CSIRO PUBLISHING

Research Paper

Environ. Chem.
http://dx.doi.org/10.1071/EN15061

First national-scale reconnaissance of neonicotinoid
insecticides in streams across the USA
Michelle L. HladikA,C and Dana W. KolpinB
A

US Geological Survey, California Water Science Center, 6000 J Street, Placer Hall, Sacramento,
CA 95819, USA.
B
US Geological Survey, Iowa Water Science Center, 400 S. Clinton Street, Iowa City, IA 52240,
USA; dwkolpin@usgs.gov
C
Corresponding author. Email address: mhladik@usgs.gov

Environmental context. Neonicotinoids are under increased scrutiny because they have been implicated inpollinator declines and, more recently, as potential aquatic toxicants. Nevertheless, there is currently little
information on concentrations of multiple neonicotinoids in surface water. This paper presents a summary ofconcentrations of six neonicotinoids in streams from across the United States in both urban and agriculturalareas. These environmental data are important in determining the potential risk of neonicotinoids to non-target
aquatic and terrestrial organisms.
Abstract. To better understand the fate and transport of neonicotinoid insecticides, water samples were collected fromstreams across the United States. In a nationwide study, at least one neonicotinoid was detected in 53 % of the samples
collected, with imidacloprid detected most frequently (37 %), followed by clothianidin (24 %), thiamethoxam (21 %),dinotefuran (13 %), acetamiprid (3 %) and thiacloprid (0 %). Clothianidin and thiamethoxam concentrations werepositively related to the percentage of the land use in cultivated crop production and imidacloprid concentrations werepositively related to the percentage of urban area within the basin. Additional sampling was also conducted in targeted
research areas to complement these national-scale results, including determining: (1) neonicotinoid concentrations during
elevated flow conditions in an intensely agricultural region; (2) temporal patterns of neonicotinoids in heavily urbanised
basins; (3) neonicotinoid concentrations in agricultural basins in a nationally important ecosystem; and (4) in-stream
transport of neonicotinoids near a wastewater treatment plant. Across all study areas, at least one neonicotinoid was
detected in 63 % of the 48 streams sampled.
Received 21 March 2015, accepted 15 April 2015, published online 18 August 2015

Introductionneeded to accurately assess potential environmental effects fromneonicotinoid exposures from stream concentrations. Current
surface-water data exist primarily for imidacloprid, the mostly
widely use neonicotinoid globally.[8] More recent studies, however, have documented mixtures of neonicotinoids in wetlands,[14–16] groundwater[12] and surface water.[11,17–19] An
example of such research documented that neonicotinoid mixtures were prevalent in streams in the Midwestern US, even in
the largest systems (i.e. Missouri and Mississippi Rivers), with
substantial temporal pulses of neonicotinoids in streams following rainfall events during crop planting likely attributed to seedtreatment applications.[11]The current study provides the first national-scale assessment of neonicotinoids in USA streams that has been conducted to date. In addition, targeted research studies wereconducted to complement these national-scale results toenhance our understanding of the contributions of both agricultural and urban neonicotinoid use to stream concentrations.
Such national- and regional-scale data sets provide important
geographic and temporal data that can be used to provide
important baseline concentration information for determining
potential environmental effects from exposure to stream neonicotinoid concentrations.

There is increasing concern about neonicotinoid insecticides
not only to pollinators[1] but also to other organisms such as
those residing in aquatic environments.[2] Elevated surfacewater concentrations of imidacloprid have been correlated withdirect effects on invertebrates[3] and indirect effects on insectivorous birds[4] and some fish.[5] Recent research has focussed
on not only acute toxicity of neonicotinoids but also chronic
toxicity, especially to aquatic invertebrates that may be exposed
to neonicotinoids by water.[2]Neonicotinoid use has continued to increase both in the
United States[6,7] and worldwide.[8,9] They are applied inboth agricultural (foliar sprays, in-furrow treatments andseed coatings) and urban (lawn and garden foliar sprays,
granular, tree injections; companion animal flea treatment)settings. Neonicotinoids are highly water-soluble (octanol–
water partition coefficients, log Kow, range from 0.55
to 1.26)[10] with fairly long soil degradation half-lives(DT50 3 to 545 days),[10] making them both mobile andpersistent with the potential for offsite transport to adjacentwater bodies.[11,12]
The lack of surface-water data is considered an important
knowledge gap for neonicotinoids.[13] This information is
Journal compilation Ó CSIRO 2015

