a growing body of research 
 shows that fruits and vegetables are 
 critical to promoting good health .
fruits and vegetables are major 
 contributors of nutrients , such as folate , magnesium , dietary fiber , 
 and vitamins a , c , and k , and essential for disease prevention . diets 
 rich in fruits and vegetables also help adults and children to achieve 
 and maintain a healthy weight . however , 
 because of the wide usage of pesticides in agriculture , diet also 
 becomes an important source of exposure to pesticides .
although relatively 
 unknown to the public , neonicotinoids are the most commonly used insecticides 
 in the world , which include acetamiprid , clothianidin , dinotefuran , 
 imidacloprid , nitenpyram , thiacloprid , and thiamethoxam . additionally , 
 flonicamid has been categorized as a neonicotinoid insecticide , although the mode of action is different from 
 that of other neonicotinoids .
these insecticides 
 act as nicotinic acetylcholine receptor ( nachr ) agonists , which cause 
 insect paralysis to death .
advantages of neonicotinoids in pest control , 
 including a broad spectrum of insecticidal activity , high receptor 
 specificity for insects relative to mammals , and versatility in application 
 methods , have led to the replacement of organophosphates , carbamates , 
 and synthetic pyrethroids .
they are now 
 registered globally in more than 120 countries and extensively used 
 in seed treatment ( such as seed dressing or film coating ) and soil 
 treatment ( by broadcast application , mechanical incorporation , soil 
 drench , or soil injection ) and are also directly applied to plant 
 foliage for crop protection .
additionally , neonicotinoids 
 have been used as insect control on pets or companion animals , such 
 as termite and flea control . because of neonicotinoids 
 wide uses and their extreme toxicity 
 to bees , neonicotinoids have been implicated in causing the steep 
 decline of the global honeybee population and specifically colony 
 collapse disorder ( ccd ) .
neonicotinoids are systemic 
 insecticides and water - soluble , which means that they have superb 
 plant - systemic activity . when applied 
 into the soil or as seed treatment , they are taken up by the roots 
 and translocated through the entire plant .
residue studies have detected low levels of neonicotinoids in the 
 pollen of treated crops and substantially high levels 
 of resides in corn grown from imidacloprid - treated corn seeds . when applied to the top surface of leaves and 
 fruits , they penetrate into the plant tissues and
for example , substantial portions of thiacloprid and clothianidin 
 residues and radiolabeled neonicotinoids were found to penetrate in 
 and beyond the outer flesh regions of apples 24 h after topical application . in another study , thiamethoxam and
acetamiprid were detected in 
 cherry leaves and the fruit s interior tissue 14 days after 
 application .
translocation of neonicotinoids 
 into plant tissues ( after either foliar application or seed / soil treatment ) 
 may potentially be subject to human consumption and subsequently dietary 
 intake . to estimate dietary exposure to neonicotinoids in humans , 
 it is 
 important to monitor neonicotinoid residues in and on foods that people 
 consume .
department of agriculture ( usda ) publishes 
 pesticide data program ( pdp ) reports annually , usually fewer than 
 15 fresh fruits and vegetables are included each year .
nevertheless , 
 imidacloprid , the most commonly used insecticide in the world , had 
 been detected in 81% of sweet bell peppers , 81% of broccoli , and 53% 
 of grapes , as reported by the usda pdp .
imidacloprid is not only widely detectable in fruits and vegetables 
 but also absorbed with high efficiency , as shown in a human intestinal 
 cell model .
imidacloprid and acetamiprid 
 have also shown excitatory effects on cultured cerebellar neurons 
 from neonatal rats , suggesting possible neurotoxicity in developing 
 mammalian brains .
these results raise 
 the concerns of potential health risks from chronic exposure to consumers 
 by dietary intake of residues with food . because half - lives for most 
 neonicotinoids in aerobic soil can range from months to years
, neonicotinoids can become persistent in the 
 environment for several years after repeated applications .
