Influences of soil pH on cadmium toxicity to eight plant species

Soil pollution by heavy metals affects soil quality worldwide. Cadmium (Cd) is of special concern because it might transfer from soil to plants, especially under acidic conditions, causing toxicity. This work aimed to evaluate the LC50 (lethal concentration to 50% of studied population), NOEC (no observed effects concentration) and LOEC (lowest observed effects concentration), by measuring the germination and growth of eight plant species (Beta vulgaris, Daucus carota, Lactuca sativa, Phaseolus vulgaris; Avena strigosa, Oryza sativa, Triticum aestivum and Zea mays) in soil under increasing Cd concentrations (0, 10, 40, 80, 160, and 320 mg kg-1) and two levels of acidity. Increasing the soil pH (from 4.1 to 6.4) by liming alleviated Cd toxicity and had a positive impact on seedling growth of all plant species studied. Germination was a less responsive endpoint and only the most sensitive species (L. sativa, B. and D. carota) were affected under the most acidic condition. These results were confirmed by the lower values found for LOEC and LC50 in these species regardless of the soil pH. Sensitive species are thus recommended as indicators of soil contamination in ecotoxicological studies, in which dicotyledonous species (e. g. L. sativa and B. vulgaris) are more suitable for risk assessments in Cd-contaminated soils at low concentrations, whilst monocotyledons (e. g. Z. mays) are more adequate for higher Cd concentrations (≥ 80 mg kg-1). Increasing soil pH by liming was demonstrated to be an efficient method in alleviating Cd toxicity in seedling growth

Fitotoxidade de cádmio e bário e derivação de lilites críticos em solos

Soil pollution by heavy metals caused by anthropogenic activities is a problem in many countries. Cadmium (Cd) is one of the most hazardous elements due to its relatively high mobility in soils and transfer to plants. The main human exposure pathway to Cd is through the vegetable consumption and depends on the exposure scenario. Thus, defining a critical limit of Cd in soil is necessary. Barium is an earth alkaline element that can be toxic to humans and plants when it is present in the free form (Ba2+). However, only few studies have focused on Ba in soil. Soil characteristics influence Cd and Ba availability for plant uptake. Both metals may affect plant growth and metabolism and cause oxidative stress. The aims of this study were: (i) to compare tropical and temperate datasets to establish critical soil Cd concentrations for the State of São Paulo, Brazil; (ii) to evaluate the influence of liming on Cd availability and accumulation in lettuce in order to calculate site specific critical soil Cd concentrations for two typical tropical soils from the State of São Paulo; (iii) to evaluate the effects of Cd and Ba concentrations on plant growth, lipid peroxidation and activities of antioxidant enzymes in leaves of soybean, grown in tropical soils with contrasting properties. The Cd uptake from the tropical dataset was higher as compared to the temperate dataset. Critical soil Cd concentrations were from 1.7 to 3.2- fold lower when tropical soil data were used. It is suggested that only literature data, regarding Cd in soils and vegetables, from tropical regions should be used for the State of São Paulo to derive critical soil Cd concentrations. Cadmium accumulated linearly in lettuce at soil concentrations up to 12 mg kg-1. In both soils, a slight reduction on Cd uptake was observed as a response to liming. The calculated critical soil Cd concentrations were lower in the Ultisol because of the differences in soil characteristics. Besides, there was a positive correlation with the vegetable consumption rates. Cadmium strongly reduced soybean growth at concentrations from 5.2 mg kg-1, while Ba only slightly reduced at 600 mg kg-1 in the sandy Entisol. The activities of superoxide dismutase, catalase and glutathione reductase were dependent mainly on the soil type: soybean plants grown in the Entisol suffered higher oxidative stress than those grown in the clayey Oxisol and, consequently, responded less to the increase of metal concentrations.A poluição do solo por metais pesados causada principalmente por atividades antrópicas é um problema em muitos países. Cádmio (Cd) é um dos elementos mais perigosos devido à sua mobilidade relativamente alta em solos e transferência para as plantas. A principal via de exposição humana ao Cd é por meio do consumo de vegetais e depende do cenário de exposição. Assim, a definição de um limite crítico de Cd no solo é necessária. O bário (Ba) é um elemento alcalino-terroso que pode ser tóxico aos seres humanos e às plantas, quando absorvido na sua forma livre (Ba2+). No entanto, há poucos estudos sobre Ba em solos. As características do solo influenciam na disponibilidade de Cd e Ba para absorção pelas plantas. Ambos os metais podem afetar o crescimento e metabolismo das plantas e causar estresse oxidativo. Os objetivos deste estudo foram: (i) comparar resultados oriundos de regiões tropicais e temperadas para determinar concentrações críticas de Cd em solos para o Estado de São Paulo; (ii) avaliar a influência da calagem na disponibilidade e no acúmulo de Cd em plantas de alface, a fim de calcular as concentrações críticas de Cd específicas para solos do Estado de São Paulo; e (iii) avaliar os efeitos das concentrações de Cd e Ba no crescimento das plantas, na peroxidação lipídica e na atividade de enzimas antioxidantes em folhas de soja, cultivada em solos tropicais com propriedades contrastantes. A absorção de Cd a partir do conjunto de dados de solos tropicais foi maior em relação ao de dados de clima temperado. As concentrações críticas de Cd no solo foram de 1,7 a 3,2 vezes menores quando os dados de solos tropicais foram utilizados. Sugere-se que apenas resultados de literatura de regiões tropicais, em relação a Cd em solos e vegetais, sejam utilizados para o Estado de São Paulo para derivação de concentrações críticas de Cd em solo. O Cd acumulou linearmente em alface em concentrações de até 12 mg kg-1 no solo. Apenas uma leve redução na absorção de Cd em resposta à calagem foi observada tanto no Latossolo quanto no Argissolo. As concentrações críticas de Cd foram menores no Argissolo do que no Latossolo, devido às diferenças nas características dos mesmos. Tais concentrações críticas tiveram correlação positiva com o consumo de hortaliças. O Cd reduziu fortemente o crescimento da soja em concentrações a partir de 5,2 mg kg-1, enquanto Ba causou apenas ligeira redução na dose de 600 mg kg-1 no Neossolo Quartzarênico. As atividades das enzimas superóxido dismutase, catalase e glutationa redutase dependeram, principalmente, do tipo de solo. Assim, as plantas de soja cultivadas no Neossolo sofreram mais estresse oxidativo do que as cultivadas no Latossolo. Conseqüentemente, a resposta das enzimas ao aumento das concentrações de metais foi pequena

