Metal dispersion and transportational activities using food crops as biomonitors

the Science of the Total Environment i n l o t h , E n * a ~ a m © n l a n d its R ~ t a t i o n , h l p w i t h ~ . n

ELSEVIER

The Science of the Total Environment 146/147 (1994) 309-319

Metal dispersion and transportational activities using food crops as biomonitors N.I. Ward*, J.M. Savage Department of Chemistry, University of Surrey, GuildJbrd, Surrey GU2 5XH, UK

Abstract The multielement (A1, Ca, Cd, Ce, Cr, Cu, Fe, Mg, Mn, Ni, Pb, Si, and Zn) levels of various common vegetables (bean, broccoli, cabbage, cauliflower, lettuce, marrow, onion, parsnip, spinach, sprouts, sweet corn, and tomato); fruits (grape and strawberry); herbs (garlic, lemon balm, marjoram, mint, rosemary and tarragon); local pasture species and surface soils collected from a commercial garden centre located within a distance of 30 m of the London Orbital Motorway (M25) is presented. Comparative values are given from a background area, namely a domestic garden located in the North Yorkshire Dales National Park area. Analysis was undertaken by inductively coupled plasma optical emission spectrometry (ICP-OES) and inductively coupled plasma-source mass spectrometry (ICP-MS) with quality control assessment using four international biological reference materials; BCR:CRM 62 Olive Leaves, NIST 1575 Pine Needles, NIST 1573 Tomato Leaves, and NIST 1572 Citrus Leaves. Inter-analytical method comparison is given using two methods of ICP-MS; namely conventional pneumatic nebulisation of sample solution, and direct solids analysis by laser ablation; and neutron activation analysis methods (NAA). For the elements listed there is a good precision obtained by ICP-MS and NAA. In particular levels of < + 1-10% (rsd) are obtained. Comparison of data with certified values and other analytical methods are generally of very good agreement. Lead levels in background areas ranged from 0.0008 to 0.340/xg/g (fresh weight) for plant material; with the lead magnitude greater for grasses > herbs > vegetables > cereals > fruits. Measured values are in good agreement with reported literature values. The lowest Pb values are for marrow, lettuce, tomato and sweet corn samples (-0.001-0.021 #g/g). 'Green' leaf material levels were -0.02-0.10/Lg/g (i.e. sprouts and cabbage). Root vegetables contain higher levels, -0.02-0.125 #g/g (especially carrot), reflecting possible metal uptake from soil. The highest vegetable Pb values are for leek and onion ( - 0.35 #g/g). Background values are also provided for nineteen elements (A1, As, B, Ba, Br, Cd, Co, Cr, Cu, Fe, Li, Mn, Mo, Ni, Rb, Se, Sr, V, and Zn). Exposure to motor vehicle activities at a site some 30 m from the M25 shows only significant increases in Pb for unwashed plant material and surface soils. Typically Pb levels of 40-80% can be removed by washing plant surfaces resulting in metal levels similar to background areas. The importance of washing fruit is shown in 82% and 88% of the Pb content of grapes and strawberries being removed by washing, reflecting both airborne dusts, and soil particle (probably via 'splash' during periods of precipitation) as sources of Pb. All edible plant portions had Pb levels below the EEC guidelines of 1 #g/g (fresh weight). Enhanced levels of other metals (Cd, Cr, Cu, Mn, Ni, and Zn) which are possibly related to the wear-and-tear of motor vehicles, are observed only in surface soils at sites along the M25. There is no evidence of other metals contaminating foodcrops. Key words." Food biomonitors; Trace metals; Motorways; Transportational;

* Corresponding author. 0048-9697/94/$07.00 © 1994 Elsevier Science B.V. All rights reserved. SSDI 0048-9697(92)03597-U

310

N.L Ward, J.M. Savage/Sci. Total Environ. 146/147 (1994) 309-319

1. Introduction

The dispersion of anthropogenic lead in potentially hazardous to man and animals via two major pathways - - the food chain and dust inhalation. Both are significantly influenced by Pb input from motor vehicle exhaust emissions. Since the early 1920s lead has been added to petrol in the form of tetraethyl or tetramethyl Pb anti-knock additives. On combination of petrol a variety of complex halide salts (namely PbBr, PbBrC1, Pb(OH)Br, (PbO)2PbBr2) are discharged in association with the particulate fraction in the exhaust gases. These compounds are subsequently converted in the atmosphere to oxides and carbonates of lead. The distribution of these particulates in the atmosphere is directly related to size (in general less than 1 #m in diameter) and general weather conditions (including wind direction and precipitation). Such small-sized particles are hazardous, being capable of penetrating deeply into the respiratory tract during inhalation. As Pb enters the environment in areas adjacent to motor vehicle activities it is capable of undergoing many complex interactions. Various studies have shown that the Pb balance in many such ecosystems results in an input which greatly exceeds its output (Kabata-Pendias and Pendias, 1984). Contamination of roadside surface soils with Pb is therefore a cumulative process resulting ultimately in an imbalance for localised biological activities (Doelman and Haanstra, 1979; Hughes et al., 1980). The subsequent uptake of Pb by plants is generally passive as it is not readily soluble in soil. However, there is evidence that Pb is taken up from soils by plant roots, at both low and high metal concentrations. This process is strongly governed by soil and plant factors, such as organic matter content, pH, temperature/humidity, soil chemistry, and the presence of other metals. It is generally agreed that Pb from a soil source is not readily translocated to edible portions of plants. The main process responsible for Pb accumulation in such plants is deposition of Pb directly onto leaf surfaces and absorption through the cell walls. The degree of Pb burden on such plant and vegetable surfaces has been illustrated in many pollution studies by the amount of metal removable from

leaf surfaces by washing with detergents (Isermann, 1977). A review of the literature reveals that the Pb content of edible portions of plants grown in uncontaminated areas ranges from 0.001 to 0.08/~g/g (fresh wt., FW), 0.05-3.0 #g/g (dry wt.; DW), and 2.7-90 #g/g (ash wt.; AW) as shown in Table 1 (Martin and Coughtrey, 1982; Kabata-Pendias and Pendias, 1984). Background level in folage plants averages 2.1/~g/g (DW) for grasses, and 2.5 /~g/g (DW) for clovers. The highest bioaccumulation of Pb is reported for leafy vegetables, with excessive levels being in relation to metal-processing industries: lettuce leaves in Canada, 596-1506/zg/g (DW) (Roberts et al., 1974); Chinese cabbage leaves in Japan, 45 /~g/g (DW) (Kobayashi, 1971); carrot roots in Poland, 27-57/~g/g (DW) (Faber and Niezgoda,

