Soil contamination by heavy metals is a challenge faced by many countries, and engineering technologies to solve this problem are expensive and can cause negative impacts on the environment. One way to minimise the levels of heavy metals in the soil is to use plants that can absorb and accumulate heavy metals into harvestable parts, a process called phytoextraction. Typical plant species used in research involving phytoextraction are heavy metal hyperaccumulators, but plants from this group are not good biomass producers and grow more slowly than most species; thus, they have an important role in helping scientists understand the mechanisms involved in accumulating high amounts of heavy metals without developing symptoms or dying. However, because of their slow growth, it is not practical to use these species for phytoextraction. An alternative approach is to use non-hyperaccumulator plants assisted by chelating agents, which may improve the ability of plants to accumulate more heavy metals than they would naturally. Chelating agents can be synthetic or organic acids, and the advantages and disadvantages of their use in improving the phytoextraction potential of non-hyperaccumulator plants are discussed in this article. We hope to draw attention to ways to improve the phytoextraction potential of non-hyperaccumulator plants that produce a large amount of biomass and to stimulate more research on phytoextraction-inducing substances.

OBJETIVO: Sedimentos artificiais com formulações simples foram utilizados para avaliar a toxicidade do Cr em C. xanthus, D. rerio e P. reticulata. MÉTODOS: Os organismos foram expostos a duas formulações: sem matéria orgânica (S0) e com 1% de matéria orgânica (SIII), contaminadas com Cr nas concentrações de 90; 180; 360; 720 e 1440 mg/kg para os ensaios com C. xanthus e 375; 750; 1500 e 3000 mg/kg para os ensaios com peixes. RESULTADOS: Os resultados dos ensaios agudos demonstraram uma redução de até quatro vezes na toxicidade frente à presença de matéria orgânica detrital biodegradável (MO). C. xanthus apresentou maior sensibilidade ao metal em relação aos peixes. A redução na toxicidade do Cr frente à presença de MO foi verificada nos valores de CL50, que estiveram mais elevados nos em SIII (C. xanthus = 1234,43 mg/kg ; D. rerio = 2263,54 m/kg e P. reticulata = 2244,48 mg/kg) em relação à S0 (C. xanthus = 340,56 mg/kg; D. rerio = 1731,04 mg/kg e P. reticulata = 1733,55 mg/kg). CONCLUSÕES: Os sedimentos artificiais com formulações simples foram satisfatórios na avaliação da toxicidade e asseguram resultados confiáveis em estudos ecotoxicológicos

AIM: Artificial sediments with simple formulations were used to assess the toxicity of Cr to C. xanthus, D. rerio and P. reticulata. METHODS: The organisms were exposed to two sediment formulations: one without organic matter (S0) and one with 1% organic matter (SIII), both contaminated with Cr at concentrations of 90, 180, 360, 720 and 1440 mg/kg for the assays with C. xanthus, and 375, 750, 1500 and 3000 mg/kg for those with the two fish species. Chromium was obtained from the potassium dichromate (K2Cr2O7). RESULTS: The results of the acute toxicity tests demonstrated a reduction of up to four times in toxicity with the presence of OM, consisting of biodegradable detritus, even at the low concentration used (1%), and that C. xanthus was most sensitive to the metal. The reduction in the chromium toxicity was indicated by the LC50 values, which were higher in SIII (1234.43 mg/kg; 2263.54 m/kg; 2244.48 mg/kg) than in S0 (340.56 mg/kg; 1731.04 mg/kg; 1733.55 mg/kg) for C. xanthus, D. rerio and P. reticulata, respectively. CONCLUSIONS: Because of the repeatability of the results obtained, the artificial sediments with simple formulations were satisfactory to assess toxicity and can thus provide reliable results in ecotoxicological studies

