Baseline metal-in-dust concentrations in Greater London

The Science of the Total Environment, 68 (1988) 25-43 Elsevier Science Publishers B.V., Amsterdam - - Printed in The Netherlands

25

B A S E L I N E METAL-IN-DUST CONCENTRATIONS IN GREATER LONDON

M.J.R. SCHWAR, J.S. MOORCROFT, D.P.H. LAXEN, M. THOMPSON and C. ARMORGIE

Air Pollution Group, London Scientific Services, County Hall, London SE1 7PB (United Kingdom) (Received J u n e 12th, 1987; accepted August 27th, 1987)

ABSTRACT Baseline concentrations of cadmium, copper, iron, lead and zinc have been measured in samples collected from surfaces remote from local sources of pollution across Greater London. The geometric means of concentrations of metals in dusts are 2.7 ~g/g Cd, 79 #g/g Cu, 23400 #g/g Fe, 370/~g/g Pb and 372 #g/g Zn. Concentrations of metals in dust have been shown to exhibit marked distributions across Greater London, and the survey has indicated the location of a n u m b e r of areas of elevated metal-in-dust levels, for example the Lee Valley industrial area in n o r t h London, central London, and parts of east and west London. The concentrations found are compared with results reported in other studies, and the potential sources of metal contamination in the London area are discussed.

INTRODUCTION

The potential risk to h u m a n health caused by elevated metal-in-dust concentrations is now well recognised. In particular, the ingestion of dust via hand to mouth activity of young children has frequently been suggested as an important pathway for the transmission of lead and other metals from the environment to the body. As a consequence of this concern, many workers have undertaken studies to measure concentrations of metals in both internal and external dusts, usually at locations which are associated with identified pollution sources. The majority of studies have been concerned with measurements of lead, and concentrations have been determined in connection with previous mining activities [1-3], old paintwork [4], vehicular emissions [5-7], and other industrial sources [8]. Concentrations of other heavy metals (commonly cadmium, copper and zinc) are frequently reported alongside results for lead. Guidelines at a national level are not available for concentrations of metals in dust, although the Greater London Council did adopt a guideline concentration for lead in dusts of 500 #g/g as requiring investigation, and 5000 ~g/g as requiring some control action [9]. In the absence of suitable guidelines, it is useful to establish baseline 'reference' levels, which can then be used to assess the impact of selected pollution sources; this is often achieved by simply collect-

0048-9697/88/$03.50

© 1988 Elsevier Science Publishers B.V.

26

ing additional samples from a suitable 'control' location. It is also important to know what is a reasonable 'minimum' c o n c e n t r a t i o n to try and achieve following clean-up measures in the event of 'action levels' being exceeded. A recent study by T h o r n t o n et al. [10] has provided such information on reference levels of metals in housedusts. To date however, there are few data available for baseline conc e nt r at i ons of metals in external dusts which have been collected on a systematic basis. The objectives of the study reported here are to establish a base level for metal-in-dust concent rat i ons to which people are exposed in the G r e a t e r London area, at locations remote from obvious local sources of pollution - to see how this base level varies over the G reat er London area with a view to identifying those parts of London where people are exposed to elevated metal-in-dust concent r a t i ons to eventually use this information as a basis for identifying the major sources of pollution contributing to any high levels which may be found. This paper reports on the first two of these objectives.

-

-

Choice of metals in the survey Surface dusts within G r eat er London are likely to be contaminated by a wide range of metals, and it was necessary to restrict the scope of the survey to elements which are of specific interest. Concentrations of lead, cadmium, copper, zinc and iron were chosen for measurement in the study. The distribution of baseline concent r a t i ons of lead in dust is of particular interest due to the widespread concern associated with potential effects upon human health, even at low levels of environmental exposure. Cadmium is also associated with h u man h eal t h effects, and in common with lead may have unquantified, longterm health effects associated with low exposure. Copper, zinc and iron are frequently linked with various industrial activities which may also process lead and cadmium, and in addition, zinc levels are strongly associated with c onc e nt r at i ons of cadmium in soil. PROCEDURES

Sampling strategy The Gr eat er London area covers approximately 1600km 2, and includes a variety of industrial, commercial, residential, open space and rural areas. One major problem associated with measuring concentrations of metals in dusts is th at levels are known to vary quite substantially over short distances. For instance, spatial variations of lead in dust concent rat i ons in a school playground have been measured by Duggan [11], and the concentrations shown to v ar y considerably over intervals as short as 10 m. However, the collection and analysis of a very large number of samples to overcome this problem is