consequently , 
 the persistence of neonicotinoids in soil would have created a reservoir 
 of residues for plant to take up over a long period of time and , therefore , 
 contaminate crops for human consumption .
in addition , because of their 
 systemic characteristics , neonicotinoids often occur as residues in 
 the plant flesh and could not be washed off easily . to the best 
 of our knowledge ,
this is the first study aiming to 
 demonstrate the presence of neonicotinoids in foods that people commonly 
 consume
. only specific neonicotinoids ( such as imidacloprid ) in fruits 
 and vegetables have been monitored and reported .
most data on neonicotinoid residues in fruits and vegetables were 
 from brief reports of the application of the newly developed analytical 
 methods .
in addition , in most of these brief reports , only up to six 
 neonicotinoids were simultaneously monitored , and eight neonicotinoids were monitored in only one study and in 
 one commodity . in recent years , the quechers 
 ( quick , easy , cheap , effective , rugged , and safe ) sample preparation 
 procedure has been widely used for extraction of a wide variety of 
 pesticides from various food matrices . in this study , we used 
 a sensitive and modified lc - ms / ms method along with the quechers procedure 
 to simultaneously measure eight neonicotinoid residues in various 
 foods incluing fruits , vegetables , and honey and in pollen .
the results provided an initial assessment of 
 the potential dietary exposure of neonicotinoids and will contribute 
 to future epidemiological research linking neonicotinoid insecticide 
 exposure to potential human health effects .
acetamiprid , flonicamid , thiacloprid , thiamethoxam , 
 and nitenpyram standard solutions were purchased from accustandard 
 ( new haven , ct , usa ) with purity 99.7% .
imidacloprid and clothianidin 
 were purchased from sigma - aldrich ( st . louis , mo , usa ) with purity 
 of 99.9% .
dinotefuran was purchased from chem service ( west chester , 
 pa , usa ) with purity of 99.2% .
the isotope - labeled internal standards 
 ( is ) for imidacloprid - d4 ( 99.2% ) , clothianidin - d3 ( 98.9% ) , and thiamethoxam - d3 ( 99.8% ) were purchased from c / d / n isotopes , inc .
lc - ms / ms grade formic acid and ammonium formate were purchased 
 from sigma - aldrich .
hplc grade reagents , including acetonitrile and 
 water , were purchased from j. t. baker ( center valley , pa , usa ) .
vial 
 ( 1.5 ml with 0.2 m nylon filter ) were purchased from vwr international 
 ( radnor , pa , usa ) .
quechers extraction salt packages , which include 
 4 g of mgso4 , 1 g of nacl , 1 g of sodium citrate , and 500 
 mg of of disodium citrate sesquihydrate in each salt pack , and 2 ml 
 of quechers dispersive spe containing 50 mg of psa + 50 mg of c18 
 + 150 mg of mgso4 or 50 mg of psa + 50 mg of graphitized 
 carbon black ( gcb ) + 150 mg of mgso4 or 25 mg of psa + 
 7.5 mg of gcb + 150 mg of mgso4 ceramic homogenizer were 
 purchased from agilent technologies ( santa clara , ca , usa ) .
the hplc system consists of a shimadzu lc scl-10avp solvent delivery 
 unit , an online solvent degasser , a gradient mixer , and a system controller 
 ( shimadzu scientific , columbia , md , usa ) , coupled with a ctc - pal autosampler 
 ( leap technologies , carrboro , nc , usa ) for injecting samples .
the 
 mass spectrometer is an api 4000 lc - ms / ms system ( ab sciex , framingham , 
 ma , usa ) equipped with a turbo v ionspray ionization source .
the shaqer 
 1500 from spex sampleprep ( metuchen , nj , usa ) was used for mixing 
 samples in the quechers extraction procedure .
neonicotinoids in pollen and honey 
 were analyzed by the lc - ms / ms method that was developed previously 
 for pollen and high - fructose corn syrup ( hfcs ) samples .
