Temporal trends in urban and rural blood lead concentrations*

C.D. Strehlow and D. Baritrop Department of Child Health, Westminster Children's Hospital, Vincent Square, London SWtP 2NS

ABSTRACT

A long term programme to assess the impact of reduced lead emissions in the UK has been estabiished in central London and rural Suffolk. Blood lead concentrations of 5 and 6 year old chiJdren and their mothers both show an urban-rural difference of about 1.5 lag/dl, which is related to the urban-rural differences in air and dust lead concentrations between areas.

INTRODUCTION

A decrease in blood lead concentrations in the United States during the years 1976-80 has been attributed to reduced atmospheric lead emissions resulting from the phasing out of lead in petrol (Annest et al., 1983; Houk, 1982). While some of the decrease was un- doubtedly due to the decreased use of lead additives, the interpretation of the data has been questioned be- cause other environmental variables were not mea- sured and the study was not without methodological weaknesses (Quinn, 1985; Elwood and Gallacher, 1984).

There is evidence that blood lead values have also decreased in the United Kingdom even though atmos- pheric emissions of lead have remained relatively con- stant. Studies in our own Department have shown a progressive decrease in mean blood lead values in chil- dren from 20.7 ~tg/100ml in 1973 (Barltrop et al. , 1975) to 14.7 in 1977 (Strehlow and Barltrop, 1978) to 9.8 in 1980 (Strehlow and Barltrop, 1983). A decline of 30% in the blood lead concentrations of women in Wales since 1972 has also been reported (Elwood, 1983). It is thought that much of this decline is due to decreased dietary intake of lead from improved standards, atten- tion to plumbosolvent water supplies and the phasing out of lead soldered cans.

On 1st January, 1986 the legal limit for lead additives in petrol in the United Kingdom was reduced from 0.4 to 0.15 g/1. Since there was inadequate evidence from previous studies to predict the impact of such a mea- sure, a long term study was undertaken to determine the distribution of blood and environmental lead values in defined populations by serial measurements before and after implementation.

The programme was designed to avoid the problems encountered in previous studies so that the effects of reduced atmospheric emissions and prevailing trends due to other factors might be distinguished. This initial report summarises the data collected up to the end of

*This paper is also being published in Proceedings of the Conference on "Lead in the Home Environment" and is one of several selected from SEGH spon- sored conferences for simultaneous publication in this journal.

1985 before lead additives were reduced, and thus forms the basis by which any future changes can be assessed.

STUDY DESIGN

The programme was directed to defined urbar~ and rural population groups. The urban population was drawn from the area served by the Westminster Chil- dren's Hospital in central London, which is both dense- ly populated and characterised by heavy traffic flows. The rural group was drawn from an area in the county of Suffolk in eastern England. tt was an area chosen because of low levels of soil mineralisation and is with- out major highways or lead emitting industries.

Young school children and their mothers were selected for study in order to allow both adult and childhood lead burdens to be assessed. Approval for the study was given by the educational and health au- thorities in both areas.

In the autumn of each year, the parents of all chil- dren aged between their 5th and 7th birthdays were informed of the study by letter and invited to partici- pate. Those who agree were visited in the home where the study was explained more ful!y and informed con- sent sought. A brief questionnaire was administered about the child's health, play habits and band washing frequency and the occupation of all adults in the house- hold. The house dust was sampled by emptying the family's vacuum cleaner and a random sample of drink- ing water obtained from the kitchen tap. An appoint- ment was made for a clinic session at the child's school where venous blood was taken from mother and child.

The blood sampling was carried out at the same time each year in order to avoid any seasonal variation in blood lead concentration. The same schools were vi- sited each year, so that participants were all drawn from the same population group. All five and six year old children were eligible each year, thus the parents of five year olds were invited to participate again the following year when the child was aged six. Therefore included in the programme is a series of overlapping paired blood samples from both mothers and children drawn at intervals of one year, thereby providing both

Environmental Geochemistry and Health, 1987, 9(3-4) , 74-79

C.D. Strehlow and D. Bar#rop 75

cross-sectional and longitudinal elements for data analysis. The age of the children studied was restricted in order to avoid any variation in blood lead with age.

