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Previous research has demonstrated that many urban soils are enriched in Pb, Cd and Zn. Culture of vegetable crops in these soils could allow transfer of potentially toxic metals to foods. 'Tanya' lettuce (Lactuca sativa L.) was grown in pots of five urban garden soils and one control agricultural soil to assess the effect of urban-soil metal enrichment, and the effect of soil amendments, on heavy metal uptake by garden vegetables. The amendments included NPK fertilizer, limestone, Ca(H2PO4)2, and two rates of limed sewage sludge compost. Soil Cd ranged from 0.08 to 9.6 mg kg(-1); soil Zn from 38 to 3490 mg kg(-1); and soil Pb from 12 to 5210 mg kg(-1). Lettuce yield on the urban garden soils was as great as or greater than that on the control soil. Lettuce Cd, Zn and Pb concentrations increased from 0.65, 23, and 2.2 mg kg(-1) dry matter in the control soil to as high as 3.53, 422 and 37.0 mg kg(-1) on the metal-rich urban garden soils. Adding limestone or limed sewage sludge compost raised soil pH and significantly reduced lettuce Cd and Zn, while phosphate fertilizer lowered soil pH and had little effect on Zn but increased Cd concentration in lettuce. Urban garden soils caused a significant increase in lettuce leaf Pb concentration, especially on the highest Pb soil. Adding NPK fertilizer, phosphate, or sludge compost to two high Pb soils lowered lettuce Pb concentration, but adding limestone generally did not. On normally fertilized soils, Pb uptake by lettuce was not exceptionally high until soil Pb substantially exceeded 500 mg kg(-1). Comparing garden vegetables and soil as potential sources of Pb risk to children, it is clear that the risk is greater through ingestion of soil or dust than through ingestion of garden vegetables grown on the soil. Urban dwellers should obtain soil metal analyses before selecting garden locations to reduce Pb risk to their children.

Non-pathogenic necroses of potato tubers have been described in the literature since the early 20th century using different names including internal rust spot, internal browning, physiological internal necrosis, internal brown fleck, chocolate spot, internal brown spot and internal heat necrosis. These reports very likely describe either the same, or a collection of similar disorders, falling under the general umbrella of "internal necrosis", with the expression of symptoms being significantly altered via genotype by environment interactions. A number of widely-grown cultivars (e.g. 'Russet Burbank', 'Atlantic' and 'Yukon Gold') are susceptible to internal necrosis, making it an economically significant problem. In Atlantic, this syndrome has been termed internal heat necrosis (IHN) in the eastern United States by several investigators because heat and drought are believed to be important triggers of this condition. Investigators in the midwestern and western United States term this same or similar disorder internal brown spot (IBS). IHN and IBS are an internal physiological disorder of potato characterized by brownish red necrotic patches of parenchymal tissue that typically, though not always, occur along and/or inside the vascular ring. Several reports indicate that IHN is most commonly associated with the vascular ring tissue near the apical end of the tuber, but IHN may form anywhere in the tuber. In many cases, it is very difficult to distinguish between IHN and IBS, and several overlapping environmental factors are associated with each of these disorders. High day and night temperatures early in the growing season, combined with low rainfall, have been shown to increase the frequency and severity of IHN and IBS in several cultivars. Considerable research has examined the role of calcium in ameliorating IHN and IBS expression. Much of this work suggests an important role for calcium in the development of IHN, but other biotic and abiotic factors undoubtedly affect IHN and IBS expression. The biochemistry and genetics behind internal necroses of potato have historically been the leastresearched facets of this problem. Research has shown that enzymes involved in protecting cells from oxidative damage may be involved, and heritability studies have demonstrated that broad-sense heritability for IHN resistance is high. This review seeks to outline previous work on physiological internal necroses of potato due to high temperatures, summarize our current knowledge of IHN, and point to new areas of investigation to develop IHN resistant potato varieties.Resumen Desde comienzos del siglo 20 se han descrito en la literatura unas necrosis no patogénicas del tubérculo de papa, usando diferentes nombres, como herrumbre interna, oscurecimiento interno, necrosis fisiológica interna, punto oscuro interno, mancha chocolate, mancha marrón interna y necrosis interna por calor. Estos nombres parecen describir ya sea la misma enfermedad o una colección de desórdenes similares que caen dentro de la descripción general "necrosis ...

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