Table 1 Reported lead levels for 'uncontaminated' vegetables, cereals, fruits, grasses and soil Lead content (#g/g) Fresh weight (FW)

Dry weight (DW)

Ash weight (AW)

0.08 -0.016 0.012 0.001 ----

1.50 0.70 0.70 1.50 0.70 1.10 0.50 0.30

37.0 28.0 28.0 38.0 5.0-13.0 35.0 90.0 34.0

--

1.20

44.0

0.001 0.002

0.05 -

2.7 --

Vegetables Bean Beet Cabbage Carrot Lettuce Onion Potato Sweet corn (grain) Tomato Fruits Apple Orange

Cereals Barley Rice Rye Wheat

Grasses Soil

0.1-0.2 0.19 0.64 0.59 0.40-3.00 5-41

Values are expressed in /zg/g fresh weight (FW), dry weight (DW), or ash weight (AW).

0.7 1.5 1.2 4.8 5.3 4.5 3.0 2.5 0.5

0.2 1.4

(12) (110) (7) (10) (280330) <1-7

0.2 0.3 1.5 0.4 0.1 4.5 3.8 (2.6) 1.2

0.9 1.4

(10) (8) (15) (12) (503410) 0,94.3%

As*

(3.4) (1.0) (I.3) (0.8) (4.526) <20150

(8.3) (9.4)

(13) (2.5) (14) (9.9) (1.3) (10.0) 6.1 (1.5) (6.0)

B

262890

(5.5) (2.3) (6.9) (8.5) (100)

0.03 0,17

0.4 0.4 1.3 0.14 0.5 (12.0) 0.7 (0.3) 0.2

Ba

0.02

0.02 0.05 0.02 0.05 0.11 0.01 0.02 0.007

Cd

(2.1) (1.9) (6.4) (6.0) (17119) 7-50

(0.02) (0.08) (0.07) (0.03) (0.080.27) 0.4

(0.002) 0.008 (0.04) 0.002

(15) (14) (4) (4) (20) 14 (4) (1) (10)

Br

0.3 0.4

1.0 6.0 3.0 3.0 7.0 3.0 3.0 6.4 3.2

Co*

2-50

(20) (12) (20) (14) (8)

Values are expressed in /~g/g fresh weight (FW) or dry weight (DW). *ng/g.

Soil

Vegetables Bean Beet Cabbage Carrot Lettuce Onion Potato Sweet corn Tomato Fruits Apple Orange Cereals Barley Rice Rye Wheat Grasses

AI

Elemental content, ~tg/g, (FW) or (DW)

(0.01) (0.01) (0.2) (0.2) (0.10.35) 7-1500

0.003 0.004

0.008 0.015 0.0013 0,018 0.008 0.002 0.018 0.037 0.004

Cr

(5.5) (2.8) (3.7) (6.7) (6.416.2) 3-300

0.03 0.11

1.7 0.9 0.3 0.22 0.11 0.7 0.4 0.6 0.7

Cu

Table 2 Reported elemental levels for 'unncontaminated' vegetables, cereals, fruits, grasses and soil

(88) (60) (65) (80) (70300) 2.2%

0.6 2.0

0.7 1.5 2.4 0.8 0.3 3.3 3.0 4.3 3.0

Fe

<5100

(1.6) (1.4) (6.6) (3.6) (0.2-3)

(0.05) (0.2)

(0.1) (0.6) 0.5 0.2 (0.3) (0.06) (0.2) (0.05) (0.02)

Li

(5.0) (4.5) (8.0) (9.0) (17300) 203500

0.01 0.05

2.3 0.5 1.1 0.1 0.1 0.6 0.7 0.9 0,9

Mn

0.04 0.04 0.02

0.05 0.045 0.042

(0.7) (0.5) (0.6) (0.4t (0.31.4) 0.8-3.3

<5150

(0.14) (0.11) (0.40) (0.38) (0.13)

0.003 0.003

0.06

0.024

0.0018 0.014

0.02 0.02 0.05 0.02 0.01

Hi

0.09 0.08 0.099 0.08 0.005

Mo

(4) (4) (6) (5) (44130) <20120

(50) (14)

(51) (45) (12) (40) (14) (32) (60) (3) (5)

Rb

(20) (40) (40) (60) (1140) 0.051.0

1.1 3

(28) 8 8 5.3 1.6 (42) 10 (11) (8)

Se*

(48) (50) (60) (60) (24219) 7-1000

(0.9) (0.5)

(18) (40) (45) (25) (74) (50) (2.6) (0.4) (9)

Sr

(7) (7) (10) (10) (180420) 0.7-98

0.01 0.04

3.4 2.6 8 8.8 5.3 10.0 1.6 0.2 0.5

V*

(20) (30) (19) (30) (30120) 13-300

0.03. 0.09

0.5 0.1-11.7 2.2 0.3 (25) 2.6

0.6-2.28

0.3-28 0.8

Zn

,_.a

?

