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Int Arch Occup Environ Health (1986) 57:225-235 

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© Springer-Verlag 1986 

EPA AIR DOCKET 

The relationship between blood-lead concentrations, 

intelligence, attainment and behaviour 

in a school population: the second London study 

Richard Lansdown1, William Yule2, Marie-Anne Urbanowicz3, and Jan Hunter2 

1

 Department of Psychological Medicine, The Hospital for Sick Children, London WC1N 3JH, 

2

 The Institute of Psychiatry, London 

3The Inner London Education Authority Research and Statistics Branch, London, 

Grait Britain 

Summary. This study replicates an earlier one carried out in London in 

which an association was found between lead and intelligence, reading and 

spelling. In the present study 194 children living near an urban motorway 

were given the same battery of tests as well as an extensive family interview 

to determine background variables. Before social factors were taken into 

account there were no significant associations between lead and outcome 

variable. Possible reasons for the negative results from this study are discussed. 

Key words: Children - Blood lead level - Attainment - Intelligence - Behaviour 

Introduction 

This study was undertaken in order to replicate a study (Yule et al. 1981,1982; 

Lansdown et al. 1983) in which 166 children aged 6 to 12 years, living within 

1 km of a London factory were assessed in school. The first battery of this pilot 

study consisted of the Wechsler Intelligence Scale for Children—Revised 

(Wechsler 1974), the Neale Analysis of Reading Ability (Neale 1958), and the 

Vernon Mathematics and Spelling Tests (Vernon and Miller 1976; Vernon 

1977). Teachers' ratings of children's behaviour were collected using the scale 

employed by Needleman et al. (1979), the Conners (1969) scale and the Rutter 

B2 scale (Rutter and Yule 1968). Blood-lead concentrations had been ascertained 

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226 R. Lansdown et al. 

9-12 months prior to the psychological assessments as part of an EEC survey. 

Social class was established from the fathers' occupations. Almost half came 

from class III, manual labour (46%), with 18.6% in classes I and II. They were, 

therefore, a predominantly working class sample. --; 

The mean blood-lead concentration in this sample was 13.52 ug/100 ml (SD 

= 4.13), and there was a small, but statistically significant relationship between-J 

body-lead burden, intelligence, reading, and spelling. This association remained** 

after social class had been accounted for. The pattern of the children's behaviour, as rated on the scale used by Needleman, was strikingly similar to that 

reported in his 1979 paper, i.e. in most categories children with higher lead 

levels showed indications of less acceptable behaviour. 

The second London study was designed to replicate the first and to improve 

on it by (a) examining the relationship between outcome measures and two estimates of blood-lead and (b) by gathering more information on social factors 

thought to be relevant. 

Method 

The sample 

The children taking part in the replication study were drawn from a population living near a , 

main road in another part of London. Blood-lead concentrations had been ascertained by the 

community physician in response to a request from some parents who had been concerned because of the proximity of their children's school to a busy road. Of a total population available 

• f/f.f'-f-'^.f.2 of 221, 87.8% participated in the study, giving a sample of 194. 

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Investigation of social factors 

Social class was again ascertained by establishing the fathers' occupation. A lengthy structured 

interview with parents was undertaken to give further information. This interview, which took 

approximately 2 h to administer, was based on one devised for another study on lead and children also carried out in London (Smith et al. 1983). It included a brief assessment of both par-

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 ents ' lntemgence, using two subtests of the Wechsler Adult Intelligence Scale (Wechsler 1955). 

f •• ii;';'•] ?'.'';{ Blood-lead ascertainment 

Blood had been collected by vein puncture and analysed in the Department of Chemical 

Pathology and Human Metabolism at the University of Southampton under the direction of 

Dr. Trevor Delves. Lead concentrations were determined on samples of blood using atomic 

absorption spectrophotometry. At a value of 15 ug/100 ml, this analytic method should 

achieve results within ± 10%, provided the quality control is meticulous (DHSS 1980). There 

is no reason to believe that quality control in these analyses was anything but meticulous. 

A second blood sample was taken from 162 children after the psychological assessment 

was completed, some 20 months elapsing between the two measures. Analysis was carried out 

in the same laboratory. 

