282

LEAD IN MENTALLY RETARDED CHILDREN

JOAN BICKNELL, BARBARA E. CLAYTON and H. T. DELVES

Queen Mary's Hospital for Children, Carshalton, Surrey

andDepartment of Chemical Pathology, Hospital for Sick Children,

Great Ormond Street, London, W.C.I

Pica is known to be frequent among retarded children and many workers haveemphasised that a high incidence of lead poisoning occurs in children with thissymptom (Greenberg, Jacobziner, McLaughlin, Fuerst and Pellitteri, 1958). Picaand lead poisoning may be related to mental retardation in one of two ways. Braindamage can result from lead poisoning in a child initially of normal developmentapart from the habit of pica for which the cause is most likely unknown (Jenkinsand Mellins, 1957). However, the child who is mentally retarded because of otherfactors, will remain at a more infantile developmental level for a longer time thanthe normal child, and this, combined with relatively more advanced locomotorability, may accentuate the problem of pica, and lead poisoning may be super-imposed on the existing brain damage (MoncrietF, Koumides, Clayton, Patrick,Renwick and Roberts, 1964; Bickneil, 1967). The controversy as to the importanceof excessive ingestion of lead as a causal or a concomitant finding has not beenfinally settled, nor do we know the extent of the danger of a persistently raisedblood lead level in a retarded child.

It is well known that the blood lead level may not accurately represent thetotal body load of lead (Chisolm, 1965), but ancillary investigations of help in theadult are still less accurate indicators of lead to.xicity in the child (Moncrieff, et al.,1964; Gibson, Lam, McCrae and Goldberg, 1967). The level of blood lead remainsone of the most informative indices of the extent of lead ingestion, but the minimumlevel that represents a detrimental load to the child is still not known.

An examination of the urinary lead levels gives additional information and thisis enhanced by assessing the increase of excretion following the use of a chelatingagent such as calcium disodium ethylenediaininetetraacetic acid (calcium E.D.T.A.)or penicillamine (American Academy of Pediatrics, 1961; Cohen, Lourie andAbernethy, 1965; Gibson, et al., 1967).

In the present study, three groups out of a population of hospitalised severelysubnormal children in long term care, were selected according to the severity of picaand degree of physical handicap. The aims of the survey were fourfold : '

1. To examine the causes of the severe subnormality in the three groups in anattempt to assess the possible aetiological role of primary lead poisoning.

2. To define more clearly the type of child with pica in such a hospital population.

3. To examine blood lead levels.

(Received June 29th, 1968)

JOAN BICKNELL, et al. 283

4. To assess the value of an oral calcium E.D.T.A. test as an index of lead ingestion,using random samples of urine on the same children.

Selection of Subjects

The population consisted of 330 severely subnormal children in long termhospital care. The senior ward staff were asked to group the children in their careinto 1 of 3 categories : (i) "scavenges so frequendy that the child is a problem inmanagement", (ii) "never or almost never scavenges", or (iii) "occasionallyscavenges". Two independent assessments were made for each child. For this studyall children in category (i) were included in the 'pica' group, and the 'no pica' andphysically handicapped groups were selected from those in category (ii). Thechildren in category (iii) were not investigated further.

