Great Britain relies heavily on imported food and Cantell (1977) has estimated that within urban areas there are over 100000 ha of dormant land (i.e. derelict and awaiting development) for which the most fundamentally valuable temporary use is growing food, since such land, Cantell claims, could yield 25 million tonnes of potatoes or 4 million tonnes of carrots annually. The national waiting list for allotments exceeds 100000 and, according to Thorpe (1969), vegetables are grown on nearly all (98-3) urban allotments. Underlying the case for encouraging the agricultural or horticultural use of dormant land is the supposition that, once cleared of junk, urban soils differ little in potential quality from farmland. But this is not necessarily so: Purves &Mackenzie (1970) have reported that vegetables grown in Scottish urban soils were contaminated by trace metals as have Warren, Delavault &Fletcher (1971) in Canada, Beavington (1973) in Australia and Davies (1978) in England. Lead is one of the commonest urban pollutants and many countries set limits on the concentration permitted in food. In Great Britain the present limit is 2 mg/kg (fresh weight) but it is planned to reduce this to 1 mg/kg. Cantell (1977) estimated that in 1971 Inner London contained 841 ha of vacant land which ‘could yield many vegetables; they could supply many housing estates’, while Greater London contained 6536 ha of unused land. This paper reports a reconnaissance investigation of lead pollution in London soils to assess whether urban land is suitable for growing vegetables. Were three public parks (Green Park, Hyde Park and Russell Square) but the remainder were private gardens or municipal allotments, extending as far as 78 km north in rural Hertfordshire. In each garden one bulk sample was taken but at the allotment sites three individual allotments were sampled and analysed separately. The sites were provisionally grouped into three zones, Central London, Greater London and rural and in each of the zones radish (Raphanus sativus L: cultivar, Webb's French Breakfast) was sown, direct in drills, in five gardens. But, because of crop losses, only 12 sites were harvested. In the laboratory soils were air-dried (15-20 C) and gently ground to pass a nylon sieve of 2 mm aperture and then extracted with 0.05 m-(NH4)2-EDTA (15 g soil, 75 cm3 solution, 60 min shake). The edible part of the radish was washed, scraped clean with a stainless-steel knife, sliced, dried at 80 C. ground, ashed at 430 C and the ash taken up in 0.01 m-HNO, Lead was determined by atomic absorption spectrophotometry (air/acetylene flame). © 1979, Cambridge University Press. All rights reserved.