--,4

r.-.

e~

312

N. L Ward, J. M. Savage / Sci. Total Environ. 146/147 (1994) 309-319

1982); and potato tubers in Canada, 350-425 #g/g (DW) (Warren, 1975). Increased Pb values have also been measured along busy roadsides. These studies showed that inedible parts of most crops (corn husk, wheat and oat chaff, soybean hulls, and the outer leaves of cabbages) had levels of 2-3-fold greater near motorways than in background areas (Prince, 1957; Warren and Delavault, 1960; Motto et al., 1970; Schuch and Locke, 1970; Ter Haar, 1970; Ward et al, 1975). In most cases, Pb contamination of the edible parts was negligible except in the case of lettuce leaves (Ter Haar, 1970). Because food is the main source of normal lead intake by people and because human food is derived directly or indirectly from plants, the effect of airborne lead contamination alongside UK motorways is very important. This is particularly supported by the fact that a significant number of domestic garden allotments are located alongside busy roadways, especially in high-density population areas. Apart from lead, very little attention has been paid to the possibility of contamination from other metals derived from motor vehicle activities. Table 2 lists reported elemental values for 'uncontaminated' vegetable and soil samples. Lagerwerff and Specht (1970) reported the presence of Cd, Ni, Zn and Pb in soils and grasses at roadsides. Similar studies have been reported by David and Williams (1975) and Ward et al. (1977). Recently Ward (1989) reported eleven elements - - V, Cr, Mn, Co, Ni, Cu, Zn, Br, Cd, Ce, and Sm - - were elevated in vegetation and surface soil samples collected alongside various UK motorways. Moreover, metal levels related to changes in mean traffic densities. To date there has been no major investigation of the possible metal contamination of vegetables or herbs grown in domestic or commercial areas alongside UK motorways. In November 1986, the northern section of the London Orbital Motorway (M25) was opened. At this time the content of Pb added to UK petrol was 0.15 g/l. By 1989 only a limited number of vehicles using this motorway (with typical daily traffic densities of - 120 000 vehicles) were using non-leaded fuels. This study reports the metal levels measured in 12 common vegetables, 2 fruits, 6 herbs, and local pasture spe-

cies collected from a site alongside the M25. Further metal values are presented from background or 'non-contaminated' areas. 2. Materials and methods

At Waltham Cross (on the northern perimeter of the M25) near Junction 25, a sampling area was established on a commercial agricultural garden located on the London (south) side of the motorway - - a distance of 30 m from the carriageway and at an elevation of - 10 m. A sparse area of 3m high birch and conifer trees surrounded the garden area. The edible portions of various plant materials (bean, broccoli, cabbage, cauliflower, lettuce, marrow, onion, parsnip, spinach, sprouts, sweet corn, and tomato), fruits (grape and strawberry), herbs (garlic, lemon balm, marjoram, mint, rosemary, and tarragon), local pasture or grass and surface soil (top 0-2 cm from the garden) were collected. In order to evaluate elemental levels for 'noncontaminated' materials, a background site was chosen within the North Yorkshire Dales National Park. This consisted of various agricultural fields and a local private garden located at a distance of > 30 m from a small road and surrounded by a 2m high stone wall. The former was more than 1 mile (1.6 km) from any roadway and the latter had a typical daily traffic density of < 10 vehicles (with a much more significant number of horses and hikers). Plant material (bean, beetroot, broccoli, cabbage, carrot, cauliflower, celery, leek, lettuce, marrow, onion, parsnip, potato, spinach, spring onion, sprouts, swede, sweet corn, and tomato); fruits (apple, gooseberry, raspberry, and strawberry); herbs (marjoram, mint, parsley, and rosemary); various grasses (flatweeds, ryegrass, and white clover); and surface soils (top 0-2 cm) were collected. Various cereals were also taken just prior to harvest from the agricultural fields; namely barley, rice (wild), rye and wheat. Random collection of material ( - 5-15 g fresh weight) was undertaken from plants located within a 0.25-m 2 grid area and placed into a clean polypropylene self-sealing bag. Surface soil fractions were taken by scraping the top 2 cm surface directly into a polypropylene bottle and sealing.

4-0.7 44.7 4-3.0 141

4-8 1214

4- 0.8 42.0 4-2.0 148

4-12 1240

±4

19 4-4 14

±4

±2

23 ±3 15

±0.1

1.6

49 4-5

± 117

4-15 1206

4-0.6 39.6 4-4 156

±2

16

49 ±11 2.3 ±0.3

4-109

4-23 1267

±0.3 41 ±4 149

17 900 4-1100 0.11 ±0.03 2.2

467 4-42

16

25

57

1206

46.6

10.3 ±1.4 60.1 ±4.7

±80 648 ±37 3.04 ±0.31

4-145 640 4-20 3.4 ±1.0 11.5 4-2.0 63 ±5

1407

1410

±0.3 2.9 ±0.3 202 4-15

4-0.7 3.4 ±0.4 208 ±22

2

0.119 ±0.006 2.4

0.147 ±0.011 1.9

0.10

4110 ±200

4089 ±194

4-7

4-14 17 500

538

520

448

11.7 ±1.9 64 4-t2

±I60 668 4-21 2.98 ±0.31

1420

±0.5 2.8 4-0.1 207 ±20

0.12 4-0.02 2.0

4205 ±315

±12

545

ICP-MS LA-ICPMS

ICPOES

Cert/ Lit d

NIST 1575 Pine Needles

62 ± 6

4-172 672 ±17 2.87 ± 0.72

1372

4-0.8 2.8 ±0.1 203 ±8

0.127 ±0.008 2.1

4089 ±191

4-14

570

NAA

61

10.~

3.5

675

1400

200

3

2.6

<0.5

4100

545

Cert/ Lit

7.8 ±2.0 59.3 4-1.2

±130 233 ±27 1.4 ±0.3

7150

±0.9 11.7 ±0.5 650 ±30

2.5 ±0.3 3.4

31 450 ±1340

4-30

1250

ICPOES ±27 30 890 ± 600 3.1 ±1.1 3.5 ±0.8 12 ±1 660 ±20 6590 ±450 271 ±11 1.0 ±0.7 5.0 ±1.3 61.8 ±4

± 14 31 040 4- 745 3.0 ±0.2 4.4 ±0.7 11.4 ±0.7 674 4-19 6870 ±160 241 ±8 1.4 ±0.6 5.8 ±1.1 62.9 ±4

~ ±7

±0.7

4-4 1.9

±145 245

6965

±1 674 ±14

±0.5 12

±0.7 3.9

4- 870 3.2

4-28 31 450

62

6.3

1.8

238

7000

b90

I1

4.5

3.0

30 000

1200

1097

1197

1190

Cert/ Lit

ICP-MS LA-ICP NAA -MS

NIST 1573 Tomato Leaves

T e n repticates of - 0 . 2 g m a s s o f R M material; m e a n 4- S.D. alnductively coupled p l a s m a - s o u r c e m a s s s p e c t r o m e t r y ( c o n v e n t i o n a l solution p n e u m a t i c nebulisation). bLaser-ablation inductively c o u p l e d p l a s m a - s o u r c e m a s s s p e c t r o m e t r y (for direct solids analysis). CNeutron activation analysis. dCertified or literature reference values.

