Soil contamination in urban areas

Palaeogeography, Palaeoclimatology, Palaeoecology (Global and Planetary Change Section), 82 (1990): 121 140

121

Elsevier Science Publishers B.V., Amsterdam - Printed in The Netherlands

Soil c o n t a m i n a t i o n

in u r b a n a r e a s 1

IAIN T H O R N T O N Environmental Geochemistry Research, Centre ]or Environment Technology, Imperial College o[ Science, Technology and Medicine, London SW7 (U.K.) (Received April 24, 1989; revised and accepted November 2, 1989}

Introduction

Soil scientists in Britain (and elsewhere) until very recently have been primarily concerned with soil as a basis for agriculture and food production. Classification systems and research into the physical and chemical properties of soils have been focussed towards the requirements of farming and forestry and to a degree towards the understanding of natural ecosystems; the urban environment, in which the majority of the population live and come into contact with the soil, has been almost totally neglected. A detailed appraisal of the characteristics of urban soils by Craul (1985) points out t h a t soils in urban and suburban areas are frequently dist u r b e d and subjected to mixing, filling and contamination with heavy metals, herbicides and pesticide residues. T h e history of land use in urban areas is often difficult to ascertain. Records of previous industrial use or waste disposal are frequently poor or do not exist. Major industrial sources of pollution from the last century may be masked by the presence of post-war housing; sequences of changing land-use and transport of fill materials m a y be reflected in the presence of contamination materials below the surface. Urban development coupled with the presence

p a p e r f o r IUGS Workshop on Past Global Changes, Interlaken, Switzerland, April 1989; based on a paper published in Soils in Urban Areas (edited by P. Bullock and R.J. Gregory, Blackwells, Oxford, 1990).

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of industrial activities within urban areas leads to varying degrees of soil contamination with one or more materials. An a t t e m p t to produce an inventory of worldwide emissions from industrial and domestic sources suggests t h a t soils are receiving large quantities of trace metals from a variety of industrial wastes, the disposal of ash residues from coal combustion and the general wastage of commercial products on land (Nriagu and Pacyna, 1988). T h e authors calculate t h a t if the total metal inputs were dispersed uniformly, annual rates of deposition would vary from 1 g per hectare for Cd and Sb to c. 50 g for Pb, Cu and Cr and over 65 g for Zn and Mn. N a t u r a l l y deposition is not uniform and industrial countries such as Britain will receive larger inputs. Changes in the chemical n a t u r e of the soil brought about by the addition of pollutants may present a hazard to construction works, may lead to adverse interactions with building materials, toxicity to soil flora and fauna including ornamental plants and trees and garden crops, or may lead to the accumulation of toxic substances in vegetables making them unsuitable for h u m a n consumption. Flux between surface soils and dusts m a y influence exposure of the population and particularly young children to toxic substances and present a hazard to human health. T h e complex nature of urban land and its m a n y uses present problems in assessing the extent and degree of contaminations. Sampling strategies for the assessment of the suitability of soil for future development usually have to be

122 site specific and will depend on the intended land use. We are reminded by Barrett (1987) than urban areas are characterised " b y the presence of large numbers of buildings, roads.., which form an impermeable largely sterile covering over much of the land surface... In general central areas will have at least 80% cover, while suburban areas will have around 50% cover". Exposed land surfaces include: (a) grass verges alongside roads, (b) private gardens and allotments, (c) public parks and gardens, (d) playing fields and golf courses, (e) cemeteries, (f) demolition and building sites, (g) wasteland and derelict land, (h) rubbish tips and spoil heaps, (i) railway land, (j) canal and river banks including disused docklands, (k) woodland, heath and commom land, (1) farmland enclosed by urban developments. Each of these units is subjected to varying degrees of contamination depending on (a) the location, (b) past and present land use and (c) the proximity to pollution sources. The following sections address specific sources of contamination, the types of land most affected, surveys of contaminants in urban soils, including some case histories, the implication of soil contamination to the construction industry and the health of the general population, and, consider pollution in the context of urban ecology and the redevelopment of contaminated land. Some of the examples cited are taken from a recent review of the classification, survey and assessment of derelict land by Bridges (1987) and others from the results of the continuing programmes of research and training in environmental and urban geochemistry of the Applied Geochemistry Research Group and the Centre for Environmental Technology, Imperial College (for example, Thornton, 1983; Thornton et al., 1986). The need for a well defined programme for the protection of soils was fully discussed at a

i. THORNTON symposium organised by the Commission of the European Communities (Barth and L'Hermite, 1987). Major impacts arising from changes in land use over the past 200 years included: (a) mass sterilisation of land resources for industrialisation and urbanisation, and (b) growth in airborne pollution and the effects of fallout on vegetation cover, soil quality and the hydrological systems (Moss, 1987). S o u r c e s of c o n t a m i n a t i o n

Classification systems for derelict land with the implication that much of this will fall within the urban environment have been reviewed previously by Bridges (1987). Haines (1981) has attempted to classify categories of contamination according to the site use, on the assumption that site use, pollutants and land contamination are linked. The classes proposed are: 1. Definitely contaminated; 2. Probably contaminated; 3. Potentially contaminated; 4. Pre-1931 housing where lead paint might be expected; 5. Mixed land use with many small potentially contaminated sites; 6. Definitely uncontaminated; 7. Unknown; 8. Previously contaminated sites that are now in 'sensitive' use. These categories are perhaps of a subjective nature though are aided by the publication of guidelines and 'trigger concentrations' for a range of toxic substances issued by the Interdepartmental Committee on the Development of contaminated Land (ICRCL, 1983, 1987). The need for such guidelines will be addressed in a later section of this chapter. However, Bridges (1987) emphasises that "classification according to the degree of contamination is not easy as there is a wide range of possible contaminants of different degrees of toxicity". The main sources of contaminant in urban areas may conveniently be characterised according to several broad descriptions of past and present day activities. However, before listing these, it is perhaps helpful to mention certain

S O I L C O N T A M I N A T I O N I N U R B A N AREAS

general factors which influence the extent and degree of such contamination. Firstly, individual pollutants may be dispersed on either a wide scale from diffuse sources, such as vehicle emissions and ammonia from farm livestock, or on a localised scale from point sources such as a metal works. Secondly, dispersion may be in the form of (a) atmospheric gases and particulate materials (b) liquid effluents from factories and sewage works and (c) in situ site contamination from operational activities and from disposal of waste products. Thirdly, dispersion may either result from controlled emissions such as those from a smelter stack or effluent pipe which are required to meet standards applied by H.M. Pollution Inspectorate or the local Water Authority of (b) uncontrolled, accidental or fugitive emissions and spillages which are difficult to quantify.

1. Construction o[ buildings and demolition The building of housing, office and industrial premises together with the installation of services and roadways involve major disturbances to the land surface, frequent soil removal and relocation and the introduction of numerous materials. The majority of building materials are relatively inert, though demolition of older buildings and industrial premises may lead to contamination of soils with heavy metals (including lead from paint), gypsum and asbestos. Accidental spillages, and the incorporation of surplus materials and rubble from demolished buildings into made ground may further change the chemical nature of the soil.

2. Household activities Cultivation of lawns, flower beds and vegetable gardens is often accompanied by over application of fertilizers, and soil ameliorants such as lime and pesticides. Soil pH values in vegetable gardens and allotments tend to fall within the range 6.5 to 7.5 irrespective of the natural parent material, and in general are higher than those found in agricultural soils. Heavy metal accumulation in household gardens is well documented (Davies, 1978: Thornton et al., 1985), lead con-

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centrations in surface (0-15 cm) soils increasing with the age of the house. Sources of metals in garden soils include the disposal of fossil fuel residues (ash and soot) and of household refuse, bonfires, and fragments of lead containing paints, long term application of phosphatic fertilisers (Cd) and deposition of atmosphere particulates from industrial processes and vehicle emissions.

3. Waste disposal Problems associated with waste disposal and management are reviewed in depth in the l l t h Report of the Royal Commission on Environmental Pollution (1985). Domestic refuse contains a number of combustible materials such as paper and timber, other organic residues, plastic, glass, ash, clinker and ferrous metal. Toxic metals are present in varying concentrations and frequently mixing of domestic and industrial wastes results in isolated packets of other hazardous materials including phenols, cyanides and asbestos. Some 90% of refuse is disposed of in landfill sites, some in urban areas, and some destined for future development four housing, etc. Microbial decay within the landfill results in the production of methane and other gases for many years. Methane is toxic and gaseous mixtures often explosive. Waste may have a high calorific value and present a fire hazard. Elevated concentrations of sulphates, sulphides and chlorides are aggressive to building materials. There is usually little loss of metallic components from landfill sites into neighbouring soils and watercourses, though leachates may contain other more soluble toxic constituents, be extremely acidic and contaminate groundwater. Unpleasant odours from landfill may persist. The other 10% of refuse is processed in municipal incinerators, from which it has been estimated that as much as 6 tonnes of cadmium and 115 tonnes of lead per year are discharged into the U.K. atmosphere (Wadge and Hutton, 1987). However, in a study around an incinerator at Edmonton, North London, which processes 4 × 105 tonnes of waste per year, there

124

[. THORNTON

was little evidence of extensive Cd and Pb contamination downwind, though surface soils within 0.2 km of the stack were enriched in Cd (12-fold) and Pb (2-fold) compared with nearby areas (Hutton et al., 1988). Land previously occupied by sewage works may be redeveloped and may include old filter beds, lagoons, etc. and extensive areas in which effluent had been dispersed. Such activities can lead to soils being contaminated with metal wastes, combustible materials and pathogens, and offensive odours and methane generation may present an on-going problem. Bridges (1987) refers to detailed studies undertaken at the Beaumont Leys Estate, Leicester, a sewage farm from 1890 to 1964, required for urban development. An area in which sludge had been spread exceeded the "trigger" concentration for zinc equivalent (ICRCL, 1983) and, as a result, was designated as an area of public open space; less contaminated areas were developed for housing and industrial premises.

