METAL DISPERSION AND TRANSPORTATIONAL ACTIVITIES USING FOOD CROPS AS BIOMONITORS

The multielement (Al, Ca, Cd, Ce, Cr, Cu, Fe, Mg, Mn, Ni, Pb, Si, and Zn) levels of various common vegetables (bean, broccoli, cabbage, caul iflower, lettuce, marrow, onion, parsnip, spinach, sprouts, sweet com, and tomato); fruits (grape and strawberry); herbs (garlic, lemon balm , marjoram, mint, rosemary and tarragon); local pasture species and su rface soils collected from a commercial garden centre located within a distance of 30 m of the London Orbital Motorway (M25) is presented. C omparative values are given from a background area, namely a domestic garden located in the North Yorkshire Dales National Park area. Analys is was undertaken by inductively coupled plasma optical emission spect rometry (ICP-OES) and inductively coupled plasma-source mass spectrome try (ICP-MS) with quality control assessment using four international biological reference materials; BCR:CRM 62 Olive Leaves, NIST 1575 Pin e Needles, NIST 1573 Tomato Leaves, and NIST 1572 Citrus Leaves. Inter -analytical method comparison is given using two methods of ICP-MS; na mely conventional pneumatic nebulisation of sample solution, and direc t solids analysis by laser ablation; and neutron activation analysis m ethods (NAA). For the elements listed there is a good precision obtain ed by ICP-MS and NAA. In particular levels of < +/- 1-10% (rsd) are ob tained. Comparison of data with certified values and other analytical methods are generally of very good agreement. Lead levels in backgroun d areas ranged from 0.0008 to 0.340 mug/g (fresh weight) for plant mat erial; with the lead magnitude greater for grasses > herbs > vegetable s > cereals > fruits. Measured values are in good agreement with repor ted literature values. The lowest Pb values are for marrow, lettuce, t omato and sweet com samples (approximately 0.001-0.021 mug/g). 'Green' leaf material levels were approximately 0.02-0.10 mug/g (i.e. sprouts and cabbage). Root vegetables contain higher levels, approximately 0. 02-0.125 mug/g (especially carrot), reflecting possible metal uptake f rom soil. The highest vegetable Pb values are for leek and onion (appr oximately 0.35 mug/g). Background values are also provided for ninetee n elements (Al, 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 so me 30 m from the M25 shows only significant increases in Pb for unwash ed plant material and surface soils. Typically Pb levels of 40-80% can be removed by washing plant surfaces resulting in metal levels simila r 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 ed ible plant portions had Pb levels below the EEC guidelines of 1 mug/g (fresh weight). Enhanced levels of other metals (Cd, Cr, Cu, Mn, Ni, a nd Zn) which are possibly related to the wear-and-tear of motor vehicl es, are observed only in surface soils at sites along the M25. There i s no evidence of other metals contaminating foodcrops.