In order to assess trends in other environmental sources of lead, a programme of air and road dust sampting was established. Air sampling units were in- stalled at 7 sites in both the urban and rural study areas, and the filters changed at monthly intervals. Monthly road dust samples were collected at various defined sites in each area, and lead in dust and rainfall was monitored at one location in each area.

Trends in dietary lead were also assessed by dupli- cate diet collections in the home. Twice a year 25 mothers and 25 children in both urban and rural areas were asked to provide 3-day duplicate diets. Dietary records were kept and the samples including all food and drink consumed during the period. Random draw drinking water samples were also taken each day by the participants. These diet collections were supplemented by analysis of one week's school dinners collected twice yearly from two schools in each study area.

To complement the studies on young children and their mothers, a programme of umbilical cord blood sampling was initiated at a London maternity hospital. Blood is sought from every birth together with basic data including residence, complications of pregnancy or delivery, sex, birthweight, gestational age, and abnor- malities evident at birth. This aspect of the study will be reported subsequently.

ANALYTICAL METHODS AND QUALITY ASSURANCE

tn order to avoid analytical drift over the period of the study programme, great care was taken in the analytical methodology and the quality control programme.

Upon receipt in the laboratory, one of the duplicate blood specimens was analysed for erythrocyte pro- toporphyrin (EPP) using an Aviv Hematofluorimeter. Both blood specimens were then sonicated and frozen prior to lead analysis. The EPP calibration was verified by analysis of split samples measured with a standard extraction procedure. The laboratory participates in the monthly quality control scheme for EPP run by the CDC.

Lead analysis was performed on the blood specimen which was not used for the EPP determination. Dupli- cate analysis by automated electrothermal atomic absorption spectrophotometry was performed on two separate occasions. The duplicates must agree both

within and between runs. Before data from any run was accepted, satisfactory results must be obtained from the five internal control samples run before and during each run. Three of the samples were whole human blood with naturally occurring blood lead concentra- tions of 7, 18, and 50 g g/100ml. These values were confirmed by anodic stripping voltometry in another laboratory. The other two internal controls were freeze dried bovine blood specimens with certified values of 15 and 40 ~tg/100ml. The laboratory also participates in two British and one American external quality control schemes for blood lead. The above quality control programme is similar to that recently reported by Delves (Delves et al., 1984; Delves, 1986).

House dust and road dust samples were analysed after drying and sieving through 1.0 mm nylon mesh. After digestion with nitric and perchloric acids, lead was determined by flame atomic absorption spectros- copy (AAS). Included in the analysis were reference materials from the National Bureau of Standards and the International Atomic Energy Agency.

Diet samples included all food and drink consumed during the balance period, and these were analysed in duplicate by the method of additions using electrother- mal AAS after wet ashing with nitric acid. In addition to using standard reference materials, the laboratory participates in an external quality assurance scheme run by the Ministry of Agriculture, Fisheries and Food.

The air, water, and dust and rainfall samples were also analysed by electrothermal AAS together with standard reference materials.

The data was then coded and analysed using standard statistical packages on the Department's computers as well as with the facilities of the Westminster Hospital Computer Centre.

BLOOD LEAD RESULTS

The blood lead data for the first three years of the programme of sampling school children and their mothers are summarised in Table 1. The geometric mean blood lead concentrations, sample numbers, and ranges are given. Year 1 in the tables refers to the sampling carried out in the Autumn of 1983, with years 2 and 3 referring to subsequent years. The mean values are considerably less than 10 txg/100ml, confirming the fall in blood lead concentrations over the last decade.

In the three years of the study, only two individuals had blood lead concentrations above the UK Depart- ment of Health and Social Security's action level of

Table I S C H O O L S T U D Y (Blood Lead Concentrations,/~g/tOOrnl) - All Participants.

