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July2005 Vol.42 Issue:      2 Table of Contents
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Prevalence of Lead Toxicity Among Secondary School Students in Sohag City (Upper Egypt) and Its Impact on Cognitive Functions

Abdel Latif M. Osman1, Hamdy N. El-Tallawy2, Hossney A. Hassan3, Sherifa A. Hamed2, Khaled A. Mohamed4, Nabiel A. Hakeem1, Mohamed A. Moneim2
Departments of Neurology, El-Azhar University1, Neurology and Psychiatry2, Biochemistry3, Psychiatry4, Assiut University

ABSTRACT

Lead is an extremely toxic metal. Lead intoxication in children has been associated with cognitive impairments. This study was designed to determine prevalence rate of lead toxicity  among secondary school children in Sohag City (Upper Egypt), sources of lead toxicity and the impact of lead toxicity on cognitive function of studied student. The studied student (600) were recruited from three school, 200 student from Elaskaria school (main stream school) and 400 student from two technical school (200 from industry and 200 from Elzekhrofia). A control group will be selected from the same sample of studied school, who proved to have normal urinary lead level (< 50µg/L). All studied students were subjected to; body measurements, clinical evaluation, soft neurological signs, social level, psychometric tests, (WAIS, CASI and WMS) – urine sample for assessment of lead level. The study revealed that the prevalence rate of lead toxicity was 50.5% and the highest rate among studied schools was reported in Elzekhrofia school (62%). Sources of lead toxicity in our community were old houses (77.9%), presence of repair shops (60.8%), Garbage combustion 60.3%, (smoking (62.1%)… etc. Soft neurological signs were significant abnormal among student with toxic urinary lead level (> 80µg/L) in comparison to student with normal lead level (<50µg/L) except in one test (standing on one foot). Student with toxic urinary lead level (> 80µg/L) had inverse proportion with social level. There were statistically significant lower scores among students with pre clinical toxicity (>50-80µg/L) and toxic level than students with normal urinary lead (<50µg/L) in total, verbal and performance Wechsler Adult Intelligence Scale (WAIS), in all Wechsler Memory Scale (WMS) subitems and in all cognitive Abilities screening instrument (CASI) subitems.

(Egypt J. Neurol. Psychiat. Neurosurg., 2005, 42(2): 505-515).

 




INTRODUCTION

 

Lead is a neurotoxicant with known behavioral and neurochemical effects1. Because of its widespread use in industry, fuels, and consumer products, it is present at elevated concentrations in many cities of the developing and developed world2.

Children are more vulnerable to lead exposure for three reasons; young children are more at risk of ingesting environmental lead through normal mouthing behaviors3, absorption from the gastrointestinal tract is higher in children than adults4, and the developing nervous system is thought to be far more vulnerable to the toxic effects of lead than the mature brain5.

The main sources of lead in children's environments are diet, lead-based paint in older housing, lead in soil and dust from contaminated lead paint and gasoline, or past and present mining and industrial activity6,7. Lead-contaminated house dust is the major source of lead intake during early childhood3.

Occupational lead exposure can cause declines in cognitive function over the course of time. Lead likely has an acute effect on neurobehavioral test scores as a function of recent dose and a longer-term (possibly progressive) effect on cognitive decline as a function of cumulative dose 8.

Various studies have found a highly significant association between lead exposure and the measured intelligence quotient (IQ) of school age children9. 

This study was designed to determine: prevalence of lead exposure and/or toxicity among secondary school students in Sohag city (Upper Egypt), determination of possible sources of pollution by lead in our community, and determination of the impact of exposure to lead on the cognitive functions and scholastic achievement.

 

SUBJECTS AND METHODS

 

The study was performed on 600 secondary schools male students from different localities in Sohag city. The study was conducted during the period from January 1st, 2000 to May 31, 2001.