4. Transport (a) Roads and motor vehicles Nearly all the lead in the air in Britain comes from the exhaust gases of petrol engines (Royal Commission on Environmental Pollution, 1983). In 1981, some 9.7 thousand tonnes of lead were used in petrol of which c. 75% was released to the atmosphere (Chamberlain et al., 1979). It has been estimated that c. 10% of emitted lead is deposited within 100 m of a road and that the remainder can be transported over considerable distances (Little and Wiffen, 1978). Page and Ganje (1970) attempted to relate accumulation of lead in Californian surface soils over a period of 35 to 50 years in regions of high and low motor vehicle traffic density and estimated an accumulation of 15 to 36 t~g/g over 40 years in the high traffic area and no measurable amount in the low area. It is now widely accepted t h a t the settling out of lead-rich aerosols derived from exhaust fumes of cars results in an increased concentration of lead in surface soil and this is demonstrated by the data in Table I

TABLE I Lead c o n t e n t s of soil a t t h r e e distances from typical main roads, calculated from d a t a in S m i t h (1976) Distance from road

Geometric mean

(m)

95% probability range

Number of samples

( ~ g P b / g soil)

< 10 15 > 30

192 161 53

18-2017 5 0 - 511 14- 203

20 6 17

calculated from Smith (1976). This topic is discussed in detail in a review by Davies and Thornton (in press). Although the lead content of petrol was reduced from 0.4 to 0.15 gill in 1986 in the U.K., resulting in levels of lead in air falling by approximately 50%, and no doubt a reduction in the deposition of airborne lead to soil, it must be stressed that lead in soil is virtually immobile, t hat contamination is in all essence a permanent phenomenon, and t hat concentrations of lead resulting from many years deposition will remain.

(b) Railways With a cutback in the British railway system in the post-war era, it is not surprising t hat the large areas of railway land, including tracks, sidings, workshops and marshalling yards should have become derelict and some have been incorporated into urban developments. Soils are usually contaminated to varying degrees with coal and ash residues, providing a potential combustion hazard, and oil, asbestos and scrap metal may also be present.

(c) Canals and docks Abandoned canal and dock areas may have accumulations of dredged material comprising organic rich sludge and sometimes toxic materials resulting from spillage. Ballast from numerous sources and coal dust may also occur in dockland areas. Possible problems relate to the presence of combustible materials, methane and many metals.

SOIL CONTAMINATION IN U R B A N AREAS

5. Industry Sources of contamination from industrial activities in or on the fringe of urban areas are many and varied and it is only possible to highlight some of the major polluters.

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Capper Pass, have resulted in some contamination of surface soils though stack and fugitive emissions, transport of metal concentrates and accidental wheel drag out. Similarly secondary metal smelters will always give rise to a limited amount of pollution, leading in some cases to public concern.

(a) MetaUi[erous mining and smelting In Britain, the oldest and most extensive sources of metal pollution are related to the history of metalliferous mining which commenced in Roman and earlier times, thrived until the end of the 19th century, and then declined rapidly. Peak output was in the mid19th century, when Britain produced 75% of the world's copper, 60% of the tin, and 50% of the lead. It has been estimated that in excess of 4000 km 2 of agricultural land (and many urban areas) in England and Wales are contaminated with one or more metals due to this legacy from our forbears (Thornton, 1980). THis subject has been reviewed in detail by Thornton and Abrahams (1984). Village and town communities developed around the mines and smelters and thus have often expanded in area onto reclaimed land previously despoiled with mine waste and smelter slag. Mine shafts may even occur within the built-up area as in Shipham, Somerset (Thornton et al., 1980). Metal contamination of soils may be considerable, with as much as 1% or more lead recorded in surface garden soils in the village of Winster, Derbyshire (Barltrop et al., 1975). In Cornwall for example, more than 600 mines have operated in the past, mainly within a belt 75 miles long and 10 miles wide. Within this area soils are contaminated to varying degrees with tin, copper and arsenic (Thornton et al., 1986). A survey of arsenic in gardens in the towns of Redruth and Hayle showed arsenic concentrations in surface soils to range widely up to nearly 900 ppm As (Xu and Thornton, 1985), compared to a median value of c. 10 ppm for uncontaminated agricultural soils (Archer and Hodgson, 1987). Other areas affected are the Mendips (Pb, Zn, Cd), north and central Wales (Pb, Zn, Cd), and the north and south Pennines (Pb, Zn, Cd, F). Primary metal smelters at Avonmouth and

(b) Coal mining and quarrying Abandoned mines (frequently with railway sidings to transport the coal) leave a legacy of waste materials including coal and coal dust which present an on-going fire hazard. Acid mine drainage may lead to the downstream deposition of orange coloured iron oxides which may discolour and contaminate alluvial soils. The extraction of sand and gravel and of clay for brickmaking mainly lead to the dispersion of inert dusts with no chemical contamination of the surrounding land. Limestone quarrying and processing (and cement works) frequently lead to surface contamination of the nearby environment with white calcareous dust, which as well as being unsightly and potentially deleterious to plant growth, can over time result in a raising of soil pH.

(c) Manu[acturing industries These are many and of various kinds. Naturally it is not possible to provide a comprehensive compendium of activities but the following list indicates the diverse nature of possible contaminants: (1) Engineering, vehicle construction (heavy metals, oil, paint, phenols, organic solvents, asbestos) (2) Printing (heavy metals, cyanide, organic solvents, acids). (3) Paint works (lead, chromium, antimony, etc. used as pigments, organic resins, etc.) (4) Rubber factories (benzine, carbon tetrachloride and other solvents, zinc). (5) Wool processing (combustible materials, insecticides and fungicides containing copper, chromium, arsenic and many organic compounds). (6) Leather industry (organic solvents, chromium).

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(d) Chemical works Again there are a large number of activities within this general description. There will almost certainly be contamination of derelict land and land used for dumping or storing wastes and possibly some contamination of the local environment. Potential pollutants include a wide range of acid and alkaline substances, heavy metals and metalloid, dioxins, phenols, PCB's and numerous other organic compounds and solvents.

(e) Gas works Many urban areas contain old gas works sites and both surface and subsurface soils on derelict sites may be contaminated with coal and coal residues, spent iron oxides, cyanides, sulphates and many organic compounds associated with tars. Waste asbestos may provide an additional hazard. Combustible materials will constitute a fire risk.

(D Oil refining and storage Leakages and spillage of oils and tars and other petroleum products together with storage of liquid wastes may result in soil contamination to a considerable depth and in the mixture of organic contaminants into the groundwater. Production of methane and the presence of combustible materials may pose problems to redevelopment.

(g) Scrap yards Storage, processing, recycling and disposal of scrap materials will always result in site contamination and often soils will be contaminated with a range of toxic substances. Heavy metals and metalloids, waste oil, PCB's and other organic and inorganic compounds may be present and removal of contaminated soil is usually necessary prior to redevelopment.

i. THORNTON pulverized fuel ash (PFA). Contamination will arise from (a) previous coal dumping and storage-combustible residues, (b) pulverized fuel ash which is alkaline (pH 11-12) and contains soluble salts, and in particular boron which is phytotoxic, (c) areas of unknown history which may contain dumped materials with toxic or combustible properties, and (d) sites of demolished buildings with possible asbestos residues, heavy metals, combustible residues, oil spillages, and polychlorinated biphenyls (PCB's) used in transformers and capacitators and common in wastes arising from the demolition of electrical equipment.

7. Agriculture and/orestry Town and countryside have always existed side by side, with urban developments encroaching onto previous agricultural areas where planning permission was forthcoming. Pockets of land under agriculture and forestry are often encircled by housing and industrial sites and it is not surprising that some contamination should be exchanged from one to the other. Under normal circumstances, fertilizer application to agricultural land will not adversely affect urban soils, though odours from organic manures and sewage sludge may be unpleasant. However, wind-blown pesticides may be carried onto neighbouring urban land or affect newly developed areas if residues are persistent. In this respect, organochlorine compounds such as DDT, aldrin and dieldrin and associated dioxins may persist for up to 10 years, and some hormone weedkillers are also persistent. Organo-phosphorus insecticides such as malathion are rapidly degraded as are some herbicides. Plant growth regulations (auxins) are widely used on cereal crops and may contain persistent dioxins.