'Pica' Group

Twenty-four children were rated by both assessors in category (i). In addition,three children di.splaying severe pica at home, admitted for a period of short termcare, were included in this group. These 27 children had a mean chronological ageof 9.0 years (range 2.6 years-16.3 years) and a mean mental age of 15.6 months(range 6.0 months-2.5 years). Four were assessed on the Stanford Binet IntelligenceTest (Form L.M.) and 23 were asse.ssed on Piaget Sensori-Motor scale of develop-ment. Of the 24 in long term care, 5.3 years was the mean length of hospital stay.Fifteen had additional serious handicaps; of these, 2 were blind, 4 had cerebralpalsy and 11 had epilepsy. Ten had a severe behaviour disturbance; of these, 3 wereoveractive, 2 withdrawn, 1 p.-;ychotic and 6 unduly aggressive, in particular bitingother children. Pica in 19 seemed completely indiscriminate, in 2 it showed someselection for paper and clothes and in 6 it was predominantly for one type of sub-stance; these were 3 for painted wood, one for fluids of all kinds, one for paper andanother for putty. The cau.se of the subnormaiity was not known in 12 cases;perinatal difficulties sufficient to cau.se brain damage had occurred in 5; a diagnosishad been made in 10 including one case in which lead poi.soning was definitely acausal factor (Berg and Zapella, 1964). Of the 12 cases in which a specific diagnosishad not been made, l)rain damage had been diagnosed in 9 before the age of 12months and prior to the onset of walking or standing which makes lead poisoningan unlikely cause of primary brain damage. In one the delay in walking raised thequestion of mental retardation which was subsequently confirmed and in twomental retardation became apparent after walking had been achieved. In one ofthese lead encephalopathy was excluded following detailed investigation at the time.Despite the deficiencies of retrospective data one may conclude that in only oneout of the 27 children with pica can lead encephalopathy be considered as anestablished primary cause, and in one a possible primary cause of the mentalretardation.

In the daily care of these children the dangers of pica other than load poison-ing have to be remembered; despite the vigilance of nursing staff, one childdeveloped reversiljle intestinal obstruction following the ingestion of balloon.s, and

284 LEAD POISONING

another caused anxiety by swallowing part of a thermometer. Both these childrendisplayed considerable guile in obtaining such objects to chew and their experientialworld is necessarily restricted because of the supervision they require.

Physically Handicapped GroupA .second group of 14 children were selected who were severely physically

handicapped, unable to walk or to feed themselves and were classified by both seniormembers of the ward nursing staff as in category (ii) "never or almost neverscavenges", most being unable to put hand to mouth. However, none were severelydebilitated or prone to frequent severe respiratory tract infection. None of thesechildren attended the hospital school, their mean chronological age was 10.3 years(range 5.3 years-13.0 years), their mean mental age 7.1 months (range 1.5-24.0months). All were assessed on Piaget Sensori-Motor scale of development. The meanlength of stay in hospital was 5.5 years. Twelve of these children had cerebral palsy.Four were blind or partially sighted and 10 had epilepsy. Two showed disturbed be-haviour on occasions. The cause of the subnormality was known in 6 cases andperinatal brain damage was thought to be the cause in an additional 3 cases. In 5the cause of their handicap was unknown.

90

80

S 70oo• ^ 60a.•a 50a

S 30

20

10

0

Mean

S.D.

PICDay 1

• • •• •

•

•

48

19.2

ADay 8

•

•

• •

45

19.9

No PDay 1

• •

19

9.4

CADay 8

Uppe

•V19

7.4

PhysHandic

Day 1

r limit o!

• * ' ' .

12

5.2

lcally•apped

Day 8

normal*

•n*

12

4 .8

Fig. 1. Blood lead levels on Day 1 and Day 8 of the oralcalcium E.D.T.A. test for the three groups.

*MoncriefF, et al. (1964)

JOAN BICKNELL, et al. 285

Wo Pica' Group

For the purpose of a control group, 12 severely subnormal children wereselected who were classified in category (ii) "never or almost never scavenges". Thesechildren were referred to as the 'no pica' group. All these children were fullyambulant, took a normal diet and all but one attended the hospital school for S.S.N.children. They were selected from among the least handicapped of the hospitalpopulation and represent the nearest possible approximation to a control group ofnormal children. These 12 children had a mean chronological age of 12.7 years(range 7.2-14.2 years) and a mean mental age of 2.3 years (range 1.5-3.5 years). Ninewere assessed on the Stanford Binet Intelligence Scale (Form L.M.), 3 assessed onPiaget Sensori-Motor scale of development. The mean length of stay in hospital was6.2 years. One child was blind, 2 had psychotic features and 2 had epilepsy. Nonehad cerebral palsy. The cause of the subnormality was not known for certain in 6cases. In 2 there were perinatal difficulties, 3 had Down's syndrome, 2 were brotherswith Hurler's syndrome and 1 was a premature twin.

The following test was carried out to compare the degree of lead ingestion inthe three groups of children.

Oral calcium E.D.T.A.—lend excretion test

Day 1 Monday — Blood specimen for lead. One single random specimenof urine.

