Heavy metal contents in water extracts of selected medicinal plants used in the folk medicine of Jordan

• Heavy metal concentrations (Cd, Pb, Ni, Cr, Hg, As, and Cu) in medicinal plants of jordan. • Measurements were performed using inductively coupled plasma optical emission spectrometric analysis (ICP-OES). • High levels of Ni, Cr, and Cu were found at locations near a highway road and a cement factory. • Monitoring the herbal quality concerning heavy metal contamination is required on a routine basis to assure the safety of herbal products. Contamination of medicinal plants with heavy metals from environmental sources may severely impact the quality and safety of botanical products. The consumption of botanicals that are contaminated with heavy metals represents a severe health-threatening danger. The present toxicological study was conducted to determine the heavy metal concentrations of Cd, Pb, Ni, Cr, Hg, As, and Cu in selected medicinal plants and their water extracts (infusions) of Achillea santolina L., Amygdalus communis L., Artemisia herba-alba Asso., Crataegus aronia L., Viscum cruciatum Sieb., and Nepeta involucrata (Bunge) Bornm. collected from different regions in the south of Jordan, including Birkhdad (site 1), Al-Rashadihya (site 2), and Ain-Lahda (sites 3 and 4). Heavy metal concentrations in the medicinal herbs and their infusions were determined by Inductively Coupled Plasma Optical Emission Spectrometric Analysis (ICP-OES). The correlation between the content of heavy metals in the studied plants, their water extracts, and the surrounding soil environment was also studied. High concentrations of Ni, Cr, and Cu were detected at all investigated sites of soil. They were in the ranges of 8.46 ± 0.02 to 18.36 ± 0.02 ppm (for Ni), 9.47 ± 0.02 to 24.97 ± 0.06 ppm (for Cr), and 9.53 ± 0.01 to 17.05 ± 1.32 ppm (for Cu), respectively. The high levels of Ni, Cr, and Cu are mainly due to the presence of a highway road that is nearby site 3 and the location of a cement factory that is nearby site 2. The potentially toxic elements of Cd, Pb, and As were non-detectable, and very low concentrations of Hg were observed in the range of 0.17 ± 0.01 to 1.82 ± 0.25 ppm in Artemisia herba-alba collected from all studied locations. High Cu concentrations (20.53 to 23.80 ppm) were detected in A. herba-alba collected from sites 1, 2, and 3 and were higher than the reported normal range of (4 to 15 ppm). On the other hand, the raw materials of all studied plants had low Ni, and Cr concentrations within the range of 0.38 (± 0.01) to 4.05 (± 0.16) ppm and 0.35 (± 0.01) to 2.82 (± 0.01) ppm, respectively. Cd and As were non-detectable in all water extracts of all studied plants. The highest Cu contents were observed in the water extracts of A. herba-alba collected from sites 2 and 3 at concentrations of 64.54 ± 6.41 ppm and 62.43 ± 1.85 ppm, respectively. The heavy metal contamination in a panel of herbal samples was below the legal limit values, except for those plants harvested close to a highway with heavy traffic or a cement factory. This points to the necessity to selecting suitable locations to culture medicinal plants for therapeutic purposes. We recommend monitoring the herbal quality concerning heavy metal contamination on a routine basis to assure the safety of herbal products for the sake of patients in Jordan and elsewhere.