27 p r o h i b i t i v e b o t h in t e r m s of e x p e n s e a n d time, a n d a c o m p r o m i s e m u s t be s o u g h t to b a l a n c e a n a c c e p t a b l e s p a t i a l r e s o l u t i o n a n d a w o r k a b l e n u m b e r of samples. T h e s t r a t e g y a d o p t e d in t h e p r e s e n t s t u d y w a s to collect a b o u t 400 d u s t s a m p l e s f r o m a grid a c r o s s t h e w h o l e of t h e G r e a t e r L o n d o n a r e a . T h i s w a s c o n s i d e r e d to be sufficient to a l l o w a g e n e r a l o v e r v i e w of m e t a l - i n - d u s t conc e n t r a t i o n s to be e s t a b l i s h e d , as well as give a b r o a d i n d i c a t i o n of a n y gross s p a t i a l v a r i a t i o n s t h a t m a y exist. T h e d u s t s a m p l e s w e r e s w e p t f r o m hard, h o r i z o n t a l s u r f a c e s (e.g. p a v e d paths, t e n n i s courts, p l a y g r o u n d s , etc.) a n d p l a c e d i n t o p l a s t i c c o n t a i n e r s w h i c h w e r e sealed a n d labelled for r e t u r n to t h e l a b o r a t o r y . T y p i c a l l y , a n a r e a of 1-5 m 2 w a s s w e p t in o r d e r to o b t a i n a sufficiently l a r g e s a m p l e for a n a l y s i s , a n d to h e l p o v e r c o m e p r o b l e m s of l o c a l i s e d s p a t i a l v a r i a t i o n discussed above. All of t h e s a m p l i n g sites w e r e c h o s e n at l o c a t i o n s r e m o t e f r o m a n y obvious, i m m e d i a t e s o u r c e s of p o l l u t i o n , s u c h as factories, b u s y roads, b u i l d i n g facades, etc. I n no case w e r e s a m p l e s c o l l e c t e d w i t h i n 100 m of a f a c t o r y , 20 m of a b u s y road, or 10 m of a b u i l d i n g facade.

1982-1983 Survey T h e m a i n p r o g r a m m e of s a m p l i n g w a s c a r r i e d o u t b e t w e e n April 1982 a n d D e c e m b e r 1983, t h o u g h t h e m a j o r i t y of t h e s a m p l e s w e r e c o l l e c t e d b e t w e e n J u l y a n d A u g u s t 1982, a n d b e t w e e n J u l y a n d N o v e m b e r 1983. S a m p l e s w e r e c o l l e c t e d on a n a p p r o x i m a t e l y 2 x 2 k m grid s q u a r e b a s i s a c r o s s t h e w h o l e G r e a t e r L o n d o n a r e a , a n d a t o t a l of 385 s a m p l i n g p o i n t s w e r e chosen. I n m o s t c a s e s it w a s possible to c o l l e c t a s a m p l e w i t h i n 0.5 k m of t h e r e q u i r e d grid point. All s a m p l e s w e r e c o l l e c t e d on a d r y day.

1985 Survey To c h e c k t h e r e s u l t s o b t a i n e d in t h e o r i g i n a l s a m p l i n g p r o g r a m m e , a s e c o n d s u r v e y w a s u n d e r t a k e n b e t w e e n April a n d J u n e 1985. I t w a s decided to i n c r e a s e TABLE1 Summary of Cd, Cu, Fe, Pb and Zn concentrations in surface dusts Cug/g) 1982/83 Survey - Greater London area (number of samples 385) Arithmetic

Cd Cu Fe Pb Zn

Geometric

Mean

SD

Mean

SD

3.3 131 27150 660 510

2.3 230 14 730 1480 475

2.7 80 24 000 370 372

1.82 2.40 2.04 2.51 2.19

SD = standard deviation.

Median

Range

2.5 71 24 000 345 370

< 1.2-20.0 4-2050 4750-12 340 30-17 900 61-3200

28 40

1

CADMIUM 30 20 lO E

0 0.0

1.5

3.0

4.5

G.0

.....

7.5

9.0

1 0 . 5 12.0

13.5

>15.0

~g/g Cd 40 30 20

0

50

100 150

200 250

300 350 400

450

500

>500

pg/g Cu 40 30 20 10 0 0

250 500 750 1000 1250 1500 1750 2000 2250 2500

>2500

lag/g Pb 40

0

250

500 750 1000 1250 1500 1750 2000 2250 2~;00 >2S00

lag/g Zn 40 IRON

30 20 10 0 0

10

20

30

40

50

60

70

80

90

1 O0

> 1 O0

lag/g Fe (xlO00)

Fig. 1. Frequency distributions of metal-in-dust concentrations.

29 the density of the sampling sites to assess this effect upon the metal-in-dust distributions; sampling was thus confined to a selected inner area of London (180 km 2) from which 209 dust samples were collected on an approximately 1 × 1 km grid square basis. An identical protocol to t hat used in the original survey was followed for sampling of the dusts.

Analytical methods The analysis of the dust was carried out according to the procedures described by Schwar [12]. The dust samples were first passed t h r o u g h a 500 #m ap er tu r e sieve to remove large material such as stones, twigs and other large debris. The dust was t hen dried at a t em perat ure of 105°C for 24 h and then homogenised by grinding to pass t h r o u g h a 180 #m apert ure sieve. About 0.4 g of material was digested in a mixture of concent rat ed hydrochloric and nitric acids, and the digests analysed for cadmium, copper, lead, zinc and iron using flame atomic absorption spectrophotometry. Duplicate samples, and a reference street dust sample, were included in the analysis as a check upon analytical precision and accuracy. Reagent blanks were also submitted. RESULTS

(1) 1982-83 Survey Table I summarises the results for c o ncent rat i ons zinc and iron in surface dusts, collected over the difference between the arithmetic mean and the indicates t h a t the data are positively skewed and

of cadmium, copper, lead, G r e a t e r London area. A median for all elements this is confirmed by the

p g / g Cd

•

:" / •,..c

•

v'~

>6.0

Fig. 2. Geographical distribution of cadmium-in-dust concentrations (1982/83Survey).

30

oo o0 0 0 0 0 0 , O0 •

O0

|o

'

bOO

OO

*

,

0

~ l g/gCu ~ i

o o

"•

0-50 > 50 - 100

•

oo

q

>100-150

~/~

CA AL LE E10Krn 0S SC

> 150 - 200

•

>200-250

Fig. 3. Geographical distribution of copper-in-dust concentrations (1982183 Survey).