Surveys 6. Power stations Sites for redevelopment at locations associated with demolished power stations may be extensive and may contain areas used for storage of waste materials and in particular

Methods of assessment taminated land have been (1987). It is impossible to strategy is nearly always into account the previous

and survey of conreviewed by Bridges generalise as survey site specific, taking history of land use,

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S O I L C O N T A M I N A T I O N IN U R B A N A R E A S

proximity to existing industrial activities, direction of prevailing winds, etc. and the proposed nature of redevelopment (i.e. housing, commercial, industrial or amenity) or the kind of present-day land-use (i.e. vegetable garden, school playing field). Baseline information on which to assess the degree and extent of soil contamination from anthropogenic sources is essential. Several regional and national geochemical surveys and soil inventories provide useful background data for a range of heavy metals and other inorganic pollutants, all of which occur, usually in small amounts, in geological and earth materials. 1. Geochemical surveys

Geochemical surveys have been undertaken in the U.K. by the Applied Geochemistry Research Group (AGRG) at Imperial College and the British Geological Survey (BGS), previously known as the Institute of Geological Sciences. These surveys have been and continue to be based mainly on the systematic collection and analysis of stream sediment samples taken at sampling densities ranging from 1 to 2 per km 2. The data obtained are available in published atlases (Table II) and in computer readable forms. The methods used in compiling the atlases, including their development, advantages and limitations, have been described previously (Plant and Moore, 1979; Webb and Howarth, 1979). Analysis of the combined fine sand, silt and clay fractions of the sediment has been undertaken for up to 26 elements by direct reading emission spectroscopy, atomic absorption spectrophotometry and the delayed neutron activation method. Maps have been plotted by computer, either using a moving average method (in the case of U) to show broad scale regional geochemical features (Atlas of Northern Ireland, scale 1 : 633,600 Webb et al., 1973 and the Wolfson Geochemical Atlas of England and Wales, scale 1 : 2 million, Webb et al., 1978), or both as point-source data and geochemical 'landscape' maps (IGS Atlas of Scotland, scale 1:625,000 Institute of Geological Sciences, 1978a, 1978b, 1979, 1982, 1983).

TABLE II Summary of chemical elements available in geochemical atlases of the United Kingdom Published atlases

Elements

Applied GeochemistryResearch Group, Imperial College

Northern Ireland

A1,As, Ba, Ca, Cr, Co, Cu, Ga, Fe, Pb, Mg, Mn, Mo, Ni, K, Sc, Si, Sr, V. Zn

England, Wales

A1,As, Ba, Cd, Ca, Cr, Co, Cu, Ga, Fe, Pb, Li, Mn, Mo, Ni, K, Sc, Sr, Sn, V, Zn

British Geological Survey

Shetland

Ba, Be, B, Cr, Co, Cu, Fe, Pb, Mn, Mo, Ni, U, V, Zn, Zr

Orkney

Ba, Be, B, Cr, Co, Cu, FeuO3,Pb, Mn, Mo, Ni, U, V, Zn, Zr

South Orkney, Caithness

Ba, Be, B, Cr, Co, Cu, Fe, Pb, Mn, Mo, Ni, Sr(partial data), Ti(partial data), U, V, Zn, Zr

Sutherland

Be, B, Cr, Co, Cu, Fe, Pb, Mn, MO, Ni, U, V, Zn, Zr

LewisLittle Minch

Ba, Be, Bi, B, Ca, Cr, Co, Cu, Fe, K, La, Pb, Li, Mg, Mn, Mo, Ni, Sr, Ti, U, V, Y, Zn, Zr

Provisional maps available for purchase through NGDB/GISA Moray/Buchan Tay/Forth Lake District Argyll Moray/Buchan Tay/Forth Lake District

Ba, Be, B, Ca, Cr, Co, Cu, Fe, K. La, Pb, Li, MgO,Mn, Mo, Ni, Rb, Sr, Ti. U, V, Y, Zn, Zr

Factors influencing their interpretation and application to studies concerning the health of plants, livestock and man in the U.K. have been discussed by Thornton and Webb (1979), Plant and Thornton (1980), Thornton (1983), Plant and Stevenson (1986) and Plant and Thornton (1986).

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I. THORNTON

TABLE III Summary statistics of the concentrations of six metals in the topsoils of England and Wales (n = 2776) (from McGrath, 1987) Zn

Cu

Ni

Cd

Cr

Pb

(mg kg- 1 air dry soil) (a) Untrans[ormed data Mean Median Standard deviation Skewness Kurtosis (b) Logw-transf ormed Geometric mean Geometric deviation Skewness Kurtosis

103 87 111 11 153 85 1.8 0.08 4.00

23 18 27 10 147 18 1.8 0.40 2.97

S i m i l a r geochemical m a p s h a v e b e e n compiled for p a r t s of t h e U n i t e d S t a t e s ( M c N e a l , 1986) a n d for several o t h e r E u r o p e a n c o u n t r i e s .

2. N a t i o n a l soil inventories C o m p r e h e n s i v e b a s e l i n e d a t a for several heavy metals, trace elements and major nutrie n t s h a v e r e c e n t l y b e e n o b t a i n e d for soils i n England, Wales and Scotland. (a) 5800 topsoil ( 0 - 1 5 cm) s a m p l e s were t a k e n b y t h e Soil S u r v e y of E n g l a n d a n d W a l e s (now r e n a m e d Soil S u r v e y a n d L a n d R e s e a r c h C e n t r e ) a t 5-kin i n t e r v a l s o n a s q u a r e s a m p l i n g grid t h r o u g h o u t E n g l a n d a n d W a l e s as p a r t of a n a t u r a l i n v e n t o r y of soils. T h e s e soils were a n a l y s e d b y t h e Soils a n d P l a n t N u t r i t i o n Department at Rothamsted Experimental Station for P, K, Ca, Mg, Na, Fe, A1, Ti, Zn, Cu, Ni, Cd, Cr, Pb, Co, Mo, M n , B a a n d S r b y I C P e m i s s i o n s p e c t r o m e t r y a n d colour m a p s p r o d u c e d (McG r a t h et al., 1986). T h e s e d a t a are s u m m a r i s e d for topsoils from W a l e s a n d C e n t r a l , S o u t h e r n and Southwest E n g l a n d in Table III in which geometric m e a n v a l u e s ( n = 2776) for lead of 48 p p m , c a d m i u m 0.9 p p m , zinc 85 p p m a n d c o p p e r 18 p p m ( M c G r a t h , 1986, 1987) are a p p r e c i a b l y lower t h a n t h o s e t o b e expected i n u r b a n soils. A s i m i l a r s u r v e y of W e l s h soils (Davies, 1986; D a v i e s a n d P a v e l e y , i n press) show lower m e d i a n

26 24 17 3 25

45 43 27 6 98

1.2

0.9 2.4 36 1621

21 2.1 - 1.20 2.75

0.9 1.8 - 0.25 0.98

75 42 338 41 1936

38 2.00 - 1.46 5.79

48 1.57

TABLE IV Summary statistics for 722 A horizon and 662 B horizon soil samples from profiles in Wales. Metal values are from a hot HC1/HNO 3 extraction and are as mg/kg dry soil, pH was determined after equilibration for 30 min in 0.05 M CaC12 and percent organic content (OM) was determined gravimetrically after ignition at 430 °C (from Davies, 1986) Minimum Maximum Mean

Median

Mean/ Medium

Pb A B

1.3 0.16

3369 2095

71 33

35 17

2.0 1.9

Zn A B

4.7 0.04

2119 1451

78 68

63 59

1.2 1.2

Cu A B

0.13 0.09

214 65

16 13

12 11

1.3 1.2

Cd A

0.01 0.01

15 12

0.14 0.14

2844 43

13 10

0.42 0.63

169 79

16 20

14 19

1.1 1.1

2493 739

601 547

4.1 1.4

12408 13649

1.1 1.2

B

Co A B

Ni

A B

Mn A B

Fe

A B

pH A B

3.0 1.7 38 12 2.0 2.3

CM A 0.29 B <0.10

(0.5%) (0.1%)

0.50 0.36

(0.12%) 14243 (0.10%) 16150 7.8 7.0 99 98

4.5 4.3 12 5.5

0.29 1.7 0.12 3.0 7.5 9.3

4.4 4.0

1.7 1.1

1.0 1.1

5.5 2.2 2.3 2.4

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SOIL C O N T A M I N A T I O N IN URBAN AREAS

values in surface soils for lead, cadmium, zinc and copper than those listed above; the difference between mean and median values recorded reflects contamination of some samples from mining and other industrial activities. Total contents of some 20 elements have been determined in horizons of some 1000 soil profiles in Scotland, representing the various soil types, using spectrographic and atomic absorption methods; data for extractable soil contents for some elements are also available (Berrow and Ure, 1986). An arithmetic mean value of 24 ppm lead has been quoted for 3944 samples from 896 soil profiles in Scotland, which in turn is lower than the median values listed in Tables III and IV for England and Wales (Reaves and Berrow, 1984). It has since been proposed that atmospheric sources contribute a major portion of lead in uncultivated upland topsoils in south and central Scotland (Berrow et al., 1987). Further comprehensive data for agricultural soils are provided by Archer and Hodgson (1987) based on analysis for total and extractable trace TABLE V Trace elements in soils of E n g l a n d a n d Wales (from Archer a n d Hodgson, 1987) a. Arsenic, c h r o m i u m and mercury: total (mg k g - 1 )

Log-derived m e a n Median Overall range ' N o r m a l ' range No. of samples

As (total) (mg k g - 1)

Cr (total) (mg k g - a)

H g (total) (mg k g - 1)

11.0 10.4 1.0-140 2.3- 53 222

42.4 54.0 4.0-160 9.9-121 192

0.09 0.09 0.01-2.12 0.02-0.40 305

b. Frequency distribution of values Range (mgkg

1)