Zn

4-0.2

24 4-6 16

±0.2

1.4

1.2

Ni

Pb

4-132

51 4-6

±235

55 4-4

Mn

Mg

Fe

Cu

Cr

Cd

17 650 18 950 4-890 4-1300 0.08 0.14 4 - 0 . 0 1 4-0.04 2.1 1.8

18 050 4-1340 0.11 4-0.04 2.7

Ca

460 4-50

439 4-23

460 4-52

AI

LA-ICP- NAA c MS b

ICPMS ~

ICPOES

BCR62 Olive Leaves

Quality control m e a s u r e m e n t s o f v a r i o u s i n t e r n a t i o n a l reference materials; values r e p o r t e d in/~g/g dry weight

Table 3

ICPMS 91.4 ±2.6 30 600 ± 400 0.025 ±0.007 0.74 ±0.11 17.2 ±1.8 94 ±4 5820 ± 270 25 ±3 0.64 ±0.11 12.9 ±2.0 27.2 4-4.1

ICPOES 86 ±10 31 250 ± 500 0.04 ±0.01 0.84 ±0.11 14.7 ±2.5 86.9 ±6.7 5550 ± 520 19.7 ±2.0 0.71 ±0.13 14.9 ±2.2 23.5 ±3,0

16.1 ±1.7 26 ±2.7

±4 0.74 ±0.15

± 460 31

±4 10i ±5 5940

0.7 ±0.3 19

± 680 0.03 ±0.01

±3.7 29 850

90

-MS

28.4 ±3.5

±2.9 0.8 4-0.1

± 320 24.1

±1.8 91 ±11 5910

0.84 ±0.08 17.1

± 480 0.04 4-0.01

±2.7 31 500

98.4

LA-ICP NAA

N1ST 1572 Citrus Leaves

29

131

0.6

23

5800

90

16.5

0.8

0.03

31 500

92

Lit

Cert/

I

4~

"-4

g

4.

3.

%

314

N.I. Ward, J.M. Savage/Sci. Total Environ. 146/147 (1994) 309-319

All vegetable material (weighed immediately on return to the laboratory) was agitated in double distilled water for 5 min to remove surface dust (especially edible root crops); dried for 3 days at 50°C, weighed (dry weight), dry-ashed at 480°C for 18 h, and the homogenized ash ( - 0 . 1 g) dissolved in 5.0 ml of 1% AnalaR HNO3. Soil samples were weighed, then dried at 50°C for 3 days, sieved through a 60-mesh sieve and a 0.1-g fraction was wet-digested using 10 ml of 50:50 (v/v) concentrated HNO3 and H F mixture; and the residue redissolved in l0 ml of 1% AnalaR HNO3. Quality control measurements were undertaken using four international reference materials (RM) in order to establish the degree of analytical precision and accuracy using the various sample dissolution procedures. The RMs were B C R : C R M 62 Olive Leaves, and N I S T (formerly NBS) SRM 1575 Pine Needles, N I S T 1573 T o m a t o Leaves, and NIST 1572 Citrus Leaves. Ten replicates of - 0 . 2 g dried weight of material were used. Interanalytical method comparison was also undertaken using ICP-OES, ICP-MS: both conventional solution pneumatic nebulisation and laserablation of solids (Ward, 1988), and neutron activation analysis (NAA). Due to instrument availability all 'noncontaminated' material was analysed by ICP-MS at the University of Surrey (utilising the enhanced sensitivity and linear range of detection capabilities) of this technique and the remaining samples by ICP-OES at Kingston Polytechnic. 3. Results and discussion

The elemental mean and standard deviation of 10 replicate analyses of the four reference materials are shown in Table 3. For the eleven elements listed there is a relatively good order of precision obtained using ICPOES. Improved values for ICP-MS are due primarily to the overall enhanced analytical capabilities of this technique and the fact that the ICP-OES system had in-run instability problems during the period of analysis, resulting in a degree of reduced signal reproducibility. In general precision levels of < + 1-10% were obtained for most elements. Comparison of data between the various

analytical methods is in very good agreement. Where certified or literature values are provided, overall levels of accuracy for the elemental values measured in this study are very good. These results Table 4 Lead content of vegetables, fruits, cereals, herbs, agricultural grasses and surface soils from background areas analysed by ICP-MS Lead content, #g/g FWa Vegetables

Bean Beetroot Broccoli Cabbage Carrot Cauliflower Celery Leek Lettuce Marrow Onion Parsnip Potato Spinach Spring onion Sprouts Swede Sweet corn Tomato

0.02-0.13 : 0.07 0.014-0.080 : 0.04 0.014-0.037 : 0.030 0.029-0.095 : 0.08 0.015-0.125:0.0 0.04-0.21:0.06 0.014-0.069 : 0.04 0.04-0.35 : 0.14 0.001-0.024 : 0.006 0.001-0.007 : 0.004 0.04-0.34 : 0.18 0.02-0.17 : 0.10 0.02-0.15:0.08 0.03-0.18:0.08 0.01-0.08 : 0.04 0.01-0.08 : 0.04 0.02-0.14:0.10 0.002-0.021:0.008 0.004-0.008 : 0.007

Fruits

Apple Gooseberry Raspberry Strawberry

0.001-0.002 : 0.001 0.0008-0.002 : 0.001 0.001-0.005 : 0.003 0.001-0.005 : 0.003

Cereals

Barley Rice Rye Wheat

0.004-0.012 0.002-0.009 0.004-0.024 0.003-0.018

: 0.006 : 0.005 : 0.011 : 0.010

Herbs

Marjoram Mint Parsley Rosemary

0.02-0.18 : 0.11 0.01-0.16 : 0.09 0.01-0.16:0.12 0.008-0.14:0.09

Grasses

Flatweeds Ryegrass White clover Surface soilsb

0.02-0.14 : 0.08 0.04-0.34 : 0.16 0.01-0.18 : 0.07 1.4-14.6:11.8

Values expressed in #g/g fresh weight (FW). aRange : mean, (n _> 20). bpH range, 5.2-8.3.

