Effect of Cadmium and Lead on Quantitative and Essential Oil Traits of Peppermint (Mentha piperita L.)

IntroductionIndustrialization has been the cause of environmental pollution and one of significant pollutant is that of heavy metals. These hazardous elements can cause to water and soil pollution. These metals can accumulate in the food chain and create damages for human and livestock. Researchers revealed that increasing Cd, Pb, Cu, Mn and Zn concentrations caused to decreasing of shoot fresh weight and essential oil yield. Scavroni et al (2005) indicated that peppermint was able to accumulate the heavy metals in shoot tissues but did not enter into essential oil. Therefore study the effect of heavy metals on morphological and quantitative traits of medicinal plants is essential.
Material and MethodThe experiment was done in the research greenhouse of the Agricultural Faculty of Ferdowsi University of Mashhad in 2011.The treatments were arranged basis on a randomized block design with three replications. Treatments were included T1:0, T2:10 ppm cd , T3:20 ppm cd,T4:40 ppm cd,T5:60 ppm cd,T6:80 ppm cd cd,T7:100 ppm cd,T8:100ppm pb, T9:300 ppm pb, T10: 600 ppm pb, T11: 900 ppm pb, T12: 1200 ppm pb and T13: 1500 ppm pb. Peppermint was cultivated with uniform weight rhizomes harvested from the research farm of Ferdowsi University of Mashhad. Every rhizome had two buds and six rhizomes were planted in pots of dimensions 30×50×35 cm. Treatments were irrigated with cdcl2 and pbcl2 with the administered doses and control was irrigated with distilled water. Plants were harvested two times at the first stages of flowering. The essential oil percentage was measured with 30 grams of dried leaves by Clevenger device.
Result and DiscussionIncreasing cadmium and lead concentrations caused a decline of fresh and dry weight, main stem height, leaf area per plant, leaf number per plant, number of nodes per plant and essential oil percentage compared to the control. At the first harvest, increasing doses of Cd caused a decrease of fresh weight. This decline was 18.16% at 100 ppm Cd and was 24.55% at 1500 ppm Pb compared to the control. At the second harvest, fresh weight declined by 15.24% and 32.72% compared to the control at 100 ppm cadmium and 1500 ppm lead, respectively. At the highest concentrations of Cd and Pb, dry weight of peppermint was dropped 22.92% and 25.88% at the first harvest. For the second harvest, decreased dry weights were 39.01% and 26.77% compared to the control, respectively. Stancheva et al (2010) revealed that increasing cadmium and lead concentrations caused to the shoot and root weights of sage (salvia officinalis L.) declined by 15 and 10%, respectively. They mentioned the glutathione-ascorbate cycle plays a vital role in neutralizing the destructive effects of ROS in sage. In this cycle, guaiacol peroxidase, ascorbate peroxidase and catalase enzymes increase and lead to diminish the ROS activity. In the same doses of cadmium and lead (100 ppm), cadmium had a more reductive effects than lead for all traits except for essential oil at the first harvest. This event is due to more toxicity of cadmium compared to lead. The toxicity threshold of cadmium and lead was reported 5 and 30 mg kg-1. Tirillini et al., (2006) reported that hypericin content in essential oil of hypericum perforatum L. was not affected by chrome stress.
ConclusionEssential oil, fresh and dry weight of peppermint did not show any significant change when the concentrations of cd and pb were maximum, so it seems that peppermint can be cultivated in polluted water or soil with cadmium and lead.