YEAR 1 YEAR 2 YEAR 3 No. GM GSD Range No. GM GSD Range No. GM GSD Range

C H I L D R E N

Suf fo lk 113 6 .80 a 1.41 3 - 3 0 96 6 .34 ~ 1.57 2 - 2 3 72 6 .37 ~ 1.38 3 - 1 7

L o n d o n 116 8 . 0 & 1.32 4 - 1 8 91 7 .60 ~ 1.45 3 - 2 4 66 8.31 ~ 1.32 5 - 1 9

M O T H E R S

Suf fo lk 118 5 .26 b 1.56 1 -20 101 4 .72 d 1.59 1 -20 109 4 .94 f 1.54 2 - 2 9

L o n d o n 138 6 .63 b 1.33 4 . 1 6 1 0 5 6 .42 d 1.53 2 - 2 3 92 6 .76 f i . 45 3 -21

GM - Geometric Mean, GSD - Geometric Standard Deviation. Statistically significant differences: a ,b,d,e,f , p < 0.00I ; c, p < 0.005.

76 Temporal trends in urban and rural blood lead concentrations

25 gg/100ml. A child in year one and a mother in the year three both living in Suffolk, had elevated blood lead concentrations confirmed on resampling which were associated with refurbishing homes containing old lead paint.

For all years mean blood lead concentrations were found to be significantly higher in London than in rural Suffolk, based upon two-tailed Student's t tests. Lon- don children had mean blood lead concentrations of 7.6 to 8.3 ,ug/100ml, which were 1.3 to 1.9 ~,g/100ml greater than those in Suffolk. The mean blood lead concentra- tions for the London mothers varied from 6.4 to 6.8 ~tg/ 100ml, which were 1.4 to 1.9 ~tg/100ml greater than the values for the mothers in rural Suffolk.

The child-mother difference can be seen more clearly in Table 2, where data are presented only for paired mothers and children. In both areas children had higher blood lead concentrations than their mothers (p< 0.001). The difference of about 1.3 ~tg/100ml was prop- ortional to the child-mother difference of 4 ~tg/100ml found when the me-an blood lead values were about 20 gg/100ml a decade previously (Barltrop et al. , 1975).

It was not always possible to obtain blood from all participants. If there was any difficulty or upset on the part of the child or mother, the sampling was discon- tinued. The response rate of parents to our invitation to participate varied from 55% in the first year to about 40% in the third year. At the beginning of the study, publicity about the effects of lead may have influenced parental attitudes. The interest of parents was main- tained by informing all parents of the results obtained and speaking to parent groups. In the third year, non- responders to our invitation were sent a second letter which yielded some additional participants. A further school was added to the programme in the London

study area in the second year and in the Suffolk area in each of the second and third years. Additional incen- tives such as the measurement of the child's immune status (Quinn, 1986) or assessment of behaviour and intelligence (Urbanowicz et al. , 1986) were not offered.

Because of the overlapping study design, a number of children and mothers were involved in two consecu- tive years (table 3). None of the Suffolk mothers or children showed a statistically significant difference in blood lead values between the first and second or be- tween the second and third years of the studyl In Lon- don, however, the children but not the mothers showed a decrease between the first and second years, and an increase between the second and third years.

In each case, the child was aged 5 for the first sample and aged six for the second sample the following year. The London children seen in the autumn of t984, who were also seen either the previous year or the following year thus had somewhat lower blood lead concentra- tions than in the other years. This was not true for the children taken as a whole, and no overall temporal trend between years could be ascertained.

Within each area there was no significant difference in mean blood lead concentrations between 5 and 6 year old children. For each age group the mean blood lead concentrations were lower in Suffolk than in L,on- don, although this was statistically significant only for both ages in the third year and for six year olds in the first study year.