Test battery 

The tests and teachers' ratings that had been used in the pilot study were employed again, 

given under the direction of the same field supervisor. All testing was carried out in the children's schools by trained psychologists who were blind to the lead levels. Behaviour was rated 

by the same scales as had been used in the pilot, plus a rating by parents (Rutter et al. 1970). 

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Lead effects on intelligence attainment and behaviour 227 

Results 

Social class distribution 

As can be seen from Table 1, the present sample contained a much higher proportion of middle class children (defined as classes I, II, and III non-manual 

labour) than had been present in the pilot study: 55.2% vs 18.6%. 

Table 1. Social-class composition of the sample and the pilot 

study 

.Table 2. Distribution of bloodlead levels measured from first 

blood sample 

Social-class 

7 

8 

9 

10 

3 

12 

8 

21 

194 

Sample Pilot 

• 

I 

II 

III non-manual 

III manual 

IV 

V 

Single parent 

Unemployed 

Not known 

N 

4 

71 

32 

68 

8 

3 

5 

2 

1 

% 

2.1 

36.6 

16.5 

35.1 

4.1 

1.5 

2.6 

1.0 

0.5 

N 

3 

11 

17 

77 

19 

2 

12 

2 

23 

% 

1.8 

6.6 

10.2 

46.4 

11.4 

1.2 

7.2 

1.2 

13.9 

Total 

Pb 

(ug/100 ml) 

N 

194 

/o 

166 

Quartiles 

1.5 

6.2 

4.1 

10.8 

11 

12 

13 

14 

15 

16 

17 

18 

19 

20 

21 

22 

23 

24 

23 

30 

32 

17 

20 

9 

4 

5 

4 

3 

0 

1 

0 

2 

11.9 

15.5 

16.5 

8.8 

10.3 

4.6 

2.1 

2.6 

2.1 

1.5 

0 

0;5 

0 

1.0 

II 

III 

IV 

Mean = 12.75 ug/100 ml; SD = 3.07 

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Table 3. Lead level by social-class 

R. Lansdown et al. 

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N SD 

I + 11 

III NM 

IIIM 

rv + v 

Single parent 

and unemployed 

66 

36 

.63 

10 

14 

12.88 

11.25: 

13.34 

13.18 

11.86 

3.22 

2.65 

2.79 

4.12 

2.34 

2.87 0.02 

Pb (ug/100 ml) First testing 

(AO 

Second testing 

(AO 

Table 4. Summary of results of 

first and second samples of 

blood-lead levels 

7-10 

11-12 

13-14 

15-27 

Total 

Mean 

SD 

37 

43 

38 

44 

162 

12.88 

3.16 

6 

.25 

50 

81 

162 

15.10 

3.23 

Table 5. Results of tests of attainment and intelligence 

Variable N SD 

Chronological age (months) 

Reading— 

accuracy (months) 

comprehension (months) 

Spelling (standard score) 

Mathematics (standard score) 

WISC-R— 

verbal IQ 

performance IQ 

full scale IQ 

194 

194 

194 

194 

194 

194 

194 

194 

109.10 

112.17 

110.10 

99.36 

99.10 

103.36 

106.41 

105.24 

25.37 

23.06 

24.35 

14.25 

16.18 

14.91 

13.81 

14.20 

Blood-lead concentrations 

Table 2 shows the distribution of the first sample of blood-lead levels. The mean 

of 12.75 ug/100 ml and the range of 7-24 jig are both smaller than those found 

in the pilot study. 

Table 3 gives the distribution of this sample by social class. In contrast to 

several other studies, including the pilot, the difference between the levels 

according to social class was small and did not reach statistical significance at 

the 0.01 level. 

Results of the second estimate of blood-lead are given in Table 4. The mean 

concentration increased by about 2ug, a somewhat surprising figure, given that 

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Lead effects on intelligence attainment and behaviour 

Table 6. Teachers' ratings of behaviour 

229 

Teachers scales 

Needleman 

B scale 

Conners 

Boys? 