The studied students were recruited from 3 schools, including Elaskaria secondary school (200 students), Elzekhrofia secondary school (200 students), and Industry secondary school (200 students). The Elaskaria secondary school represent main stream and pre-university stage, while other two selected school are technical schools with many subspecialties. They were included on basis that many of these subspecialties may predispose to lead exposure especially Elzekhrofia school.

A control group will be selected from the same sample of studied schools who proved to have normal urinary lead level (£50µg/L).

 

Exclusion criteria:

1-     All students with mental subnormality, IQ less than 70 scores.

2-             Neurological disorders.

3-             Psychiatric disorders.

4-     Any systemic diseases of acute or chronic onset.

 

Blood samples from school students were prohibited by law among school children in Egypt,  so we measured  lead level in the urine.

 

All the studied students will be subjected to:

I-      Body measurements: (Weight, Height, Mid-arm circumference  and Head circumference).

II-     Sources of environmental pollution with lead: All studied students were subjected to inquiry about sources of environmental pollution with lead; (house and school), with special reference to bad habits among studied students; “such as putting pencil in the mouth …et” and smoking habits of the students or between their parents (Passive smoking).

III-   Soft neurological examinations specially Coordination tests:

a.    Equilibratory coordination:

1-   Standing on one foot for one minute.

2-   Maximum bending forward for one minute.

3-   Maximum bending backward for one minute.

b.    Non equilibrator coordination:

٭ Position holding tests

1-   Touching the tips of the fingers by the thumb

2-   Alternate tapping

IV-           Social scale.10

V-            Psychometric tests:

a.      Wechsler Adult Intelligence Scale (WAIS).11

b.      Cognitive Ability Screening Instrument (CASI).12

c.    Wechsler Memory Scale (WMS).13,14,15

VI-           Urine sample:

Random urine sample was obtained from each student. This urine samples were collected in sterilized and closed cup for each student. These cups frozened -15°C temperature in refrigerator. These samples were used for determination of lead level. Atomic absorption Spectrophotometery used to measure the urinary lead levels. Lead (pb) determined by Atomic absorption/Flame-emission Spectrophotometery (Shimadzu – model AA – 630-02). Using an air-acetylene flame and hollow cathode lamps, wave length at 283.3 nm, lamp current = 6 (MA) and the spectral band pass (slit width) of 109 A°. The results were obtained from standards 2.5, 5 ppm and expressed in µg/L.

 

Written consent was obtained from each student involved in this study. Agreement of  Ethical committee of our college was obtained.

 

RESULTS

 

Sources of environment Pollution with lead in our community:

Students living in old houses (77.9%), in the presence of repair shops (60.8%) and garbage combustion (60.3%) near the house or school, and lastly students using pumping water (68.2%) showed high percent of students with toxic urinary lead level (>80 µg/L).                                        

Students taking food in newspapers (63%), and students using pencils (51.8%) showed high percent of students with toxic urinary lead level (>80 µg/L).                                        

Students smoking (62.1%), students going to school by traffic (55.2%), and lastly students standing for ridding cars (71.6%) showed high percent of students with toxic urinary lead level (>80 µg/L).

Table (1) shows that prevalence rate of lead exposure and/or toxicity was 50.5% among our studied students, out of them 44.8% have urinary lead level >80 µg/L (toxic level). As regards different studied schools, at urinary lead level >80 µg/L students of Elzekhrofia had the highest level (61.5%) followed by Industry school students (41.5%), and lastly Elaskaria students (31.5%).

Table (2) Shows that all studied soft neurological signs specially coordination tests were significantly abnormal among students with toxic urinary lead level (>80µg/L) in comparison to students with normal urinary lead level (<50µg/L) except in one test (standing on one foot).

Students with toxic urinary lead level (>80 µg/L), Elzekhrofia school students had high significant abnormal soft neurological signs specially coordination tests among the three studied schools.