Awww.publish.csiro.au/journals/env

M. L. Hladik and D. W. Kolpin

Explanation
Nationwide study site
Targeted research site

Puerto Rico

500 miles

0

250

0

250 500 km

Fig. 1. Map showing sample locations for the nationwide study (2012–14) and targeted research studies(2011–14).
Table 1. Site information, neonicotinoid concentrations and instantaneous loads for samples collected from Iowa stream and rivers after heavy rains
and flooding in 2014
Samples collected in 2013 for these sites are also included
Site

USGS
site ID

Drainage
area
(km2)

Date

Discharge(m3 s1)

Clothianidin(ng L1)

Imidacloprid(ng L1)

Thiamethoxam(ng L1)

Total
neonicotinoidload (g s1)

Missouri River at Omaha, NE

06610000

836 000

1150
2080

18
25

4.4
11

11
18

0.038
0.11

North Fork Maquoketa Rivernear Fulton, IA

05418400

1310

28
77

74
98

4.8
11

40
40

0.003
0.011

Old Mans Creek near Iowa City,
IA

05455100

521

36
157

84
68

23
25

26
20

0.005
0.018

Iowa River at Wapello, IA

05465500

32 400

1420
3030

62
53

15
19

30
20

0.15
0.28

Big Sioux River at Sioux City, IA

06485950

24 400

1821

77

20

38

0.25

Turkey River at Garber, IA05412500

4000

19-Jun-13
18-Jun-14–
24-Jun-13
19-Jun-14–
26-Jun-13
01-Jul-14–
01-Jul-13
03-Jul-14–
20-Jun-14–
20-Jun-14

708

132

26

73

0.16

Experimental
Sampling
National study
To obtain the first nationwide data set on neonicotinoids, 38
streams across 24 US states and Puerto Rico were sampled one
time for neonicotinoids between November 2012 and June 2014
(Fig. 1; Table S1). These samples were collected as part of larger
project to assess the human and ecological health risks associatedwith exposure to complex chemical mixtures.[20] Thirty-four ofthe streams were specifically selected owing to a wide range ofcontaminant sources within their watersheds (e.g. agricultural andurban sources). In addition, four streams were selected as

biological reference sites because they are considered to havefish and aquatic macroinvertebrate communities that have beenminimally disturbed by human development. The sampled watersheds range in size from 12 to 16 200 km2 (median ¼ 170 km2).[20]All water samples were collected from the centroid of flow.
Additional information on the site characteristics can be foundin Table S1.
Streams during elevated hydrologic conditions:Iowa, 2014
To determine neonicotinoid concentrations in streams during
elevated hydrologic conditions in an intensely agricultural
region, grab samples from six sites in Iowa (Table 1; Fig. 2a)
BNeonicotinoids in US surface water

were collected from the centroid of flow following heavy
rainfall and after most row crops (corn and soybeans) had beenplanted in these watersheds. Four out of the six sites were above
flood stage and all samples were collected near the crest of thehydrograph. The drainage area for the basins sampled ranged
from 521 to 836 000 km2.