analysis of neonicotinoids in fruits and vegetables 
 was conducted by using the modified method for pollen and hfcs . briefly
, 
 the chromatographic separation was performed on a ymc ods - aq column 
 ( 100 mm  2.1 mm , 3 m particle size , ymc , allentown , pa , 
 usa ) with the mobile phase , consisting of water with 5 mm ammonium 
 formate and 0.1% formic acid ( mobile phase a ) and acetonitrile / water 
 ( 95:5 v / v ) with 5 mm ammonium formate and 0.1% formic acid ( mobile 
 phase b ) , running gradient at 170 l / min in 11 min for each 
 analysis . the mobile phase gradient was as follows : 0% b for 1.3 min ; 
 linearly increased to 100% b from 1.3.0 to 2.3 min , and then maintained 
 at 100% b from 2.3 to 7.5 min , back to 0% b from 7.5 to 8.0 min , and 
 maintained at this proportion from 8.0 to 11.0 min . injection volume 
 into the lc - ms / ms is 10 l . the mass spectrometer equipped with 
 an electrospray was operated in the positive ionization mode with 
 multiple reaction monitoring ( mrm ) . the mass / charge
( m / z ) ratios monitored were 223/126 , 250/169 , 203/129 , 
 230/203 , 256/209 , 271/225 , 253/126 , and 292/211 for acetamiprid , clothianidin , 
 dinotefuran , flonicamid , imidacloprid , nitenpyram , thiacloprid , and 
 thiamethoxam , respectively .
the m / z of the internal standards ( is ) of imidacloprid - d4 , clothianidine - d3 , and thiamethoxam - d3 were 260/213 , 253/172 , 
 and 294/214 , respectively .
the quantification of neonicotinoids was 
 made from matrix - matched standard calibration curves using peak - area 
 ratio of analyte versus is .
the calibration curves were constructed 
 using weighted ( 1/x ) linear least - squares regression . 

a calibration standard curve and two concentrations of qcs ( qc low 
 and qc high ) in duplicate were incorporated into each analytical run . 

the qcs provide the basis for accepting or rejecting the run ( within 
 20% of accuracy and precision ) .
twenty - nine fresh fruit and vegetable 
 samples were purchased from several neighborhood grocery stores in 
 boston in 2012 .
honey samples were collected directly from hives located 
 in urban and suburban areas in massachusetts ( n = 
 3 ) or purchased from a local grocery store in boston ( n = 5 ) and from a store in israel in 2012 ( n = 2 ) . 

six pollen samples from new zealand were collected by using pollen 
 collectors set out under three hives located near a kiwifruit orchard 
 during peak flowing for 2 days in 2011 .
the pollen samples were then 
 separated into kiwifruit pollen and others ( nonkiwifruit ) pollen on 
 the basis of the color of the pollen pellets .
another seven pollen 
 samples were collected from hives located in seven different locations 
 in the central massachusetts area in july 2012 .
a prior analysis of neonicotinoid - free 
 pollen , honey , and organic fruits and vegetable samples , which were 
 used as blank matrix samples , was performed and confirmed to have 
 no contamination of neonicotinoids .
these blank samples were used 
 for calibration , qcs , and blanks for the analysis .
in addition , as 
 a background check for any possible interference , blank matrix samples 
 were also injected immediately after high - level standards to check 
 the carry - over of the instrument .
all calibration , qcs , and blanks were generated in 2 
 g blank matrix for pollen , 5 g for honey , and 10 g for fruits / vegetables . 

calibration curves for eight neonicotinoids at seven levels ranging 
 from 0.1 to 100 ng / g ( except 0.150 ng / g for honey ) were prepared 
 by adding aliquots of intermediate standard solutions ( preparation 
 steps can be found in the previous study ) to blank sample matrix .
the qc samples at two concentration levels , 
 5 ( qcl ) and 50 ng / g ( qch ) ( except 2 ( qcl ) and 40 ng / g ( qch ) for honey ) , 
 were prepared the same way as the blank sample matrix .
the standards 
 and qcs were stored at 20 c . the 
 fruit and vegetable samples were washed 
 under cold water for 15 s and allowed to drain for at least 2 min 
 on paper toweling .
