Metais pesados no solo e em hortaliças de folhas cultivadas no município de Nova Friburgo-RJ

Abstract

The mountain region of Rio de Janeiro is characterized by the great production of vegetables, being the main producing region of the state. However, the management practices adopted, with high utilization of mineral and organic fertilizers, have increased risk of soil contamination, and consequently of the plants. The objective of this study was to evaluate the contamination by heavy metals (Cu, Ni, Cd, Pb, Cr, Co and Zn) of soils cultivated with lettuce (Lactuca sativa L.) and parsley (Petroselinum crispum M.) in the municipality of Nova Friburgo-RJ, identifying which factors most contributed to the enrichment of these toxic elements in the soil, and their transferring to the plants, as well as the plants quality based on the limits acceptable by ANVISA. The study was carried out in 32 family farms, 18 with lettuce and 14 with parsley production, where samples of soil and plants were collected. The soil was sampled at two depths (0-20 and 20-40 cm), and digested in the laboratory according to the 3050B method (USEPA, 1996). The plants samples were separated into leaves and roots, and the method 3050 (USEPA, 2008) was used for digestion. In soils cultivated with lettuce, the contents of Co, Zn and Cu are possibly associated with characteristics of the parent material. However, the Pb, Cd, Ni and Cr contents are probably associated with a greater anthropogenic contribution, being Pb by means of organic fertilization, and for Cd, Ni and Cr, through mineral fertilization. In soils cultivated with parsley, the Cu, Ni, Co, and Zn contents are possibly related to the geochemical character of the parent material, and the presence of Zn is also probably associated with anthropogenic sources through mineral fertilization, and Pb from mineral fertilization, mainly organic. The contents of Cd and Cr are possibly related to the anthropogenic source, through mineral fertilization. In general, the areas cultivated with lettuce or parsley, which presented higher organic matter content and acidity (lower pH, higher H+Al and higher Al+3) favored a higher bioavailability, absorption, translocation and greater accumulation of toxic metals by the lettuce and parsley plants. About 50% of the lettuce plants, and 80% of the parsley grown in more acidic soils, presented Pb concentration above the maximum limits recommended by ANVISA. About 40% of the parsley plants, cultivated in more acidic soils, also indicated Cu contamination. The consumption of lettuce plants in a scenario of high contamination can lead to Cd and Pb intake at values above the maximum acceptable for adults and children. The consumption of parsley plants with high contamination by Pb and Cu does not exceed the maximum values of daily intake of these metals, due to the small amounts of this vegetable consumed in the meals. In both crops, the amount (g ha-1) of metals extracted by the plants was lower than the amount that were added to the soil by means of mineral and organic fertilizations, practices that could enrich the soils cultivated with lettuce and parsley with these toxic metals.