• :: . . - . • I 0

•

O0

oq

>.o..o

... J

>500-750

/ /

J ~

•

>750-1000

~'J

~

•

> I000-1250

,~.

~

_ ~

0

c-'

0 SCALE SCALE 10 I0krn km

Fig. 4. Geographical distribution of lead-in-dust concentrations (1982/83 Survey).

frequency distributions illustrated in Fig. 1; the geometric mean therefore provides the most satisfactory statistic for the results. The geometric means of concentrations of metals in dusts are 2.7#g/g (cadmium), 79ttg/g (copper), 23400#xg/g (iron), 370tig/g (lead) and 372#g/g (zinc). Relatively high concentrations were found in some dusts for all metals; 9% of dusts exceeded 6 #gig cadmium, 250pg/g copper and 1250#g/g lead; 8% of dusts exceeded 1250pg/g zinc; and 7% of dusts exceeded 50000#xg/g iron. (These concentrations did not necessarily occur in the same samples.) Four samples were noted to contain in excess of 5000 #gig of lead.

31

0000

t IJO0~ god Vii lag/g

.

•

,

l

> 500- 750 >.750-1000

•

>1000-1250

Fig. 5. Geographical distribution of zinc-in-dust concentrations (1982/83 Survey).

00

QQO oQ 0

• O0

• O- I0,000

~

• >10,000-20,000 •

>20,000-30,000

•

>3o,ooo-4o,ooo

•

> 40,000

I!

•

/ ~ , ~ lJ

•

~ 17k m

Fig. 6. Geographical distribution of iron-in-dust concentrations (1982183 Survey).

Geographical distributions The distributions of c onc e nt r at i ons of cadmium, copper, lead, zinc and iron across the G r e a t e r London area are illustrated in Figs 2-6. In order to identify the underlying patterns in the metal distributions, the data have been smoothed to reduce the effect of localised high individual concentrations, and, in each case, the moving nine point median for each 4 × 4 km square has been calculated to produce the individual points shown plotted on the maps. From the maps it can be seen t h a t generally lower concent rat i ons of all metals are found in the out er areas of G r e a t e r London. This coincides with a gradual tr ans f or m at i on in the use of land from a mixture of commercial,

32 i n d u s t r i a l a n d residential activities w i t h i n the c e n t r a l areas, to a p r e d o m i n a n t ly r u r a l / r e s i d e n t i a l one with i n c r e a s i n g d i s t a n c e from the centre. This effect is p a r t i c u l a r l y n o t i c e a b l e in the s o u t h - e a s t and n o r t h - e a s t areas, w h i c h are con-. sistently the least c o n t a m i n a t e d for all five metals. T h e r e are, of course, localised e x c e p t i o n s to these o v e r l y i n g patterns. S e v e r a l distinct areas are h i g h l i g h t e d as d i s p l a y i n g r e l a t i v e l y h i g h conc e n t r a t i o n s for a n u m b e r of metals, and in some cases these c a n be identified with the position of possible p o l l u t i o n sources. T h u s elevated levels of cadmium, copper, lead and zinc are seen a l o n g the line of i n d u s t r i a l a c t i v i t y in the Lee Valley a r e a w h i c h s t r e t c h e s d o w n from the n o r t h of L o n d o n . H i g h c o n c e n t r a t i o n s of iron are seen to follow the line of the River T h a m e s in the east, a n d m a y reflect the long h i s t o r y of i n d u s t r i a l / c o m m e r c i a l a c t i v i t y c e n t r e d in this region. Several a d d i t i o n a l h o t s p o t s for lead c a n be seen; in a c e n t r a l a r e a of L o n d o n to the s o u t h of the r i v e r (elevated c o n c e n t r a t i o n s of c o p p e r and zinc are also r e c o r d e d in this region), in E a s t L o n d o n to the n o r t h of the river, and in a small a r e a of n o r t h - w e s t L o n d o n . No specific localised p o l l u t i o n s o u r c e s h a v e been identified to explain these results. The m a p for c a d m i u m shows a m a r k e d c o n t r a s t from the o t h e r metal distributions, and the n o r t h and west areas of L o n d o n a p p e a r to h a v e m u c h h i g h e r overall c o n c e n t r a t i o n s , as c o m p a r e d with east and s o u t h - e a s t regions, a l t h o u g h a g a i n no specific s o u r c e of c o n t a m i n a tion has been traced. It should, however, be n o t e d t h a t the r a n g e of c a d m i u m c o n c e n t r a t i o n s is quite small. Small a r e a s of h i g h c o n c e n t r a t i o n s for all metals, o t h e r t h a n iron, c a n be seen in the n o r t h - w e s t c o r n e r of L o n d o n , a l t h o u g h these are n o t a l w a y s n e c e s s a r i l y the h i g h e s t m e a s u r e d w i t h i n L o n d o n .

(2) 1985 Survey Table 2 s u m m a r i s e s the results for c o n c e n t r a t i o n s of cadmium, copper, lead, zinc a n d iron in surface dusts collected o v e r the i n n e r L o n d o n area. A g a i n the d a t a are seen to be positively skewed. The g e o m e t r i c m e a n s for c o n c e n t r a t i o n s TABLE 2 Summary of Cd, Cu, Fe, Pb and Zn concentrations in surface dusts (pg/g) 1985 Survey London area (number of samples 209) Arithmetic

Cd Cu Fe Pb Zn

Geometric

Mean

SD

Mean

SD

3.5 155 26 000 1030 680

1.7 223 12100 2810 706

3.3 102 23 900 574 508

1.74 2.19 1.51 2.34 2.09

SD = standard deviation.