1.40 0.80 1.20 1.45

0.40 0.70 0.45 0.70

0.74 0.68 0.42 0.40

(1.7)

6.6

8.4 10.7 9.3

2.4 3.5 4.1 3.0

1.0 1.5 1.4 2.0

0.1 0.4 0.4 0.4

0.8 2.3 2.9 3.4 2.3 1.5 1.8 1.4 2.5 1.0 2.5 2.5 4.0 4.5 3.0 2.0 2.7 1.0 0.4

As a

9.0

5.8 6.7 4.7

1.4 1.3 0.8 1.4

0.3 0.1 0.2 0.1

0.4 0.3 0.4 0.4

0.4 0.2 0.8 1.0 0.8 0.7 0.6 1.2 0.2 0.3 1.4 1.2 0.7 0.9 1.1 1.0 1.4 0.2 0.4

B

490

8.4 2.4 4.6

1.8 2.2 1.4 1.4

0.4 0.2 0.8 1.1

0.06 0.07 0.10 0.07

0.8 1.4 0.7 1.3 0.4 1.8 1.4 0.7 0.4 0.2 0.8 1.1 1.4 0.7 0.8 0.7 2.4 0.2 0.2

Ba

24

1.8 2.7 1.4

1.7 2.7 1.8 1.4

0.14 0.22 0.16 0.24

0.008 0.014 0.010 0.008

0.7 1.8 0.3 0.4 0.3 1.2 0.7 1.1 0.8 0.2 1.8 1.4 2.7 1.0 0.8 0.7 1.4 0.2 0.4

Br

0.65

0.008 0.020 0.014

0.02 0.4 0.008 0.011

0.004 0.006 0.006 0.004

0.006 0.008 0.010 0.010

0.04 0.09 0.02 0.02 0.06 0.02 0.03 0.04 0.05 0.02 0.11 0.04 0.02 0.03 0.~ 0.008 0.04 0.004 0.008

Cd

8.3

2.4 1.6 4.5

4.6 8.3 11.4 7.6

2.4 1.8 3.4 2.8

0.5 1.1 1.0 0.8

0.8 3.4 1.4 3.0 4.5 3,2 2.1 4.6 4.5 1.3 6.0 4.5 4.0 3.5 6,0 2.7 5.8 2.7 3.0

Co a

45

0.045 0.104 0.044

0.046 0.072 0.080 0.022

0.002 0.004 0.004 0.008

0.004 0.007 0.006 0,008

0.~6 0.004 0.014 0.018 0.022 0.014 0,046 0.012 0.033 0.~8 0.~7

0,020

0.013 0.020 0,014 0.008 0.014 0.018 0.014

Cr

18

0.60 1.45 0.72

1.45 0.80 1.10 1.05

0.45 0.22 0.47 0.75

0.08 0.07 0.14 0.34

2.6 4.1 0.8 0.4 2.4 1.3 1.0 0.8 0.4 0.3 2.4 1.4 1.8 1.4 2,2 0.8 1.7 0.4 0.4

Cu

(2.2)

8.4 14.7 9.0

8.9 14.7 7.2 6.0

4.5 4.1 6.0 4.5

0.8 1.4 0.9 1.1

1.7 2.4 1,2 1.8 3.4 1.4 1.4 2.7 0.4 0.1 2.9 1.8 3.7 2.8 1.9 2.0 3.4 1.4 2.0

Fe

12.4

0.045 0.022 0.017

0.025 0.018 0.033 0.024

0.014 0.020 0.014 0.026

0.001 0.004 0.004 0.004

0.008 0.014 0,~7 0.025 0,048 0.~8 0.~8 0.~7 0.004 0.~3 0.045 0.027 0.045 0.022 0,034 0.027 0.009 0.005 0.002

Li

Values expressed in #g/g, fresh weight except (i) ang/g; and (ii) numbers in brackets, which are percentages.

Surface soils

Flatweeds 8.40 Ryegrass 2.14 White clover 2.50

Grasses

Marjoram Mint Parsley Rosemary

Herbs

Barley Rice Rye Wheat

Cereals

Apple Gooseberry Raspberry Strawberry

Fruits

Bean 0.14 Beetroot 0.36 Broccoli 0.42 Cabbage 0.29 Carrot 0.34 Cauliflower 0.40 Celery 0.22 Leek 0.29 Lettuce 0.08 Marrow 0.06 Onion 3.29 Parsnip 0.64 Potato 1.90 Spinach 1.40 Spring onion 1.20 Sprouts 0.30 Swede 1.80 Sweet corn 0.20 Tomato 0.74

Vegetables

AI

Elemental content, t~g/g [FW]

490

1.40 0.82 1.42

1.72 1.06 3.45 1.40

0.14 0.12 0.42 0.35

0.04 0.03 0.07 0.04

1.4 2.7 1,8 1.4 3.9 1.0 1.0 3.4 0.8 0.2 4.1 2.9 3.7 1.4 3.0 1.4 2.2 0.4 0.2

Mn

1.5

0.040 0.022 0.045

0.040 0.050 0.075 0.040

0.014 0.020 0.040 0.035

0.002 0.008 0.008 0.008

0,04 0.14 0.02 0.07 0.12 0.04 0.08 0.12 0.008 0.004 0.04 0.07 0.08 0.06 0.12 0.04 0.09 0.02 0.04