Avaliaram-se os teores de Cu em função da variação do pH e da adição de cama-de-frango de dois solos com elevados teores deste elemento. Foram coletadas amostras da camada superficial (0 a 10 cm) de um typical dystrophic Lithic Udorthent - LU (Neossolo Litólico distrófico típico) e de um Humic Dystrudept - HD (Cambissolo Húmico alumínico típico) da região da Serra do RS, cultivados com parreirais que receberam aplicações sucessivas de produtos à base de Cu. Foram determinados os teores de Cu solúvel em DTPA e pelo método Mehlich III, além do Cu trocável em CaCl2. A disponibilidade de Cu foi afetada principalmente pelo pH do solo. O extrator CaCl2 foi o que melhor se correlacionou com os teores de Cu em solos contaminados em função dos tratamentos aplicados. A adição de cama-de-frango não diminuiu a disponibilidade de Cu destes solos. Os teores de Cu total variaram entre 1.300 e 1.400 mg kg-1 nos dois solos. Considerando os teores totais de Cu nos solos, as frações "disponíveis", extraídas por DTPA, por CaCl2 e por Mehlich III representaram, em média, 35%, 0,20% e 63% do total de Cu presente no solo, respectivamente.

Copper (Cu) concentration was evaluated as a function of pH variation and addition of poultry litter to a Dystrophic Lithic Udorthent and a Humic Dystrudept from the state of Rio Grande do Sul, Brazil, cultivated with vines treated with successive applications of Cu-based product. Samples were collected from the surface layer (0 to 10 cm). Soluble Cu concentration was determined using DTPA and Mehlich III as extractants, and exchangeable Cu was determined in CaCl2. The availability of Cu was mainly affected by the soil pH. CaCl2 extractant had the best correlation with Cu concentration in contaminated soils, according to treatments applied. The addition of poultry litter did not reduce Cu availability in these soils. Total soil Cu content varied between 1,300 and 1,400 mg kg-1 in both soils. Copper available fractions, extracted by DTPA, CaCl2 and Mehlich III, averaged 35, 0.2 and 63%, respectively, of the total Cu present in the soil.

O trabalho teve como objetivo avaliar a distribuição de formas de cobre, em função do pH e da adição de cama-de-frango, em amostras da camada superficial (0 a 10 cm) de um Neossolo Litólico distrófico típico e de um Cambissolo Húmico alumínico típico, da região da Serra Gaúcha, cultivados por mais de 15 anos com parreirais que receberam aplicações sucessivas de produtos fitossanitários à base de cobre. Para avaliar os efeitos da variação do pH e do teor de matéria orgânica do solo nas formas de cobre, cinco doses de HNO3 (50, 100, 200, 300 e 400 mmol kg-1) e quatro doses de cama-de-frango em base seca (10, 20, 40 e 80 t ha-1) foram adicionadas aos solos. As frações observadas foram: trocável; ligada à matéria orgânica; ligada a óxidos de Fe, de Al e de Mn; e fração residual. A maior proporção do cobre dos solos esteve ligada à fração orgânica (entre 70 e 80%). Com a diminuição do pH (de 6,8 para 3,8), os teores de cobre trocável aumentaram, enquanto os teores de cobre ligados às frações matéria orgânica, óxidos e residual diminuíram. A adição de cama-de-frango não afetou significativamente a distribuição das formas de cobre nos solos, com exceção dos teores trocáveis.

The objective of this study was to evaluate the distribution of forms of copper as affected by pH and poultry litter addition in samples of surface layers (0 to 10 cm) of a Dystrophic Lithic Udorthent and a Humic Dystrudept, both from Serra Gaúcha (Rio Grande do Sul highlands), Brazil, cultivated for more than 15 years with vines treated with successive applications of copper-based products. To evaluate the effects of pH variation and soil organic matter content in copper forms, five doses of HNO3 (50, 100, 200, 300 e 400 mmol kg-1) and four doses of poultry litter in dry basis (10, 20, 40 e 80 t ha-1) were added to the soils. The following fractions were evaluated: exchangeable; bound to organic matter; bound to Fe, Al, and Mn oxides; and residual. The largest proportion of copper of the soil was bound to organic matter fraction (from 70 to 80%). As the pH decreased from 6.8 to 3.8, the copper exchangeable contents increased, while copper bound to organic matter, oxides, and residual fractions decreased. The application of poultry litter did not significantly affect the distribution of forms of copper in both soils, except for the exchangeable fraction.