Influência de métodos de digestão e massa de amostra na recuperação de nutrientes em resíduos orgânicos

The influence of nitric-perchloric, aqua regia, dry ashing and microwave digestion methods, in combination with 100 and 200 mg of sample, on the characterization and recovery of nutrients in samples of sludge sewage, poultry, swine, quail and bovine manures, organic compost, organic substrate and humic material were studied. Nitric-perchloric digestion with 200 mg samples recovered the higher nutrient contents. The nitric-perchloric method recovered also low levels of K. Dry ashing caused S volatilization and microwave digestion produced dark color extracts and this impaired S determination. Aqua regia recovered the lowest contents of nutrients in the organic residues evaluated

Transfer of cadmium and barium from soil to crops grown in tropical soils

Phytotoxicity and transfer of potentially toxic elements, such as cadmium (Cd) or barium (Ba), depend on the availability of these elements in soils and on the plant species exposed to them. With this study, we aimed to evaluate the effect of Cd and Ba application rates on yields of pea (Pisum sativum L.), sorghum (Sorghum bicolor L.), soybean (Glycine max L.), and maize (Zea mays L.) grown under greenhouse conditions in an Oxisol and an Entisol with contrasting physical and chemical properties, and to correlate the amount taken up by plants with extractants commonly used in routine soil analysis, along with transfer coefficients (Bioconcentration Factor and Transfer Factor) in different parts of the plants. Plants were harvested at flowering stage and measured for yield and Cd or Ba concentrations in leaves, stems, and roots. The amount of Cd accumulated in the plants was satisfactorily evaluated by both DTPA and Mehlich-3 (M-3). Mehlich-3 did not relate to Ba accumulated in plants, suggesting it should not be used to predict Ba availability. The transfer coefficients were specific to soils and plants and are therefore not recommended for direct use in risk assessment models without taking soil properties and group of plants into account