Mo

40

0.02 0.04 0.04

0.08 0.04 0.04 0.04

0.04 0.02 0.02 0.03

0.008 0.008 0.008 0,008

0.08 0.06 0.04 0.09 0.14 0.04 0.04 0.08 0.02 0.01 0.14 0.08 0.08 0.04 0.08 0.04 0.04 0.01 0.01

Ni

Table 5 Elemental content of vegetables, fruits, cereals, herbs, agricultural grasses and surface soils from 'bound' areas analysed by ICP-MS

47

4.9 2.7 1.8

1.4 2.7 2.4 4.5

0.4 0.4 0.7 0.4

0.2 0.3 0.3 0.4

2.1 3.5 1.4 3.0 4.5 1.4 1.8 2.0 0.8 0.4 3.4 4.6 4.5 2.0 1.8 0.8 2.4 0.3 0.4

Rb

0.9

3.0 4.0 2.7

4.5 6.0 3.2 8.4

1.8 2.2 2.3 2.7

1.1 0.7 0.7 0.7

2.7 3.0 2.9 4.5 5.9 1.9 2.0 2.0 2.0 1.0 6.0 2.0 2.0 3.0 2.0 1.4 2.0 0.8 0.8

Se a

450

9.4 8.3 7.2

8.0 6.0 4.2 6.8

4.5 3.0 6.0 4.5

0.7 0.5 0.5 0.4

1.1 2.4 4.5 4.7 6.8 4.7 3.0 4,9 3.5 2.0 4.8 4.7 3.3 4.9 4.8 4.0 3.3 1.4 1.4

Sr

71

4.0 2.0 2.1

12.0

11.7 9.3 14.9

0.8 0.7 1.4 1.4

0.04 0.04 0.04 0.04

0.4 0.8 1.0 0.8 1.4 2.0 1.4 2,0 0.8 0.8 3.5 1.0 2.1 6.0 4.5 2.0 1.8 0.7 0.4

Va

96

2.9 4.6 3.0

8.9 4.6 7.2 I 1.3

1.9 3.0 1.4 2.7

0.08 0.14 0.07 0.11

1.4 1.6 1.2 2.9 1.5 2.0 1.8 1.4 0.7 0.3 2.7 2.4 1.0 1.9 1.4 0.8 2.2 1.4 0.7

Zn

,j,

..q

-n

316

N.1. Ward, J.M. Savage/Sci. Total Environ. 146/147 (1994) 309-319

validate both the various sample digestion and dissolution steps used and provide a degree of confidence in comparing results obtained by two analytical methods, namely ICP-OES and ICP-MS. The lead content of 'vegetables', fruits, cerealsl herbs, agricultural grasses, and surface soils taken from background areas and analysed by ICP-MS are shown in Table 4. Values are expressed in/~g/g fresh weight (FW). Typical lead values range from 0.001 to 0.350 /xg/g for vegetables, 0.0008-0.005 /~g/g for fruits, 0.002-0.024 /~g/g for cereals, 0.008-0.180 /~g/g for herbs, 0.01-0.34 /~g/g for grasses, and 1.4-14.6 /zg/g for surface soils. Overall lead magnitude is greater for grasses > herbs > vegetables > cereals > fruits. For vegetables the lowest Pb levels are for marrow < lettuce < tomato < sweet corn (typically -0.001-0.021 /~g/g). 'Green' leaf material (sprouts, cabbage, etc.) are generally 0.02-0.10 #g/g Pb, with root vegetables the highest, 0.02-0.125 /zg/g Pb (especially carrot). Whilst various washing procedures were undertaken to remove surface soil contamination, these values may reflect the existence of Pb uptake from soil. The highest vegetable Pb values are for leek and onion (-0.35 #g/g). All background values measured in this study are in good agreement with the limited number of reported literature values (Table 1). The other elemental values (for AI, As, B, Ba, Br, Cd, Co, Cr, Cu, Fe, Li, Mn, Mo, Hi, Rb, Se, Sr, V and Zn) measured by ICP-MS for the corresponding 'background' samples are also shown in Table 5. Values are expressed in either t~g/g or in t~g/g fresh weight (FW). Most elements show a degree of variation in their magnitude for the vegetable material analysed in this study. Various elements - - As, Co, Se and V - - are typically at levels of ng/g (FW). There is a vast difference in plant/soil ratios with elements such as AI and Fe (both being at percent levels in soil) typically 0.00005; for Cu and Zn -0.025; and B -0.1. From Table 4, a plant/soil ratio of 0.01 is typical for Pb. Table 6 reports the mean lead content (/~g/g FW) of vegetables, fruit, herbs, grass, and surface soil collected from a site adjacent to the M25. Values are expressed unwashed and washed portions,

with a corresponding calculated percentage removable by washing. Overall, there is a significant elevation in lead content with respect to unwashed plant material. The airborne nature of Pb deposition or soil-related burden is reflected for both aerial and root-based plants, with 40-80% of the metal content removable by washing. Even supposedly enclosed vegetable components (i.e. bean) show some degree of surface Pb contamination. Compared with background Pb values (Table 4) only the low Pb-burden washed vegetables (lettuce and tomato) and surface soil reflect any increases in Pb content; 0.006 to 0.02 and 11.8 to 25 /~g/g (background to motorway site), respectively. All other plant material washed portions are similar to background Pb levels. Clearly, whilst

Table 6 Mean lead content (#g/g, fresh weight) of vegetables, fruits, herbs, grass, and surface soil collected adjacent to the M25 Mean lead content,/~gg-I FW

Vegetables Bean Broccoli Cabbage Cauliflower Lettuce Marrow Onion Parsnip Spinach Sprouts Sweetcorn Tomato Fruit Grape Strawberry

Unwashed

Washed

Percent removable by washing~

0.034 0.143 0.122 0.123 --0.475 0.101 0.112 0.101 -0.083

0,029 0.028 0,045 0,048 0,013 0,028 0.088 0.065 0.025 0.053 0.048 0.021

15 80 63 61

0.212 0.447

0.039 0.053

82 88

0.150

49

0.165 0.142 0.037

42 45 42

Herbs Garlic 0.059 Lemon balm 0.293 Marjoram 0.216 Mint 0.100 Rosemary 0.282 Tarragon 0.260 Grass 0.064 Surface soil 24.5 b apercent removable Unwashed] x 100. bFresh weight only.

