Volatile constituents in the flowers of Elsholtzia argyi and their variation: a possible utilization of plant resources after phytoremediation

Abstract

Phytoremediation effectiveness and remediation costs are driving factors of this project. Full utilization of plant resources after their being used for phytoremediation is an unsolved problem. GC/MS technique was used to investigate the volatiles of the flowers from Elsholtzia argyi (PFE1: Purple Flower Elsholtzia) and their variation (WFE: White Flower Elsholtzia), naturally growing in Pb/Zn mined area, and Elsholtzia argyi (PFE2: Purple Flower Elsholtzia), naturally growing in Jiuxi uncontaminated agriculture soil. Seventeen compounds constituting 86.88% of total essential oils were identified in PFE1, with 2,6-octadienoic acid,3,7-dimethyl-methyl ester being the main constituent (63.30%). Sixteen compounds accounting for 95.32% of total essential oils were identified in WFE, with caryophyllene being the main component (55.02%). Compared to PFE1, PFE2 contained lower level of 2,6-octadienoic acid,3,7-dimethyl-methyl ester (31.76%), which was the main constituent in the total essential oils of PFE2. Caryophyllene is the main ingredient of flavor. Elsholtzia ketone was identified in all the three Elsholtzia plants. It can be concluded that the selected Elsholtzia argyi plants can be exploited on their versatile uses as fragrances and antiseptics due to the perfume ingredient and antibacterial components existing in their essential oils.

INTRODUCTION

Some plant species endemic to metalliferous soil accumulate large amounts of heavy metals in their shoot parts so that they show great potential for phytoremediation of metal contaminated soil. Elsholtzia argyi exists widely in Southeast China and grows in some ancient Pb/Zn-mining areas. In the old Pb/Zn mined area, healthy growth of Elsholtzia argyi (PFE1: Purple Flower Elsholtzia) was observed in the soil with extractable Zn, Pb and Cu of approximately 90, 160, and 2.5 mg/kg, shoot concentrations of Zn, Pb and Cu were 180~480, 73~74, and 12~17 mg/kg, respectively (Jiang et al., 2004). Variation of E. argyi (WFE: White Flower Elsholtzia) was also found at the same Pb/Zn contaminated soil, and can accumulate more metal in its shoot parts than PFE1. Both plants grow well at the contaminated soil with high levels of Zn, Pb, but low levels of Cu. With the large-scale phytoremediation for the metal contaminated soil by Elsholtzia argyi, the disposition and utilization of these recourses of plants raise a severe environmental problem.

E. argyi is an endemic, herbaceous, annual plant, whose essential oils are very fragrant and have broad-spectrum antibacterial and antiseptic properties to resist Bacillus, Coccus, and so on (Ke, 1980; Zhu et al., 1992). But little information is available on E. argyi and its variation naturally growing in the metal contaminated soil. In this study, the volatiles components of different E. argyi plants–Purple Flower Elsholtzia (PFE1) and White Flower Elsholtzia (WFE) from the old Pb/Zn mined area, and Purple Flower Elsholtzia (PFE2) from Jiuxi uncontaminated agriculture soil were compared to make full use of these plant resources, especially after their being used for phytoremediation.

MATERIALS AND METHODS

E. argyi (PFE1) and their variation (WFE) were harvested in November 2003 from Pb/Zn mined area in Sanmen County of Zhejiang Province, and the uncontaminated E. argyi (PFE2) from Jiuxi agriculture soil in Hangzhou County of Zhejiang Province.

A simple laboratory quickfit apparatus with a 2000 ml steam generator flask, a distilling flask, a condenser, and a receiving vessel, was used for the steam distillation. Eighty gram air-dried and chipped flower parts of Elsholtzia plants were subjected to steam distillation in the assembly described above. The volatile components were collected into the receiving flask during 1.5 h of steam distillation, dehydrated by Na₂SO₄, and identified by GC/MS (TRACE2000 series, ThermoQuest) technique with a DB-5MS 30 m×0.25 mm quartz capillary column, current gas was N₂, inject temperature was 280 °C, and 0.2 μl was injected (split ratio of 10:1). MS conditions were as follows: 200 °C EI source temperature, 70 eV electron energy, 250 °C interface temperature, 250 eV detector voltage and 2.0 s scan rate. The relative proportions of the essential oil components were expressed as percentages obtained by GC peak area normalization. The identification of their components was based on comparisons of their relative retention times and mass spectra with those of GC/MS library data.