anything that would not normally be consumed , 
 such as apple core , pepper core , orange seeds , and the leafy tops 
 of strawberries , were also removed .
then the samples were chopped 
 into small pieces and blended in a magic bullet until a homogeneous 
 paste was achieved .
if the sample was homogenized in portions , all 
 portions were mixed together in a clean container to ensure an evenly 
 mixed sample .
the sample extraction procedures 
 for fruits and vegetables were modified from the method that we developed 
 previously for pollen and hfcs samples , and the procedure for honey 
 samples was the same as that for hfcs .
ten grams of homogenized fruit and vegetable samples was weighed 
 in a 50 ml centrifuge tube , and 10 ml of acetonitrile and 20 l 
 of is solutions were added . for calibration standard and qcs , 10
g 
 of homogenized organic samples was fortified with appropriate levels 
 of working standard solutions .
double - blanks and blanks were also 
 prepared in parallel with and without is added , respectively .
the 
 tube was subsequently shaken for 30 s in a shaqer at 1500 strokes 
 per minute .
an additional 5 ml of n - hexane was added 
 to all olive samples .
the tubes were shaken vigorously for 40 s in 
 the shaker and centrifuged for 4 min at 4000 g .
one 
 milliliter from the acetonitrile layer was transferred to a 2 ml quechers 
 dispersive spe vial .
pollen , honey , and olive samples were added to 
 d - spe vials containing 50 mg of psa , 50 mg of c18 , and 150 mg of mgso4 ; spinach sample was added to d - spe containing 50 mg of psa , 
 50 mg of gcb , and 150 mg of mgso4 ; and all the rest of 
 the fruits and vegetables were added to d - spe containing 25 mg of 
 psa , 7.5 mg of gcb , and 150 mg of mgso4 .
the next d - spe 
 extraction , sample drying , and transfer steps were the same as presented 
 before .
in this study , we analyzed various types of fruits , including oil 
 fruits , stone fruits , pome fruits , citrus fruits , and berries , and 
 vegetables , including leafy vegetables and root vegetables , as well 
 as honey and pollen .
table 1 shows the performance 
 of this method including the limit of quantification ( loq ) and the 
 average recoveries ( and the variations ) of eight neonicotinoids in 
 various sample matrices .
loq was calculated as 10 times the signal - to - noise 
 ratio of the quantitative ion transition in the matrix and was 0.1 
 ng / g for neonicotinoids in pollen , honey , fruits , and vegetables with 
 the exceptions of 0.5 ng / g for flonicamid and 0.5 ng / g for nitenpyram 
 in pollen and dinotefuran in honey .
a sample was considered positive 
 when residue levels were above the loq . as shown in table 2 , all fruit and vegetable samples in our study tested 
 positive for one or more neonicotinoids , except nectarine and tomato . 

five neonicotinoids , including clothianidin , dinotefuran , flonicamid , 
 imidacloprid , and thiamethoxam , were detected in both fruits and vegetables ; 
 however , acetamiprid and thiacloprid were found only in fruits .
nitenpyram 
 was the only neonicotinoid that is not detectable in any fruit or 
 vegetable samples .
imidacloprid not only was detected with the highest 
 concentration in a green pepper sample ( 7.2 ng / g ) , but also was the 
 most frequently detected neonicotinoid in both fruits and vegetables 
 with the overall detection rate of 70% .
the results in table 2 show that not only are neonicotinoids widely found 
 in fruits and vegetables but also multiple neonicotinoids are often 
 detected in a single sample , especially in apples .
seventy - two percent 
 of fruits and 45% of vegetables were found to have multiple neonicotinoids . 