Turkey RiverBig Sioux River

Temporal patterns in urban streams in the Southeast
Two urban-affected streams (Sope Creek, 80 km2, 39 %urban; Chattahoochee River, 6300 km2, 18 % urban) were
frequently sampled (67 total samples) in Georgia to better
understand temporal variations in stream neonicotinoid concentrations derived from urban sources (Fig. 2b). All water
samples from these sites were collected through depth andwidth-integrated composites.[19,21] Samples were collectedfrom Sope Creek every 2 weeks on a set schedule for 2 years
starting in October 2011 (48 samples collected). Samples werecollected from the Chattahoochee River on an alternating onceor twice per month set schedule (19 samples collected). No
samples from these two sites were collected in relation to any
specific flow conditions.

North Fork Maquoketa River
Old Mans Creek

Fourmile Creek
Missouri River
Iowa River

Explanation
Targeted research site
030
60 miles
030 60 km

Sope Creek

Streams in a nationally important ecosystem:
Chesapeake Bay
As part of a larger study to determine if chemical exposure iscontributing to fish health issues being observed in the Chesapeake Bay watershed,[22–24] water samples were collected fromthree sites in this watershed (Fig. 2c): six samples from Antietam
Creek (725 km2, 25 % cultivated crops, 10 % urban); sevensamples from Big Pipe Creek (270 km2, 41 % cultivated crops,
2 % urban); and four samples from Chillisquaque Creek,(290 km2, 32 % cultivated crops, 2 % urban). Automatic samplers were used to collect water.

Chattahoochee River

Explanation
Targeted research site
030
60 miles0

In-stream transport: Fourmile Creek, Iowa
To better understand the contributions of neonicotinoids tostreams from wastewater treatment plant (WWTP) discharge
and their in-stream fate, a 4.8-km reach of Fourmile Creek,
located near Ankeny, Iowa, was investigated (Fig. 2a). The
study reach extends from 1.9 km above the WWTP outfall(46 106 L day1; activated sludge treatment) to 2.9 km downstream of the WWTP outfall. In addition to a WWTP effluent
sample, stream samples were collected at 1.9, 1.6, 0.08,
0.05, 0.05, 0.33 and 2.9-km distance in relation to WWTP
outfall. Samples were collected in a Lagrangian approach, inwhich the same approximate parcel of water was tracked as it
moved downstream, as was conducted previously in this study
reach.[25–27] All samples were collected at the centroid of flow.
The proportion of stream flow derived from WWTP effluent
below the outfall varies depending on antecedent moisture
conditions. The first sampling of this study reach occurred from
5 to 6 December 2012 during a time of prolonged drought
conditions. Thus, the stream flow below the outfall was
0.17 m3 s1, with 99 % of this flow derived from effluent. The
second sampling occurred on 20 June 2013 during more normal
early-summer flow conditions, with the stream flow below theoutfall at 1.7 m3 s1, with 11 % of this flow derived from
effluent.

30 60 km

Chillisquaque Creek

Big Pipe Creek
Antietam Creek

Chesapeake Bay

Explanation
Targeted research site
030
60 miles
0

30

60 km

Fig. 2. Sites sampled as part of targeted research studies: elevatedhydrologic conditions and in-stream transport in an intense agricultural
region in Iowa (a); urban streams in the south-eastern USA (b); andChesapeake Bay (c).

clothianidin, dinotefuran, imidacloprid, thiacloprid and thiamethoxam) were measured in the water samples using a previously published method.[19] Samples were filtered with a
0.7-mm glass-fibre filter (Whatman, Piscataway, NJ), spiked
with a surrogate (imidacloprid-d4; Cambridge Isotope,
Andover, MA), and passed through an Oasis HLB solid-phase

Analytical method
All samples were placed in 1-L amber glass bottles and chilled at
4 8C until extraction. The six neonicotinoids (acetamiprid,CM. L. Hladik and D. W. Kolpin

Concentration (ng L⫺1)

200

100

150

100
10
50

0

1
Sum of
Neonicotinoids

Imidacloprid
37 %Clothianidin
24 %Thiamethoxam
21 %Dinotefuran
13 %Acetamiprid
3%

