5 Plant Uptake from Biosolid Amendment
A significant pathway for pharmaceutical exposure to terrestrial organisms is
through application of sludge derived from wastewater to terrestrial environments.
During wastewater treatment, especially biological treatment processes, large quantities of waste sludge are produced from biomass and inorganic matter. Wastewater
sludges are typically high in organic carbon that can enhance their association
through sorption with pharmaceuticals, especially pharmaceuticals with physicochemical properties that can promote this interaction. Physicochemical properties
that can lead to enhanced sorption include a high (e.g. >10
3 ) octanol-water partition
coefficient (K ow ) and ionisation of functional groups, especially where cationic or
zwitterionic species are formed [85]. A broad range of pharmaceuticals have been
detected in wastewater sludges, with antibiotics being particularly prominent, as well
as NSAIDs, β-blockers and carbamazepine, with concentrations typically in the μg/
kg to low mg/kg concentrations [86–89]. In the case of some classes of antibiotics
that contain cationic functional groups at ambient pH, such as fluoroquinolones and
tetracyclines, association with wastewater sludge can be substantial. This is despite
relatively low K ow (or D ow , which represents the ionised K ow value) values, which
can occur for the fluoroquinolones [85]. In contrast, pharmaceuticals such as
NSAIDs with primarily anionic functional groups at ambient pH are much less
likely to associate with negatively charged surfaces of biosolids [88]. In the case
of the antimicrobial triclosan, it is also likely to be at least partially negatively
charged at ambient pH (pK a ~ 8), but the presence of unionised triclosan, which
has a high K ow value, leads to its common detection in wastewater sludges
[87, 88, 90].
Following wastewater treatment, sludges are then further stabilised to produce
biosolids that can be beneficially reused in terrestrial environments for improving
soil condition in agriculture and landscape rehabilitation. The amount of biosolid
production and reuse varies globally. For example, in China, there are more than
3,500 WWTPs producing more than 6 million tonnes (dry weight) of sludge, of
which the majority is appropriately landfilled, incinerated or reused in construction,
whilst ~40% is applied to land [91–93]. Land application is likely to include
agricultural use, although the amount diverted for this purpose varies considerably
between regions. Although the overall land application of sludge as fertiliser in
China is <40%, this can vary from none to all depending on the city or region where
the sludge is produced [91]. Similarly, in the USA, reuse of biosolids can vary
greatly depending on the state where the biosolids are produced, with an overall
production of ~7 million tonnes/year with ~50% reuse in agriculture [94]. In the EU,
around 10 million tonnes/year are produced, with the UK producing ~3.5 million
tonnes/year of this for 78% agricultural use [95, 96]. Reuse of biosolids is reasonably
consistent across regions in other countries such as Australia, which produces
around 370,000 tonnes/year, of which 70% is reused for agriculture [97]. In contrast,
New Zealand produces relatively low amount of biosolids (~70, 000 tonnes/year)
but only uses ~6% for agriculture [97].
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L. J. Carter et al.
A significant pathway for pharmaceutical exposure to terrestrial organisms is
through application of sludge derived from wastewater to terrestrial environments.
During wastewater treatment, especially biological treatment processes, large quantities of waste sludge are produced from biomass and inorganic matter. Wastewater
sludges are typically high in organic carbon that can enhance their association
through sorption with pharmaceuticals, especially pharmaceuticals with physicochemical properties that can promote this interaction. Physicochemical properties
that can lead to enhanced sorption include a high (e.g. >10
3 ) octanol-water partition
coefficient (K ow ) and ionisation of functional groups, especially where cationic or
zwitterionic species are formed [85]. A broad range of pharmaceuticals have been
detected in wastewater sludges, with antibiotics being particularly prominent, as well
as NSAIDs, β-blockers and carbamazepine, with concentrations typically in the μg/
kg to low mg/kg concentrations [86–89]. In the case of some classes of antibiotics
that contain cationic functional groups at ambient pH, such as fluoroquinolones and
tetracyclines, association with wastewater sludge can be substantial. This is despite
relatively low K ow (or D ow , which represents the ionised K ow value) values, which
can occur for the fluoroquinolones [85]. In contrast, pharmaceuticals such as
NSAIDs with primarily anionic functional groups at ambient pH are much less
likely to associate with negatively charged surfaces of biosolids [88]. In the case
of the antimicrobial triclosan, it is also likely to be at least partially negatively
charged at ambient pH (pK a ~ 8), but the presence of unionised triclosan, which
has a high K ow value, leads to its common detection in wastewater sludges
[87, 88, 90].
Following wastewater treatment, sludges are then further stabilised to produce
biosolids that can be beneficially reused in terrestrial environments for improving
soil condition in agriculture and landscape rehabilitation. The amount of biosolid
production and reuse varies globally. For example, in China, there are more than
3,500 WWTPs producing more than 6 million tonnes (dry weight) of sludge, of
which the majority is appropriately landfilled, incinerated or reused in construction,
whilst ~40% is applied to land [91–93]. Land application is likely to include
agricultural use, although the amount diverted for this purpose varies considerably
between regions. Although the overall land application of sludge as fertiliser in
China is <40%, this can vary from none to all depending on the city or region where
the sludge is produced [91]. Similarly, in the USA, reuse of biosolids can vary
greatly depending on the state where the biosolids are produced, with an overall
production of ~7 million tonnes/year with ~50% reuse in agriculture [94]. In the EU,
around 10 million tonnes/year are produced, with the UK producing ~3.5 million
tonnes/year of this for 78% agricultural use [95, 96]. Reuse of biosolids is reasonably
consistent across regions in other countries such as Australia, which produces
around 370,000 tonnes/year, of which 70% is reused for agriculture [97]. In contrast,
New Zealand produces relatively low amount of biosolids (~70, 000 tonnes/year)
but only uses ~6% for agriculture [97].
200
L. J. Carter et al.