Table 1.

General Features and the Results of the Studies of Lead Exposure in Children with ADHD

Author, Year, County	Study Type	Sample Description	Blood Lead Measurement Method	Blood Lead Levels of Sample	ADHD Symptom Measured	ADHD Symptom Measurement Method
Canfield, 2003, U.S.	Cohort	170 infants recruited from a list of live births in urban hospitals in Rochester, NY.	Mean of 2 venous blood draws taken. Mean BLL at 48 months was used for analysis in study.	Mean BLL of all blood draws were <10 μg/dL. Average BLL at 48 months was 6.49 µg/dl; 48 months.	Attention	shape school task test at age 48 months (160/170 children)
Canfield 2004, U.S.	Cohort	Initial cohort was performed on 276 children. 174 remained at final	Venous blood tested Detection limit of BLL was 1 μg/dL.	Lifetime average BLL was 7.2μg/dL.	Attention	Children at age 5.5 years were tested with Shif Task Test.
Chiodo, 2004, U.S.	Cross- Sectional	337 African American children at 7.5 years of age, lead was unavailable for 91 children, and 9 BLL excluded from analysis due to very heavy prenatal alcohol exposure. Of the 237 children remained in the sample	Venous blood drawn at age 7.5 years by one of three phlebotomists at a children's hospital. Internal and external quality control measures taken. Limit of detection was 2 μg/dL.	Mean BLL was 5.4 ± 3.3 μg/dL. 92.4% BLL were below 10 μg/dL.	Inattention, Hyperactivity Impulsivity	Child's teacher completed the Barkely- DuPaul ADHD Scale and the Achenbach Child Behavior Checklist Teacher Report Form (TRF).
Braun, 2006, Mexican Americans, and non-Hispanic blacks	Cohort	Among children 4–15 years of age, 5,171 were available for analysis. Of the 4,704 eligible children 4–15 years of age, 344 (8.2%) had only parent reported ADHD and 154 (4.3%) reported stimulant medication use	Venous blood collected at beginning of study. No internal/external quality control measures were stated in the paper.	The limit of detection was reported to be 0.3 μg/dL (48) children had blood lead levels below this threshold. No detectable values were given values of 0.2 (0.3 divided by √2).	DSM-IV symptoms of ADHD–	Parent reported ADHD was based on the parent or guardian’s response.
Author ,Year, County	Study type	Sample description	Blood lead measurement method	Blood Lead Levels of sample	ADHD Symptom Measured	ADHD Symptom Measurement Method
Min, 2007, South Korea	Cross- Sectional	Participants recruited at family health examination in an office in Seoul, Korea. 61 children ages 7 16 years (33 boys and 28 girls).	Venous blood drawn at time of study. External quality controls for blood lead were taken.	Mean BLL Was 2.94μg/dL; All BLL Below 5μg/dL.	Attention	Children completed the SPES-K (Korean version of SPES)
Chiodo, 2007, U.S.	Cross- Sectional	Laboratory testing was obtained from506 African American children born in the Detroit area between Sept. 1, 1989- Aug.	Venous blood drawn at age years at a children's hospital in Michigan. Internal and external quality control measures taken.	91.1% had BLL below 10μg/dL; Mean BLL was 5 ± 3 μg/dL.	Attention, Hyperactivity Impulsivity	Child completed Conner’s Continuous Performance Test (CPT) to measure impulsivity and inattention
Nigg, 2008, U.S	Case- Control	Final sample size: 150 children age 8-17 years: 53 non-ADHD controls, 47 ADHD inattentive type; 50 ADHD combined type.	Venous blood drawn at time of study. Analysis of BLL was done twice to ensure accuracy. Limit of BLL detection was 0.3μg/dL.	Maximum BLL was 3.4 μg/dL. Mean BLL for ages 8-11 Was 1.0 μg/dL.Mean BLL for ages 12-17 Was 1.03μg/dL.	Attention, Hyperactivity, ADHD diagnosis	Conners' Rating Scale Revised And ADHD Rating Scale. Completed by parents and Teachers. Parents also completed The K-SADS-E During interview With a clinician.
Wang, 2008, China	Case-Control	Chinese Children aged 4-12 were recruited There were 630 controls who were not diagnosed with ADHD and 630 were diagnosed with ADHD using DSM-IV-R Criteria.	Venous blood Samples collected. Limit of detection was 1.0 μg/dL. Each sample was analyzed for times to internal quality control.	Mean BLL for ADHD group was 8.77 μg/dL ± 3.89) and for controls was 5.76 μg/dL ± 3.39.	Diagnosed ADHD vs. Non-ADHD diagnosed controls	Children diagnosed after meeting criteria in the K-SADS-E modified to include the Aberrant Behavior Checklist completed by parents/ teachers.