Day 2 Tuesday — Random urine*Day 3 Wednesday — Random urine 1 Oral calcium E.D.T.A.Day 4 Thursday — Random urine I 250 mgm. b.d. for 3Day 5 Friday — Random urine J days

*Day 6 Saturdav — Random urineDay 7 Sunday — No specimens needed

*Day B Monday — lilood and random urine specimens* Fhese spcciiiieiis proved uiinecessary—see Results Section.

Sample Collection

Blood samples"~were taken by venepuncture into heparinised plastic disposablesyringes and stored in the freezer compartment of a refrigerator until required foranalysis.

Urine samples were collected into a plastic pot which had previously been rinsedwith water and transferred to 100 ml. polythene bottles (cleaned by washing with10% v/v lead-free HNO.-, solution and de-ionised water) which contained 2 ml. of50% v/v lead-free HNOn solution as preservative.

RESULTSThe blood lead levels for the three groups before and after the administration

of oral calcium E.D. r..A. (Day 1 and Day 8 respectively) are shown in Fig. 1.

286 LEAD POISONING

There was no significant difTerence in these le\els for each group before andafter the administration of calcium E.D.T.A. (p >0.5 for all 3 group.s), but thedifference in the blood lead levels between the 'pica' group and the other two groupswas highly significant (p <0.001 in each case). There was also a significant differ-ence (p <0.0.5) between the blood lead level? on Day 1 of the physically handi-capped group, and the 'no pica" group. 18 children (67%) in the 'pica' grouphad blood lead levels in excess of 36 /xgm./lOO ml. One child (8%) of the 'no pica'group and no f)hysically handicapped children had blood lead levels greater than36 /^.gm./100 ml.

An analysis of blood lead le\els where the pica was selective or fairly selecti\erevealed that tho.se chewing paper, clothes and drinking fluids had, as expfcted,lower blood lead levels (4 children with a mean blood lead level of 33 /jgm., 100ml., range 22-.5O ugm./lOO ml.) than tho.se seeking painted wood and putty (4childreri with a mean blood lead level of 66 ^.gm./lOO ml., range 39-8f) //gm./100 ml.).

Tlie mean urinary lead lfnels for Day 1 to Day 8 in response to oral calciumE.I). T.A. is shown for eacli group in Fig. 2.

The results of urinary lead excretion are expressed as //gin./litre vvliirli wa>considered preferable to a comparison with the urin.-try creatinine ie\el, becausethere i> evidence of considerable \ariations in the urinary output of creatinine inthe individual (Selander. Cramer and Hallberg. 1966).

Oral E.D.T.A. 250mg. b.d.

1000

900

800

700

600

500

400

300

200

100 ;

0

//

/ J

• X- - X P I C A

0---0 No PICAa—t Physically

HandicappecJ;̂ J S.E. of Mean (-1\

\\

\\

1 2 3 4 5Day of Test

P i g . 2 . 1 hf- i v u - a i i i i r i t i a r y I c a r l If-\f-|^ i u r f ^ p ^ i n - f - f . >

K . l J ' l . . - \ : f o r t h f i h r . - . - t r r r a i p ' .

JOAN BICKNELL, cl al. 287

The mean urinai7 lead levels for the 'pica' group were significantly greater(p <0.025) tlian those for the other two groups for each day of the investigation.The increase in the urine lead levels was greater in response to calcium E.D.T.A.for tlie 'pica' group than for the other two groups.

In order to minimise errors due to the use of random specimens of urine andthe possible variation in urine lead levels throughout the day, the base line levels(the mean of Days 1 and 2) and calcium E.D.T.A. response levels (the mean of Days4 and 3) were calculated for each child. The results of the urine collection on Day3 were omitted from these calculations since the urine may have been collectedbefure or after the administration of the first tablet of E.D.T.A. Fig. 3 shows themean vahies of the urine lead levels for the two base line days and two calciumE.D. T.A. response days for the three groups.

10,000

1,000

_; 100

(U

c

c

^ 10

M?nnS.D.