Inner

Median

Range

3.6 92 23 700 540 515

< 1.2-8.7 24-2050 140(~98 200 84-15 300 97-6800

33

I

10 km

I

[]

Major industrial areas (adaptedCr~ Gteater London Development Plan, 1969)

H.M. Industrial Air Pollution Inspectorate registered works •

Processes associated w i t h Pb,Zn,Cd,Cu,iron & steel

•

Processes associated w ; t h other metals, refining, smelting etc.

Fig. 7. Location of major industrial areas and registered industrial processes in Greater London. of metals in dusts are 3.3 ~g/g (cadmium), 102 ~g/g (copper), 23900 pg/g (iron), 574 pg/g (lead) and 508 ~g/g (zinc). A number of relatively high concentrations were found again for all metals in some dusts; 9% of dusts exceeded 350 #g/g (copper), 1500 ~g/g (lead); 10% of dust exceeded 6pg/g (cadmium), 40000 ~g/g (iron) and 1250 #g/g (zinc). These concentrations did not necessarily occur in the same samples.

Geographical distributions The distributions of cadmium, copper, lead, zinc and iron concentrations in inner London dusts are illustrated in Figs 8-12. The data have been smoothed by use of nine point medians calculated for each 2 × 2 km grid square. A region of low concentrations for all metals is seen in the north-west corner of the inner London area, and indicates the position of Hyde Park. Elevated

34

Hyde Park

pglg Cd •

0-1.5

•

>1.5-3.0

•

>3.0-4.5

•

>4.5-6.0

•

>6.0

0

SCALE

I

I0 J

Fig. 8. Geographical distribution of cadmium-in-dust concentrations (1985 Survey).

pglg Cu •

0 - 50

•

>50-

•

>100-150

100

>150-200

•

> 2 0 0 - 250 0 [

SCALE

I0 I

Fig. 9. Geographical distribution of copper-in-dust concentrations (1985 Survey). c o n c e n t r a t i o n s of copper, iron, lead a n d zinc c a n be s e e n in t h e e a s t e r n s e c t i o n of t h e m a p s , a n d m a y reflect p a s t a n d p r e s e n t i n d u s t r i a l a c t i v i t i e s in this area. A p a r t f r o m t h e s e two areas, the c o n c e n t r a t i o n s of m e t a l s a r e fairly u n i f o r m l y d i s t r i b u t e d t h r o u g h o u t t h e s u r v e y area.

(3) Comparison of 1982/83 and 1985 survey results F o r t h e p u r p o s e of c o m p a r i s o n of r e s u l t s o b t a i n e d from the t w o studies, a n a l y s i s of t h e d a t a h a s b e e n confined to t h e i n n e r L o n d o n a r e a defined in t h e

35

IJg/g Pb •

0-250

•

>250- 500

•

>500-750

•

>750-1000

•

>1000-1250 SCALE

Fig. 10. Geographical distribution of lead-in-dust concentrations (1985 Survey).

pg/g Zn •

0-250

•

>250- 500

•

>500- 750

•

>750-1000

•

>1000-1250 o I

SCALE

10 J

Fig. 11. Geographical distribution of zinc-in-dust concentrations (1985 Survey). 1985 s u r v e y . S u m m a r y d a t a f r o m t h e 1982/83 s u r v e y b a s e d on s a m p l e s c o l l e c t e d f r o m this i n n e r L o n d o n a r e a only, a r e s h o w n in T a b l e 3. C o m p a r i s o n of t h e s t a t i s t i c a l d a t a s h o w s little d i f f e r e n c e b e t w e e n t h e r e s u l t s of t h e two s t u d i e s s h o w n in T a b l e s 2 a n d 3. G e o m e t r i c m e a n s for all e l e m e n t s o t h e r t h a n i r o n a r e s l i g h t l y h i g h e r for the 1985 s u r v e y . T h e s e d i f f e r e n c e s a r e s t a t i s t i c a l l y s i g n i f i c a n t for c o p p e r (p < 0.02) a n d c a d m i u m (p < 0.05), b u t n o t for t h e o t h e r metals. S o m e m a r k e d d i f f e r e n c e s in t h e s p a t i a l d i s t r i b u t i o n s of all t h e m e t a l c o n c e n t r a t i o n s c a n be s e e n f r o m t h e maps. In p a r t i c u l a r , t h e small a r e a in c e n t r a l L o n d o n , s o u t h o f t h e river, w h i c h w a s identified as a n a r e a of

36

pg/g Fe •

O- 10,000

•

> 10,000 - 20,000

•

>20,000-30,000

•

>30,000-40,000

•

>40,000 0

SCALE

I

10 I

Fig. 12. Geographical distribution of iron-in-dust concentrations (1985 Survey). TABLE 3 Summary of Cd, Cu, Fe, Pb, and Zn concentrations in surface dusts (#g/g) 1982/83 Survey - Inner London area (number of samples 77) Arithmetic