these percentages included 5 of 8 apples , which were detected with 
 three different neonicotinoids , and 6 of 10 fruits and 5 of 11 vegetables 
 were positive for two neonicotinoids .
because most commercially available 
 products do not contain multiple neonicotinoids as the active ingredients , 
 except for clothianidin , which could be the breakdown product of thiamethoxam , 
 this result indicates that these fruit and vegetable plants were likely 
 treated multiple times during their lifespan with different neonicotinoids 
 or absorbed neonicotinoid residues accumulated in the soil .
the persistence 
 of neonicotinoids in aerobic soil is highly likely due to the accumulation 
 of repeated applications of neonicotinoids , especially ones with long 
 half - lives .
in addition to fruits and vegetables , 
 we analyzed 10 domestic and 
 foreign honey samples collected from urban , suburban , and rural areas . 

table 3 shows that five neonicotinoids , including 
 acetamiprid , clothianidin , imidacloprid , nitenpyram , and thiamethoxam , 
 were found in these honey samples .
similar to fruits and vegetables , 
 imidacloprid was found in 9 of 10 honey samples , including 2 organic 
 honey samples purchased from a local grocery store .
the highest concentration 
 of imidacloprid of 1.3 ng / g was found in a domestic organic honey 
 sample .
the usda organic regulations allowed residues of prohibited 
 pesticides up to 5% of the tolerance set by the u.s . environmental 
 protection agency ( epa ) in organic products , but there are no defined 
 tolerances for most neonicotinoids ( including imidacloprid ) in honey .
only one honey sample collected 
 from a hive located in the rural area was free from neonicotinoid 
 contamination .
the high frequency of detections of neonicotinoids , 
 especially imidacloprid , in these samples indicates the wide usage 
 of neonicotinoids in the environment where honeybees often foraged .
we also tested 13 pollen samples ; 7 of them were from 
 central massachusetts 
 and 6 from new zealand .
as shown in table 4 , imidacloprid continued to be the most commonly detected neonicotinoid 
 with a detection frequency of 77% in all 13 pollen samples . among 
 the seven pollen samples from massachusetts , the five that tested 
 positive
were collected from central massachusetts within the so - called 
  quarantine area  , where trees were injected with imidacloprid 
 to combat the asian longhorn beetle problem in 20112012 .
the 
 other two pollen samples containing no neonicotinoids were collected 
 outside the  quarantine area 
the degree of neonicotinoid contamination 
 in pollen samples collected in new zealand is more extensive than 
 that of samples collected from central massachusetts areas , as shown 
 in table 4 .
all six samples contained multiple 
 neonicotinoids , and five of those six samples contained three neonicotinoids . 

it is also noticeable that nonkiwifruit ( others ) pollen samples contained 
 higher concentrations of imidacloprid and clothianidin than kiwifruit 
 pollen .
those nonkiwifruit pollen samples were likely from nearby 
 dandelion , clover , and other weed flowers , on the basis of the color 
 of the pollen pellets . because kiwifruit has little nectar ,
honeybees 
 need to forage widely ( as far as 2 km ) to get their nectar feed for 
 energy . in this search
, bees could pick up other pollens containing 
 higher levels of neonicotinoids around the kiwifruit orchard than 
 the pollen of kiwifruit ; therefore , higher levels of neonicotinoids 
 showed up in these  others  pollen .
this finding is 
 consistent with the systemic property of neonicotinoids because upon 
 application ( such as spray ) , neonicotinoid residues can penetrate 
 and translocate through the plant / weed , including nectar and pollen , 
 located near the adjacent area . because pollen is honeybees 
 main source of protein and neonicotinoids
have been linked to ccd , the widespread presence of neonicotinoids in these pollen samples 
 could pose a potential threat to the survival of honeybees .
pollen samples were collected 
 from 
 honeybees in hives from seven different locations of central massachusetts .
pollen samples were collected 
 from 
 2 day collections from three hives in a kiwifruit orchard at the beginning 
 of their pollination assignment in new zealand in 2011 .
other pollens collected were a range 
 of colors , according to their host plants , such as clovers and dandelions , 
 in the proximity of the kiwi orchard .
in addition , neonicotinoids , such as imidacloprid , 
 clothianidin , 
 and thiacloprid , have often been used as soil treatment for insect 
 controls because of their long half - lives in aerobic soil ( half - lives 
 for imidacloprid and clothianidin are 26229 and 1481155 
 days , respectively ) and water solubility .