Base Line (Day lSi2)

PICA

•

9 • • *

-

e

121104

NoPICA

Upper HI

359

PhysicallyHandicapped

nit of normaf

3521

E.D.T.A. Response

PICA

•

751

1030

NoPICA

Upper lir

*•

11066

Day 4&5)

PhysicallyHandicapped

nit for Test ••

•.A

•

4223

Fig. .•?. Urinary lead t̂ xcretion for the three groups during thebaseline period (mean of days 1 and 2) and in response to

lali-iiim E.D.T.A. (mean of days 4 and .5).

*80 /;gni/l Kehoe (1964); Griggs, et al. (1964); Cohen, et al.(1965); Herman (1966).

**2.'iO ,/igm/l (The mean -|- 2 S.D. for the 'no pica' group is246 /l)

288 LEAD POISONING

It can be seen from Fig. 3 that 16 children (59%) of the 'pica' group but nochildren from either of the other two groups had base line urine lead levels inexcess of 80 /ngm./litre, the upper limit of normal for children (Kehoe, 1964;Griggs, Sunshine, Newill, Newton, Buchanan and Rasch, 1964; Cohen, et al., 1965;Berman, 1966).

There was no significant difference between the base line urine lead levelsfor the 'no pica' group and the physically handicapped group (p >0.5), but thedifference between the ba.se line levels of the children in the pica group and ofthose in the other two groups was highly significant (p <0.001).

There were 16 children (59%) from the 'pica' group but none from the othertwo groups with mean urine lead levels in excess of 250 /xgm./litre (the proposedupper limit for this test) in response to oral calcium E.D.T.A. There was a consider-ably greater increase in the mean urine lead levels in response to calcium E.D.T.A.for the pica group compared with the no pica and physically handicapped groups(p <0.001 in each case). There was also a significant difference on Days 4 and 5in the response of the two latter groups to calcium E.D.T.A. (p <0.01 for Day 4,and p <0.25 for Day 5) (see Fig. 2).

The blood lead levels, base line urine lead levels and the levels reached inresponse to calcium E.D.T.A. were ihei; compared. (See lable 1.)

Nineteen children (18 in the 'pica' group and 1 in the 'no pica' group) hadraised blood lead level? on Day 1 of the test. Of these 14 (65%) had raised baseline urine lead levels, and 16 (75%) an abnormally high response to calciumE.D.T.A. All these children were in the 'pica' group. Only 2 (6%) of the remain-ing 33 children had a raised base line urine lead level. Both of these childrenwere in the 'pica' group and one, in addition to having an equivocal blood leadof 35 figm./lOO ml. had an abnormally high response to calcium E.D.T.A. Noother child with a normal blood lead level showed an abnormal response to calciumE.D.T.A.

l^able 1The number of children in each group showirii; an abnormality in the oral

Calcium E.D.T.A.—lead excretion test

No. of children/group

Blood lead level above36 ju,gm./100 ml. (Day 1)

Base line urine lead level (meanof Days 1 & 2) above 80 /j,gm./litre

Response to oral Calcium E.D.T.A. (meanof urine lead levels Days 4 & 5) above250 ngm./litre

Pica

27

18

16

16

NoPica

12

1

0

0

PhysicallyHandicapped

14

0

0

0

No. of children with at leasttwo abnormal results 19

JOAN BICKNELL, et al. 289

DISCUSSION

An examination of the clinical records of the group of 27 children with picahas shown that in one, lead poisoning was the primary cause of mental retardationand in only one other was it a possibility. In a similar study Woods and Walters(1964) decided lead was the probable primary cause in 3 of 30 retarded children.Our study, therefore, ofFers no evidence that the presence of pica and possiblyraised blood lead levels in established mental retardation are related to the primarycause of the cerebral abnormality apart from the exceptional case. Those withpica were more alike in their current behaviour patterns than in their past history.All the children but one were ambulant despite low mental ages, many hadadditional handicaps, behaviour problems or were unduly aggressive. Biting hasalso been noted by other workers to be frequent among children with pica (Jenkinsand Mellins, 1957). Mouthing and swallowing of inedible objects has often beenregarded as purely a function of mental age and therefore usually indiscriminate.However, in 6 of the group (22%) it was selective and nursing staff supported theview that it was higlily motivated.