29 36 78 48 75

by washing = [(Unwashed - Washed)/

2.48

1.64

0.26

0.53

--

--

2.87

4.74

7.79

0.46

--

Cabbage

Cauliflower

Lettuce

Marrow

Onion

Parsnip

Spinach

Sprouts

Sweet corn

Strawberry

9.89

0.82

Rosemary

Tarragon

Symbols."

108.4

(3.2%)

174.0

357.0

238.1

320.7

--

324.9

152.5

163.4 ( 15,1 )

*

*

0.069

308.7

*

--

0.039

*

0.004

*

--

0.02

*

*

0.02

--

*

0.02

0.018

0.03

*

U

212.4

320.5

298.3

297.1

55.4

128.5

100.4

29.9

28.5

94.9

52.3

71.4

65.3

41.3

62.4

236.8

198.8

141.3

99.7

W

Cd

*, below determination

3.09

0.79

3.55

0.82

1.36

0.98

0.10

0.79

145.3

34.3

0.82

--

0.37

109.1

59.9

73.3

80.5

--

--

343.8

368.3

230.4

0.25

0.19

1.73

0.17

0.15

0.16

, no sample;

(1.1%)

1.19

Mint

Surface soil

--

Marjoram

4.73

1.89

Lemon balm

Grass

--

Garlic

Herbs

1.07

2.64

Grape

Fruits

Tomato

0.49

0.31

0.08

0.36

Broccoli

0.20

U

W

U

Bean

Vegetables

Ca

AI

Elemental content, txg/g [FW]

(54)

0.26

0.96

0.59

0.71

0.44

0.76

--

0.37

0.24

--

0.43

0.17

0.36

0.18

--

--

0.64

0.59

0.54

0.32

U

0.22

0.47

0.33

0.48

0.47

0.15

0.21

0.21

0.07

0.06

0.31

0.12

0.21

0.13

0.09

0.16

0.35

0.29

0.09

0.17

W

(125)

*

0.070

*

*

--

0.056

0.002

*

*

-

0.029

*

0.019

0.028

--

0.033

0.027

0.037

*

U

Cr

*

*

*

*

0.003

*

*

*

*

*

0.002

*

*

*

*

0.001

*

*

*

*

*

W

124)

0.54

1.27

1.28

1.14

--

1.15

0.12

0.49

0.79

0.33

1.18

1.48

--

0.60

0.46

0.88

1.78

U

Cu

0.43

0.98

1.10

1.00

0.69

1.07

0.24

0.09

0.37

1.35

0.45

0.64

0.28

1.09

0.75

0.48

0.14

0.40

0.39

0.60

1.14

W

(2.4'%,)

1.77

2.76

16.86

2.14

5.36

5.42

2.41

1.85

1.72

16.46

7.77

5.98

--

1.46

3.23

1.63

2.47

U

Fe

(2.1%)

15.1

81.5

76.3

49.4

98.4

72.2

42.9

43.9

-

21.4

27.0

82.7

32.5

--

18.7

20.7

42.0

43.9

U

Mg

11.6

64.1

65.6

48.4

98.3

90.1

33.9

50.3

35.5

28.4

51.6

16.8

25.6

57.8

28.6

28.2

17.1

18.4

18.8

20.1

42.3

W

W. washed.

1.34

2.12

6.06

2.09

3.53

3.02

1.14

1.98

1.08

0.88

1.29

0.56

1.23

1.62

1.94

0.52

2.10

0.57

0.83

1.02

1.14

W

l i m i t (i.e. d e t e c t i o n l i m i t x d i l u t i o n f a c t o r ) ; U , u n w a s h e d ;

*

*

*

*

*

*

*

*

*

*

*

*

*

*

*

*

*

*

*

*

*

W

Ce

Mean elemental content (/~g/g, fresh weight) o f vegetables, fruit, herbs, grass species, and surface soil grown adjacent to the M 2 5

Table 7

(540)

2.04

2.87

1.45

0.64

2.15

3.83

0.27

0.15

-

0.35

0.64

0.96

0.37

--

0.15

0.54

0.57

0.38

U

Mn

1.29

0.23

0.88

0.44

1.33

1.92

0.33

1.71

0.20

0.08

0.69

0.14

0.20

015

0.34

0.13

0.21

0.14

0.27

0.18

0.21

W

,

__

(58)

,

0.060

,

,

0.105

0.003

,

0.06

,

0.021

_

__

0.065

0.022

0.087

0.037

U

Ni

,

0.009

,

,

0.022

0.043

0.007

*

,

,

*

,

*

,

,

,

*

*

0.004

*

W

35.6

89.3

34.9

31.7

38.7

14.9

25.9

26.8

10.2

28.9

12.3

~8 4

23.9

35,8

61.4

70.4

15.7

8.8

29.6

W

101.15 49.2

123.8

145.7

64.2

--

84.7

--

89.3

88.7

86.9

--

48.4

7t.2

73.3

161.7

--

37.1

20.5

153.3

U

Si

(121 )

0.60

3.74

0.79

0.44

--

2.43

--

1.06

1.09

0.95

0.89

0.93

0.82

3.13

--

--

0.80

1.39

0.94

U

Zn

0.47

2.48

0.77

0.32

1.69

2.24

1.09

0.49

0.72

0.45

1.07

0.23

0.49

0.38

0.47

0.63

0.34

0.69

1.29

0.89

W

I

,..q

r.-,.