Table (3) Shows that students with toxic urinary lead level (>80 µg/L) had inverse proportion with social levels. Students with toxic urinary lead level (>80 µg/L) among studied three schools, Elzekhrofia students had significantly higher percent (84.9%) in low and very low social levels. There was highly significant inverse proportion between social level and toxic urinary lead level (>80 µg/L) in the studied three schools.

Table (4) Shows that there were statistically significant lower scores among students with preclinical toxicity (>50-80µg/L) and toxic urinary lead level (>80 µg/L) in comparison to students with normal urinary lead level (<50 µg/L) in total, verbal and performance Wechsler Adult Intelligence Scale (WAIS).

Students with toxic urinary lead level (>80 µg/L) of secondary Industry school had significantly lowest scores in total and performance WAIS among the three studied schools, while secondary Elzekhrofia school had significantly the lowest scores in verbal WAIS.

There were statistically significant lower scores among students with toxic urinary lead level (>80 µg/L) in comparison to students with normal urinary lead level (<50 µg/L) in all verbal WAIS subtests.

There were statistically significant lower scores among students with toxic urinary lead level (>80µg/L) in comparison to students with normal urinary lead level (< 50µg/L) in all Wechsler Adult Intelligence Scale (WAIS) performance subtests.

Table (5) Shows that there were statistically significant lower scores among students with toxic urinary lead level (>80 µg/L) in comparison to students with normal urinary lead level (<50 ug/L) in all Wechsler Memory Scale (WMS) subitems.

The students with preclinical toxicity (>50-80 µg/L) shows significantly lower scores in all WMS subitems in comparison to students with normal urinary lead level (<50 µg/L) except mental control and visual memory.

Comparison of different levels of urinary lead levels in each studied school revealed that students with toxic urinary lead level (>80 µg/L) had significantly lower scores than students with normal urinary lead level (<50 µg/L) in all WMS subitems in Elaskaria and Elzekhrofia schools, and in all WMS subitems except digital backward, mental control and visual memory in the secondary Industry school.

Tables (6) Shows that there were statistically significant lower scores among students with toxic urinary lead level (>80 µg/L) in comparison to students with normal urinary lead level (<50 µg/L) in all Cognitive Abilities Screening Instrument (CASI) subitems.

The students with preclinical toxicity of urinary lead level (>50-80 µg/L) shows significantly lower scores in all CASI subitems except attention and language in comparison to students with normal urinary lead level (<50 µg/L).

Comparison of different levels of urinary lead levels in each studied school revealed that students with toxic urinary lead level (>80µg/L) had significantly lower scores than students with normal urinary lead level (<50µg/L) in all CASI subitems in Elaskaria and Elzekhrofia schools. Lastly secondary Industry school had significant lower scores in long term memory, mental manipulation and concentration, orientation, abstract thinking and judgment, and total score of CASI subitems.


 

 

 

 Table 1. Prevalence of  urinary  lead  level among  studied school students Per 100.

Urinary lead level

Studied  students

 80 µg/L

< 50-80 µg/L

≤ 50 µg/L

%

No

%

No

%

No

44.8

269

5.7

34

49.5

297

 

 Total Students        

          N =  600    

31.5

 

63

8

16

60.5

121

[1] Elaskaria school    

          N = 200

41.5

83

8.5

17

50

100

[2] Industry school      

          N = 200 

61.5

123

0.5

1

38

76

[3] Elzekhrofia school

          N=200

 

  Abnormal urinary lead level >50 µg/L(16)

  By chi-square between urinary lead level and type of students p= 0.03*

 

 

 

Table 2. Soft neurological signs (Coordination tests) among studied students with different urinary lead levels.