<1 >/1-<5 5 - 10 10- 20 2 0 - 40 4 0 - 60 6 0 - 80 80-100 100-120 >~ 120

As (total) no. of samples

Cr (total) no. of samples

Range (mgkg

4 11 88 87 18 7 2 1 1 3

0 2 7 21 32 46 63 16 3 2

< 0.1 173 >/0.1- < 0.2 93 0.2-0.5 93 0.5-1.0 7 2.12 1

1)

Hg (total) no. of samples

T A B L E VI T r a c e elements in solids of E n g l a n d a n d Wales (from Archer a n d Hodgson, 1987) a. Lead: total a n d extractable c o n t e n t s Pb (total) ( m g k g l)

Pb (HOAc) ( m g d m :3)

Pb ( E D T A ) (mgdm-~)

Log-derived m e a n 39.8 1.4 12.4 Median 36.8 1.6 11.2 Overall range 4.5-2900 < 1.0-1080 0.25-633 ' N o r m a l ' range 10.9- 145 0.13- 16 2.7- 56 No. of s a m p l e s 1521 1286 984 b. Frequency distribution of values Range ( m g k g -a)

Pb (total) R a n g e Pb (HOAc) Pb ( E D T A ) no. of ( m g d m -3) no. of no. of samples samples samples

< 5 >/5-<10 10- 20 20-2n40 4 0 - 60 6 0 - 80 80-100 100-120 120-140 140-160 160-180 180-200 200-300 300-400 400-500 730 850 895 1200 2900

0 12 130 713 339 150 63 29 16 17 12 12 15 5 3 1 1 1 1 1

< 2 683 >/2-<5 470 5 - 10 90 1 0 - 20 32 20-30 6 3 0 - 40 0 4 0 - 50 0 5 0 - 60 2 6 0 - 70 2 7 0 - 80 0 8 0 - 90 0 90-100 0 100-200 0 200-300 0 530 0 633 0 1080 1

8 49 341 389 100 39 12 8 9 6 3 6 8 4 1 1

Log Pb ( E D T A ) = 2.48 + 0.28 log Pb (HOAc), r = 0.40, 819 pairs, t = 12.42.

elements on samples taken between 1973 and 1980 from farms selected for annual Surveys of Fertiliser Practice. The data (0-15 cm surface soils) are illustrated for total concentrations of arsenic, chromium and mercury in Table V and total and extractable lead in Table VI. S o u r c e s of t r a c e e l e m e n t s a n d m e t a l s i n s o i l s

The main sources of trace elements in soils are the parent materials from which they are derived. Usually this is weathered bedrock or overburden t h a t has been transported by wind,

130

i. T H O R N T O N

water or glacial activity. Overburden m a y be local or exotic, t h o u g h in Britain, transported material is mainly of local origin. T h e earth's crust is made up of 95% igneous rocks and 5% sedimentary rocks; of the latter a b o u t 80% are shales, 15% sandstones and 5% limestones (Mitchell, 1964). Sedimentary rocks tend to overlie the igneous rocks from which they were derived and hence are more frequent in the surface weathering environment. T h e degree to which trace elements in igneous rocks become available on weathering depends on the type of minerals present. The more biologically imp o r t a n t trace elements such as Cu, Co, Mn and Zn occur mainly in the more easily weathered materials such as hornblende and olivine (Mitchell 1974). Of the sedimentary rocks, sandstones contain minerals t h a t weather slowly and usually contain only small a m o u n t s of trace elements. On the other hand, shales m a y be of organic or inorganic origin, and usually contain large a m o u n t s of trace elements (Mitchell, 1964).

Black shales in particular are enriched in a number of elements including Cu, Pb, Zn, Mo and Hg, sometimes a t levels deleterious to plant a n d / o r animal health. Soils derived from the parent materials tend to reflect the chemical compositions of their p a r e n t materials. This is illustrated b y the d a t a for Scottish soils shown in Table V I I (Berrow and Ure, 1986). Soils developed from the weathering of coarse-grained sediments such as sands and sandstones, and from acid igneous rocks such as rhyolites and granites tend to contain smaller a m o u n t s of nutritionally essential elements such as Cu and Co, t h a n those derived from fine-grained sedimentary rocks such as clays and shales and from basic igneous rocks. Potentially toxic a m o u n t s of trace elements in soils m a y be derived as the result of weathering of metal-rich source rocks (Table VIII). For example, some calcareous soils developed from inter-bedded shales and limestones of the Lower Lias formation (Jurassic) in south-

TABLE VII Arithmetic mean contents (#g/g) in B-horizon samples of Scottish soil profiles from different associations (from Berrow and Ure, 1986) Association

Parent material

% of land area

No. of samples

Co

Cu

Ab

Ni

88 35 30 16 14

27 29 25 22 21

2.3 1.1 1.3 1.4 1.4

1540 57 51 41 36

Igneous and metamorphic materials Leslie Ultra basic rocks Incsh Basic igneous rocks Darleith Basaltic rocks Sourhope Intermediate lavas Foudland Slates

0.12 0.67 3.53 1.71 3.25

13 21 58 42 67

Strichen

Dalradian schists

7.98

102

i0

14

0.29

29

Tarves Countesswells Corby/Boyndie

Mixed igneous and metamorphic rocks Granite rocks Fluvioglacialsands and gravels

2.07 5.75 3.08

60 59 81

25 5.5 5.0

33 7.7 7.5

3.9 2.7 0.60

57 22 19

Sedimentary materials Stirling Silts and clays Ettrick Greywackesand shales Rowanhill Carboniferous drifts Balrownie Lower CRS sandstones Thurso Middle CRS flagstones Hobkirk Upper CRS drifts Canisbay Middle CRS sandstones Cromarty CRS drifts

0.54 9.26 3.06 1.83 1.35 0.75 0.39 0.31

19 86 66 89 36 16 37 58

17 16 15 16 8.3 7.6 6.6 2.9

16 22 21 20 17 8.0 12 3.9

1.1 1.4 1.6 0.81 1.9 1.0 1.7 0.8

47 55 46 46 35 28 30 22

Organic soils Peat

9.94

351

2.1

6.5

2.3

Peat profiles

8.0

131

SOILCONTAMINATIONIN URBANAREAS TABLE VIII Trace elements and metals in soils derived from normal and geochemically anomalous parent materials in Britain Typical normal range in soil (ppm)

Metal-rich soils (ppm)

Sources

Possible effects

As

< 5 - 40

up to 2 5 0 0 up to 250

Cd

<1- 2

up to 30 up to 20

Mineralization Metamorphosed rocks around Dartmoor Mineralization Carboniferous black shale Ultrabasic rocks in Scotland Mineralization Mineralization Mineralization Marine black shales of varying age Ultrabasic rocks in Scotland Mineralization

Toxicity in plants and lifestock; excess in food crops Excess in food crops

Cr Cu Fe Hg Mo

15-300 2- 60 20-500 0.008- 0.19 < 1- 5

Ni

2-100

Pb

10-150

Se

< 2-

2

up to 3 5 0 0 up to 2 0 0 0 1% or more 1' 10-100 up to 800 1% or more up to 7 up to 500

Zn

25-200

1% or more

Marine black shales in England and Wales Namurian shales in Ireland Mineralization

west E n g l a n d c o n t a i n 20 p p m Mo or more, a n d are associated with molybdenosis and m o l y b d e n u m - i n d u c e d c o p p e r deficiency in grazing cattle. T h e influence of p a r e n t m a t e r i a l s on t h e t o t a l c o n t e n t a n d form of t r a c e elements in soils is modified to v a r y i n g degrees b y pedogenetic processes t h a t m a y lead to t h e m o b i l i s a t i o n a n d r e d i s t r i b u t i o n of t r a c e elements b o t h w i t h i n t h e soil profile a n d b e t w e e n n e i g h b o u r i n g soils. In the United Kingdom and similar temperature areas, m o s t of t h e soils are r e l a t i v e l y y o u n g a n d t h e p a r e n t m a t e r i a l r e m a i n s t h e d o m i n a n t factor. U n d e r t r o p i c a l c l i m a t e s a n d on m o r e m a t u r e l a n d surfaces, such as t h o s e in A u s t r a l i a , w e a t h e r i n g processes h a v e been vigorous or of m u c h g r e a t e r d u r a t i o n a n d r e l a t i o n s h i p s between t h e chemical c o m p o s i t i o n of t h e original p a r e n t m a t e r i a l s a n d t h e soil m a y be c o m p l e t e l y o v e r r i d d e n by t h e m o b i l i s a t i o n a n d s e c o n d a r y d i s t r i b u t i o n of chemical elements a n d t h e form a t i o n of s e c o n d a r y minerals. T h e processes of gleying, leaching, surface

