28
K. Kuroda and J. Kobayashi
Infiltration of contaminated surface waters was found to be a major source and
pathway of PPCPs and ASs in groundwater in Asia, as reported in China, India, and
Vietnam (Table 1.6). Rivers and lakes are typical sources of nearby groundwater,
and the recharge issuing from them brings the contaminants from the surface water
to the groundwater (Díaz-Cruz and Barceló 2008). In Shahu County, central China,
the mean concentrations of multiple antibiotics showed a high correlation between
surface water and groundwater, indicating possible surface water–groundwater interaction (Tong et al. 2014). In Vietnam, untreated wastewater is often disposed into
nearby ponds and streams in suburban and rural areas; while, in urban areas, untreated
wastewater and effluents from septic tanks are transported by canals. These ponds
and canals have been suggested to be a source of PPCPs in the groundwater in Hanoi
and Ho Chi Minh City (Duong et al. 2015; Kuroda et al. 2015).
Another major source and pathway of PPCPs and ASs is leakage from sewerage
systems, as reported in the urban and residential areas of Japan, Korea, and Singapore
(Table 1.6). In Tokyo, based on calculations using carbamazepine as a marker of
sewage, 0.8–1.7% of the dry weather flow of sewage was estimated to exfiltrate into
the unconfined aquifers (Kuroda et al. 2012).
There are multiple other sources and pathways of PPCPs and ASs in Asian groundwater, such as leakage from septic tanks and direct discharge of untreated wastewater
(Table 1.6). Identifying the sources and pathways of groundwater pollution is often
difficult because of insufficient available information; thus, multiple sources and
pathways are often considered. For example, in the Ganges River Basin, where infiltration of the river water through bank infiltration or irrigation is considered as the
main source of PPCPs and ASs in groundwater, other possible sources might include
leakage from septic tanks (or unpaved septic tanks) and leaching from landfills, flaws
in sewage disposal practices, and stormwater runoff filtration via unpaved drainage
systems (Sharma et al. 2019).
Once PPCPs and ASs enter into the subsurface, they undergo various processes
that affect their fate, such as volatilization, adsorption to soil organics, and biodegradation. Groundwater residence time, redox conditions, and total loading are also
important factors in determining the presence and persistence of PPCPs and ASs
in the subsurface and groundwater (Lapworth et al. 2012). It is widely known that
the biological activity which degrades organic pollutants is higher in the soil zone
than in the groundwater, where the bacterial population is less abundant and diverse
(Alvarez and Illman 2005). Moreover, microbial degradation of organic pollutants
generally prefers aerobic to anaerobic conditions (Watanabe et al. 2010). Several
persistent PPCPs and ASs, such as carbamazepine, sulfamethoxazole, and sucralose,
can remain in groundwater for long periods and reach into deep confined aquifers
(Kuroda et al. 2012; Lapworth et al. 2018; Tong et al. 2014). Intense exploitation of
groundwater may play a role in this deep migration of anthropogenic contaminants;
excessive pumping, for example, has been common in many Asian cities, and in
some cases has even changed the groundwater flow and recharge regimes (Haque
et al. 2013). In Hanoi, Vietnam, excessive pumping has reportedly led to elevated levels of arsenic in deep aquifers (Kuroda et al. 2017b; Winkel et al. 2011), suggesting
vulnerability in the deep aquifers of Asian cities.
K. Kuroda and J. Kobayashi
Infiltration of contaminated surface waters was found to be a major source and
pathway of PPCPs and ASs in groundwater in Asia, as reported in China, India, and
Vietnam (Table 1.6). Rivers and lakes are typical sources of nearby groundwater,
and the recharge issuing from them brings the contaminants from the surface water
to the groundwater (Díaz-Cruz and Barceló 2008). In Shahu County, central China,
the mean concentrations of multiple antibiotics showed a high correlation between
surface water and groundwater, indicating possible surface water–groundwater interaction (Tong et al. 2014). In Vietnam, untreated wastewater is often disposed into
nearby ponds and streams in suburban and rural areas; while, in urban areas, untreated
wastewater and effluents from septic tanks are transported by canals. These ponds
and canals have been suggested to be a source of PPCPs in the groundwater in Hanoi
and Ho Chi Minh City (Duong et al. 2015; Kuroda et al. 2015).
Another major source and pathway of PPCPs and ASs is leakage from sewerage
systems, as reported in the urban and residential areas of Japan, Korea, and Singapore
(Table 1.6). In Tokyo, based on calculations using carbamazepine as a marker of
sewage, 0.8–1.7% of the dry weather flow of sewage was estimated to exfiltrate into
the unconfined aquifers (Kuroda et al. 2012).
There are multiple other sources and pathways of PPCPs and ASs in Asian groundwater, such as leakage from septic tanks and direct discharge of untreated wastewater
(Table 1.6). Identifying the sources and pathways of groundwater pollution is often
difficult because of insufficient available information; thus, multiple sources and
pathways are often considered. For example, in the Ganges River Basin, where infiltration of the river water through bank infiltration or irrigation is considered as the
main source of PPCPs and ASs in groundwater, other possible sources might include
leakage from septic tanks (or unpaved septic tanks) and leaching from landfills, flaws
in sewage disposal practices, and stormwater runoff filtration via unpaved drainage
systems (Sharma et al. 2019).
Once PPCPs and ASs enter into the subsurface, they undergo various processes
that affect their fate, such as volatilization, adsorption to soil organics, and biodegradation. Groundwater residence time, redox conditions, and total loading are also
important factors in determining the presence and persistence of PPCPs and ASs
in the subsurface and groundwater (Lapworth et al. 2012). It is widely known that
the biological activity which degrades organic pollutants is higher in the soil zone
than in the groundwater, where the bacterial population is less abundant and diverse
(Alvarez and Illman 2005). Moreover, microbial degradation of organic pollutants
generally prefers aerobic to anaerobic conditions (Watanabe et al. 2010). Several
persistent PPCPs and ASs, such as carbamazepine, sulfamethoxazole, and sucralose,
can remain in groundwater for long periods and reach into deep confined aquifers
(Kuroda et al. 2012; Lapworth et al. 2018; Tong et al. 2014). Intense exploitation of
groundwater may play a role in this deep migration of anthropogenic contaminants;
excessive pumping, for example, has been common in many Asian cities, and in
some cases has even changed the groundwater flow and recharge regimes (Haque
et al. 2013). In Hanoi, Vietnam, excessive pumping has reportedly led to elevated levels of arsenic in deep aquifers (Kuroda et al. 2017b; Winkel et al. 2011), suggesting
vulnerability in the deep aquifers of Asian cities.