Purpose Soil pollution is a major problem worldwide. Some anthropogenic activities, such as mining, may exceed soil capacity, causing relevant health and ecosystem hazards. The use of mineral amendments can help reduce soil pollution. Gypsum mining spoil (GS) is a waste material highly produced in gypsum mining industry, which has never been used in soil remediation despite its high potential as amendment of polluted soils. In this study, we carried out an ex-situ experiment to assess for the first time the capacity of GS to both reduce the availability of Potentially Harmful Elements (PHEs) in soils and promote seed emergence. Methods Soils affected by residual pollution after the Aznalcóllar mine spill were collected, treated with GS in three different proportions, and sown with seeds of two non-genetically related species. Seed emergence and biomass production were monitored, and PHE content in soils and plants were analysed. Results We have observed a direct and very positive relation between GS and both the reduction of PHE availability and PHE uptake by plants, and the increase of plant emergence and growth, especially with the addition of the highest doses of the amendment. Conclusion This study highlights the promising results of GS as a novel soil amendment to be used in the remediation of polluted soils and vegetation recovery. Moreover, using GS as soil amendment will bring the opportunity to sustainably manage this waste material and reduce its social and environmental impact parallelly to the mitigation of PHE hazards.

Rosmarinus officinalis advantageously competes with other species in restored gypsum outcrops, and further research is needed to understand the causes. Specifically, we focus on the potential allelopathic effects derived from its terpenes on the emergence of gypsum species. To this end, we established 120 circular subplots in a previously restored gypsum outcrop, and randomly applied four different treatments based on the presence/absence of rosemary plants and their leaves on the soil. Afterwards, we conducted an experimental sowing of native gypsophiles. All subplots were monitored to estimate seedling emergence, and soil and leaf samples were analysed for terpenes. The results show that the treatments had significant effects on the overall emergence of seedlings, and terpenes were found in rosemary leaves and soils, with no significant differences in terpene composition. In particular, we identified a clear negative effect in the treatment where rosemary plants were eliminated but its leaves were left along with allelopathy (2.57 ± 0.54 individuals/subplot). Unexpectedly, the presence of rosemary plants seems to facilitate the emergence of gypsum species (9.93 ± 1.61 individuals/subplot), counteracting the effects of the allelopathic substances in the soil. Consequently, we do not suggest removing rosemary plants in early stages to encourage the emergence of gypsum species in restored areas.