No known effect Toxicity in cereal crops Fluorosis in lifestock No known effect Molybdenosis or molyb-denuminduced hypocuprosis in cattle Toxicity in cereal and other crops Toxicity in lifestock; excess in foodstruffs No effect Chronic selenosis in homes and cattle Toxicity in cereal crops

organic m a t t e r a c c u m u l a t i o n a n d podzolisation, t o g e t h e r w i t h soil p r o p e r t i e s such as r e a c t i o n (pH) a n d redox p o t e n t i a l (Eh) m a y affect t h e d i s t r i b u t i o n , t h e form a n d t h e m o b i l i t y of t r a c e elements in t h e soil. T r a c e elements, including Se, are often leached from t h e surface l a y e r s of podzols a n d enriched in t h e B horizon ( S m i t h , 1983). Soil in m i n e r a l i s e d areas are often enriched in t h e ore m e t a l s a n d in B r i t a i n f r e q u e n t l y c o n t a i n high c o n c e n t r a t i o n s of one or more of t h e elem e n t s Cu, Pb, Zn, Cd a n d As. I t is of i n t e r e s t t h a t t h e c o n c e n t r a t i o n s of lead a g r i c u l t u r a l soils in t h e U.S.A. a p p e a r lower t h a n t h o s e in B r i t a i n . H o l m g r e n et al. (1983) r e p o r t a m e d i a n v a l u e of 11 p p m Pb for 3001 surface (Ap horizon) soils from U.S.A. c r o p l a n d s ( a r i t h m e t i c m e a n 18 p p m Pb), c o m p a r e d w i t h t h e m e d i a n value of 37 p p m b y A r c h e r a n d H o d g s o n (1987) for E n g l a n d a n d Wales. T h e l a t t e r value w a s b a s e d on a wide range of 4.52900 p p m Pb, reflecting some h e a v i l y cont a m i n a t e d soils w i t h i n t h e d a t a set. However,

132

I. T H O R N T O N

the relatively high values in British topsoils probably indicate a widespread low level contamination arising from two centuries or more of industrial and mining activities. A statistical examination of soil data from England and Wales (Davies, 1983) indicates that the normal lead content of surface (0-15 cm) soil lies between 15 and 106 ppm with a geometric mean of 42 ppm Pb. Metals in u r b a n soils and d u s t s

Within the last two decades, several investigations have provided evidence of elevated metal concentrations in garden soils and in house, street and playground dusts as shown for lead in Table IX. IN order to provide systematic data in the United Kingdom, a national survey of metals in urban soils and dusts was commissioned by the Department of the Environment in 1981. Sampling and analytical protocols used and detailed discussions of the findings are provided by Thornton et al. (1985) and Culbard et al. (1988).

100 households were sampled in each of 53 city boroughs, towns and villages in England, Scotland and Wales, selected on the basis of population, geographical location and degree of ind u s t r i a l / u r b a n development. Locations included London Boroughs and several geochemical hotspots with a specific history of mining activity. The results for lead, cadmium and zinc are shown in Tables X, X1 and XII. The geometric mean concentrations of Pb in surface garden soils (composite of 25 subsamples from exposed surfaces at 0 5 cm), vegetable plot soils (composite of 25 subsamples at 0-15 cm) and amenity area soils (25 subsamples at 0-5 cm) are significantly higher than those values usually quoted for agricultural soils. Concentrations of Pb, Cd, Zn and Cu are appreciably higher in housedusts than in their associated garden soils (Pb x 2, Cd x 6, Zn x 4 and Cu x 4). This probably reflects contributions made by internal sources such as lead-rich paint and abraded plastics. Lead was present in soils of the Derbyshire mining villages (a geochemical hotspot) in the largest concentrations with a geometric mean

T A B L E IX Some previously cited Pb concentrations in household dusts and garden soils Location

Year

Housedust n

Mean (mgkg -I)

Garden soil Range

n

Mean (mgkg

Reference b Range 1)

United Kingdom Lancaster Birmingham

1979 4 1976 806 1982 117 Present s t u d y 159

716 2780 3500 a 419 ~

London Central London Greater London Outer London Derbyshire

Present study 683 1975 64 Present study 100

1010 1370 1870 a

510970 100-280000 30-158000 27 58- 22000 160

570 a 279 a

3 1 0 - 1800 48- 1310

14 647 7 250 9 322 5- 36900 579 647 190 25 000 72 3580 606- 7020 100 5610 a

196- 2410 78- 854 42 2070 1-13700 130- 28 000 1180-22 100

Harrison (1979) Archer and B a r r e t t (1977) Dep. Environ. (1982)

Rundle and Duggan (1980) Davies et al. (1979) t h o r n t o n et al. (1985) T h o r n t o n et al. (1985)

United States Boston and Cambridge, MA Hartford, CT ChampaignUrbana, IL

1972 1975 1976

27

1200 (suburbs) 2000 (city) 59 11,000 4900- 17000 123 1200 12 600 170- 1440

Kreuger (1972) e 700- 1750"* Lepow et al. (1975) Solomon and Hartford (1976)

a G e o m e t r i c m e a n . b S t u d y references, c Mainly parks and hospital grounds, d Outside dirt. e Proj. 72-4, Kreuger Ent., Inc., Cambridge, MA.

SOIL CONTAMINATION

133

IN URBAN AREAS

v a l u e in excess of 5000 p p m Pb. T h e m e a n v a l u e

TABLE XI

for t h e 7 L o n d o n B o r o u g h s of c. 650 p p m P b w a s

Cadmium concentrations in survey locations according to sample type (part of table published in Culbard et al., 1988)

more than

twice that

of t h e m a j o r i t y of t h e

l o c a t i o n s s a m p l e d . H i g h l e a d c o n c e n t r a t i o n s in C e n t r a l L o n d o n w i t h d e c l i n i n g v a l u e s in t h e suburbs have been d e m o n s t r a t e d by Davies et

Sample type

al. (1979). D e t a i l e d s t u d i e s in 97 i n n e r - c i t y h o u s e s in B i r m i n g h a m s h o w e d soil l e a d c o n c e n t r a t i o n s t o be s i g n i f i c a n t l y i n c r e a s e d in (a) h o u s e s o v e r 35 y e a r s of age, (b) t h o s e n e a r c o m m e r c i a l garages,

All study locations less hotspots

London Boroughs

(mg kg- 1 ) Housedust N Geo. mean Range

4640 6.9 < 1-8040

683 7.6 < 1-336

241 2.7 ~ < 1-373 Exterior dusts

Road dust N Geo. mean Range

400 2.0 < 1- 280

62 4.2 < 1-280

27 (1) 23.8 (2) 41.3 a 3.87 4-252

Playground dust N 220 Geo. mean 2.0 Range < 1 68

34 2.4 < 1- 12

None collected

Garden soil N 4128 Geo. mean 1.2 Range < 1- 40

579 1.3 < 1- 40

522 100 a 2-460

Vegetable plot soil N 193 Geo. mean 1.2 Range < 1-

9

29 1.4 < 1- 4

228 89 a < 2-520

Public garden soil N 221 Geo. mean 1.2 Range < 1 - 11

35 1.0 <1- 2

None collected

(c) t h o s e n e a r m e t a l p l a t i n g i n d u s t r i e s a n d (d) t h o s e w i t h i n 10 m of t h e n e a r e s t r o a d ( T a b l e XIII)

( D a v i e s e t al., 1987). I n B r i g h t o n ,

the

c o n c e n t r a t i o n s of l e a d in g a r d e n soil ( 0 - 5 cm), v a c u u m dust and road dust was clearly related t o t h e age of t h e p r o p e r t y , w i t h soil l e a d r a n g i n g

TABLE X Lead concentrations in survey locations described according to sample type (part of table in Culbard et al., 1988) Sample type

All study locations less hotspot

London Boroughs

Derbyshire mining villages

(mg kg 1) Housedust N Geo. mean Range Road dust N Geo. mean Range

4638 561 5-36 900

683 1010 5-36 900

100 1870 606- 7020

Shipham Zn mining village

400 786 45- 9660

65 1354 172- 9660

9 1260 1190- 4620

Playground dust N 220 Geo. mean 289 Range 11- 6860

34 430 93- 6860

5 4390 1190-13400

Garden soil N 4126 Geo. mean 266 Range 13-14100

578 654 60-13 700

89 5610 1180-22100

Vegetable plot soil N 193 Geo. mean 270 Range 24- 2560

29 571 137- 2560

5 8730 1140-26500

T h e l a r g e c o n c e n t r a t i o n s of m e t a l s f o u n d in s o m e B r i t i s h u r b a n soils a n d d u s t s b o t h f r o m

Public garden N Geo. mean Range

35 294 28- 1260

5 3030 2140- 4920

i n g t o s e v e r a l s t u d i e s i n t o p o s s i b l e p a t h w a y s of c o n t a m i n a n t s t o t h e p o p u l a t i o n t h r o u g h (a) soil

soil 221 185 20- 1820

a Arithmetic mean; (1) samples in June 1979, (2) sampled in September 1979.

f r o m a g e o m e t r i c m e a n of 131 p p m P b in h o u s e s built over the period 1960-1986 compared with 1146 p p m P b in t h o s e pre-1870.