e~

318

N.L Ward, J.M. Savage / Sci. Total Environ. 146/147 (1994) 309-319

surface soil reflects a degree o f lead contamination as a result o f m o t o r vehicle activities, the location o f this commercial gardening site ( - 30 m from the motorway) with its surrounding perimeter o f trees shows that all the plants analysed reflect no significant increases in absorbed Pb. Moreover, all vegetables, fruit, and herbs have Pb levels for their washed portions well below the E U guideline o f 10 #g/g (FW). However, these results clearly show the significant reasons for carefully washing foodcrops grown near transportation activities, as highlighted for the two fruit varieties. Grape shows an 82% Pb burden as surface dusts directly related to airborne sources (the fruit was located at a typical height o f - 1 . 5 m above the ground) whilst strawberry shows a similar Pb burden, - 8 8 % , through both airborne dust deposition, and via soil particle 'splash' during periods o f heavy precipitation (supported by the fact that the associated surface soil u p o n which the fruit is located has increased Pb levels), The mean elemental levels (/~g/g FW) for the same plant and soil samples collected at a site adjacent to the M25 are shown in Table 7. Measurements were made by ICP-OES. Values are quoted as both unwashed (u) and washed (w) portions. There appears to be no direct evidence that the presence o f m o t o r vehicle activities some 3 0 - 5 0 m away has resulted in enhancement of metal levels in the washed portion o f foodcrops grown at this site. However, there is a significant increase in metal content for the surface soils c o m p a r e d with values for background soils (Table 5). The respective soil values for b a c k g r o u n d and m o t o r w a y sites are: AI, 1.1-1.7%; Cd, 0.65-15.1%; Cr, 4 5 - 1 2 5 #g/g; Cu, 18-24 t~g/g; Fe, 2.2-2.4%, Mn, 4 9 0 - 5 4 0 ~tg/g; Ni, 40-58/zg/g; and Zn, 96-121 #g/g. Whilst this may only reflect variation in the 'natural' chemistry o f the respective soil types from both sites (as indicated by AI and Fe), the remaining metals are known to be associated with the wearand-tear o f m o t o r vehicles (Ward, 1988, 1989). Moreover, the difference observed between elemental levels for unwashed and washed portions is suggestive of contamination from soil particles or dusts. This is supported by the fact that a large proportion of metal is removable by washing from

root-derived vegetables compared with aerial vegetables. However, in conclusion, the enhanced existence o f these other metals in surface soils suggest that there is the potential o f m o t o r vehicle activities changing the overall magnitude o f soil metal chemistry at sites along motorways. However, like that for lead, provided care is taken to remove surface dust or soil particles from foodcrops - - especially fruits and herbs - - there appears to be no significant risk to the health o f humans.

4. References David, D.J. and C.H. Williams, 1975. Heavy metal contents of soils and plants adjacent to the Hume highway near Marulan New South Wales. Aust. J. Exp. Agric. Anim. Husb., 15: 414-418. Doelman, P. and L. Haanstra, 1974. Effect of lead on soil respiration and dehydrogenase activity. Soil Biol. Biochem., 11: 475. Faber, A and J. Niezgoda, 1982. Contamination of soils and plants in the vicinity of a zinc and lead smelter. Rocz. Glebozn., 33: 93. Hughes, M.K., N.W. Lepp and D.A. Phipps, 1980. Aerial heavy metal pollution and terrestrial ecosystems. Adv. Ecol. Res., 11: 217. Isermann, K., 1977. Method to reduce contamination and uptake of lead by plants from car exhaust gases. Environ. Pollut. 12: 199. Kabata-Pendias, A. and H. Pendias, 1984. Trace Elements in Soils and Plants. CRC Press, Boca Raton FL. Kobayashi, J., 1971. Air and water pollutions by cadmium lead, and zinc attributed to the largest zinc refinery in Japan. In: D.D. Hemphill (Ed), Trace Substances Environ. Health, vol. 5. University of Missouri, Columbia MO, p. 117. Lagerwerff, J.V. and A.W. Specht, 1970. Contamination of roadside soil and vegetation with cadmium, nickel, lead, and zinc. Environ. Sci. Technol., 4: 583-6. Martin, M.H. and P.J. Coughtrey, 1982. Biological Monitoring of Heavy Metal Pollution. Applied Science Publishers, Essex. Motto, H.L., R.H. Daines, O.H. Chilko and C.K. Motto, 1970. Lead in soils and plants. Its relationship to traffic volume and proximity to highways. Environ. Sci, Technol.~ 4: 231-237. Prince, A.L., 1957. Trace element delivering capacity of 10 New Jersey soil types as measured by spectrographic analysis of soils and mature corn leaves. Soil Sci., 84: 413-418. Roberts, T.M., W. Gizyn, and T.C. Hutchinson, 1974. Lead contamination of air, soil, vegetation, and people in the vicinity of secondary lead smelters. In: D.D. Hemphill (Ed), Trace Substances Environ. Health, vol. 8. University of Missouri, Columbia MO, p. 155.

N.I. Ward, J.M. Savage/Sci. Total Environ. 146/147 (1994) 309-319 Schuch, E.A. and J.K. Locke, 1970. Relationship of automotive lead particulates to certain consumer crops. Environ. Sci. Technol., 4: 324-330. Ter Haar, G. 1970. Air as a source of lead in edible crops. Environ. Sci. Technol., 4: 226-229. Ward, N.I., 1988, Environment analysis using ICP-MS. In: A.R. Dati and A.L. Gray (Eds), Applications of Inductively coupled Plasma Mass Spectrometry. Bladue, Glasgow. Ward, N.I., 1989. Multielement contamination of British motorway environments. In: J-P Vernet (Ed), Heavy Metals in the Environment. CEP Consultants Ltd., Edinburgh, pp. 279-282. Ward, N.I., R.D. Reeves, and R.R. Brooks, 1975. Lead from

319

motor-vehicle exhausts in sweet-corn plants and soils along a highway in Hawkes' Bay, New Zealand. N. Z. J. Sci., 18: 261-267. Ward, N.I., R.R. Brooks, E. Roberts and C.R, Boswell, 1977. Heavy metal pollution from automotive emissions and its effects on roadside soils and pasture species in New Zealand. Environ. Sci. Technol., 11: 917-920. Warren, H.V., 1975. Environmental geochemistry in Canada a challenge. In: Heavy Metals Environment. Toronto. Canada, p. 55. Warren, H.V. and R.E. Delavault, 1960. Observations on the biogeochemistry of lead in Canada. Trans. R. Soc. Canada, 54:11-20.