 

P-Value

Percent of urinary lead level (N = 600 students)

Tests for coordination

>80 µg/L

>50-80 µg/L

≤50 µg/L

No

 

 

0.001

 

 

 

0.001

 

 

 

 

N.S

 

 

 

0.05

 

 

 

0.05

 

 

43**

64.2

 

 

42.8**

61.2

 

 

44.5

45.9

 

 

44*

58.3

 

 

42.9*

58.9

 

 

6.2

0.0

 

 

6.4

0.0

 

 

6

4.7

 

 

6

0.0

 

 

6.5

0.0

 

 

50.8

35.8

 

 

50.8

38.8

 

 

49.5

49.4

 

 

50

41.7

 

 

50.7

41.1

 

 

547

53

 

 

533

67

 

 

452

148

 

 

564

36

 

 

527

73

[1] Touching the tips of the fingers by the thumb :

         - Normal

         - Abnormal

 

[2] Alternate tapping :

         - Normal

         - Abnormal

 

 [3] Standing on one foot :

        - Able

        - Unable

 

[4] Bending forward :

       - Able

       - Unable

 

[5] Bending backward :

       - Able

       - Unable

P value between urinary lead level ≤ 50 µg/L with > 80 µg/L by using Chi-squares test:

p value between urinary lead level > 80 µg/L in each Source of lead pollutions by using Chi-squares test:

  * <0.05                                        ** <0.01                                *** <0.001

 

 

 

Table 3. Study of social levels* among studied students with different urinary lead levels.

 

Social  levels

Percent  of  urinary  lead level  of studied  students

P-value

No

 50 µg/L

< 50- 80 µg/L

<80 µg/L

[1]   High

107

82.2***

0.0

17.8

0.001

[2]   Moderate

238

55.9*

3.8

40.3

[3]   Low + very low

255

29.8

9.8

60.4***

* Social scale (Fahmy and El-Sherbini 1983)

P  value between urinary lead level < 80 µg/L of the 3 social levels by using Chi-squares test:

P value between urinary lead level ≤ 50 µg/L and<  80µg/L in different social levels by using Chi-squares test: 

* > 0.05                                 **  > 0.01                               *** > 0.001

 

Table 4. Study of Wechsler Adult Intelligence Scale (WAIS) among studied students with different urinary lead levels.

 

 

WAIS

Urinary  lead  levels

Multivariant

P-value

≤  50 µg/L

<50–80 µg/L

< 80 µg/L

N = 297

N = 34

N = 269

Total IQ

Range

M±SD

75 – 128

90.9 ± 8.9

76 – 99***

86.2 ± 7.1

73 – 111***

82.3 ± 6

P = 0.001

Verbal  IQ

Range

M±SD

46 – 120

87.1± 10.6

68 – 106*

83.7 ± 9.0

38 – 109***

79.2 ± 7.7

P = 0.02

Performance IQ

Range

M±SD

78 –130

93.3± 7.4

78 – 102**

89.9 ± 6.1

73 – 112***

87.6 ± 6.5

P = 0.01

 

 

P   value between urinary lead level ≤ 50 µg/L with < 50 – 80 µg/L, and ≤ 50 µg/L with < 80 µg/L by using Student t-test:

a > 0.05                                 b  > 0.01                               c > 0.001

 

 

Table  5. Study of Wechsler Memory Scale (WMS) among studied students with different urinary lead levels.

 