Cd Cu Fe Pb Zn

Geometric

Mean

SD

Mean

SD

3.3 116 27 600 1100 655

2.1 115 17 300 2730 582

2.7 79 23400 509 460

1.82 1.38 1.78 2.88 2.34

Median

Range

2.5 67 23800 475 435

< 1.2-11.0 18-565 5500~1200 85-17900 72-2300

SD = standard deviation. h i g h c o n t a m i n a t i o n for c o p p e r , l e a d a n d z i n c i n 1982/83, d i d n o t s h o w u p i n t h e 1985 r e s u l t s . T h e i n c r e a s e d s a m p l i n g d e n s i t y of t h e 1985 s u r v e y h a s p r o d u c e d a h i g h e r s p a t i a l r e s o l u t i o n a n d h a s p e r m i t t e d t h e i d e n t i f i c a t i o n of s m a l l e r f e a t u r e s n o t s e e n o n t h e 1982/83 m a p s , e.g. t h e p o s i t i o n o f H y d e P a r k is c l e a r l y s e e n as a n a r e a c o n s i s t e n t l y l o w for c o n c e n t r a t i o n s o f a l l m e t a l s . I t is o f i n t e r e s t t o c o m p a r e r e s u l t s for t h o s e s a m p l e s c o l l e c t e d w i t h i n t h e i n n e r L o n d o n a r e a of t h e 1982/83 s u r v e y , w i t h t h o s e c o l l e c t e d f r o m t h e w h o l e s u r v e y a r e a as i n d i c a t e d i n T a b l e s 1 a n d 3. T h e g e o m e t r i c m e a n s a r e s i g n i f i c a n t ly h i g h e r i n t h e i n n e r a r e a for l e a d a n d z i n c (p < 0.05).

(*geometric means)

Cairo (streets with light traffic)

65

London road dusts (main & residential) London (residential side street) London (busy trunk road) London (outer urban streets) London (rural samples) North Petherton, Somerset (mainly residential roads) Glasgow road dusts (unspecified type) Manchester (streets with light traffic) Manchester (rural locations, playgrounds and parks) Lancaster (residential side streets) Lancaster (rural roads) 18

4

7

850 (620-1240) 570 (410-870) 496 (121~56)

85

2346 920 35 370 (49-1432) 780

1354" (172-9664) 1045

Pb

25

237

115" (18-2400) 181

Cu

937

1.5 (0.1-3.6) 1.4

3.1

4.0* (< 1-280) 2.2

Cd

53

35

1 18 7 32

1

No. of sites

Sample type and location

268 (44~56) 1000

527

513" (121-5152) 401

Zn

Nasrella [19]

As above

Harrison [18]

As above

Day et al. [17]

GEAR [16]

As above Duggan and Williams [14] As above Moorcroft et al. [15]

Hamilton et al. [7]

Thornton et al. [10]

Concentrations of Cd, Cu, Pb and Zn in dusts (ug/g) (all values reported are arithmetic means unless otherwise indicated: range of values given in parentheses when available)

TABLE 4

38

DISCUSSION

Comparison with other studies As previously discussed, there are few data reported in the literature which indicate baseline concentrations of metals in surface dusts. In a number of studies however, samples have been collected from background 'control' sites for the purposes of comparison, and some reported results are summarised in Table 4. The majority of measurements reported refer to lead concentrations only, and no suitable data for concentrations of iron are available. Direct comparison with results reported in other studies is further complicated by the use of a variety of techniques for sample collection, preparation and analysis, and the reporting of results in terms of arithmetic or geometric means. Account must also be taken of the changing concentrations of lead in petrol, from around 0.5 g/1 during the early 1970s, to around 0.38 g/1 during the early 1980s. The concentrations of cadmium, copper and zinc measured in this survey lie within the range of levels reported by other workers. Mean levels of all three metals are lower than those previously reported for London road dusts [10], though this is to be expected as road traffic has been found to be a source of these metals. The mean levels of cadmium in the present study were higher than those reported for residential roads in North Petherton, Somerset [15], and Glasgow street dusts [16], though levels of zinc were much lower than those reported for Glasgow. Cadmium, copper and zinc levels measured in the central area of London are of the same order as those reported for a busy London trunk road [7], as are concentrations of cadmium in the west of London. The mean concentration of lead was lower than those reported for London street dusts [7, 10], even for samples from outer urban areas [14]. Similar levels of lead in dusts have been reported for other areas [15-19], in samples collected from residential and rural roads (allowing for differences between reported arithmetic and geometric mean). Concentrations of lead measured in this study within the central London area are of the order of those reported for urban pavement samples in London [14] and major roads in Manchester [17]. Samples collected in the outer suburban areas in the south-east of Greater London are at a level of about twice those reported for rural areas in Manchester [17].

Representativeness of data In interpreting the geographical distributions, it is important to consider to what extent single dust samples, collected on a widely spaced grid, can be expected to reflect the true distribution of metal concentrations within Greater London. As previously discussed, concentrations of metals in dusts are subject to variations over both quite short distances and periods of time. There are, however, few data to describe these spatial and temporal variations. Duggan [11] has measured lead in dust concentrations at a number of single sites, and estimated the temporal variation to be between 25 and 50%.

39 TABLE 5 Variations in metal-in-dust concentrations [20] Cd Mean SD V

5.2 0.6 12%

Cu

Pb

Zn

265 42

2010 377 19%

1310 386 29%

16%

Mean is the average median value over the six sampling periods. SD is the standard deviation. V is the variation (SD/mean x 100%). Some estimate of var i a t i on has also been provided by Jones [20]. Dust samples have been collected from eight sites around the County Hall on an approximately monthly basis, and analysed for a range of metals; the sites include both roadside and pedestrian walkway areas. The median concentr atio n (from the eight sites) of each of the metals cadmium, copper, lead and zinc, has been calculated for six consecutive sampling periods, April to December 1985. The data are summarised in Table 5, which indicates the v ar iatio n of median values over the 9 month period. If this applies to ot he r locations, it would suggest t h a t the median concent r a t i o n for dust samples from several sites would vary with time by less t h a n 30% for all metals. Thus, even t hough the results for individual sampls may be subject to some doubt, if the results are analysed by taking the median of a number of samples, a reasonably reliable picture of the metal distributions can be attained.