a recent study has shown that clothianidin 
 was found in both soil and dandelion flowers grown adjacent to a clothianidin - treated 
 agriculture area .
another study has shown 
 that untreated sunflowers grown in fields previously treated with 
 imidacloprid a year ago can still take up imidacloprid from the soil .
therefore , some neonicotinoids can become persistent 
 for several years and accumulated in the environment after repetitive 
 applications and , therefore , cause concern for prolonged exposure .
this result from pollen samples is consistent with that from the 
 fruit and vegetable samples in this study because most of these types 
 of fruits and vegetables testing positive were pollinated by honeybees . 

our study also raises the concern of pollen contaminated with neonicotinoids 
 because not only is pollen the primary protein source for honeybees 
 but also it could be readily available for human exposure via inhalation 
 as well .
table 5 shows the summary results 
 of neonicotinoid 
 residues detected in all samples that were analyzed in this study . 

both imidacloprid and clothianidin were found in all four types of 
 foods followed by thiamethoxam ( three types of foods ) ; acetamiprid , 
 dinotefuran , flonicamid , and thiacloprid ( two types of food ) ; and 
 nitenpyram ( in only one honey sample ) .
results from this study were 
 generally consistent with what have reported by the usda pdp during 
 20042011 ( table 6 ) .
consistent with 
 having the highest frequency of detection among all neonicotinoids 
 in samples that we analyzed , imidacloprid was found in seven of eight 
 apple samples in this study , as well as in apples / applesauce / apple 
 juice samples reported by pdp from 2004 to 2010 ( table 6 ) . along with imidacloprid
, apples / applesauce / apple juice 
 have the highest detection frequency of acetamiprid in almost every 
 year from 2004 to 2010 , although the frequency of detection for acetamiprid 
 has gradually decreased from 100% in 2004 to approximately 30% in 
 2007 .
similarly , apple , applesauce , or apple juice has consistently 
 been the commodity with the highest frequency of detection for thiacloprid 
 every year from 2004 to 2010 and has an increasing trend of use from 
 4.7% in 2007 to 9% in 2009 to 12.6% in 2010 .
although clothianidin 
 was not detectable in apples or apple juice in pdp from 2007 to 2009 , 
 clothianidin was found in three of eight apples in the current study 
 conducted in 2012 .
consistent with results from pdp , the current study 
 has confirmed the wide use of imidacloprid , clothianidin , acetamiprid , 
 flonicamid , and thiacloprid on apples , ranging from 38 to 88% .
unfortunately , 
 we were not able to continue monitoring the trend of neonicotinoid 
 residues in apples because they were not included in pdp after 2010 . 

we found a higher frequency of detection of imidacloprid than usda 
 pdp reported primarily because we used a more sensitive analytical 
 method with lower loqs for all neonicotinoids in this study than those 
 used by usda pdp with a limit of detection 1 ng / g .
smaller 
 sample sizes in our study could be another reason for higher frequency 
 of detection ; however , the commodities testing positive in our study 
 matched the commodities reported by pdp .
for instance , the highest 
 concentration of thiamethoxam detected in our study was from a cucumber 
 sample ( 13.2 ng / g ) , and cucumber was found with the highest detection 
 rate of 12% in 2009 and an even higher rate of 16% in 2010 by pdp . 
 the highest concentration of dinotefuran in our study was found in 
 a cantaloupe sample , which was also reported by pdp in 2010 and 2011 
 with the highest detection rates of 15 and 12% , respectively .
frequency of detection 
 ( % ) in apples 
 or applesauce or apple juice as a comparison .
this study has demonstrated the 
 widespread presence of neonicotinoids 
 in foods that people commonly consume and in pollen and honey that 
 honeybees bring back to hives from the environment . although those 
 levels were low ,
studies have suggested a link to adverse health effects 
 in honeybees as the results of sublethal exposure to neonicotinoids .