Total neonicotinoid concentration (ng L⫺1)

Fig. 3. Box plot of total neonicotinoids detected at 38 sites in a nationwide study from 2012 to 2014. Scatterplots show therange of individual neonicotinoid concentrations for the five compounds detected (out of six measured); overall detection
frequency is listed underneath the compound names.

extraction (SPE) cartridge (6 mL, 500 mg; Waters Corporation,
Milford, MA). The cartridge was eluted with 10 mL of 50 : 50
dichloromethane : acetone, reduced under nitrogen and aninternal standard, 13C3-caffeine, was then added. Extracts wereanalysed on an Agilent 1260 bio-inert liquid chromatograph(LC) coupled to an Agilent 6430 tandem mass spectrometer(MS-MS) (Santa Clara, CA). The theoretical level of detection(LOD) was 2 ng L1 and the method detection limits (MDL)
ranged from 3.6 to 6.2 ng L1.[19]Neonicotinoid concentrations were validated against a set of
quality control parameters including: field blanks (9), replicate
samples (17), matrix spikes (8) and surrogate recovery. No
compounds were detected in any of the blanks, field replicates
had relative percentage differences (RPD) between the regularand replicate sample of ,25 %. Matrix spike recoveries ranged
from 70 to 102 %. Recovery of the surrogate (imidacloprid-d4)
ranged from 70 to 120 % for all samples; data presented here
were not recovery-corrected.

400

Imidacloprid
Clothianidin
Thiamethoxam
Dinotefuran
Acetamiprid

300

200

100

0
5

10

15

20

25

30

35

Site
Fig. 4. Concentrations of neonicotinoid insecticides at 38 individual sites
collected as part nationwide study from 2012 to 2014. The site number
corresponds to the full names given in Table S1.

Results and discussion

detected concentration of 19 ng L1. When summed, the highest
total neonicotinoid concentration for a given sample was 450 ng
L1 (Fig. 4). Mixtures of multiple neonicotinoids in a single
sample were common; two or more were detected in 26 % of thesamples, three or more were detected in 11 % of the samples, andone sample (3 %) had five neonicotinoids detected (Table S1).
To provide a better understanding of neonicotinoid sources,
an examination of the relationship between concentration andland-use (Table S1) was conducted (Table S2). This analysis
determined a significant, positive relation (using Spearman’srank correlation) to cultivated crops for clothianidin (r ¼ 0.465,
P ¼ 0.003) and thiamethoxam (r ¼ 0.472, P ¼ 0.003) and apositive relation to urban land-use for imidacloprid (r ¼ 0.474,
P ¼ 0.003). These were expected relations to land-use based on
the primary use of these neonicotinoids. In addition, a significant positive relation was observed between the two principal
agriculturally used neonicotinoids, clothianidin and thiamethoxam (r ¼ 0.668, P , 0.001). Their co-occurrence can atleast partially be explained by the fact that both neonicotinoids

A total of 149 stream samples were collected and analysed forsix neonicotinoids in one national-scale and four complementary research studies. A summary of the results of these efforts
follows.
National study
Five of the six neonicotinoids measured were detected in thisfirst ever national-scale study (Table S1). Although these samples represent only a single snapshot in time for the 38 sites
sampled, they do represent spatial variations in stream neonicotinoid concentrations across the USA (Fig. 1). At least one
neonicotinoid was detected in 53 % of the 38 sites sampled.
Imidacloprid was the most frequently detected neonicotinoid(37 %, maximum concentration 140 ng L1), followed by clothianidin (24 %, 66 ng L1), thiamethoxam (21 %, 190 ng L1),
dinotefuran (13 %, 130 ng L1) and acetamiprid (3 %, 40 ng L1)
(Fig. 3, Table S1). Thiacloprid was not detected in any of thesamples collected. Of the 37 detectable concentrations of individual neonicotinoids, 92 % were ,100 ng L1 with the medianDNeonicotinoids in US surface water(a)