Author ,Year, County	Study Type	Sample Description	Blood Lead Measurement Method	Blood Lead Levels of the Sample	ADHD Symptom Measured	ADHD Symptom Measurement Method
Chandra mouli, 2009, U.K.	Cohort	All births from April 1, 1991- December 31, 1992 at Avon Health Authority in U.K. were eligible, resulting in total cohort of 14,062. 1135 participants from cohort were randomly selected to participate in study. Blood sample collected from488 participants.	Venous blood drawn at age 30 months. One sample differed by >2.5 μg/dL)	94% of sample had BLL below 10 μg/dL. He mean±SD BLL was 3.67±1.47	Hyperactivity	Parent and teacher of child completed the Strengths and Difficulties Questionnaire when child was 7 years old to measure Hyperactivity.
Froehlich, 2009, U.S	Cross-Sectional	National Health and Nutrition Examination Survey data collected from 3907 children age 8-15 years living in the US. Current BLL available for 2588 Children.	Venous blood drawn at time of survey completion. Limit of detection was 0.3μg/dL. No internal/external quality control measures were stated in the paper.	BLL range was 0.2 5 μg/dL. Children grouped into tertiles: first tertile (0.2-0.8 μg/dL), second tertile (0.9-1.3 μg/dL) and Third tertile (>1.3μg/dL).	DSM-IV criteria for ADHD	Child's caregiver completed The National Institute of Mental Health Diagnostic Interview Schedule for Children (DISC) to measure ADHD criteria.
Ha, 2009, South Korea	Cohort	2211 first and second grade students from 10 elementary schools from 6 South Korean cities were recruited. 1778 children ages 6-10 years had complete data (928 boys and 850 girls).	Venous blood collected at beginning of study. No internal/external quality control measures were stated in the paper.	Mean BLL was 1.8 μg/dL (in 2008 was 1.64 μg/dL and in 2010 was 1.60 μg/dL .	ADHD scores overall	Parents completed the Conner's Scale for ADHD symptom screening (higher score means higher severity of symptoms).
Cho, 2010, Korean cities	cross-sectional	A total of 667 children (age range 8–11) were recruited from nine schools in five Korean cities	Venous blood collected at beginning of study.	The mean blood lead level was 1.9 μg/dl ± .67 (range .53–6.16)	inattentive, hyperactive, and total scores	Teachers & parents completed the Korean version of the ADHD Rating Scales (KARS(
Author, Year, County	Study type	Sample description	Blood lead measurement method	Blood Lead Levels of sample	ADHD Symptom Measured	ADHD Symptom Measurement Method
Nicolescu, 2010, two Romanian cities were studied, namely Bucharest and Pantelimon	Cross-Sectional	83 children ages 8-12 years 49% girls and 51% boys. All children were asymptomatic for ADHD symptoms when recruited	Venous blood collected at beginning of study. Detection limit of BLL was 0.1μg/dL	Mean BLL in Bucharest was 3.2μg/dL; Mean BLL in Pantelimon was 5.1μg/dL	Inattention, Hyperactivity Impulsivity	Computerized German test called KITAP
Kim, 2010, Korean	Cross-Sectional	measured blood lead levels collected in 256 Korean children.	The detection limit for lead using method was 0.058 μg/dL.	Total mean blood lead level (N=205) with Mean±S.D= 5.40±8.4.	Inattentive hyperactive symptoms total score	Teachers ADHD Rating Scale (T-ARS)-IV.
Nigg, 2010, U.S	Case-Control	140 blood sample in children age 6-17 years	Venous blood collected at time Of study. BLL detection limit Was 0.3μg/dL.	Mean BLL Was 0.73 (SE=0.3) μg/dL. BLL range was <0.3 μg/dL to 2.2 μg/dL.	Inattention, Hyperactivity /Impulsivity, Diagnosed ADHD subtypes	K-SADS-E interview; Parents and teachers completed ADHD Rating Scale and Conners'-Revised.
Darugar, 2010, Iran	Case-Control	They randomize examine 100 children for case and 100 for control = 200 children	Venous blood was collected from each child( Blood was collected from the cubital vein of each child)	In Cases minimum BLL was 2.9 μg/dL and maximum was 18.6 μg/dL. Average BLL level for for cases was 7.2 μg/dL	Inattention Hyperactivity	Recognized by a psychologist based by Conner’s method
Boucher, 2012, Montreal	Cohort	Most of the participants (n = 208) were initially recruited under the auspices of the Cord Blood Monitoring Program 279(294 children and their mothers).	Venous blood collected at beginning of study. No internal/external quality control measures were stated in the paper.	Mean BLL Was Cord Pb (μg/dL): 4.7 and Current Pb (μg/dL): 2.7	A teacher report of at least six DSM-IV symptoms of ADHD -Inattentive type, Hyperactive impulsive type, ODD and CD.	ADHD (hyperactive impulsive type) based on the DBD (DSM-IV). The Teacher Report Form (TRF)
Kim, 2013, USA	Case-Control	71 ADHD cases and 58 non-ADHD controls=129	Venous blood collected at time of study.	Mean BLL was In cases Geometric mean(range) is 1.29 μg/dL (0.28–9.99) and in controls 1.33 μg/dL (0.42–6.05) and blood Pb levels(< 5 mg/dL)	DSM-IV criteria	Child's teacher completed the Barkely-DuPaul ADHD Scale and the Achenbach Child Behavior Checklist Teacher Report Form (TRF).