neonicotinoid insecticides are 
 known to selectively target insects nicotinic acetylcholine 
 receptors ( nachrs ) and therefore were previously thought to pose less 
 toxicity in mammals . however , a growing amount of evidence has shown 
 that neonicotinoids are capable of directly activating and/or modulating 
 the activation of mammalian nachrs . both in vitro and in vivo studies 

have shown that imidacloprid can change the membrane properties of 
 mouse neurons , significantly impair sensorimotor 
 performance , and elevate glial fibrillary acidic protein expression 
 in the motor cortex and hippocampus of neonatal rats after in utero 
 exposure to a single sublethal dose .
most 
 mammalian adverse toxic effects of neonicotinoids are associated with 
 their action on binding to the 42 nachr subtype . in an in vitro study ,
imidacloprid and other 
 neonicotinoids have been shown to directly activate and modulate human 
 42 nachr subtypes .
the 
 42 nachr subtype is the most prominent nachr subtype 
 in the mammalian brain , with the highest density of receptors in the 
 thalamus .
the 42 nachr 
 is involved in various brain functions , such as cognition , memory , 
 and behavior .
there is strong evidence for a role of 42 
 nachr and alteration of the receptor density in cns disorders , such 
 as alzheimer s disease , parkinson s disease , schizophrenia , 
 and depression . in the developing brain ( such 
 as perinatal stage ) , 42 nachr subtypes have been implicated 
 in neuronal proliferation , apoptosis , migration , differentiation , 
 synapse formation , and neural - circuit formation .
in addition , absorption studies using the human 
 intestinal cell line have shown that neonicotinoids can be absorbed 
 by active transportation .
neonicotinoids and 
 some of their metabolites are also shown to be able to pass through 
 the blood 
brain barrier in mice , and some metabolites having 
 enhanced potency to nachr are even more toxic than their parent compounds .
therefore , there is an inevitable question if 
 neonicotinoids could pose potential health risks to humans as well . in conclusion
, this is the first paper to document the widespread 
 presence of neonicotinoid residues in fruits , vegetables , and honey 
 that are readily available in the market for human consumption .
we 
 also reported neonicotinoid residues in pollen collected by honeybees 
 in areas where neonicotinoids are known to be used , and the variation 
 of neonicotinoid levels in pollen likely reflects the amount of neonicotinoids 
 applied .
it is important to note here that although all neonicotinoid 
 residues reported in this study were below the maximum residue levels , 
 or tolerances , established by the epa , the determination of these 
 tolerances is based on the best field practice and studies conducted 
 in test animals exposed at acute and chronic toxic levels , and therefore 
 does not take into sufficient account the protection of human health 
 from long - term low - dose exposure . in light of the extensive use of 
 neonicotinoids on fruit and vegetable crops and their widespread presence 
 in foods along with new information on the toxicological effects of 
 neonicotinoids in mammals , it is therefore warranted to conduct epidemiological 
 studies to assess dietary neonicotinoid intakes in humans and the 
 health effects .
 this 
 study quantitatively measured neonicotinoids in various foods 
 that are common to human consumption . 
 all fruit and vegetable samples 
 ( except nectarine and tomato ) and 90% of honey samples were detected 
 positive for at least one neonicotinoid ; 72% of fruits , 45% of vegetables , 
 and 50% of honey samples contained at least two different neonicotinoids 
 in one sample , with imidacloprid having the highest detection rate 
 among all samples . 
 all pollen samples from new zealand contained multiple 
 neonicotinoids , and five of seven pollens from massachusetts detected 
 positive for imidacloprid . 
 these results show the prevalence of low - level 
 neonicotinoid residues in fruits , vegetables , and honey that are readily 
 available in the market for human consumption and in the environment 
 where honeybees forage . in light of new reports of toxicological effects 
 in mammals , 
 the results strengthen the importance of assessing dietary 
 neonicotinoid intakes and the potential human health effects . 
Introduction
Experimental
Procedures
Results and Discussion