Sope Creek near Marietta, GA
100

100

80
10

60
1
40

0.1
20

0
Oct

0.01
Jan

Apr

Jul

Oct

Jan

Apr

Jul

2012

2011

(b)

Oct

2013

Chattahoochee River near Whitesburg, GA
1000

Total neonicotinoid concentration (ng L⫺1)

140

Imidacloprid

Discharge (m3 s⫺1)

imidacloprid concentration (ng L⫺1)

Imidacloprid

Dinotefuran
Acetamiprid

120

100

100

80
60
10
40

20

0
Sep

1
Oct

Nov

Dec

Jan

Feb

Mar

Apr

May

Jun

Jul

Aug

Sep

Oct

2012

2011

Fig. 5. Concentrations of imidacloprid and the corresponding stream discharge from October 2011 to
October 2013 for Sope Creek (a). Concentrations of imidacloprid, dinotefuran and acetamiprid along withthe corresponding stream discharge from September 2011 to September 2012 for Chattahoochee River (b).
Black bars represent samples where no neonicotinoids were detected.

years. Although stream concentrations were similar between
2013 and 2014, the wet conditions in 2014 did cause substantially higher stream flows compared with 2013, which translated
to higher instantaneous neonicotinoid loads (Table 1); thus,
neonicotinoid loads were two to four times higher in 2014 thanin 2013. These results confirm that precipitation is an importantdriver of neonicotinoid transport to streams following periods ofuse; even when such precipitation is heavy enough to cause
substantial stream flooding, the neonicotinoid concentrations
were not reduced.

are primarily used on cultivated crops and that clothianidin isalso a transformation product of thiamethoxam.[7,28] There wereno significant relations among the other neonicotinoids underinvestigation (Table S2).
Streams during elevated flow conditions: Iowa, 2014
Because of the generally wet conditions across much of Iowa
during the spring and early summer of 2014, a set of water
samples from six sites were collected (Fig. 2a) to determine theeffect such elevated flow conditions would have on stream
neonicotinoid concentrations in an intensely agricultural region.
Neonicotinoids were present in all six samples collected(Table 1). These 2014 results were similar to those collectedduring this same general time period in 2013[11]; median individual neonicotinoid concentration was 23 ng L1 in 2014 and25 ng L1 in 2013 for sites with samples collected during both

Temporal patterns in urban streams in the Southeast
For this research component, stream samples were collectedfrom two urban-affected streams (Fig. 2b): Sope Creek and theChattahoochee River on a fixed sampling schedule. Not surprisingly, imidacloprid was the dominant neonicotinoid present
E

M. L. Hladik and D. W. Kolpin

Antietam Creek near Sharpsburg, MD(a) 25in these urban-affected streams, being detected in 87 % of 67
samples collected. Dinotefuran (10 %) and acetamiprid (7 %)were detected sporadically and were found along with imidacloprid (Table S3).
Imidacloprid was present in almost every sample (90 %)collected from the heavily urbanised Sope Creek (39 % urban)(Fig. 5a). Unlike what has been observed in agricultural streams
in the Midwest,[11] there was no significant relation between
imidacloprid concentrations and stream flow (r ¼ 0.21,
P ¼ 0.17). This may have been at least partially due to the lackof a distinct use period for imidacloprid in such an urbanaffected basin and the lack of a distinct growing season in thewarmer climate of the south-eastern United States. In addition,
the frequent events (e.g. frequent flushing of the system)
observed in Sope Creek (Fig. 5a) and the warmer climate(possibly leading to increased degradation rates) may also havecontributed to differences when comparing these urban-affected
results with agricultural areas of the Midwest.
For the Chattahoochee River, which includes the Sope Creekdrainage, one or more neonicotinoids were detected in 79 % ofsamples, two or more in 37 %, and three or more in 16 % of thesamples collected. Imidacloprid was the most frequently
detected neonicotinoid (79 %), followed by dinotefuran (32 %)and acetamiprid (5 %; Table S3). The more varied neonicotinoid
detections in the Chattahoochee River compared with Sope
Creek were likely a reflection of the more diverse land-use
because the larger Chattahoochee watershed is 18 % urban andincludes 9 % pasture (no cultivated crops, however). As with
Sope Creek, there were frequent runoff events (Fig. 5b), with nosignificant relation between imidacloprid concentrations andstream flow (r ¼ 0.05, P , 0.87).