The mean mental age of those with partially selective and selective pica was15.0 months (8 children) which was the same for the group as a whole. In additionthere was no preponderance of behaviour problems or additional handicaps inthese children. There is therefore no evidence from this study that pica is selectivein the more disturbed child but the numbers are small and the population selected.

A control series of children with comparable mental age and additional handi-caps was not examined but the children with pica may be regarded as someof the most demanding of nursing and teaching skill because of the behaviouralproblems involved. This would suggest that pica may be a symptom of behaviourdistur))ance as well as an accentuation of a particular developmental phase. Thisi.s being examined further in another study.

The reported overall incidence of raised blood lead levels among retardedchildren varies greatly. The probaljle reasons for .such variations include the degreeof mental handicap, behaviour disturbance, the type of environment and the levelof blood lead considered to be abnormal. Raised blood lead levels were foundin 45% of 122 children by .MoncriefT, et al. (1964), in 40% of 30 children byWoods and Walters (1964), in 58% of 40 children by Oliver and O'Gonnan (1966),in 15% of 40 children by Gibson, et al. (1967) and 16% of 147 children by Gordon,King and MacKay (1967) who also found an incidence of 17% raised blood levelsin a group of 60 control children. No attempt to define the incidence of raisedblood lead levels in this way has been attempted in this paper as we feel themore meaningful approach at the present time is an examination of blood leadlevels in relation to the degree of pica clinically observed. Evidence of excessivelead ingestion in almost 70% in the pica group indicates that the clinician candefine a group of mentally retarded children at risk with accuracy.

In a recent survey in Glasgow, Gibson, et al. (1967) studied blood lead levelsin three groups of 20 children (a) of normal intelligence, (b) mentally retarded

290 LEAD POISONING

where the aetiology was known and (c) where the cause of the retardation wasunknown. The aims of their study—to define criteria for lead poisoning in child-hood and to compare the incidence of raised lead levels in normal children withthose in mentally retarded children of unknown and known causes, imply that theauthors were possibly seeking an aetiological relationship between raised lead levelsand established mental deficiency. They concluded however, that a proportionof normal and mentally deficient children have raised blood lead levels providingthey are sufficiently mobile, and this occurred twice as frequently in mentallydeficient children as in normal children because of the increased incidence of pica,which accords with our own experience.

However, other studies have produced conflicting results. In a similar studyby Gordon, et al. (1967) of retarded children kept at home, blood lead levels wereexamined in groups of (a) retarded children of unknown aetiology, (b) mongols and(c) controls. They found no significant difference in the mean blood lead levelsin the three groups and thereby concluded that lead poi.soning had little to dowith mental retardation. Unfortunately no data concerning mental age or behaviourdisturbance is given. This paper has been critici.sed by Barltrop (1967) who onceagain points to the difficulty of relating blood lead levels in mentally deficientchildren to the primary aetiology of their brain damage.

In the present study the group of physically handicapped children wereincluded in order to see the variation in the iesults of the oral calcium E.D.T.A.—lead excretion test with prolonged immobilisation, probable osteoporosis ofunused bones and a minimal intake of lead due to inability to explore their worldor transfer anything to their mouths. As expected the blood lead levels were lowerthan in the other two groups and there was no significant response to calciumE.D.T.A. In addition to a minimal intake of lead, it is po.ssible that there ismalabsorption of lead in the bowel in .such children; that lead may not be depositedin osteoporotic bones or may not be mobilised as readily by calcium E.D.I .A.Woods and Walters (1964) examined the blood lead levels of 5 children withccrol)ral palsy and found a mean level of only 13 /xgm./100 ml., which is in accord-ance with our findings.

The oral calcium E.D.I .A.—lead excretion test as used in this survey wasdesigned to be applicatile to a busy ward for retarded children where many aredoubly incontinent. While the urinary lead conrentration is most meaningful ona 24 hour specimen of urine this is difficuh to obtain from the normal child andimjjossible for practical purposes vvith the suljnormal child. Our results have shownthat it is sufficient to collect random urines on days 1, 2, 4, and 5 only. An intra-mu.scular calcium E.D.T.A. test was described Ijy Whitaker, Austin and Nel.son(1962) and results were expres.sed as values for urinary lead per litre becau.se of thedifficulty of collecting 24 hour specimens. Intramuscular calcium E.D.T.A. howeveris painful, needs frequent administration and cannot be recommended if a .suitaljlealternative test with an oral chelating agent is available.