I m p l i c a t i o n s of c o n t a m i n a t i o n to h e a l t h

inner-city areas and from 'geochemical hotspots' h a v e g i v e n rise t o s o m e d e g r e e of c o n c e r n lead-

a n d d u s t i n g e s t i o n a n d i n h a l a t i o n a n d (b) con-

134

I. THORNTON

TABLE XII Zinc concentrations in survey locations according to s a m p l e t y p e (part of table u n p u b l i s h e d in Culbard et al., 1988) Sample type

All s t u d y location less hotspots

London Boroughs

S h i p h a m Zn m i n i n g village

(mg k g - 1)

Housedust N Geo. m e a n Range

4639 1090 81-115000

683 1324 81-115000

241 2100 a 624-8200

Road dust N Geo. m e a n Range

400 338 4 6 - 22 900

65 513 121-

Data unavailable 5150

Playground dust N Geo. m e a n Range

220 340 11-

5430

34 620 134-

None collected

handwipe samples were analysed, based on the homes of 97 children. Behavioural measurements were also made using a portable video recorder filming each child for approximately 4 hours. Results are summarised in Table XIV. The correlation between blood level and soil lead concentration (r = 0.18) was similar to that with dust lead concentration and lower that with dust lead loading (r = 0.46) (which is the product of dust loading and lead concentration. An exposure model was developed using multiple linear regression, showing a positive relationship between blood lead and a factor calculated from the dust lead loading multiplied by the rate the child's hands touch all objects (including the floor) together with concentration of lead in water). A summary assessment of the exposure of these children to lead shows that

3740

Garden soil N Geo. m e a n Range

4127 278 13- 14600

579 424 5 8 - 13100

519 9340 a 230-50000

29 552 104-

215 8750 a 180-64000

Vegetable plot soil N Geo. m e a n Range

193 321 41-

2780

2780

TABLE XIII Lead levels in h o u s e d u s t a n d garden soil from 87 Bir m i n g h a m households, s h o w i n g a n u m b e r of s u b g r o u p s identiffed from questionaire responses. (from Davies et al., 1987) Geometric m e a n lead value Housedust Concentration (gg g-l)

Public garden soil N Geo. m e a n Range

221 180 34-

1360

35 183 34-

None collected 482

Arithmetic mean.

sumption of home-grown foods. The following three case histories illustrate these.

1. Lead exposure in inner-city Birmingham Over the period November 1984 to February 1985, a comprehensive study, commissioned by the U.K. Department of the Environment, was undertaken in Birmingham in an attempt to quantify lead intake from dust (dust composition is influenced by the presence of contaminants in garden soil) in relation to other sources of lead intake by the 2-year old child (Davies, 1987; Davies et al., 1987). Housedust, pavement and roaddust, soil, air, water, food, blood and

Loading (/~ g m - 2 )

Soil concentration (~ g - ' )

H o u s e age < 35 years? Yes 221 e No 498

15 c 81

176 b 342

Decorating? Yes No

94 52

331 300

92 c 27

365 b 224

547 a 393

N e a r commercial garage? Yes 506 b No 313

N e a r waste l a n d / d e m o l i t i o n s i t e / t i p ? Yes 443 80 No 417 48

364 ~ 267

Near m e t a l - u s i n g i n d u s t r y ? Yes 453 No 408

407 c 248

81 47

H o u s e < 10 m from n e a r e s t road? Yes 481 78 a No 361 42

389 c 216

Significance levels: a P < 0.05; b p < 0.01; Cp < 0.001.

135

SOIL CONTAMINATION IN URBAN AREAS

TABLE XIV Lead in blood, environmental samples, handwipes, diet and water Sample

Units

Blood Air playroom bedroom external Dust Soil Dust "loading" Handwipes Diet (food and beverages) Water

N

/zl/100 ml ~ g / m ;3 # g/m3 # g / m :3 ~g/g /~g/g /~g / m 2 ~g # g/week ~ g/1

97 607 599 605 94 87 93 704 96 96

intake from the inhalation accounts for only 3% of the total lead uptake (Table XV), while the contribution of dust intake to lead uptake is around twice that attributable to diet.

2. Metals in vegetables grown in urban soils Urban gardening is widespread in Britain and vegetable growing considered both a valuable source of fresh produce and a leisure pastime. Lettuce, radish and carrot were grown in replicated experimental plots in household gardens at 2 locations in each of 5 cities/towns in 1979. The locations were selected as typical urban gardens. Concentrations of lead, zinc and cadmium in soils, radish and lettuce are shown in Table XVI and have been discussed in detail by Thornton and Jones (1984). Most of the soils were enriched in copper, lead and zinc, with the two London sites (4100, 2180 ~ g / g Pb) the most heavily contaminated, followed by those in Newcastle-on-Tyne. Soils at older sites contained more metals than those recently develTABLE XV Intake and uptake of lead by young children in Birmingham Intake route

Pathway

Lead uptake (#g/d)

Inhalation Ingestion

Air Diet Dust

1.1 12.2 22.5

3 34 63

35.8

100

Total

Total uptake (%)

Geometric Mean

Percentiles 5th

95th

11.7 0.27 0.26 0.43 424 313 60 5.7 161 19

6 0.08 0.09 0.12 138 92 4 1.9 82 5

24 0.88 0.81 1.53 2093 1160 486 15.1 389 100

oped. Concentrations of lead in radish and in lettuce increased with soil lead content (r = 0.96 and 0.97 respectively). It was concluded that lead in radish was largely due to uptake from contaminated soil. Between 40 and 80% of lead in washed lettuce at the London and Newcastle sites was apparently associated with foliar uptake or soil splash, as concentrations of lead in plants grown in a control soil at these locations were large. Chamberlain (1984) has reviewed the subject of lead fallout onto crops and concludes that foliar deposition of air-borne lead accounts for most of the lead in grasses and in other plants having a high leaf surface per unit mass. These criteria would apply to lettuce and other large leaved garden crops such as cabbage, kale and spinach. In the present study up to 75% of lead, nickel and iron was removed from lettuce by washing. However, in spite of the elevated levels of metal in some of these soils, only lettuce and radish from London exceeded the statutory limits of 1 ppm Pb fresh weight. Lead derived from this source may be important when lead exposure from other sources is also above normal. Another study was centred on an area of west Cornwall in which arsenic (together with tin and copper) had been mined. In July 1984, soils, vegetable and salad crops were sampled in 32 gardens in the towns of Hayle and Camborne as described by Xu and Thornton (1985). Concentrations of arsenic in topsoils (0-15 cm), lettuce onion, beetroot, carrot, pea and bean are

136

I. THORNTON

T A B L E XVI Pb, Zn and Cd in g a r d e n / a l l o t m e n t soils ( # g / g ) a n d in radish a n d lettuce grown directly in t h e soils ( # g / g , dry m a t t e r ) (taken from T h o r n t o n a n d Jones, 1984) Location

Pb

Zn

Cd

Soil

Radish

Lettuce

Soil

Radish

Lettuce

London

4100 2180

23.3 11.9

23.5 16.4

1562 2182

267 333

144 309

Newcastle on T y n e

840 1608

12.2 7.3

9.4 8.5

506 660

65 52

Leeds

690 136

3.3 3.2

3.8 4.1

554 190

Stoke on T r e n t

224 90

1.6 1.5

4.4 1.7

Scunthorpe

108 64

1.4 2.0

Control soil

92

-

Radish

Lettuce

2.8 1.8

0.7 0.7

0.8 0.8

97 101

1.4 1.8

0.4 0.5

0.6 0.6

47 26

87 76

1.2 0.6

0.3 0.6

0.4 0.7

276 174

127 50

166 99

0.8 0.6

0.3 0.2

2.3 0.8

2.0 2.2

258 320

42 42

81 83

< 0.1 0.2

0.2 0.3

0.4 0.3

-

160

-

0.5

-

-

listed in Table XVII. Total concentrations of arsenic in soils range widely (144 to 892 #g/g; geometric mean 322 # g/g), compared with norreal soils in the U.K. (5-100 #g/g). Arsenic concentrations in the edible tissues of the 6 garden crops are not high, but are species dependant with maximum concentrations in lettuce (geometric mean 0.85 # g / g dry matter). Relationships between arsenic in soil and in beetroot, lettuce, onion and pea are significant. The authors derived regression equations based on soil arsenic to predict arsenic levels in the vegetables and used ridge regression analysis to test the effect of other soil variables. Total soil iron reduced the uptake of arsenic by lettuce and phosphorous increased arsenic uptake. The statutory limit for arsenic in most foods offered for sale in the U.K. is 1 ppm fresh

Soil

weight. In the study reported, although arsenic levels in vegetables were above those recorded elsewhere in the U.K. (MAFF, 1982), even in this 'geochemical hotspot' situation all the vegetables examined were blow this permitted level and most were below 0.2 ppm As fresh weight. 3. Cadmium exposure in Shtpham, Somerset The geochemical survey of England and Wales referred to earlier (Webb et al., 1978), drew attention to several areas in which soils contain high concentrations of cadmium, usually associated with large amounts of zinc and sometimes lead. In the vicinity of Shipham, surface agricultural soils reclaimed from and near old mine workings ranged from 30 to 800 ppm Cd, com-

T A B L E XVII Concentrations of As in garden soils a n d vegetables ( # g / g , dry m a t t e r ) in Cornwall (taken from X u a n d T h o r n t o n , 1985) T o t a l As in soil (#g/g)

Lettuce (#g/g)

Onion (#g/g)

Beetroot (#g/g)

Carrot (#g/g)

Pea (#g/g)

Bean (#g/g)