Clothianidin
Thiamethoxam
100

20
15

10

10
5

1
May

Jun

Big Pipe Creek at Bruceville, MD(b) 150

Clothianidin
Thiamethoxam

100

10

50

1

0
Apr

(c)

100

Discharge (m3 s⫺1)

Total neonicotinoid concentration (ng L⫺1)

0
Apr

0.1
May

Jun

Chillisquaque Creek at Chillisquaque, PA
200
Clothianidin
Imidacloprid
Thiamethoxam

150

100

10

Streams in a nationally important ecosystem:
Chesapeake Bay
For this research component, stream samples were collectedfrom three agriculturally affected streams (Fig. 2c): Antietam
Creek, Big Pipe Creek and Chillisquaque Creek, with a specificemphasis on collection of runoff samples during the planting
season of cultivated crops. Overall, neonicotinoids weredetected in 59 % of the stream samples. Clothianidin was themost frequently detected neonicotinoid (59 %), followed bythiamethoxam (29 %), and imidacloprid (6 %) (Table S4,
Fig. 6). The thiamethoxam and imidacloprid detections were all
found in the presence of clothianidin.
Similar to previous research on agricultural streams in the
Midwestern USA,[11] an increase in neonicotinoid concentrations was observed in these streams during runoff conditions
associated with the planting season of cultivated crops (Fig. 6).
Although there were not enough samples to test statistically, theconcentrations of clothianidin and thiamethoxam (the two
neonicotinoids primarily used for agricultural purposes) generally increased as the amount of land used in cultivated crops
increased. The highest concentrations for each site occurred on
16 May 2014 and sites ranked the same with respect to percentage cultivated crops and clothianidin plus thiamethoxam concentration: Big Pipe Creek (41 %; 93 ng L1) . ChillisquaqueCreek (32 %; 64 ng L1) . Antietam Creek (21 %; 11 ng L1).
The measurement of neonicotinoids is one component in determining if chemical exposures are contributing to fish healthissues being observed in the Chesapeake Bay watershed. Future
work will seek to determine the relative effects from various
chemicals (e.g. neonicotinoids) and additive or synergistic

100

1

50

0
Apr

0.1
May

Jun

2014
Fig. 6. Concentrations of clothianidin, imidacloprid and thiamethoxam
and the corresponding stream discharge at three sites in the Chesapeake Bay
area sampled in 2014. Black bars represent samples where no neonicotinoids
were detected.

effects from chemical mixtures (e.g. pesticides, hormones,
pharmaceuticals) on fish health.
In-stream transport: Fourmile Creek, Iowa
The two different sampling events of the 4.8-km study reach forthis research component captured two vastly different WWTPderived flow scenarios (99.5 and 11.0 % flow-derived effluent
below the WWTP). The December 2012 sampling occurred
during a time of prolonged drought conditions and months after
any agricultural use of neonicotinoids had taken place. Thus, theflow of Fourmile Creek below the WWTP outfall was 99 %effluent at this time. Only imidacloprid and clothianidin weredetected during this December sampling (Table S5). During thistime, the input of WWTP effluent into Fourmile Creek caused anincrease in stream concentration for imidacloprid and a decreaseFNeonicotinoids in US surface water