WMS items

Urinary   lead   levels

Multivariant

P-value

50 µg/L

>50-80 µg/L

< 80 µg/L

N = 297

N = 34

N = 269

[1] Digital  forward                        

Range

M ± SD

4 – 8

5.9 ± 0.9

4 – 7**

5.4 ± 0.7

4 – 7***

5.3 ± 0.8

N.S

[2] Digital  backward

Range

M ± SD

3 – 7

4.2 ± 1.0

3 – 5***

3.6 ± 0.6

3 – 6***

3.6 ± 0.8

P = 0.04

[3] Total  Digitals

Range

M ± SD

7 – 14

10.1 ± 1.7

8 – 12***

9  ± 1.1

7 – 13***

8.9 ± 1.4

P =  0.001

[4] Mental  control

Range

M ± SD

1 – 4

3.3 ± 0.9

2 – 4

3.1 ± 1.0

1 – 4***

2.6±1.0

N.S

[5] Logical memory

Range

M ± SD

7 – 16

12  ± 1.7

9 – 15***

10.9±1.5

7 – 15***

10.4 ± 1.7

P = 0.03

[6] Associate learning

Range

M ± SD

8 – 21

16.4 ± 2.9

11 – 19***

14.6 ± 2.5

7 – 21***

13.2 ± 3.0

P = 0.0001

[7] Visual memory  

Range

M ± SD

1 – 4

3.3 ± 0.8

2 – 4

3.3 ± 0.8

1 – 4***

2.7 ± 0.9

N.S

[8] Total score of scale      

Range

M ± SD

28 – 56

45.1± 6.9

34 – 51***

40.9  ± 5.2

26.5 – 54***

37.8 ± 6.7

 

 

P value between urinary lead level ≤ 50 µg/L with < 50 – 80 µg/L,  and  ≤ 50 µg/L with < 80 µg/L by using Student t-test:

* > 0.05                                 **  > 0.01                               *** > 0.001

 

Table 6. Study of Cognitive Abilities Screening Instrument (CASI) among studied students with different urinary lead levels.

CASI items

Urinary  lead  levels

Multivariant

P-value

≤  50 µg/L

<50-80 µg/L

< 80 µg/L

N = 297

N = 34

N = 269

[1] Long Term memory

Range

M±SD

7 – 10

9.9 ± 0.3

7 – 10***

9.4 ± 0.8

6 – 10***

9.2 ± 1.0

N.S

[2] Short term memory

Range

M±SD

5.5 – 12

9.9 ± 1.4

6.8 – 12.5***

8.7 ± 1.3

5.3 – 11.5***

8.3 ± 1.3

P = 0.001

[3] Attention

Range

M±SD

5 – 9

7.7 ± 0.6

6 – 8

7.5 ± 0.7

4 – 9***

7.1± 0.9

N.S

[4] Mental manipulation  and

      concentration

Range

M±SD

2 – 11

8.6 ± 1.6

4 –10***

7 ± 1.5

2 – 10***

6.7 ± 1.6

P = 0.03

[5] Orientation

Range

M±SD

13 – 18

17.3 ± 1.1

14 – 18***

16.0 ± 1.3

10 – 18***

15.5 ± 1.5

P = 0.01

[6] Drawing

Range

M±SD

6 – 10

9.2 ± 0.8

7 – 10*

8.8 ± 0.9

5 – 10***

8.2 ± 1.1

P = 0.04

[7] Abstract thinking and

       judgment

Range

M±SD

4 – 12

8.7 ± 1.8

5 – 10***

6.8 ± 1.3

4 – 11***

6.7 ± 1.4

P = 0.001

[8] Fluency

Range

M±SD

5 – 10

8.7 ± 1.1

7 – 10***

7.8 ± 0.9

4 – 10***

7.7 ± 0.9

P = 0.01

[9] Language

Range

M±SD

5 –10

9.7 ± 0.4

8.7 –10

9.7 ± 0.3

6.5 –10***

9.3 ± 0.6

N.S

 

 

P-value between urinary lead level ≤ 50 µg/L with < 50 – 80 µg/L; and  ≤ 50 µg/L with < 80 µg/L by using Student t-test:

* > 0.05                                 **  > 0.01                             *** > 0.001

 

 


DISCUSSION

 

Lead is a pervasive chemical that is well known for its toxicity17. Lead causes neurological, physiological and behavioural problems in children, ranging from raised hearing threshold and decrease in intelligence quotient (IQ) at low blood lead concentrations to acute encephalopathy, memory loss and death at high blood lead concentrations. The harmful effects of lead, at even relatively low levels of exposure, have led WHO and the US Centers for Disease Control and Prevention (CDC)(18) to consider lead concentrations in blood >10 µg/dl  as elevated19.

