Using pine bark and mussel shells as soil amendments to establish a rehabilitation strategy for Cu polluted viticultural soils

Cu tends to accumulate in the upper layers of vineyard soils, given the historical application of copper-based fungicides in viticulture. Reducing the susceptibility of soils to Cu contamination is crucial because the literature has previously extensively documented on the possible adverse effects of this accumulation in the soil to the various ecosystem compartments. This can be achieved through the development of practices that decrease its mobility and bioavailability in vulnerable soils (more acidic and poorer in organic matter), such as the use of amendments, that can modulate the behaviour of Cu in soils. Therefore, the potential of soil amendments to remediate copper polluted soils was assessed, with the aim of identifying a strategy to safeguard vulnerable soils to Cu. This was accomplished by incorporating two soil amendments - pine bark and mussel shell - to a viticultural soil spiked with different concentrations of Bordeaux mixture. The effects of the amendment’s addition to vineyard soils, their ability in reducing their vulnerability to Cu contamination and its mobilization to the aquatic compartment, were evaluated through a battery of ecotoxicological assays with both terrestrial and aquatic species. It was possible to assess if soil amendments modulated Cu bioavailability for soil biota, and to what extent these treatments have influenced Cu mobility to the aqueous phase. For the most part, amendments were responsible for improving results of ecotoxicological assays, when comparing with those of the non-conditioned soil, being the aquatic plant L. minor the exception to this trend. Regarding Cu contamination, soil amendments brought benefits to the performance of all the tested species, which can be corroborated by the EC50 results. The EC50 values for these assays compared with the ones obtained for the non-conditioned soil were generally higher, although not in a linear way with increasing amendment concentrations. But in a general manner, the 24 mg kg-1 of the amendment’s mixture had a positive effect in improving soil habitat and retention functions. This being said, the mixture of milled mussel shells and pine bark appears to have the potential of being used to improve the vulnerability of soils to Cu contamination, working as a conditioning agent mitigating Cu toxicity and its mobility in the soil. It was stated, however, that the effect of these amendments does not provide benefits in a linear relation with their concentration. Therefore, it is of high relevance to further study the underlying mechanisms for the verified reduction of Cu toxicity, to better select proper proportions and concentrations of such products for different soil types.