December 2012

June 2013

Clothianidin

Imidacloprid

Fig. 7. Concentrations (ng L1) of clothianidin and imidacloprid collected along Fourmile Creek near
Ankeny, Iowa, at two sampling times, December 2012 and June 2013. The concentrations in red are thosefound at the outfall of the wastewater treatment plant (WWTP).

thiamethoxam were detected (Table S5). Given the strong
agricultural use for clothianidin and thiamethoxam, the higher
stream concentrations in the upper portion of the reach, derived
from row-crop production in the headwaters, compared with thatobserved during the December 2012 sampling were expected.
As was observed previously, only clothianidin and imidacloprid
were detected in the WWTP effluent, with clothianidin being
present at lower concentrations than imidacloprid. In addition,
the input of WWTP effluent into Fourmile Creek again caused
an increase in stream concentrations for imidacloprid and aslight decrease in stream concentrations for clothianidin (Fig. 7).
This trend, however, was dampened by the much lower influence of the WWTP on stream flow below the outfall (11 %effluent-derived stream flow) compared with the December

in stream concentration for clothianidin (Fig. 7). This trend was
not unexpected owing to the primary uses for these neonicotinoids (i.e. agricultural use for clothianidin and urban use forimidacloprid). These neonicotinoids appear to be transported
conservatively through this study reach because similar concentrations were found from the uppermost sampling point tojust above the WWTP outfall and from just below the WWTP
outfall to the lowermost sampling point (Fig. 7).
The June 2013 sampling occurred during a time of normal,
early-summer flow conditions (i.e. median flow) and soon after
the primary period of the agricultural use of neonicotinoids hadtaken place in the headwaters. Correspondingly, the flow ofFourmile Creek below the WWTP outfall was 11 % effluent at
this time. During this sampling, clothianidin, imidacloprid andGM. L. Hladik and D. W. Kolpin

2012 sampling (99 % effluent-derived stream flow). As with theDecember sampling, conservative transport of neonicotinoids
was observed, with similar concentrations from the uppermost
sampling point to just above the WWTP outfall and from justbelow the WWTP outfall to the lowermost sampling point(Fig. 7).

[6]

[7]

Summary[8]

In this first wide-scale investigation of neonicotinoids, they were
frequently detected in streams across the USA, with 63 % of the
48 streams samples having a detection of at least one neonicotinoid. Both urban and agricultural uses contributed to stream
neonicotinoid concentrations, with imidacloprid occurrence
significantly related to the amount of urban land-use and clothianidin and thiamethoxam significantly related to the amount ofcultivated crops. Similarly to previous research, transport tostreams in agriculturally affected basins is driven by use andprecipitation. The present study, however, has documented this tobe true even when precipitation is heavy enough to cause substantial flooding. Research within a 4.8-km study reach of
Fourmile Creek found that the input of WWTP effluent into thesystem caused stream concentrations of imidacloprid to increase
and clothianidin to decrease. Both neonicotinoids, however,were found to be transported conservatively throughout the
study reach. Although the present research provides important
baseline data on neonicotinoid concentrations in streams andhelps expand our understanding of their sources and environmental fate, more research is needed to understand the potential
direct effects to aquatic organisms and indirect effects to bothaquatic and terrestrial organisms from these stream neonicotinoid concentrations.

[9]

[10]

[11]

[12]

[13]

Acknowledgements
We thank Dan Calhoun and Pat Phillips for providing samples and site
information for Georgia and Chesapeake Bay respectively; Jim Orlando forgenerating maps and the land-use data; Megan McWayne and Corey Sanders
for sample processing; and all of the field crews from across the UnitedStates who collected the various stream samples. Funding or support wasprovided by the US Geological Survey (USGS) Toxic Substances Hydrology
Program, USGS Priority Ecosystems Science, USGS National Water
Quality Assessment Program and the Georgia Department of Agriculture.
Any use of trade, firm or product names is for descriptive purposes only anddoes not imply endorsement by the US Government.

[14]

[15]

[16]

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