1.91 

3.18 

9.76 

SD 

2.34 

3.97 

10.91 

Girls X 

1.04 

2.13 

6.54 

SD 

1.67 

2.69 

6.72 

F ratio 

8.57 

4.57 

5.93 

P 

0.01 

0.01 

0.05 

the children were almost 2 years older and blood levels usually decrease with increasing age. What is more, the increase is almost double that which might have 

been expected by chance, given that, as noted above, ± 10% is excepted. The 

correlation of 0.54 between the two measures was similar to that reported by 

Ewers et al. (1982), suggesting that the rank order of the children may be more 

stable than the absolute estimate of blood level. 

Because of an uncertainty about which was the more valid estimate for our 

purposes, analyses were carried out using both first and second estimates and an 

average of the two. 

Intelligence and attainment 

Table 5 indicates that the results of the tests used were what would be predicted 

for a mainly middle class sample. There was no significant difference between 

the results of the whole sample, and the subsample comprising the smaller, 

second blood lead group. 

Behaviour ratings 

Very few children were rated as deviant on any items by parents or teachers. 

Table 6, as well as showing sex difference, bears out the low level of unacceptable behaviour in school. It should be noted that for the Rutter B scale, a cut-off 

score of 9 is generally regarded as indicating behaviour disturbance. 

Social variables 

The picture obtained from the family interview was one of a stable group. In 

90% of the sample the natural parents were married and living together; only 

2% of the families contained 4 or more children; 83% of parents owned their 

own homes and 44% had been at the same address for more than 8 years. All 

houses had basic amenities and over 90% had their own garden. Seventy-one 

percent of mothers were or had been in non-manual-labour occupations, and 

the mean scores of both parents on the WAIS subtests were above average, 

being between 11.1 and 12.2 (the average is 10.0). 

The association between lead, age, social class, IQ and attainment 

Table 7 shows the results of analyses of covariance; the first lead estimate is 

used and the group divided at the median into upper and lower levels. There 

was a social class effect, as expected, but no lead effect. 

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Table 7. Analyses of covariance showing adjusted means—first blood-lead estimate 

PbB group 

7-12 

13.24 

Age 

Social-class 

PbBl 

N 

80 

82 

Accuracy 

(months) 

114.53 

111.51 

P = 0.001 

NS 

NS 

Comprehension 

(months) 

112.77 

109.33 

P = 0.001 

P = 0.02 

NS 

Spelling 

100.72 

98.61 

NS 

NS 

Mathematics 

110.24 

98.66 

NS 

NS 

Verbal IQ 

104.48 

103.43 

P = 0.001 

NS 

Performance 

108.20 

106.32 

i° = 0.04 

NS 

Full-scale IQ 

106.86 

105.18 

P = 0.001 

NS 

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Lead effects on intelligence attainment and behaviour 231 

Table 8. Multiple regression analyses: Log first blood-lead with age and social class on IQ and 

attainment (N = 86) 

Dependent variable 

Accuracy (age) 

Comprehension (age) 

Spelling 

(standard score) 

Mathematics 

(standard score) 

Verbal IQ 

Performance IQ 

Full-scale IQ 

Predictor 

(in order of 

F value) 

Age 

Social-class 

Log lead 

Age 

Social-class 

Log lead 

Social-class 

Log lead 

Age 

Age 

Social-class 

Social-class 

Age 

Log lead 

Social-class 

Log lead 

Age 

Social-class 

Age 

Log lead 

Coefficient 

of regression 

0.64 

-3.05 

-8.00 

0.69 

-3.07 

-3.65 

-2.05 

-4.57 

-0.02 

0.16 

-1.53 

-3.33 

-1.10 

1.91 

-1.94 

2.38 

0.02 

-2.94 

-0.05 

2.15 

F 

195.40 

8.36 

2.73 

200.70 

7.33 

0.49 

4.40 

1.03 

0.22 

16.75 

2.53 

11.20 

5.43 

0.17 

4.01 

0.29 

0.25 

9.15 

1.34 

0.23 

P 

0.000 

0.004 

0.10 

0.000 

0.007 

0.48 

0.04 

0.31 

0.64 

0.000 

0.11 

0.001 

0.02 

0.68 

0.05 

0.59 

0.62 

0.003 

0.25 

0.63 

OIAR2 

0.56 

0.55 

0.03 

0.09 

0.10 

0.02 

0.06 

A similar pattern emerged from the second and averaged blood lead estimates. 