I-Vom the data presented, the children with pica were distinguished from theother two groups by raised blood lead levels, raised base line urine lead levels in

JOAN BIGKNELL, et al. 291

single random specimens of urine, and by a raised excretion of urinary lead inresponse to oral calcium E.D.T.A. No undesirable side effects were found in theadministration of oral calcium E.D.T.A. in the dosage used in this test. However,this does not imply that calcium E.D.T.A. in therapeutic dosage may be givenby mouth with impunity.

It would appear therefore, that the oral calcium E.D.T.A.—lead excretiontest may be an additional guide to the degree of lead load in the body.

It is suggested that excessive lead ingestion may be diagnosed when a childexhibits two of the three following features : (1) A blood lead level greater than36 /xgm./100 ml. (2) a base line urine lead level greater than 80 /xgm./litre and(3) A urine lead level in response to an oral calcium E.D.T.A. test as describedin this paper greater than 250 /xgm./litre.

The question as to whether a persistent moderate rise in blood lead level mayexaggerate existing mental defect remains unsolved. In a further study it is hopedto estimate blood lead levels in children with pica over a longer period and analysethe longitudinal development of these children in an attempt to achieve a greaterunderstanaing of this problem.

SUMMARYFrom a population of hospitalised severely subnormal children in long term

care, three groups were selected (a) with pica, (b) physically handicapped withoutpica and (c) mobile children without pica.

Excessive ingestion of lead by approximately 70% of subjects in the 'pica' groupwas shown from a study of blood lead levels and the urinary lead excretion inresponse to oral calcium E.D.'l .A.

'Ihere was no evidence that moderately raised blood lead levels had anyrelationship to the original cause oi the mental retardation. Pica appears to bemore common in the disturbed retarded child and may be both selective and highlymotivated even with a low mental age.

The oral calcium E.D.T.A.—lead e.xcretion test with random specimens ofurine appears to be safe and free from unpleasant side effects. It may be a usefulsupplement to blood and urine lead levels when equivocal results have been pre-viously obtained.

ACKNOWLEDGEMENTSWe wish to acknowledge financial assistance from the Nuffield Foundation

and the Wellcome Trust. We are grateful to Mrs. P. Edwards, F.I.M.L.T., andMiss G. Shepherd for their skilled technical assistance. Dr. J. Stern, Dr. B. H.Kirman, and Dr. V. Gowie for their helpful advice throughout the study, theNursing Staff of Queen Mary's Hospital for their diligent collection of specimensfrom the children, Mrs. E. Elliot for secretarial help and Mr. J. Davis for transportof blood and urine specimens. The study would not have been possible but forthe anonymous donor of the auto analyser.

292 LEAD POISONING

REFERENCES

AMKRICAN ACADEMY OF PEDIATRICS (1961) Report of sub-committee on accidental poisoning.Statement on diagnosis and treatment of lead poisoning in childhood. Pediatrics, 11, 676.

BARI.TROP, D . (1967) Lead absorption in children. Brit. med. ]., 1, 699.BERO, J . M . , and ZAPELI.A, M . (1964) Lead poisoning in childhood with particular reference

to pica and mental sequelae. / . ment. Defic. Res., 8, 44.BERMAN, E. (1966) The biochemistry of lead. Clin. Pediat. {Philad.), 5, 287.BiCKNKi.L, J. (1967) Selective pica and lead poisoning in a severely subnormal child. / . ment.

Defic. Res., I I , 278 .

CHISOI.M, J . J . jun. (1965) (Ihronic lead intoxication in children. Develop. Med. ChildNeural., 7, 529.

(ioiiKN, G. J., LouHiK, R. S., and ABKRNETHY, W . (1965) Pica and lead poisoning. Clin. Proc.Child. Hasp. (Wash.), 21, 193.

DEI.VKS, H . 1"., and VINTER, P. (1966) Semi-automatic determination of lead in whole blood../. clin. Path., 19, 504.