Sources of contamination and geographical distributions Despite samples having been collected from sites which were located away from any identifiable pollution source, the results show some marked distribution in c o n c e n t r a t i o n s across G r e a t e r London, with some unexpectedly high values being found consistently in several areas. In addition, a number of individual samples were found to contain anomalously high concent rat i ons of some metals. In an ar e a such as G r e a t e r London, with a varied range of land use and activities, it is likely t h a t the input of metals will be a multi-source problem, though, in some cases, specific contributions may dominate. The main sources of metals present in dusts are well known and include the deposition of airborne par t i c ul a t e material from, for example, vehicles, power stations, metal foundries and smelters, etc., t o g e t h e r with debris derived from a variety of industrial processes, deteriorating paintwork and soil. The geographical distributions of the baseline metal concent rat i ons may be :usefully compared to Fig. 7, which describes the main industrial regions in the Gr eater London area (adapted from ref. 13), and also indicates the location of

40

! I I~¢ "1 I l-ffl

L:::i i t ] I ~

I J J I I I I |1 !!! Ikl I I I I~,l I I I~l |i:i~

m

I I I k:::l J ~ : : l

| f:,~-:~:::1 ~

[ ] I ] I [ [ [ ~:::~;:::[~L

I i::~ I I I I I I I Ir~!~::::~ I::::l::::g~(V~l h::t::::tfl [:!::~!:i:~:::t I I I I lY/I [ E::~::::~I I I I~_1 1 I Ikl I I:i::k:::l I I'~ E:~k ~ t:~t;~:~:k::~::::] Ji:::J:::/.:::l ~ I~[:::] [:::t I I I::i~ ~!~:::I:::] I I::::E:::h::k::f'1"~J I E:i:]ll I:i:il gS~,,tr::]-'~i:~¢~ J ~ ~ I I:i:]i:i~ ~:i:~i:il]~i:!:] I fl:.-~i:i~ ~!:!~ I I I I I t~::::l~ I E:i:] I~l I I I E:] I I I I : : . ~ : : : -I~ I ~ I I I I I E:i~/li:il~i.,-[~] E:i:] I I I t:i:J I~,l I I~l I I f:!:l I ~:i:~]:il lk~l:i:il I |!:i~::~!:il~l ~r't2:~l ¢.~Tl"%;i:]::] I l~:::~i:iJ I~J I'~t!:i:l I I II I ~ : t I~l I~l ~!"k*'l:W:;:f:~:] ~:i:]%t,l:~:] I I!~-'eq- I F:i:~tl~4"t1:] [:i:] I)l II I I II I [iil I'N I ~4:-.q ~ I I ~ F::I I I'?'~:~ I~ I I::::~:::l:~i~:::~ I~E::~it J i~'~l~i::~ I F~! I I I F:i~ 2 I I I I I I ~ I I~'~]3 I I I ¢'T:.'-:I::::g~ t~:::~l I 1_~::~33~,g1:::$S~" I~I::::l I ti:iI::::] ~I~::::I~t:M ~:::~:::t I I I ~lll ~ × : : × : : : : : : : ~:::~ ~:::l ~'~1 I.-LI f l L::~:::I I~lt~/'l ~--:: ::: ::: :::~ I I ~4:"ed,'a~'t'-¢,~ I I I 1~ " ~ ~ : :< ~ I I I I / I T Ill l'lxl~l I k-'~'l I l l ~ . :211[ I ~ 1 I Ill I II~] IJr i I~,i:""I"~:~----:-~-'-:~,s ~.ELI" ::~:{~::: ~ & ~ ~i:il ~i:il I I Itl I I k ~ I

I I

~-~:::~:::]::::

:::

If I:~:] k::t Itl I

;::"

~

II~l I I I ~ ' ~ ~ rt4.,~i::::~ i ~ : 1~.'~41 I I Illl

I ~

:::: ::

~

[]

- t l l ~ 1 ~ 1 ~ I I ~::~ I ~::::::::~:'-'vt~t-~f

I ~:i: !:i ~

~

kqP

Traffic

densities

for petrol-driven

R:~:::I

I~

I I I F::~::~-I

~::N.l'x[:::lAl I I I I ~/I 14 METRES ~ 1,,-t:::NI-::I I .I '~VEHIrf:LEI~YFI ILO I::::1 I'~Ji i i I I::::l::::~J PER E

~

k I::::t::::l:::: :::

h ~ ~ : : : t

:::::::

MI I HII

:::: :::

~ ~ ~ E : i : ]

Fig. 13.

"

i_r

:2

~1

:

:::

>" 0 000

ti:il i!:il i I i li:i:l i i ~1 :::] i i i i

I I I::::1 I~ I I r I I I::::1 I I vI ::~ I I I::::1 I I ~ I

lll*

vehicles

llllllll

in Greater

London

[]

3o,ooo-<45,0oo

[]

(1984).