The highest prevalence rate of lead toxicity (50.5) in our study especially in Elzekhrofia school (62%) was in agreement with Hamdy et al. (1998) they reported a prevalence rate of lead toxicity (urinary lead level > 50 µg/L) among secondary school (210 student) 60.5, in secondary Agricultural school (166 student) 44.5% and among industrial secondary school (158 student), 36%. However Albalak20 in his study in Jakarta, Indonesia reported that 35% of children (6-12 years) had blood lead level > or = 10 micrag/dL and 2.4% had blood lead level > or = 20 microg.dl. Kaiser21 evaluated children at five primary schools in Dhaka, Bangaladesh and reported that 87.4% had blood lead level above 10 microg./dL.

Lastly in disagreement with our results, sadaruddin22 revealed that the overall mean blood lead level was 3.22 µg/dL boys aged 13 to 19 years residing in chakshahzad area of Islamabad.

Sources of lead in the environment that have been shown to contribute greatly to elevated blood lead concentrations include petrol, paint, water, food, cosmetics and lead-glazed ceramics23,24. The present study clarified that presence of source of lead pollution (old houses, repair shops garbage combustion, smoking …etc) near house and / or school had significant higher percent of toxic lead level (> 80 µg/dL).

This is in agreement with Roberts(25) who reported that children living in old houses (before 1950) were 3.9 times more likely to have an elevated blood lead levels than children living in recent houses (after 1977). Also, Ginot26 estimated the prevalence of exposure to lead in a representative sample of older buildings, they revealed that the prevalence of lead poisoning among children living in those buildings, where high levels of lead had been found.

Suplido and Ong27 found that children living in the immediate vicinity of battery shops had significantly higher mean PbB levels (49.88 µg/dL) compared to radiator shop children (11.84 µg/dL) and unexposed children (9.92 µg/dL). Zaki28 found in Alexandria, Egypt, higher risk of lead toxicity among children working in a battery workshops.

In agreement with our results, Hamdy29 found that 41% of children had toxic urinary lead level (>50 µg/L) in presence of garbage combustion near the house or school. Garbage contains wasted materials contains lead, so burning this materials elaborates lead to the environment, which increase the air pollution by lead.

Other investigators reported that environmental factors, such as living in area with high traffic density, living close to lead emitting source, and occupation or hobbies may influence the exposure to lead30,31,32.

Ducoffre32 reported that smoking is positively associated with the level of lead in blood. Also, Kristiansen33 showed that blood lead is increased by cigarette smoking.

Smoking may enhance the lead intake by more frequent hand to mouth contacts34, or through transportation of airborne lead into the lungs by smoke particles35.

Our results showed that all studied soft neurological signs specially coordination tests were significantly abnormal among students with toxic urinary lead level (>80 µg/L) in comparison to students with normal urinary lead level (£50µg/L) except standing on one foot test. In agreement with our results, a study done by Hamdy29 studied the effect of lead on the coordination of children (n=1057), they found that children with abnormal coordination were higher among those with urinary lead level >50 µg/L. The differences were significant in tests of touching the tips of the fingers by thumb and alternate tapping.

Marantidou36 did a study of 30 moderately exposed children living in the vicinity of a longstanding lead smelter in Greece, they found that children with blood lead levels in the range of 35 to 60 µg/dl had significantly lower scores on both the gross and fine motor composite subtest of the Oseretesky Scales when compared to a group of control children residing in an unexposed area of the province. Lynette37 did an epidemiological study of 281 young adults was conducted to determine whether environmental exposure to lead during childhood was associated with current adverse neurobehavioral effects. They found that hand-eye coordination, simple reaction time latency significantly associated with exposure group.

In several studies, investigators have explored the possible interaction between PbB level and social class on cognitive development. In cross-sectional studies38,39 and two prospective cohort studies40,41, researchers reported that the children in the low-SES families were more sensitive to lead toxicity than those from socially advantaged backgrounds.