Range

144-892

0.15-3.88

0.10-0.49

0.02-0.93

0.10-0.93

0.01-0.11

0.02-0.09

Geometric m e a n

322

0.85

0.20

0.17

0.21

0.04

0.04

No. of samples

32

28

23

23

19

19

7

137

SOIL CONTAMINATION IN URBAN AREAS

pared with a normal value of less than 2 ppm Cd. Zinc was mined in and around this village from around 1700 to 1850, mainly as the ore calamine (smithsonite, ZnCOa) , which was used with copper to produce brass. Mineral veins run under parts of the village and several housing developments lie on land reclaimed from old workings. Results of a survey of metals in garden soils in Shipham and in a nearby control village North Petherton have been published by Thornton et al. (1980) and Moorcroft et al. (1982) and further discussed by Thornton (1988). Surface soils (0-5 cm) in Shipham had median concentrations of 91 ppm Cd and 7660 ppm Zn compared with 0.6 ppm Cd and 158 ppm Zn in North Petherton. In Shipham over 90% of soils contained in excess of 20 ppm Cd and 50% exceeded 60 ppm Cd. There was a strong correlation between cadmium and zinc in these soils with a mean Zn : Cd ratio around 90 : 1. The identification of such large amounts of cadmium in garden soils, which are unique in Britain, resulted in one of the most ambitious environmental h e a l t h investigations ever mounted, involving national and local government, Westminster Hospital Medical School and Imperial College. These studies have been recently published collectively in 'The Shipham Report' (Morgan, 1988). It is not possible to describe these in detail but the findings may be summarised as follows: (a) the household garden soils greatly exceeded the levels of cadmium in polluted paddy soils associated with the well documented "itai-itai" disease in Japan. (b) Samples of housedust averaged 26 ppm cadmium and 2300 ppm zinc. (c) From studies of metals in locally grown vegetables and diets, an average intake for human beings of 200 #g cadmium per week was calculated, compared with the average intake in the United Kingdom of 140~g cadmium per week. Individual intakes rarely exceeded the World Health Organisation's provisional tolerable weekly intake of 450-500 ~g cadmium. (d) Health inventories and biochemical tests on 548 residents of Shipham and on 543 control subjects from a nearby uncontaminated village

showed only slight differences attributable to cadmium. Though elevated concentrations of cadmium were found in home grown crops, the actual levels found only to a small degree reflected those on the soil, probably because the metal was not very mobile or plant-available due to the high soil pH and calcium carbonate content and other soil factors (Alloway et al., 1988). In this unique situation it is also possible that the large amounts of zinc and calcium present in the environment afford some degree of protection against the possible adverse effects of cadmium.

Research requirements (1) Firstly it must be emphasised that with the exception of heavy metals, there is relatively little systematic information on the extent and degree of urban soil contamination with pesticides and herbicides, hydrocarbons, fertilisers, asbestos, etc. This lack of data is due in part to difficulties and high costs of analysis. (2) The chemistry of pollutants, including metals, in urban soils is far from understood and has received little research effort. Without careful evaluation it is difficult to know to what degree knowledge on the behaviour of chemicals in agricultural soils can be transposed, as the presence of concrete, rubble and the disturbed nature of urban soils may well modify chemical and physical processes operating in the relatively undisturbed rural soil environment. (3) The dynamics of pollutants added to urban soils need to be studied both for the individual contaminants found and for possible synergenetic and antagonistic interactions between them. For example, to what degree and at what speed do contaminants interact with urban soil constituents to reduce bio-availability of the contaminating substance? (4) The incorporation of data on contaminants into a classification system for urban soils needs to be addressed together with methods of data collation, storage and retrieval. To what degree should urban soils be classified on the basis of their chemical analysis (or calorific value) or the presence of one or more chemicals

138

being present above threshold or action trigger concentration? (5) There is little or no quantitative information on the inpacts of contaminants in urban soils on vegetation (both natural and cultivated) and on soil flora and fauna including microorganisms. In this context it must be remembered that contaminants rarely occur in isolation and that possible 'cocktail' effects and interactions are likely. References Alloway, B.J., Thornton, I., Smart, G.A., Sherlock, J.C. and Quinn, M.J., 1988. Metal availability. In: H. Morgan (Editor), The Shipham Report, Sci. Total Environ., 75: 41-69. Archer, F.C. and Hodgson, I.H., 1987. Total and extractable trace element contents of soils in England and Wales. J. Soil Sci., 38: 421-432. Assink, J.W., 1986. Extractive methods for soil decontamination; a general survey and review of operational treatment installations. In: J.W. Assink and W.J. van den Brink (Editors), Contaminated Soil. Martinus Nijhoff, Dordrecht, pp. 655-667. Barltrop, D., Strehlow, C.D., Thornton, I. and Webb, J.S., 1975. Absorption of lead from dust and soil. Postgrad. Med. J., 51: 801-804. Barrett, I., 1987. Research in Urban Ecology. Rep. Nat. Conserv. Conc. Barth, H. and L'Hermite, P., (Editors), 1987. Scientific Basis for Soil Protection in the European Community. Elsevier, Barking, 639 pp. Beaver, S.H., 1946, Report on Derelict and Land in the Black Country. Minist. Town Ctry. Plann., London (Mimeography). Berkett, M.J. and Simms, D.L., 1986. Assessing contaminated land: U.K. policy and practice. In: J.W. Assink and W.J. van den Brink (Editors), Martinus Nijhoff, Dordrecht, Contaminated Soil. Berrow, M.L. and Ure, A.M., 1986. Trace element mapping of Scottish soils, In: I. Thornton (Editor), Proc. First Int. Symp. Geochem. Health. Science Reviews, Northwood, pp. 59-62. Berrow, M.L., Stein, W.M. and Ure, A.M., 1987. Lead in Scottish soils. In: I. Thornton and E. Culbard (Editors), Lead in the Home Environment. Science Reviews, Northwood, pp. 37-45. Bewley, R.J.F., 1986. A microbial strategy for the decontamination of polluted land. In: J.W. Assink and W.J. van den Brink (Editors), Contaminated Soil. Martinus Nijhoff, Dordrecht, pp. 759-768. Bridges, E.M., 1987. Surveying Derelict Land. Clarendon Press, Oxford, 137 pp. Cairney, T., 1986. Soil cover reclamation experience in Britain. In: J.W. Assink and W.J. van den Brink (Editors)

I. THORNTON Contaminated Soil. Martinus Nijhoff, Dordrecht, pp. 601-614. Chamberlain, A.C., Heard, M.J., Little, P., Newton, D., Wells, A.C. and Wiffen, R.D., 1978. Investigations into Lead from Motor Vehicles. At. Energy Res. Establishment Rep. No. R9198, H.M.S.O., London. Collins, W.G. and Bush, P.W., 1969. The definition and classification of derelict land. J. Town Plann. Inst., 55: 111-115. Craul, P.J., 1985. A description of urban soils and their desired characteristics. J. Arboricult., 2: 330-339. Culbard, E.B., Thornton, I., Watt, J., Wheatley, M., Moorcroft, S. and Thompson, M., 1988. Metal contamination in British surban dusts and soils. J. Environ. Qual., 17: 226-234. Davies, B.E., 1978. Plant-available lead and other metals in British garden soils. Sci. Total Environ., 9: 243-262. Davies, B.E., Conway, D. and Holt, S., 1979. Lead pollution of London soils: a potential restriction on their use for vegetable growing. J. Agric. Sci. Cambridge, 93: 749-752. Davies, B.E., 1983. A graphical estimation of the normal lead content of some British soils. Geoderma, 29: 67-75. Davies, B.E., 1986. Baseline survey of metals in Welsh soils. In: I. Thornton (Editor) Proc. First Int. Syrup. Geochem. Health, Science Reviews, Northwood, pp. 45-51. Davies, B.E. and Paveley, C.F., 1988. Baseline trace metal survey of Welsh soils with special reference to lead. In: I. Thornton (Editor) Proc. First Int. Symp. Geochem. Health. Science Reviews, Northwood. Davies, B.E. and Thornton, I., 1990. Environmental Pathways of Lead into Food. A Review. Lead Zinc Res. Organ., New York, N.Y. Davies, D.J.A., 1987. An assessment of the exposure of young children to lead in the home environment. In: I. Thornton and E. Culbard (Editors) Lead in the Home Environment. Science Reviews, Northwood, pp. 189-196. Davies, D.J.A., Thornton, I., Watt, J.M., Culbard, E.B., Harvey, P.G., Delves, H.T., Sherlock, J.C., Smart, G.A., Thomas, J.F.A. and Quinn, M.J., 1987. Relationship between blood lead and lead intake in two year old urban children in the U.K. In: S.E. Lundberg and T.C. Hutchinson (Editors), Heavy Metals in the Environment 1987. CEP Consultants, New Orleans, Edinburgh. Davies, D.J.A. and Thornton, I., 1987. The influence of house age on lead levels in dusts and soils in Brighton, England. Environ. Geochem. Health, 9: 65-67. Davies, D.J.A., Watt, J.M. and Thornton, I., 1987. Lead levels in Birmingham dusts and soils. Sci. Total Environ., 67: 177-185. De Kreuk, J.F., 1986. Microbial decontamination of excavated soil. In: J.W. Assink and W.J. van den Brink (Editors) C o n t a m i n a t e d Soil. M a r t i n u s Nijhoff, Dordrecht, pp. 669-678. De Leer, E.W.B., 1986. Thermal methods developed in the Netherlands for the cleaning of contaminated soil. In: J.W. Assink and W.J. van den Brink (Editors), Contaminated Soil. Martinns Nijhoff, Dordrecht, pp. 645654. Downing, M.F., 1977. Survey information. In: B. Hackett