H.M. Industrial Air Pollution Inspectorate registered works connected with metal smelting or reprocessing. It is not considered that registered works are a major source of metal contamination in dusts, but that these locations may be an indicator of general industrial activity. The presence of small industrial works, scrapyards, waste tips, etc. is difficult to assess in terms of potential metal input to the environment, though they have been demonstrated to provide an important local contribution, particularly in those cases where anomalously high concentrations are found [6, 21]. Small amounts of solder, electrical wire, rust, etc. will have a significant effect upon the measured concentrations of metals, though levels are likely to be extremely variable, and may not be reproducible in repeat sampling. Several factors may play a role in producing elevated concentrations of metals within the inner areas of London. The contribution to lead in dusts from the aerosol of petrol-driven vehicles is now well recognised, and concentrations have been noted to be higher in the vicinity of major rather than minor roads [7, 14]. A map indicating the density of petrol driven vehicles in Greater London is illustrated in Fig. 13; traffic densities are seen to be much higher in the central and western area of London than in other areas, particularly in the south-east. Concentrations of lead within the inner London area were noted to be elevated, and may indicate the contribution from lead in

41 petrol as a significant source, even though samples were collected away from busy roads. However, the central area is so congested t h a t most sampling sites selected will be relatively close to heavily-trafficked roads and direct deposition may play a significant role. In addition, the processes of re-suspension, attachment of particles to the shoes of pedestrians, etc., may lead to a significant transport of contaminated dusts away from major roads. Although the lead content of petrol has been reduced since this study was undertaken, the concentrations of lead in dust at sites remote from roadside locations have so far not declined significantly [22]. The density of traffic may also affect concentrations of metals other t h a n lead. Zinc concentrations in street dusts have been associated with tyre wear from vehicles [23, 24]; automobile exhaust particles have been found to contain large amounts of iron [23], and rust falling from vehicles may also increase levels of iron. Analysis of the London housing stock may be used to reveal some marked differences between the age of buildings within the inner and outer areas; inner London Boroughs have 63% of housing built pre-1919, as opposed to outer Boroughs where only 29% of housing is of this age [13]. In addition, the density of housing within inner London housing is greater; 43% of the population is contained within only 23% of the total residential land for Greater London. Various lead and other metal compounds are known constituents of some paints. Although current U.K. legislation limits the lead content of paints now available, old paints have frequently been found to contain up to 10% of lead in the dry film [4], and occasionally as much as 70% [25]. Large quantities of old paintwork still exist on the exterior surfaces of older buildings, and significant amounts of lead and other metals may be released into the environment if the paint deteriorates and flakes, or during redecoration processes. Very high levels of lead in dust have been found in the above studies as a result of old paintwork. In addition to older houses presenting a greater potential for contamination via paintwork, it has also been shown t h a t an enrichment of heavy metal concentrations in soil increases with the age of housing [26]. Soil has been shown to be a major constituent of urban dust by a number of workers [23, 18], and contaminated soils may also be responsible for elevated levels of metals in dusts within the central areas. CONCLUSIONS Baseline metals-in-dust concentrations in samples collected from surfaces remote from obvious local sources of pollution have been found to exhibit marked variations across Greater London. Moving nine-point median concentrations show that: - for cadmium, about half the area surveyed was below 3 ttg/g, with one part of north London up to about 6 #g/g; for copper, more than half the area surveyed was below 100 #g/g, significant parts were in the range 150-200 ~g/g, and some exceeded 200 ttg/g; - for iron, over three-quarters of the area surveyed was below 20000 #g/g, and

-

42

-

-

in p a r t s of L o n d o n a l o n g the lower r e a c h e s of the Thames, levels were of the o r d e r of 50000 #g/g; for lead, m o r e t h a n h a l f of the a r e a s u r v e y e d was below 500 #g/g, significant p a r t s were in the r a n g e 750-1000#g/g, and in c e n t r a l L o n d o n , levels just exceeded 1000 pg/g; for zinc, a b o u t h a l f the a r e a s u r v e y e d was less t h a n 500 #g/g, significant p a r t s were in the r a n g e 750-1000#g/g, and in c e n t r a l L o n d o n , levels were in the r a n g e 1000-1250 #g/g. In c e n t r a l L o n d o n , baseline c o n c e n t r a t i o n s of cadmium, copper and zinc were f o u n d to be similar to those o c c u r r i n g at r o a d s i d e sites, a l t h o u g h in o t h e r a r e a s of L o n d o n , levels were lower. C o n c e n t r a t i o n s of lead in dust for samples collected in the o u t e r s u b u r b a n a r e a s of L o n d o n are at a level of a b o u t twice t h o s e f o u n d in r u r a l a r e a s of M a n c h e s t e r . It is also n o t a b l e t h a t a small n u m b e r of samples in the L o n d o n a r e a exceeded 5000 #g/g lead, the a c t i o n level established by the G r e a t e r L o n d o n Council. The s u r v e y has h i g h l i g h t e d the l o c a t i o n of a n u m b e r of a r e a s of h i g h metalin-dust c o n c e n t r a t i o n s , for example the Lee Valley I n d u s t r i a l a r e a in n o r t h L o n d o n , c e n t r a l L o n d o n , p a r t s of east L o n d o n , and p a r t s of west London. Superficially, the o v e r l y i n g p a t t e r n in the spatial d i s t r i b u t i o n of baseline levels c o r r e s p o n d s to c e n t r e s of p o p u l a t i o n and g e n e r a l i n d u s t r i a l activity, a n d it is likely t h a t observed levels arise from a m u l t i t u d e of sources b o t h as r e g a r d s type a n d number. A n o m a l o u s l y h i g h c o n c e n t r a t i o n s in i n d i v i d u a l samples are likely to h a v e r e s u l t e d from p o l l u t i o n from local industries, s c r a p y a r d s , flaking p a i n t w o r k , etc. F u r t h e r i n v e s t i g a t i o n s are n e c e s s a r y to establish the e x t e n t to w h i c h the results of this s t u d y c a n be used to t r a c k the s o u r c e s a n d activities w h i c h are likely to be c o n t r i b u t i n g to the h i g h levels found.