The child's sex also had little influence on blood lead concentrations, with the only significant male/female difference being in Suffolk for the second year. In the second year, only the London females had significantly greater blood lead concentrations than Suffolk females, while in the first and third years both males and females

TabLe 2 S C H O O L S T U D Y (Blood Lead Concentrations, Bg/lOOml) - Paired Mothers and Children,

YEAR 1 YEAR 2 YEAR 3 No. GM GSD No. GM GSD No. GM GSD

SUFFOLK Children 11 t 6.76 1.40 93 6.38 1.57 70 6.41 1.38 Mothers 1 ! 1 5.35 1.53 93 4.42 1.54 70 5.37 t.43

LONDON Children 113 8.05 1.32 86 7.41 1.42 61 8.25 !.33 Mothers 113 6.71 1.34 86 6.58 1.58 61 6.96 L46

G m - Geometric Mean, GSD - Geometric Standard Deviation. All mother-child pairs are significantly different, p<0.001.

Table 3 S C H O O L S T U D Y (Blood Lead Concentrations,/xg/lOOml) - Children and Mothers Seen in Two Years~

YEAR 1 and YEAR 2 YEAR 2 and YEAR 3 No. GM GSD GM GSD No. GM GSD GM GSD

SUFFOLK Child ren 28 7.05 I. 51 6.68 !. 39 26 6.62 i, 02 6,48 1.45 Mot he rs 36 4.88 [. 52 5.02 1.45 36 4.66 l. 74 4.84 7.47

LONDON Children 24 8.43 ~ 1.32 7.37" 1.50 17 7.10 b 1.32 8.20 ~' !.33 Mothers 29 7.21 1.39 6.80 1.56 19 5.83 I. 43 6.33 T 49

GM - Geometric Mean, GSD - Geometric Standard Deviation. Statistically significant differences: a,b, p <0.05.

C:D. Strehlow and D. Barltrop 77

Table 4 SCHOOL STUDY (Blood Lead Concentrations, Izg/lOOml) - and Frequency of Washing Hands Before Snacks.

YEAR 1 YEAR 2 YEAR 3 No. GM GSD No. GM GSD No. GM GSD

S U F F O L K I. Always 0 - - 2 5.09 1.72 2 5.84 i.10 2. Usually 4 6.18 1.38 5 4.!6 2.58 4 4.81 1.35 3. Occasionally 17 6.34 1.20 14 6.07 1.43 7 6.81 1.49 4. Rarely 92 6.91 1.44 75 6.61 1.51 59 6;46 1.37

L O N D O N 1. Always 8 6.55 a 1.22 5 8.21 1.51 3 6,25 1.22 2. Usually 5 6.98 1.36 4 5.46 1.27 3 6.76 1.15 3, Occasionally 12 8.13 1.39 17 7.48 1.39 21 8.28 1.33 4. Rarely 91 8.26" 1.31 65 7.74 1.47 39 8.48 1.32

GM - Geometric Mean, GSD - Geometric Standard Deviation. Statistically significant difference: a, p <0.01.

had significantly greater blood lead concentrations in London than in Suffolk.

Children who washed their hands infrequently before meals or snacks (Table 4) tended tO have higher blood lead concentrations than those who washed more often, but it was difficult to demonstrate any statistically signi- ficant differences. The only difference found was for the before snack category in London for the first year, where the group who rarely washed their hands (n = 91) had a greater mean blood lead concentration than those who always washed their hands before snacks (n = 8, p<0 .01) . When comparisons were made between the combined 'always' and 'usually' categories and the 'occasionally' and 'rarely' categories, only the London 'snack' group showed a statistically significant difference in the first and third years.

The data above indicate that for the chosen study populations age, sex and frequency of handwashing had tittle influence on blood lead concentrations of chil- dren. Over the time span studied, no temporal trend was noted. The major factors observed were an urban/ rural difference of about 1:4 ~tg/100ml for both mothers and children, and a similar difference between mothers and children within each area.

