Anthropression as a Factor Affecting the Content of Heavy Metals in the Flowers of Sambucus nigra L.—A Medicinal Plant Affecting Human Health

The harvesting of herbs from urban and peri-urban areas requires systematic monitoring of soils and plants, especially of trace element concentrations. The aim of the study was to assess the phytoaccumulation of selected trace elements (Zn, Cu, Fe, and Mn) in elderberry flowers from the Kuyavian-Pomeranian province (Poland). The enzymatic activity of soils was also assessed in the context of the impact of metals on the biological properties of soils at risk of contamination with trace elements. Soil and plant samples were taken from seven locations with different anthropopressures. Flowers from sites with a high frequency of road traffic were characterized by a greater number of elements (location 1, 3–7) than from areas away from busy roads (location 2). The correlation analysis showed that Cu and Zn contents were highly correlated in the flowers of elderberry as compared to the corresponding soils seven locations with different anthropopressures Regarding the Zn content, only flowers from habitats 1, 2, 7 met the conditions specified in the WHO standard for herbs used in herbal medicine (<50 mg·kg −1 ). Based on the conducted research, it was found that the level of soil enzymatic activity in the tested soils varied within wide limits but clearly depended on their location. The highest enzyme activity in the soil was found in soil from town center 1 (location 3), where high DHA dehydrogenase DHA (114.5 mg TPF·g −1 ·24 h −1 ), fluorescein diacetate hydrolysis FDA (51.26 μg F·g −1 ·h −1 ), and β-glucosidases GLUC activity (4.833 μg pNP·g −1 ·h −1 ) were determined, as well as in soil from residential area 2 (location 3), where high DHA (165.9 mg TPF·g −1 ·24 h −1 ) and FDA (48.23 μg F·g −1 ·h −1 ) activity were determined. Analyzing the soil properties, it can be concluded that the content of Cu t and Zn t in the soil and their forms available for plants, as well as DHA activity, correlates most closely with the content of organic matter.