Table 8 summarizes the result of unforced step-wise regression analyses in 

which lead, social class, and age are entered according to the proportion of 

variance accounted for in the dependent variable. 

Similar results were obtained for the second and average lead estimates. In 

no case does lead account for a significant amount of residual variance in any of 

the measurements of IQ or attainment. 

Table 9 gives a full scale IQ results for the first lead estimate divided into 

manual and non-manual groups according to father's occupation. It will be seen 

that there is a trend towards an effect in manual groups, but this did not reach 

statistical significance, possibly because the numbers were relatively small. The 

results of the second and averaged estimates were similar. 

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Lead and behaviour 

With so few children showing signs of disturbed behaviour, it was not surprising 

that no significant relationships were found between lead and any of the ratings. 
P.9 

232 R. Lansdown et al. 

Table 9. Analyses of variance dividing sample into manual and non-manual groups, using 

approximate quartiles of Pb distribution 

IBIIft-f 

Vf-''.'• '•'" 

Dependent variable 

Non-manual group 

Verbal IQ 

Performance IQ 

Full-scale IQ 

Manual group 

Verbal IQ 

Performance IQ 

Full-scale IQ 

Lead groupings: 1 = 

11 = 

m = 

IV = 

Pb group N 

I 

II 

III 

IV 

I 

II 

III 

IV 

I 

II 

III 

IV 

I 

II 

III 

rv 

i 

ii 

in 

IV 

i 

n 

in 

rv 

28 

26 

27 

21 

28 

26 

27 

21 

28 

26 

27 

21 

16 

25 

21 

25 

16 

25 

21 

25 

16 

25 

21 

25 

7-10ug/100ml 

11-12 ug/100 ml 

13-14 

15-24 

ug/100 ml 

ug/100 ml 

Mean 

102.29 

109.88 

103.67 

110.52 

104.07 

110.61 

106.33 

112.29 

103.39 

111.42 

105.33 

112.52 

102.31 

98.32 

98.95 

99.48 

110.19 

103.64 

103.48 

103.40 

106.87 

100.68 

101.09 

101.32 

SD 

16.57 

14.55 

14.39 

15.25 

13.13 

15.99 

15.18 

9.65 

13.52 

14.94 

15.03 

12.81 

12.54 

9.30 

14.74 

16.09 

13.59 

14.65 

10.97 

14.63 

12.98 

11.48 

13.16 

15.73 

F 

1.93 

1.85 

2.52 

0.31 

1.04 

0.83 

P 

0.13 

0.14 

0.06 

0.82 

0.38 

-

0.48 

The association between lead and social variables 

Table 10 summarizes individual items correlating with lead levels. 

There is little consistency in these findings. Of the 13 items found to correlate significantly by Smith et al. (1983)1

, only 7 in this study were found to be significantly associated with either the first or second blood levels and only two 

(pica and age of housing) with both. 

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Lead effects on intelligence attainment and behaviour 233 

Table 10. Parent interview: Pb effects, first and second lead estimates. Spearman correlation: 

P = 0.01 

Pbl N = 194 

Birthweight 

(i.e., more 

normal weight = Pb) 

Type of school father attended 

("better" school = higher Pb) 

Father's personality disorder 

(more severe disorder 

= lower Pb) 

Mother's working hours week* 

(less hours working = 

higher Pb) 

Thumb-sucking 

Pica: past for toys 

past for earth* 

past duration for earth 

rs 

-0.18 

0.17 

-0.23 

-0.19 

0.27 

0.17 

0.19 

0.19 

Pb2/V=162 

Method of delivery 

(i.e., more normal delivery = 

higher Pb) 

Age at weaning* 

(later = higher Pb) 

Father's occupation; 

further education; 

satisfaction with outings alone 

Mother's occupation*— 

previous (includinghousewife); 

now 

Total quarrels/bickering 

Family cleanliness 

State of inside paintwork 

Work on car 

Terraced house in area 

Frequency of father playing 

out with child* 

Frequency of mother playing 

out with child* 

(i.e. less outside play = 

higher Pb) 

rs 

-0.19 

0.20 

0.21 

-0.22 

-0.18 

0.23 

0.23 

0.19 

0.24 

0.18 

-0.21. 