Gin.soN, S. L. M., LAM, C . N . , MCCHAF., W . M . , and GOIDBF.RG, A. (1967) Blood lead levelsin normal and.mentally deficient children. Arch. Dis. Childh., 42, 573.

GORDON, N . , KING, E., and MAOKAY, R . L (1967) Lead absorption in children. Brit. med. ].,2, 480.

GREENHERG, M . , JACOBZINER, H . , MCL.\UGMI IN, M . ()., FUER.ST, H . T . , and PELLITTERI, O .

(1958) A study of pica~in relation to lead poisoning. Pediatrics, 22, 756.GRIGGS, R. C;., SUN.SHINK, L , NEWII.I., V. A., NEWTON, B. VV., BUCHANAN, S., and RA.SCH,

(!. A. (1964) Environmental factors in childhood lead poisoning. ]. Amer. med. Ass.,J87, 703.

JENKIN.S, C;. D. , and MEI I.IN.S, R . B. (1957) Lead poisoning in children. A study of 46 cases.Arch. Neural. Psychiat. (Chic), 77, 70.

KEHOE, R. A. (1964) .Normal metabolism of lead. Arch, environm. Hlth, 8, 232.MONCRIEFF, A. A., KOUMIDE.S, O. P., Gl.AYTON, B. E., PATRICK, A. D., RENWICK, A. G. C.,

and RoBERT.s, G. E. (1964) Lead poisoning in children. Arcli. Dis. Childh., 39, 1.OLIVER, B. E., and O'GORMAN, G. (1966) Pica and blood lead in psychotic children. Develiip.

Med. Child. Neural., 8, 704.SEI.ANDER, D. , CRAMER, K. , and }1AI.I.BI:RG, Iy. (1966) Studios in lead poisoning. Oral therapy

with penicillaniine: relationship between lead in blood and other laboratory tests.Brit. ]. industr. Med., 23, 282.

WHITAKEK, J . A., AUSTIN, W. , and NEI SON, J. D. (1962) Edathamil calcium disodimn(Versejiate) diagnostic test for lead poi.soning. Pediatrics, 29, 384.

WooD.s, G. E. and WALTERS, R. M . (1964) Lead poisoning in mentally subnormal childreiL]Mncet, 2, 592.

.APPENDIX

lhtcrvunation of lead

Hlood and urine lead analyse.'; were carried out using a slightly modifiedversion of tlie .semi-automated method of Delves and Vinter (1966).

Blood The method used was as deserihed except that only C^O ml. of bloodwas used per determination and the volumes of digestion mixture and acidammonium citrate .solution were redueed to ."i.O and 2.50 ml. respectively.

I •line 5.0 ml. of urine were digested with .5.0 ml. of the dige.stion mixtureas described for lilood. The residue; after digestion was dissolved irj 5.0 ml. of theacid ammonium citrate .solution. The ammonia concentration of the injfTer .solution

JOAN BICKNELL, et al. 293

was increa.sed to 2.") ml. of (S.G. 0.88) ammonia solution per litre to prevent the pHof the aqueous phase for the extraction of lead dithizonate heing lowered (to< pH 9.0) hy the salts of the digested urine samples.

The mean recoveries of lead standards added to hlood and urine samples were93.5% (S.D. =̂ 9.4%) and 101% (S.D. = 8.8%) respectively. Further details aregiven in Tahle 2.

Sample*

Blood

Blood

Urine

Urine

I ahle 2Replicate blood and urine

Mean cancentration

12 ^g./100ml.

22 /ig./IOO ml.

15 ^ig./\.

260 ug./l.

analyses

± S.D.

2.2 ^g./lOO ml.

3.2 /ig./IOO ml.

5.8 ii^./\.

14.0 ue./l.

Replicate analyses were carried out on eacb sample.

To .show the precision ohtained from repeated analy.sis using O..'j() ml. hlood,two large hlood samples were analysed twice a week, in duplicate for two months.Thirty analyses were carried out on each samj)le. The results ohtained wereSample I mean value 14 /xg/lOO ml., S.D. 3.2 /ig/100ml. and Sample II meanvalue 129 /j.g/HKi ml., S.D. fi.l /j.g/100 ml.