E N V I R O N M E N T A L D A T A

The airborne lead data are Summarised in Figure 1. For both areas, there was a tendency to greater lead con-

1.0, Lead in air

0.8-

0,6,

0.4-

0.2-

1984 1985

F i g u r e t

::I.

w

Monthly mean air lead concentrations for all sites.

centrations in the winter months than in the summer, which is at t r ibuted to a greater frequency of inversion conditions during the winter season. For the calendar years 1984 and 1985, the overall mean air lead concen- tration in the London study area was 0.50 ~tg/m 3, with a range of 0.23 to 0.82 in the monthly means. In the Suffolk area, the overall mean was 0.10 ug/m 3, with a range of 0.05 to 0.17.

There was a tendency to lower values in the second year, which may also have been related to meteorold- gical conditions, as the summer of 1985 was extremely wet and cool. The lead anti-knock concentration in petrol remained near the previously permitted max- imum of 0.4 gg/100ml until the end of December 1985 (D. Turner, personal communication), and thus cannot account for any decrease in atmospheric lead concen- trations.

Lead in dust and rainfall showed an o rde r of magni- tude difference between the urban and rural sites, with total deposition rates of about 50 ug/m 2 day in Suffolk and about 800 ~tg/m 2 day in London. A similar differ- ence was noted in the road dust data.

Road dusts were taken, weather permitting, adjacent to the schools in the two study areas. The distribution and statistics presented in Table 5 indicate lower road dust concentrations during 1985 than 1984, as was noted for airborne lead. The geometric mean concen- tration for lead in London road dust decreased from 1881 tO 1552 ~g/g (p <0.05) and in Suffolk fell from 144 to 83 ~tg/g (p<0.0001) . This change may be a result of wetter conditions during 1985.

Housedust data (Table 6) also showed a marked urban/rural difference, but with no apparent trend with time. The lead in London housedusts was about 3 times greater than in Suffolk (850 versus - 3 0 0 ~tg/g), in con- trast to the difference of about 15 between mean road dust concentrations. The Suffolk housedusts were found to contain :more lead than the corresponding road dusts. This finding has also been noted in o ther non-contaminated environments, and could indicate the general level of lead exposure from sources within the home.

Both urban and rural areas have hard water supplies, and this is reflected in the water lead data. About 80% of samples have concentrations less than 3 ~tg/1 and 95% are below 10 ~tg/1 in both areas.

78 Temporal trends in urban and rural blood lead concentrations

Table 5 DISTRIBUTION OF R O A D DUSTS B Y L E A D CONTENT.

LONDON SUFFOLK Lead 1984 1985 Lead 1984 1985 #g/g (n) (n) ktg/g (n) (n)

0 - 500 0 6 0 - 100 37 57

500 - 1000 15 15 100 - 200 66 28 1000 - 1500 25 14 200 - 300 15 6

1500 - 2000 22 22 300 - 400 2 2

2000 - 2500 22 20 400 - 500 5 1

2500 - 3000 8 5 500 - 600 3 0

3000 - 3500 5 2 600 - 700 2 0

3500 - 4000 6 3 700 - 800 0 0

4000 - 4500 5 1 800 - 900 1 0

4500 - 5000 4 1 900 - 1000 1 0

5 0 0 0 - 5500 0 1 1000 - 1100 1 0

5500 - 6000 3 0

Total 115 90 133 94

STATISTICS

Ari thmetic Mean 2163 1770 185 105

Std.Dev. 1198 958 166 77

Geometr ic Mean 188t" 1552 ~ 144 b 83 b

Geo.Std.Dev. 1.70 1.79 1.96 2.02

Minimum 582 353 30 10

Maximum 5720 5430 1037 450

Statistically significant differences: a, p<0.05; b, p<0.0001.

T a b l e 6 D ISTR IB U TIO N OF HOOSEDO2gTS B Y L E A D CONTENT.