-0.18 

0.34 

0.17 

' Significant at either 0.01 or 0.05 level for both Pbl and Pb2 

Discussion 

The overall conclusion from this study is that there is no evidence of a significant effect of lead on IQ, attainment or behaviour once other variables are 

accounted for. 

The second study was more sophisticated in design than the first but, in the 

event, the additional information was not used quite as had been intended. The 

uncertainty about the variations in blood lead levels meant several analyses had 

to be carried out in an exploratory manner. The social data were satisfactory, 

but the absence of any significant relationship between lead and the outcome 

variables meant that there was no need to invoke the social information so 

laboriously collected. 

The failure to replicate the results of the first jtudy remains to be explained. 

A possible explanation may be found in that the only immediately apparent dif-

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ferences between the two groups was in the social composition of the families: 

the second contained a far greater proportion of middle class parents than the 

first. A possible hypothesis to apply to the results of the first and second study 

taken together is that lead might have an effect only when other factors leading 

to disadvantage are present. 

Some support for this argument is given by a suggestion of a relationship between lead and behaviour in our second study but only amongst working-class 

children. Further support is given in the work of Winneke and Kraemer (1984), 

who analysed their data to find that the lead effect was, to some extent, stronger 

in their socially disadvantaged children and from Harvey et al. (1984) who reported indications of similar social class differences in apparent lead effects. 

However, there is at the moment no more than a suggestion that this is likely to 

be a satisfactory explanation for the observed findings. 

Even if one allows for the possibility of such social factors interacting with 

lead, there is nothing in the present study to suggest that within normal, low 

levels of exposure lead will account for more than 2%-3% of the variance in 

measured intelligence, far less than is accounted for by genetic and other environmental factors. The possible interaction between social variables and lead 

discussed above remains worthy of further consideration. 

Acknowledgements. This research was supported by Medical Research Council Special Project Grant G 80/11564. The Inner London Education Authority and the teachers in the schools 

concerned are thanked for their kind assistance. 

References 

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Psychiatry 126:884-888 

DHSS (1980) Lead and health. The report of a DHSS working party on lead in the environment. Her Majesty's Stationery Office, London 

Ewers U, Winneke G, Freir I, Jermann E, Kraemer U (1982) Lead in deciduous teeth of children living in a non-ferrous smelter area and a rural area of the FRG. Int Arch Occup 

Environ Health 30:139-151 

Harvey PG (1984) Lead and children's health—recent research and future questions. J Child 

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Chichester 

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levels. N Engl J Med 300:689-695 

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Rutter M, Tizard J, Whitmore K (1970) Education health and behaviour. Longman, London 

Smith M, Delves T, Lansdown R, Clayton B, Graham P (1983) The effects of lead exposure 

on urban children: the Institute of Child/Southampton Study. Dev Med Child Neurol 

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Vernon PE (1977) Vernon graded word spelling test. Hodder & Stoughton, London 

Vernon PE, Miller RM (1976) Vernon graded arithmetic-mathematics test. Hodder & 

Stoughton, London 

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Lead effects on intelligence attainment and behaviour 235 

Wechsler D (1955) The Wechsler adult intelligence scale Psychological Corporation, New 

York 

Wechsler D (1974) The Wechsler intelligence scale for children - revised Psychological Corporation, New York 

Winneke G, Kraemer U (1984) Neuropsychological effects of lead in children interactions 

with social background vanable Neuropsychobiology II 195-202 

Yule W, Lansdown R, Millar LB, Urbanowicz MA (1981) The relationship between blood 

lead concentrations, intelligence and attainment tn a school population, a pilot study Dev 

Med Child Neurol 23 567-576 

Yule W, Lansdown Rt Urbanowicz MA (1982) Predicting educational attainment from 

WISC-R in a primary school sample Br J Clin Psychol 31 43-46 

Received June 19/Accepted October 10, 1985 

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