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DO AMARAL-SOBRINHO (3) ; NELSON MAZUR (3) ;LÚCIA HELENA CUNHA DOS ANJOS (3) ; ALESSANDRA ALEXANDRE FREIXO (4) RESUMONo Brasil ainda não foram definidos os níveis de referência de metais pesados, para avaliação da contaminação do solo. Objetivou-se com este trabalho caracterizar diversos solos brasileiros, em condições naturais, quanto aos teores totais dos metais pesados Cd, Cr, Cu, Fe, Mn, Ni, Zn e correlacionar algumas propriedades do solo com a ocorrência desses elementos. Utilizaram-se 162 amostras de solo, da soloteca da Embrapa Solos (RJ), correspondendo aos horizontes A e B de 81 perfis, das principais classes de solos brasileiros, especialmente os Argissolos (27%) e Latossolos (42%). Os teores totais de metais pesados extraídos com água-régia foram analisados em ICP-AES. À exceção do cádmio, as concentrações médias dos metais estudados foram, em geral, inferiores aos valores médios encontrados na literatura internacional, e inferiores aos valores desses metais considerados tóxicos para as plantas. As amostras de solo foram agrupadas por semelhança, utilizando-se como variáveis os conteúdos de argila, silte, Mn e Fe e CTC (T). Estabeleceram-se as faixas de concentrações das variáveis de solos nos diversos grupos e uma aproximação dos teores naturais dos metais pesados para outras amostras de solos com características similares às de cada grupo. Palavras-chave: teores naturais, análise de agrupamento, componentes principais, água-régia. ABSTRACT NATURAL CONTENTS OF HEAVY METALS IN SOME BRAZILIAN SOIL CLASSESThe heavy metals background levels for evaluation of a possible contamination are still not defined in Brazilian soils. The objective of this study was to measure the content of the heavy metals Cd, Cr, Cu, Fe, Mn, Ni, Zn, in several brazilian soils, under natural conditions, and to correlate some soil properties with the occurrence of these elements. Soil samples from EMBRAPA Soils' (RJ) collection were used (162 in total), corresponding to A and B (or C) horizons from 81 profiles, of the main classes of Brazilian soils, especially Ultisols (Argissolos) -27% and Oxisols (Latossolos) -42%. Heavy metal levels were determined using an ICP-AES, after extraction with acqua regia. The average metal concentrations were below average values reported in the literature for soils found abroad, with exception to Cd. They were also lower than values considered toxic to plants, including Cd values. Soil samples were clustered by similarity, based on the variables content of clay, silt, Mn, and Fe, and value of soil CEC (T value). This enabled separation of the soil samples in seven groups which have distinct ranges for the soil variables contents, which allowed an estimation of the heavy metals background levels for soil samples with characteristics within the range of each group.

To date, neither the method nor diagnostic indices employed in Cuba to evaluate erosion of Red Ferralitic or Ferrasol Rhodic soil in karstic regions has taken into consideration morphogenesis in such geo‐ecosystems or their relationship with erosion, which has led to sequential degradation of the most productive soils in Cuba. We explore the case for considering A + B horizon depth as one of the basic indices for evaluating the severity of erosion. There is no methodology available for estimating the volume of soil lost through karstic absorption forms (dolines). This article forecasts loss of soil cover using a model which estimates losses of 268·52 to 450·52 mm y−1 for future scenarios (periods of 25 and 50 years). A mean loss rate of 1·07 mm y−1 was found in areas cultivated as pastureland during the period from 1986 to 2009, which exceeds the tolerance thresholds proposed by the Universal Soil Loss Equation and the soil formation rates estimated for limestone in Cuba and it is likely there is with a marked tendency for this to increase. These results should be interpreted as a first estimate for setting loss tolerances as there is no similar experience with own data for a more precise definition of the erosion of soil in karstic regions. Copyright © 2012 John Wiley & Sons, Ltd.

Specialized literature continues classifying Red Ferralitic soil, or Rhodic Ferralsol in the World Reference Base, as "not eroded" in spite of the gradual degradation of the most productive soils in Cuba. Depth of Red Ferralitic soil has traditionally been the dominant criterion for estimating ancestral erosion rates. However, this did not take karst erosion into consideration. This new approach considers the influence of karstic morphogenesis on soil erosion using the amount of karst formation as a diagnostic index for evaluating soil erosion in karst regions. The potential and current erosion indices were mapped as medium and high using the CORINE and EVERC methodologies. Quantitative soil losses of as much as 13.71 t ha −1 year −1 were found with the Morgan-Morgan-Finney method. This article, based on research done over more than two decades in reference localities in the west of the country, revalidates the influence of intensive anthropogenesis. This reinforces water and karst erosion, which coexist spatially by zones in karst plains and highlands karst environments, and have a strong tendency to increase, threatening Cuban "red soils," traditionally considered to be the most productive in the world, with extinction. F: rate of soil scattered by splashing 16.90 (t ha −1 ) G: surface flow transport capacity Watershed A: 1.63 (t ha −1 year −1 ) Watershed B: 1.14 (t ha −1 year −1 ) Watershed C: 0.47 (t ha −1 year −1 ) Adapted from Vega-Carreño and Febles-González (2013). FIG. 7. Stones and clastic rocks widely strewn on the surface impede farm work.

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