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Correlation between phytotocixity and total and bioavailable heavy metals of composts

Composting is one of the methods mostly used for organic solid wastes recycling. The compost is mainly used as a soil conditioner due to its carbon and nitrogen content. Although such applications are beneficial to soil, concern about possible environmental hazards, like odor, water pollution, veterinary hazards, and contamination by heavy metals have to be considered. The main limiting factor, in order to use compost as soil amendment, is the total concentration of heavy metals. Therefore, it is important to understand the heavy metals fractionation and their bioavailability to the soil-plant system, which may be correlated with the composts phytotoxicity.

Further Authors:
A.C. Cunha-Queda
J.F.C. Carneiro - Departamento de Ambiente
L. Teixeira de Lemos - Departamento de Ambiente
E.P.C da Silva - Departamento de Ambiente
I.P.L. Brás - Departamento de Ambiente

The purpose of this work was to determine the content of six heavy metals (Zn, Pb, Ni, Cu, Cr and Cd) and their bioavailability in composts commercialized in Portugal and correlate with their phytotoxicity. Four commercial composts, two from non-separated municipal solid waste (MC1, MC2), one from source-separated municipal solid waste (MC3), and one produced from poultry litter (PC), were analysed. The stability of composts was characterised using the self-heating test. The fraction of heavy metals was evaluated following the sequential BCR (Community Bureau of Reference) extraction; the composts were treated with a chain of reagents to quantify the elemental concentration in 4 different fractions (exchangeable/bioavailable, reducible, oxidiseable and residual). The phytotoxicity tests were performed using two different types of seeds: cress (Lapidium sativum) and radish (Raphanus sativus). All the composts presented organic matter content higher than 35% and pH values between 8 and 9. The MC3 and PC composts showed the lowest heavy metal content. Zn was the heavy metal present in the highest concentration (861 mg/kg dry matter), while Cd was the least representative (3.0 mg/kg dry matter). When using a sequential extraction method, only Zn (9% - 23%) was bound to the exchangeable fraction (bioavailable form). The highest proportion of the heavy metals were associated with the fractions more resistant to extract, namely to the residual fraction. The compost MC3 was the most stable, and PC compost presented the highest germination index (72%), which suggests that it was the only compost without phytotoxicity. A correlation analysis indicated that the chemical properties of the composts, such as the organic matter content, can influence the germination index, besides the Cr content in the oxidisable and reducible fractions. These results showed that others parameters besides the bioavailable heavy metals might influence the phytotoxicity of the composts.

Copyright:	© European Compost Network ECN e.V.
Quelle:	Orbit 2012 (Juni 2012)
Seiten:	8
Preis:	€ 0,00
Autor:	Maria Elisabete F. Silva O. C. Nunes
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