26
K. Kuroda and J. Kobayashi
The above-mentioned differences in ASs concentrations among the studies would
reflect the difference in sources, usage, consumption rate, and environmental attenuation of the respective ASs. Many studies have suggested that wastewater is a major
source of ASs in surface water and groundwater (e.g., Lange et al. 2012; Oppenheimer et al. 2011; Tran et al. 2014a). In Singapore, wastewater from residential and
commercial areas showed significantly higher AS concentrations than hospital and
industrial wastewaters (Tran et al. 2014a). Some ASs are added to livestock feed
(e.g., NHDC, sucralose, and saccharin in China; Gan et al. 2013), and sulfonylurea
herbicides are known to generate saccharin upon degradation in soil (Buerge et al.
2011). Therefore, pig manure and sulfonylurea herbicides used in upstream farmlands may be a source of saccharin in the Tianjin groundwater (Gan et al. 2013).
ASs can also be present at fairly high concentrations in precipitation (e.g., up to
0.16 μg/L for acesulfame and up to 0.91 μg/L for cyclamate; Gan et al. 2013), and
precipitation is inferred to be an important source of saccharin and cyclamate in the
surface waters in Tianjin (Gan et al. 2013). In terms of biodegradation, it has been
reported that acesulfame is the most persistent AS, followed by sucralose, saccharin,
and cyclamate, in biological treatment and soil–water systems (Buerge et al. 2009,
2011).
Diethyltoluamide (DEET) is the most commonly used active ingredient in insect
repellents. Nearly all insect repellents sold to consumers are applied as lotions, solids,
or sprays (Aronson et al. 2012; Merel and Snyder 2016; Weeks et al. 2012), and DEET
that has been applied to skin or clothing may volatilize to a small degree, be absorbed
dermally, or be washed off into wastewater. Meanwhile, some fraction of DEET will
enter the air, and some overspray may enter the soil and groundwater.
As shown in Table 1.5, the occurrence and concentrations of DEET in Asian
groundwater varied among the studies. Singapore had the highest detection rate
(100%) and maximum concentration (3481 ng/L; Tran et al. 2014b). This may be
because of the high consumption of DEET in this tropical country; DEET concentrations in surface waters and wastewater tend to be highest during the summer months
(Dumouchelle 2005; Hinkle et al. 2005). In Singapore, DEET was abundant not only
in groundwater from sewered catchments, but also in background groundwater taken
from a catchment with no known wastewater sources, possibly because of outside use
of DEET (Tran et al. 2014b). The concentration ranges of DEET in Asian groundwater are similar to those in groundwater from North America and Europe (Merel
and Snyder 2016).
1.5 Sources, Pathways, and Fates of PPCPs and ASs
in Asian Groundwater
The sources of groundwater pollution can be categorized into point sources and nonpoint (diffuse) sources. Pollution by point sources refers to contamination by spatially
discrete sources, such as effluents from industrial plants and hospitals, or discharge
K. Kuroda and J. Kobayashi
The above-mentioned differences in ASs concentrations among the studies would
reflect the difference in sources, usage, consumption rate, and environmental attenuation of the respective ASs. Many studies have suggested that wastewater is a major
source of ASs in surface water and groundwater (e.g., Lange et al. 2012; Oppenheimer et al. 2011; Tran et al. 2014a). In Singapore, wastewater from residential and
commercial areas showed significantly higher AS concentrations than hospital and
industrial wastewaters (Tran et al. 2014a). Some ASs are added to livestock feed
(e.g., NHDC, sucralose, and saccharin in China; Gan et al. 2013), and sulfonylurea
herbicides are known to generate saccharin upon degradation in soil (Buerge et al.
2011). Therefore, pig manure and sulfonylurea herbicides used in upstream farmlands may be a source of saccharin in the Tianjin groundwater (Gan et al. 2013).
ASs can also be present at fairly high concentrations in precipitation (e.g., up to
0.16 μg/L for acesulfame and up to 0.91 μg/L for cyclamate; Gan et al. 2013), and
precipitation is inferred to be an important source of saccharin and cyclamate in the
surface waters in Tianjin (Gan et al. 2013). In terms of biodegradation, it has been
reported that acesulfame is the most persistent AS, followed by sucralose, saccharin,
and cyclamate, in biological treatment and soil–water systems (Buerge et al. 2009,
2011).
Diethyltoluamide (DEET) is the most commonly used active ingredient in insect
repellents. Nearly all insect repellents sold to consumers are applied as lotions, solids,
or sprays (Aronson et al. 2012; Merel and Snyder 2016; Weeks et al. 2012), and DEET
that has been applied to skin or clothing may volatilize to a small degree, be absorbed
dermally, or be washed off into wastewater. Meanwhile, some fraction of DEET will
enter the air, and some overspray may enter the soil and groundwater.
As shown in Table 1.5, the occurrence and concentrations of DEET in Asian
groundwater varied among the studies. Singapore had the highest detection rate
(100%) and maximum concentration (3481 ng/L; Tran et al. 2014b). This may be
because of the high consumption of DEET in this tropical country; DEET concentrations in surface waters and wastewater tend to be highest during the summer months
(Dumouchelle 2005; Hinkle et al. 2005). In Singapore, DEET was abundant not only
in groundwater from sewered catchments, but also in background groundwater taken
from a catchment with no known wastewater sources, possibly because of outside use
of DEET (Tran et al. 2014b). The concentration ranges of DEET in Asian groundwater are similar to those in groundwater from North America and Europe (Merel
and Snyder 2016).
1.5 Sources, Pathways, and Fates of PPCPs and ASs
in Asian Groundwater
The sources of groundwater pollution can be categorized into point sources and nonpoint (diffuse) sources. Pollution by point sources refers to contamination by spatially
discrete sources, such as effluents from industrial plants and hospitals, or discharge