Calagem em latossolo sob influência de coberturas vegetais: neutralização da acidez

A movimentação dos produtos da dissolução do calcário e a correção da acidez podem ser influenciadas pelo manejo da calagem e pela quantidade e qualidade da matéria orgânica presente no solo. Avaliou-se a correção da acidez de acordo com a aplicação de calcário superficial ou incorporado nas profundidades de 0-10, 0-20 cm, em um Latossolo Vermelho distroférrico (LVdf) sob diferentes coberturas vegetais anteriores (mata, eucalipto, pinus e pastagem). O estudo foi realizado de novembro de 2002 a janeiro de 2003 no Departamento de Ciência do Solo da UFLA, sendo avaliados, depois de 30 dias de reação do calcário, e antes do cultivo do algodão, os teores trocáveis de Ca2+ e Al3+, o pH e os níveis de saturação por bases (V) em amostras de solo coletadas nas profundidades de 0-5, 5-10, 10-20 e 20-40 cm. A calagem superficial causou, na camada de 0-5 cm, uma elevação do pH e V para níveis acima dos considerados adequados para o cultivo do algodoeiro, caracterizando uma calagem excessiva. Foram verificados acréscimos, em relação à área sem calagem, do pH, Ca2+ e saturação por bases em camadas de solo além das camadas de incorporação do corretivo, principalmente nas amostras de solo com maior teor de matéria orgânica, mas esses efeitos não se estenderam à camada de subsolo (20-40 cm)

Biochar Phosphate Fertilizer Loaded with Urea Preserves Available Nitrogen Longer than Conventional Urea

Biochar, a carbon-rich material obtained by pyrolysis of organic wastes, is an attractive matrix for loading nutrients and producing enhanced efficiency fertilizers. In this study, poultry litter (PL) was enriched with phosphoric acid (H3PO4) and MgO to produce a biochar-based fertilizer (PLB), which was loaded with urea in a 4:5 ratio (PLB:urea, w/w) to generate a 15–15% N–P slow-release fertilizer (PLB–N) to be used in a single application to soil. A greenhouse experiment was carried out in which a common bean was cultivated followed by maize to evaluate the agronomic efficiency and the residual effect of fertilization with PLB–N in Ultisol. Six treatments were tested, including four doses of N (100, 150, 200, and 250 mg kg−1) via PLB–N in a single application, a control with triple superphosphate (TSP—applied once) and urea (split three times), and a control without N-P fertilization. The greatest effect of PLB–N was the residual effect of fertilization, in which maize showed a linear response to the N doses applied via PLB–N but showed no response to conventional TSP + urea fertilization. Biochar has the potential as a loading matrix to preserve N availability and increase residual effects and N-use efficiency by plants

Cadmium Uptake by Lettuce (Lactuca sativa L.) as Basis for Derivation of Risk Limits in Soils

The availability and uptake of Cd by lettuce (Lactuca sativa L.) in two common tropical soils (before and after liming) were studied in order to derive human health-based risk soil concentration. Cadmium concentrations ranging from 1 to 12 mg kg(-1) were added to samples from a clayey Oxisol and a sandy-loam Ultisol under glasshouse conditions. After incubation, a soil sample was taken from each pot, the concentration of Cd in the soil was determined, lettuce was grown during 36 d, and the edible parts were harvested and analyzed for Cd. A positive linear correlation was observed between total soil Cd and the Cd concentration in lettuce. The amount of Cd absorbed by lettuce grown in the Ultisol was about twice the amount absorbed in the Oxisol. Liming increased the soil pH and slightly reduced Cd availability and uptake. CaCl2 extraction was better than DTPA to reflect differences in binding strength of Cd between limed and unlimed soils. Risk Cd concentrations in the Ultisol were lower than in the Oxisol, reflecting the greater degree of uptake from the Ultisol. The derived risk Cd values were dependent on soil type and the exposure scenario.Fundacao de Amparo a Pesquisa do Estado de Sao Paulo (FAPESP)Fundacao de Amparo a Pesquisa do Estado de Sao Paulo (FAPESP) [07/56350-9