Lead LONDON, % SUFFOLK, % #g/g Year l Year2 Year3 Year l Year2 Year3

0 - 200 10 6 10 39 31 36

200 - 400 10 16 15 26 29 26 400 - 600 16 14 21 i7 18 17

6 0 0 - 800 13 12 10 8 5 6

800 - 1000 10 11 1t 6 0 3 1000 - 2000 22 24 17 9 4 8

2000 - 4000 8 6 6 2 7 3

4000 - 6000 5 6 4 1 2 0

6000 - 8000 1 1 1 0 1 1

8000 - 10000 3 0 1 0 i 1

10000 - 20000 1 5 3 1 2 0

20000- 30000 1 0 2 1 i 0

Number 146 109 112 119 t04 112

STATISTICS

Ari th .Mean !846 1839 t985 808 1272 582

Std.Dev, 3102 3250 4314 2657 3530 i131

Geom.Mean 893 889 790 333 374 291

Geo.Std.Dev. 3.22 3.06 3,42 2.96 3.75 3.01

Minimum 51 59 58 22 7 20

Maximum 26755 18865 29980 26620 27148 8170

T a b l e 7 3 D A Y D U P L I C A T E DIETS. Lead intake, #g Pb/3 days.

Winter

LONDON CHILDREN I984 1985

Summer Winter Summer Winter

SUFFOLK CHILDREN 1984 t 985

Summer Winter Summer

No. 23 26 24 18 25 25 25 24

Ari thmetic mean 180 111 94 104 146 149 84 104

Std.Dev. 124 64 43 39 91 99 38 70

Geometric mean 1542 98 ~ 84 97 125 123 b 76 ~" 91

Geo.std.dev. 1.71 1.61 1.61 1.49 1.75 1.88 1.56 1.60

Minimum 68 35 31 49 46 41 25 47

Median 147 107 83 98 131 ! 16 73 88

Maximum 636 335 155 114 460 415 200 348

LONDON MOTHERS SUFFOLK MOTHERS

No. 24 25 23 20 25 24 24 23

Ari thmetic mean 177 149 139 149 173 130 [30 92 Std.Dev. 105 59 64 74 79 56 62 43 Geometric mean 154 137 128 133 c ]55 105 t20 84 c

Geo.std.dev. 1.73 1.52 1.48 1.64 1.67 1.65 1.47 1.54

Minimum 61 5 8 65 62 41 30 72 39

Median 166 135 116 157 172 126 126 82

Maximum 555 272 340 280 315 226 305 184

a,b,c- Statistically significant differences, two-tailed Studenfs t on geometric means, p < 0.005.

C.D. Strehlow and D. Baritrop 79

No meaningful difference was found between the dietary lead intake in London and Suffolk. The dietary data summarised in Table 7 are for all food and drink consumed during the 3 day period. Only in one of the four diet collecting periods was the dietary intake signi- ficantly different, being lower for mothers in Suffolk than in London. Between periods, there was a statisti- cally significant decrease in dietary lead intake for Lon- don children between winter and summer 1984, and for Suffolk children between summer 1984 and winter 1985.

The mean dietary intake ranged from 25 to 50 ~g/day from food and drink for both areas and for both mothers and children. The similar total lead intakes for mothers and children implies that the children had a greater lead intake relative to body size or surface area, and may therefore have accounted for the difference in blood lead concentrations observed.

SUMMARY

The data coJlected through the end of 1985 have de- monstrated a marked urban/rural difference in blood lead concentrations for both young children and their mothers, as well as in airborne lead, dust and rainfall, house dust and road dust lead values. Superficially, any of the environmental differences would account for the blood lead differences observed.

The observed urban/rural difference in blood lead is similar to that reported by others, and agrees with the air lead/blood lead relationships reviewed by Chamber- lain (1983). Since a similar difference was found be- tween urban and rural mothers and between urban and rural children, the blood lead differences must be ascribed to air lead differences, unless it is accepted that dusts are a major route of lead exposure for both mothers and children.

A comprehensive data base has been developed for the 3 year period before the reduction of lead additives

in petrol in the United Kingdom. This will allow pre- vailing trends to be distinguished from effects attri- buted to reduced atmospheric emissions.

ACKNOWLEDGEMENTS

This research programme was funded by the Interna- tional Lead Zinc Research Organisation. Statistical advice has been obtained from Professor M. Heaty of the London School of Hygiene and incorporated into the design of the study and the quality assurance prog- f a m i n e .

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