Quality standards for urban waste composts: The need for biological effect data

The recently approved European Union (EU) Circular Economy Package intends to boost the production of fertilizing products, such as composts obtained from urban wastes (UWC) and the harmonization of their quality standards (certification), to avoid market rejection. UWC quality assessment frameworks in Europe, including the Portuguese and EU latest proposal on regulation of UWC production/commercialization are mostly based on physical-chemical and agronomical characterization. These do not provide any insight on the fraction of contaminant/mixture of contaminants bioavailable for non-target organisms, nor the existence of potential antagonistic and/or synergistic effects on them. The main objective of the present work if to evaluate the effects of UWC application on crop soils using seven standard ecotoxicological tests. Five UWC, two derived from source-separated organic wastes and three from mixed urban wastes were selected and tested using a battery of ISO guideline assays with plants and soil invertebrates. The tested doses intended to simulate over-use and repeated application scenarios, common practices among farmers. The results showed that the highest toxicity was observed for the UWC originated from source-separated organic wastes, when using concentrations slightly above the maximum annual doses. Excepting for this UWC, all the derived NOEC (No Observed Effect Concentration) were equal or higher than the maximum annual doses. The UWC toxicity for the tested species increased as follows: T. aestivum < L. sativa < E. crypticus < F. candida < E. andrei. UWC salinity, rather than the content of potentially toxic elements (PTEs), could explain the negative effects observed, considering that the composts are all equally stabilized. These results reinforce the need to include data from biological susceptibility of the receptors at risk on the existing regulation, to obtain a more realistic view of the potential risks and to adapt the UWC application practices, ultimately boosting the confidence of target-consumers.