S O I L C O N T A M I N A T I O N IN U R B A N AREAS

(Editor) Landscape Reclamation Practice. IPC Sci. Technol. Press, London, pp. 17-36. Haines, R., 1971. Contaminated Sites in the West Midlands. A Prospective Survey, JURUE, Univ. Aston, Birmingham. Hilberts, B., Eikelboom, D.H., Verheul, J.H.A.M. and Heinis, F.S., 1986. In situ techniques. In: J.W. Assink and W.J. van den Brink (Editors) Contaminated Soil. Martinus Nijhoff, Dordrecht, pp. 679-978. Holmgren, G.G.S., Meyer, M.W., Daniels, R.B., Kabota, J. and Chaney, R.L., 1983. Cadmium, zinc, copper and nickel in agricultural soils of the United States. Agron. Abstr., 1983: 33. Hutton, M., Wadge, A. and Milligan, P.J., 1988. Environmental levels of cadmium and lead in the vicinity of a major refuse incinerator. Atmos. Environ., 22: 411-416. Interdep. Comm. Reclam. Contam. Land, 1983. Guidance on the assessment and redevelopment of contaminated land. ICRCL Paper 59/83, Dep. the Environ., London. Interdep. Comm. Reclam. Contam. Land, 1987. Guidance on the assessment and redevelopment of contaminated land. ICRCL Paper 59/83. Dep. Environ., 2nd ed., London. Institute of Geological Sciences, 1978a. Geochemical Atlas of Great Britain: Shetland Islands. Inst. Geol. Sci., London. Inst. Geol. Sci., 1978b. Geochemical Atlas of Great Britain: Orkney Islands. Inst. Geol. Sci., London. Inst. Geol. Sci., 1979. Geochemical Atlas of Great Britain: South Orkney and Caithness. Inst. Geol. Sci., London. Inst. Geol. Sci., 1978a. Geochemical Atlas of Great Britain: Sutherland. Inst. Geol. Sci., London. Jessberger, H.L., 1986. Techniques for remedial action at waste disposal sites. In: J.W. Assink and W.J. van den Brink (Editors), Contaminated Soil. Martinus Nijhoff, Dordrecht, pp. 587-599. Little, P. and Wiffen, R.D., 1978. Emission and deposition of lead from motor exhausts--II. Ariborne concentration, particle size and deposition of lead near motorways. Atmos. Environ., 12: 1331-1341. Minist. Agric., Fish. Food, 1982. Survey of arsenic in food. Food Surveillance Pap. No. 8, HMSO, London. McGrath, S.P., 1986. The range of metal concentrations in topsoils of England and Wales in relation to soil protection guidelines. In: D.D. Hemphill (Editor), Trace Substances in Environmental Health 20. Univ. Missouri, Columbian, pp. 242-252. McGrath, S.P., 1987. Computerised quality control statistics and regional mapping of the concentrations of trace and major elements in the soil of England and Wales. Soil Use Manage., 3: 31-38. McGrath, S.P., Cunliffe, C.H. and Pope, A.J., 1986. I~ad, zinc, cadmium, copper, nickel and chromium concentrations in the topsoils of England and Wales. In: I. Thornton (Editor), Proc. First Int. Symp. Geochem. Health. Science Reviews, Northwood, pp. 52-58. McNeal, J.M., 1986. Regional scale geochemical mapping in the United States. In: I. Thornton, (Editor), Proc. First Int. Symp. Geochem. Health. Science Reviews, Northwood, pp. 116-30. Mitchell, R.L., 1974. Trace element problems in Scottish soils. Neth. J. Agric. Sci., 2: 295-304.

139 Mitchell, R.L., 1964. Trace elements in soils. In: F.E. Bear (Editor), Chemistry of the Soil. Reinhold, New York, N.Y., pp. 320-368. Moen, J.E.T., Comet, J.P. and Evers, C.W.A., 1986. Soil Protection and Remedial actions: criteria for decision making and standardisation of requirements. In: J.W. Assink and W.J. van den Brink (Editors), Contaminated Soil Martinus Nijhoff, Dordrecht, pp. 441-448. Moorcroft, S.J., Watt, J., Wells, J., Thornton, I., Strehlow, C.D. and Barltrop, D., 1982. Composition of dusts and soils in an apparently uncontaminated rural village in southwest England--implications to human health. In: D.D. Hemphill (Editor), Trace substances in Environmental Health, 16. Univ. Missouri, Columbia, pp. 1551162. Moss, G.H., 1987. Wasting Europe's Heritage--the need for soil protection. In: H. B a r t h and P. Lithermite (Editor), Scientific Basis for Soil Protection in the European Community. Elsevier, Barking, pp. 17-28. Morgan, H., 1988. The Shipham Report. Sci. Total Environ., 7: 1-143. Morgan, H. and Simms, D.L., 1988. Setting trigger concentrations for contaminated land. In: K. Wolf, W.J. van den Brink and F.J. Colen (Editors), Contaminated Land '88. Kluwer, Dordrecht, pp. 327-337. Nriagu, J.O. and Pacyna, J.M., 1988. Quantitative assessment of worldwide contamination of air, water and soils by trace metals. Nature, 333: 134-139. Page, A.L. and Ganje, 1970. Accumulations of lead in soils for regions of high and low motor vehicle traffic density. Environ. Sci. TechnoL, 4: 140-142. Plant, J.A. and Moore, P.J., 1979. Regional geochemical mapping and interpretation in Britain. Philos. Trans. R. Soc. Lond., B288: 95-112. Plant, J.A. and Thornton, I., 1980. Regional geochemical mapping and health in the United Kingdom. J. Geol. Soc. Lond., 137: 575-586. Plant, J.A. and Stevenson, A.G., 1986. Regional geochemistry and its role in epidemiological studies. In: C.F. Mills, I. Bremner and J.K. Chesters (Editors), Trace Element Metabolism in Man and Animals. Rowett Res. Inst., Aberdeen, 5, pp. 900-906. Plant. J. and Thornton, I., 1986. Geochemistry and health in the United Kingdom. In: I. Thornton (Editor), Proc. First Int. Symp. Geochem. Health. Science Reviews, Northwood, pp. 1-15. Reaves, G.A. and Berrow, M.L., 1984. Total lead concentrations in Scottish soils. Geoderma, 32: 1-8. R. Comm. Environ. Pollut., 1983. Lead in the Environment. 9th Rep. CMDN 8852, H.M.S.O., London. R. Comm. Environ. Pollut., 1985. Managing Waste: the Duty of Care. l l t h Rep. CMND 9675, H.M.S.O., London. Simms, D.L. and Beckett, M.J., 1987. Contaminated land: setting trigger concentrations. Sci. Total Environ., 65: 121-234. Smith, C.A., 1983. The distribution of selenium in some soils developed on Silurian, Carboniferous and Cretaceous systems in England and Wales. Thesis, Univ. London. Smith, W.H., 1976. Lead contamination of the roadside ecosystem. J. Air Pollut. Control Fed., 25: 753-766.

140 Thornton, I. and Webb, J.S., 1979. Geochemistry and health in the United Kingdom. Philos. Trans. R. Soc. Lond., B288: 151-168. Thornton, I., 1980. Geochemical aspects of heavy metal pollution and agriculture in England and Wales. In: Inorganic Pollution and Agriculture (MAFF Reference Book, 326). H.M.S.O., London, pp. 1015-25. Thornton, I., John, S., Moorcroft, S. and Watt, J., 1980. Cadmium at Shipham--a unique example of environmental geochemistry and health. In: D.D. Hemphill (editor), Trace Substances in Environmental Health, 16. Univ. Missouri, Columbia, pp. 27-37. Thornton, I., 1983. Geochemistry applied to agriculture. In: I. Thornton (Editor), Applied Environmental Geochemistry. Academic Press, London, pp. 231-266. Thornton, I. and Abrahams, P., 1984. Historical records of metal pollution in the environment. In: J. Nriagu (Editor), Changing Metal Cycles and Human Health. Springer, Berlin, pp. 7-25. Thornton, I. and Jones, T.H., 1984. Sources of lead and associated metals in vegetables grown in British urban soils: uptake from soil versus air deposition. In: D.D. Hemphill (Editor), Trace Substances in Environmental Health, 18. Univ. Missouri, Columbia, pp. 303-310. Thornton, I., Culbard, E.B., Moorcroft, S., Watt, J., Wheatley, M., Thompson, M. and Thomas, J.F.A., 1985. Metals

I. THORNTON in urban dusts and soils. Environ. Technol. Lett., 6: 137-145. Thornton, I., Abrahams, P.W., Culbard, E., Rother, J.A.P. and Olson, B.H., 1986. The interaction between geochemical and pollutant metal sources in the environment: Implications for the community. In: I. Thornton and R.J. Howarth (Editors), Applied Geochemistry in the 1980's. Graham and Trotman, London, pp. 270-308. Thornton, I., 1988. Metal content of soils and dusts. In: H. Morgan (Editor), The Shipharn Report. Sci. Total Environ., 75: 21-39. Wadge, A. and Hutton, M., 1987. The cadmium and lead content of suspended particulate matter emitted from a U.K. refuse incinerator. Sci. Total Environ., 67: 91-95. Webb, J.S., Nichol, I., Foster, R., Lowenstein, P.L. and Howarth, R.J., 1973. Provisional Geochemical Atlas of Northern Ireland. Appl. Geochem. Res. Group, Imperial College Sci. Technol., London. Webb, J.S., Thornton, M., Howarth, R.J. and Lowenstein, P.L., 1978. The Wolfson Geochemical Atlas of England and Wales. Oxford Univ. Press., Oxford. Webb, J.S. and Howarth, R.J., 1979. Regional geochemical mapping. Philos. Trans. R. Soc. Lond., B288: 81-93. Xu, J. and Thornton, I., 1985. Arsenic in garden soils and vegetable crops in Cornwall, England: Implications for human health. Environ. Geochem. Health, 7: 131-133.