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Ecotoxicological assessment of the potential impact on soil porewater, surface and groundwater from the use of organic wastes as soil amendments

Publication . Alvarenga, Paula; Mourinha, Clarisse; Farto, Marcia; Palma, Patrícia; Sengo, Joana; Morais, Marie-Christine; Cunha-Queda, Cristina

This study aimed to assess the potential impact on soil porewater, surface and groundwater from the beneficial application of organic wastes to soil, using their eluates and acute bioassays with aquatic organisms and plants: luminescence inhibition of Vibrio fischeri (15 and 30 min), Daphnia magna immobilization (48 h), Thamnocephalus platyurus survival (24 h), and seed germination of Lolium perenne (7 d) and Lactuca sativa (5 d). Some organic wastes' eluates promoted high toxic responses, but that toxicity could not be predicted by their chemical characterization, which is compulsory by regulatory documents. In fact, when organisms were exposed to the water-extractable chemical compounds of the organic wastes, the toxic responses were mare connected to the degree of stabilization of the organic wastes, or to the treatment used to achieve that stabilization, than to their contaminant load. That is why the environmental risk assessment of the use of organic wastes as soil amendments should integrate bioassays with eluates, in order to correctly evaluate the effects of the most bioavailable fraction of all the chemical compounds, which can be difficult to predict from the characterization required in regulatory documents. According to our results, some rapid and standardized acute bioassays can be suggested to integrate a Tier 1 ecotoxicological evaluation of organic wastes with potential to be land applied, namely luminescence inhibition of V fischeri, D. magna immobilization, and the germination of L. perenne and L sativa.

2016-04Journal article

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Recycling organic wastes to agricultural land as a way to improve its quality: A field study to evaluate benefits and risks

Publication . Alvarenga, P.; Palma, Patrícia; Mourinha, C.; Farto, M.; Dores, J.; Patanita, M.; Cunha-Queda, C.; Natal-da-Luz, T.; Renaud, M.; Sousa, J. P.

A field study was established to assess the effects of a sewage sludge (SS), a mixed municipal solid waste compost (MMSWC) and a compost produced from agricultural wastes (AWC), in a Vertisol, using Lolium multiflorum L The amendments were applied for two consecutive years: 6, 12 and 24 t dry matter ha(-1) for SS, and the amendment doses for MMSWC and AWC were calculated to deliver the same amount of organic matter (OM) per unit area. The amendments had significant beneficial effects on some soil properties (e.g. soil OM, N-Kjeldahl, extractable P and K), and on plant productivity parameters (e.g. biomass yield, chlorophyll, foliar area). For instance, soil OM increased from 0.78% to 1.71, 2.48 and 2.51%, after two consecutive years of application of 24 t dry matter ha(-1) of SS, MMSWC and AWC, respectively, while the plant biomass obtained increased from 7.75 t ha(-1) to 152.41, 78.14 and 29.26 t ha(-1), for the same amendments. On the plant, effects were more pronounced for SS than for both compost applications, a consequence of its higher capacity to provide N to the plant in a readily available form. However, after two years of application, the effects on foil properties were more noticeable for both composts, as their OM is more-resistant to mineralization, which endures their beneficial effects on soil. Cadmium, Cr, Ni and Pb pseudo-total concentrations, were not affected significantly by the application of the organic wastes to soil, in all tested doses, neither their extractability by 0.01 M CaCl2. On the contrary, Cu and Zn pseudo-total concentrations increased significantly in the second year of the experiment, following the application of the higher rate of MMSWC and AWC, although their extractability remained very low (<0.5% of their pseudo-total fraction). Trace elements concentrations in the aboveground plant material were lower than their maximum tolerable levels for cattle, used as an indicator of risk of their entry into the human food chain. Despite these results, it is interesting to note that the SS promoted a significant increase in the foliar concentrations of Cu, Ni and Zn that did not happen in composts application, which can be explained by the reduction of the soil pH, as a consequence of SS degradation in soil. Concluding, if this type of organic wastes were to be used in a single application, the rate could be as high as 12 or even 24 t ha(-1), however, if they are to be applied in an annual basis, the application rates should be lowered to assure their safe application (e.g. to 6 t ha(-1)). Moreover, it is advisable to use more stable and mature organic wastes, which have longer lasting positive effects on soil characteristics. (C) 2017 Elsevier Ltd. All rights reserved.

2017-03Journal article

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Quality assessment of a battery of organic wastes and composts using maturity, stability and enzymatic parameters

Publication . Alvarenga, Paula; Mourinha, Clarisse; Farto, Marcia; Palma, Patrícia; Sengo, Joana; Morais, Marie-Christine; Cunha-Queda, Cristina

Chemical and biological parameters (NH4+-N/NO3--N ratio, humification indices, and the activities of hydrolytic exoenzymes), commonly used to assess compost maturity and/or stability, were considered for the quality evaluation of a battery of organic materials, intended to be land applied. Acid and alkaline phosphatases, beta-glucosidase, proteases and beta-glucosaminidase activities proved to be reliable tests to distinguish the organic materials that were in an active stage of microbial activity, highly correlated to the chemical parameters NH4+-N content and NH4+-N/NO3--N ratio. In fact, these chemical parameters evidenced as important in the quality assessment of an organic material, strongly correlated with the biological parameters. The same was not true for the majority of the humification indices, which proved inadequate to compare the quality of such diverse organic materials. This was demonstrated by a multivariate statistical treatment of data, performed with these results in combination with results from the Dewar self-heating test, respiration activity and germination index, obtained in previous studies. Concluding, in a similar scenario, where the organic materials in evaluation are varied, both in the raw material an in the stability of the organic matter, the quality should be assessed by the integrated use of both chemical and biological parameters.

2016-07Journal article

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Beneficial use of dewatered and composted sewage sludge as soil amendments: behaviour of metals in soils and their uptake by plants

Publication . Alvarenga, Paula; Farto, Márcia; Mourinha, Clarisse; Palma, Patrícia

In Portugal, where soils have a very low topsoil organic matter content, the use of sewage sludge (SS) as organic soil improvers seems an attractive option, because it would enable organic matter, N, P, K and other nutrients to be recycled. However, the risk of this practice must be properly assessed. The aim of this study was to evaluate the potential risk of the use of dewatered and composted SS as soil amendments. For this purpose, SS from two different wastewater treatment plants (SS1 and SS2), and a compost produced from SS and agricultural wastes (AWSSC), were characterized for their total metal concentrations, organic contaminants and indicator pathogens, and used in a pot experiment with three application rates, 6, 12 and 24 ton dry matter/ha, cultivated with a hybrid variety of sorghum and Sudan grass (Sorghum bicolor x Sorghum sudanense var. Rocket). SS1 and AWSSC met the legal requirements to be applied to soils, but SS2 had a high content of pathogens, which compromised its use. Both dewatered SS had a marked beneficial effect on plant production and on soil nutritional characteristics, more pronounced than in the case of AWSSC application, without a significant increase in total and in mobile metals concentration in soils. Bioaccumulation factors for metals in plants were low, and their concentrations in the aboveground plant material were lower than the maximum tolerable level for cattle, used as a risk indicator of metal entry into the human food chain. However, it will be necessary, in future studies, to evaluate the potential risk of the observed increase in the mobilisable content of Cu and Zn in soil, as a consequence of the application of these organic materials.

2016-10Journal article

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