As regarding the social levels in relation to urinary lead levels, our results showed that students with toxic urinary lead levels (>80 µg/L) had inverse proportion with social levels. This was in agreement with Von Schirnding42, who found that children with low maternal educational levels and low socioeconomic status were important risk factors for elevated childhood blood lead levels. Also, Chao-Ling43 found that the social economic status of parents convey information about a child’s potential exposure. Father’s SES, mother’s educational level, and class ranking were all significantly related to blood lead.

In disagreement with our results Ebba44 found that, no association between socioeconomic status and blood lead level in their study at ages 15 years and follow-up at ages 17 years. But they explain their results as the socioeconomic difference in Sweden are smaller than in many other countries.

Investigators have observed repeatedly that increased lead absorption causes cognitive impairment in children45. Our results showed that, there were statistically significant lower scores among students with preclinical toxicity (>50-80 µg/L) and toxic urinary lead level (>80 µg/L) in comparison to students with normal urinary lead level (£ 50 µg/L) in total, verbal and performance Wechsler Adult Intelligence Scale (WAIS).

Tong46 examined the association between environmental exposure to lead and children’s intelligence at age 11-13 years (N=375), the results revealed a consistent inverse relation between blood lead concentrations (PbB) and scores for all 12 subscales of the Wechsler Intelligence Scale for Children Revised (WISC-R). The magnitude of the deficit in IQ with increased PbB was similar for the verbal and performance scales. The mean score for full scale IQ declined 3 points for a doubling of lifetime PbB from 10 to 20µg/dL. Individual subscales scores showed varying degrees of inverse association with lifetime PbB lead levels. However, those showing the strongest associations were the information, arithmetic, block design, and maze subscales. The negative impact of lead exposure is generally stronger on verbal IQ than on performance IQ47.

In our study there were statistically significant lower scores among students with toxic urinary lead level (>80 µg/L) in comparison to students with normal urinary lead level (<50 µg/L) in all Wechsler Memory Scale (WMS) subitems. This clarify that lead had great effect on the memory.

In our study there were statistically significant lower scores among students with toxic urinary lead level (>80 µg/L) in comparison to students with normal urinary lead level (<50 µg/L) in all Cognitive Abilities Screening Instrument (CASI) subitems. This clarify the possible impact of lead on cognition.

In partial agreement with our results Dudek and Merecz48 examined group consisted of school age children 6-15 years old. Out of 4548 children with measured blood lead concentration, two groups were selected one with the highest exposure levels (12-27.2 µg/dL) and the other drawn from the remaining children, with low blood levels. They revealed that, the short term memory deteriorates with growing level of exposure.

Also, Lanphear49 examined the relationship of relatively low blood lead concentrations especially concentrations <10 µg/dL with performance on tests of cognitive functioning (arithmetic, skills, reading skills, non verbal reasoning, and short term memory) in a representive sample (N=4853) of US children and adolescents (ages 6-16 years). There was inverse relationship between blood lead concentration and scores of four measures of cognitive functioning. For every 1 µg/dL increase in blood lead concentration, there was a 0.5 point decrement in mean scores on a measure of short term memory.

It is observed from our study that just students had toxic urinary lead level more than >80 µg/L, the effect of lead on cognitive functions did not show more deterioration of cognition among studied students. In disagreement with our results, reviews of studies concluded that a 10 µg/dl increase in blood lead can be associated with a 2-2.5 point decrease in IQ18,47.

 

Conclusion

Lead is more common among secondary Industry and Elzekhrofia students schools due to their nature of the school to more hazardous exposure to lead.  Living in old houses, presence of repair shops and garbage combustion near the house or school can increase the body burden of lead. Toxic urinary lead level (>80 µg/L) can cause abnormal soft neurological  signs special coordination tests. There is significantly lower scores among students with toxic urinary lead level (>80 µg/L) in total, verbal and performance Wechsler Adult Intelligence Scale (WAIS), also all Wechsler Memory Scale (WMS) subitems, and lastly Cognitive Abilities Screening Instrument (CASI) subitems.

 

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