Effect of polyvinyl chloride and polypropylene microplastics on nutrient status in two vineyard soils of contrasting pH

Compared with the widespread knowledge about the supply of soil with nutrients for optimal vine growth, the possible effect of microplastics in vineyard soils has not yet been addressed. Little is known about how microplastics may affect the bioavailability and fractionation of nutrients in vineyard soils of contrasting pH. In this study, a 120-day soil incubation experiment was performed to investigate the effect of new and aged polypropylene (PP) microplastics and polyvinyl chloride (PVC) microplastics on the soil pH, nitrogen availability (NH₄⁺ and NO₃^-) and binding behaviour of macro- (phosphorus (P), potassium (K), calcium (Ca) and magnesium (Mg)) and micro-nutrients (iron (Fe), copper (Cu), manganese (Mn) and zinc (Zn)). The results showed that the presence of microplastics in soils increased the pH and decreased the bioavailability of macro- and micronutrients in the soil, with the acid soil being more affected. Furthermore, the presence of PVC microplastics had a stronger impact on nutrient availability than PP microplastics. The most important finding of this study was that micro-PVC particles in soil utterly reduce the bioavailability of nitrate (NO₃^-) in both calcareous and acid soil samples. This pronounced negative effect was only measured for the micro-PVC particles from the PVC tube ties used in the vineyards and not from the standard PVC material (Sigma Aldrich). Wine producers should be aware that PVC microplastics reduce the bioavailability of nitrate in soils. However, further studies are in progress to clarify the mechanisms involved in the reduction of soil nitrate bioavailability by PVC microplastics from degraded vineyard strings, in particular from the microbial side.