Vulnerability of Portuguese vineyards soil to copper contamination: understanding regional variations

Abstract

Viticulture has a strong dependence on copper-based fungicides application. As two of the United Nation goals aimed to achieve the sustainable management and efficient use of natural resources such as the soil (SDG 15), and a sustainable production (SDG 12), the constant use of these products is an environmental concern that jeopardizes the reaching of this target. Indeed, all the years of Cu-based fungicides use lead to an accumulation of this potential toxic element in vineyard soils. However, its behaviour and availability will differ between soil types as it is dependent on physical and chemical properties such as texture, pH, and organic matter. This is specially concerning in a country like Portugal, that has different wine regions with different soil types. Thus, it is important to understand which soil properties most contribute to Cu behaviour/availability and vulnerability to be able to tackle this environmental problem. Thus, soil samples from different Portuguese wine regions were collected (Vinhos Verdes, Douro, Dão, Bairrada and Alentejo regions) and several physical and chemical properties were determined, including total Cu concentration. After this first screening, soils were contaminated in laboratory conditions with different concentrations of Cu (0, 46, 72, 111, 173, 268, 416, 645 and 1000 mg kg-1) in the form of Bordeaux mixture and left to acclimate for a month at room temperature and natural photoperiod. Following this period, ecotoxicological assays were performed with aquatic species (using soil elutriates) and terrestrial organisms (using whole soil). For the aquatic assays several endpoints were evaluated namely the bioluminescence inhibition of Allivibrio fischeri (following manufacturers guidelines), growth inhibition of Lemna minor (OCDE guideline 221) and Raphidocelis subcapitata (OCDE guideline 201) and immobilization of Daphnia magna (OCDE guideline 202). As for the terrestrial assays, the reproductive output of Eisenia fetida (OCDE guideline 222) and Folsomia candida (OCDE guideline 232) as well as the germination and growth of Medicago sativa (OCDE guideline 208) were assessed. In addition, Cu levels in the soil elutriates and tissues of earthworms and plants were evaluated. With these analyses, it was possible to determine that the soil from Vinho Verde region (the one with the lowest pH) was the one that showed more vulnerability towards Cu contamination as lower Cu concentrations already impaired the viability of the organisms tested. Furthermore, the species tested showed different levels of vulnerability when exposed to Cu which could be related with Cu levels found in the whole soil and in the soil elutriates as these also differed. In conclusion, this work made it possible to understand that the problem of soil vulnerability to copper contamination highly depends on its pH and that protective measures must be taken taking this into consideration, prioritizing soil with lower pH values.