacturing facilities, which in some instances can be
substantial [151, 152]. These sources of wastewater are likely to contribute to
indirect wastewater irrigation of crops, albeit at potential high concentrations
[153]. Furthermore, as shown in Fig. 1, few studies have investigated uptake from
210
L. J. Carter et al.