ACKNOWLEDGEMENTS The a u t h o r s wish to t h a n k b o t h R a c h e l S e x t o n and W e n d y Sayles for t h e i r a s s i s t a n c e in this project. The analysis of samples was c a r r i e d o u t by the A n a l y t i c a l Services G r o u p of LSS, and t h e i r help is g r a t e f u l l y a c k n o w l e d g e d . REFERENCES 1

D. Barltrop, C.D. Strehlow, I. Thornton and J.S. Webb, Absorption of lead from dust and soil. Postgrad. Med. J., 51 (1975) 801 804. 2 I. Thornton, S. John, J.S. Moorcroft, J. Watt, C.D. Strehlow, D. Barltrop and J. Wells, Cadmium at Shipham - A unique example of environmental geochemistry and health, in D.D. Hemphill (Ed.), Trace Substances in Environmental Health - - XIV, Conference Proceedings, University of Missouri-Columbia, 1980, pp. 27-37. 3 B.E.Davies, P.C. Elwood, J. Gallacher and R.C. Ginnerver, The relationships between heavy metals in garden soils and house dusts in an old lead mining area of North Wales, Great Britain, Environ. Pollut., 9 (1985) 225-266. 4 S. Rundle and M.J. Duggan, Lead pollution from the external redecoration of old buildings, Sci. Total Environ., 57 (1986) 181-190. 5 R. Caswell and D.P.H. Laxen, Lead 'hot spots', a survey of lead in air and dust in roadside

43

6 7 8 9 10 11 12

13 14 15

16 17 18 19 20 21 22

23 24 25 26

areas in London, Scientific Services Branch, Greater London Council, London, U.K. Report DG/SSB/ESD/R 142, 1984. P. Little and M.J. Heard, Measurement of environmental exposure to lead: a case study in West London, Chem. Ind., (1983) 264-270. R.S. Hamilton, D.M. Revitt and R.S. Warren, Levels and physico-chemical associations of Cd, Cu, Pb and Zn in road sediments, Sci. Total Environ., 33 (1984) 59-75. R.A. Jensen and D.P.H. Laxen, Sources of lead in urban dust: Identification of a contribution from newspaper print works, Sci. Total Environ., 46 (1985) 19-27. Greater London Council, An action level for lead in surface dust, Scientific Adviser's Report to Recreation and Community Services Policy Committee, RCS 210, 31 October 1980. I. Thornton, E. Culbard, J.S. Moorcroft, J. Watt, M. Wheatley, M. Thompson and J.F.A. Thomas, Metals in urban dusts and soils, Environ. Technol. Lett., 6 (1985) 137-144. M.J. Duggan, Temporal and spatial variations of lead in air and in surface dust - implications for monitoring, Sci. Total Environ., 33 (1984) 37-48. M.J.R. Schwar, Sampling and measurement of environmental lead present in air, surface dust and paint. London Environmental Supplement No. 1, Summer 1983 (Scientific Services Branch, Greater London Council). GLC, Greater London Development P l a n - Report of Studies Greater London Council, London U.K., 1968. M.J. Duggan and S. Williams, Lead in dust in city streets, Sci. Total Environ., 7 (1977) 91-97. J.S. Moorcroft, J. Watt, I. Thornton, J. Wells, C.D. Strehlow and D. Barltrop, Composition of dusts and soils in an apparently uncontaminated rural village in southwest England implications to human health, in D.D. Hemphill (Ed.), Trace Substances in Environmental Health - XVI, Conference Proceedings, University of Missouri-Columbia, 1982, pp. 155-163. Glasgow Eastern Area Renewal, GEAR Air Pollution Survey, Volume 2, Scottish Development Agency, 1983. J.P. Day, M. Hart and M.S. Robinson, Lead in urban street dust, Nature, 253 (1975) 343-345. R.M. Harrison, Toxic metals in street and household dusts, Sci. Total Environ., 11 (1979) 89-97. M.M. Nasrella, Lead in Jeddah urban dust, Environ. Pollut. Ser. B, (1984) 133-141. K. Jones, London Scientific Services, County Hall, London, U.K., personal communication. P. Blake, C.S. Chamberlain, D. Chambers, B. Clarke and J. Mendham, Heavy metal contamination near scrap metal yards and car breakers yards, Sci. Total Environ., 59 (1987) 9-18. R.A. Jensen and D.P.H. Laxen, Environmental lead levels during the phase-down of lead in petrol. Investigation of Air Pollution Standing Conference, Winter 1986, IASPC 1/8, Warren Springs Laboratories, Stevenage, U.K. P.K. Hopke, R.E. Lamb and D.F.S. Natusch, Multielemental characterisation of urban roadway dust, Environ. Sci. Technol., 14 (1980) 164-172. J.E. Fergusson and D.E. Ryan, The elemental composition of street dust from large and small urban areas related to city type, source and particle size, Total Environ., 34 (1984) 101-116. J.S. Moorcroft, Lead measurements at Melcombe School. Scientific Services Branch, Greater London Council, London, U.K. Report DG/SSB/ESD/R 147, 1984. B.E. Davies, Plant-available lead and other metals in British garden soils, Sci. Total Environ., 9 (1978) 243-262.