RESULTS AND DISCUSSION

The total ion chromatograms (TIC) of essential oils from the flowers of the Elsholtzia plants are presented in Fig.1. The results of GC/MS analyses are listed in Table 1. Seventeen compounds identified in PFE1 constituted 86.7% of total essential oils. The essential oils of the flowers of PFE1 contained a high level of 2,6-octadienoic acid,3,7-dimethyl-methyl ester (1) (63.3%). Dehydroelsholtzia ketone (5.5%), caryophyllene (4.5%) and 7,11-dimethyl-3-methylene-1,6,10-dodecatriene (Z)- (2) (7.9%) were identified. Sixteen compounds amounting to 95.3% were identified in the volatile oils of WFE; caryophyllene (3) (55.0%) was the main ingredient of fragrances. 2,6-octadienoic acid,3,7-dimethyl-methyl ester (1) (10.2%), dehydroelsholtzia ketone (2.8%) and 7,11-dimethyl-3-methylene-1,6,10-dodecatriene (Z)- (6.5%) were obtained. 7,11-dimethyl-3-methylene-1,6,10-dodecatriene (E)- (4) (10.6%) was identified in WFE but not in PFE1 and PFE2. PFE1 and WFE have evolved to survive in the same Pb/Zn mined area, but showed different phytochemical properties. These compounds are shown as follows:

Fig. 1.

The total ion chromatograms (TIC) obtained from the volatile oil in the flower of (a) the variation of E. argyi naturally growing in Pb/Zn mined area; (b) E. argyi naturally growing in Pb/Zn mined area; (c) E. argyi naturally growing in the uncontaminated agricultural soil

Table 1.

The main components of the essential oils from Elsholtzia argyi

No.	Compounds	Molecular formula	MW	Relative level (%)
				WFE*	PFE1*	PFE2*
1	Acetophenone	C8H8O	120	–	0.07	0.29
2	6-methyl-5-hepten-2-one	C8H14O	126	0.37	0.32	0.02
3	1-octen-3-ol	C8H16O	128	–	0.09	0.39
4	3-octanol	C8H18O	130	–	–	–
5	1-methyl-5-(1-methylethenyl)-cyclohexene	C10H16	136	–	0.01	–
6	(1,3-dimethyl-2-methylene-cyclopentyl)-methanol	C9H16O	140	–	–	0.06
7	Nonanal	C9H18O	142	–	–	0.11
8	3,7-dimethyl-(Z)-2,6-octadienal	C10H16O	152	1.77	0.34	5.41
9	3,7-dimethyl-(E)-2,6-octadienal	C10H16O	152	–	0.17	7.77
10	Eucalyptol	C10H18O	154	–	–	–
11	3,7-dimethyl-1,6-octadien-3-ol	C10H18O	154	–	0.03	0.09
12	Dehydroelsholtzia ketone	C10H12O2	164	2.77	5.47	10.28
13	Elsholtzia ketone	C10H14O2	166	1.39	1.68	3.22
14	Geranic acid	C10H16O2	168	–	1.36	–
15	2,6-octadienoic acid,3,7-dimethyl-methyl ester	C11H18O2	182	10.16	63.30	31.76
16	2,6-octadien-1-ol,3,7-dimethyl-acetate, (Z)-	C12H20O2	196	–	–	0.14
17	Caryophyllene	C15H24	204	55.02	4.48	5.86
18	trans-α-bergamotene	C15H24	204	–	0.16	–
19	7,11-dimethyl-3-methylene-1,6,10-dodecatriene, (Z)-	C15H24	204	6.48	7.86	5.91
20	7,11-dimethyl-3-methylene-1,6,10-dodecatriene, (E)-	C15H24	204	10.56	–	–
21	1-methyl-5-methylene-8-(1-methylethyl)-1,6-cyclodecadiene [s-(E,E)]-	C15H24	204	0.19	0.08	-
22	2,6-dimethyl-6-(4-methyl-3-pentenyl)-bicyclo[3.1.1]hept-2-ene	C15H24	204	–	–	0.09
23	α-farnesene	C15H24	204	–	–	0.03
24	2,6,10-trimethyl-dodecane	C15H32	212	–	–	0.03
25	Caryophyllene oxide	C15H24O	220	4.15	0.94	8.21
26	1,5,5,8-tetramethyl-12-oxabicyclo[9.1.0]dodeca-3,7-diene	C15H24O	220	0.38	0.08	0.36
27	Farnesene epoxide, E-	C15H24O	220	–	–	0.11
28	4,4-dimethyl-tetracyclo[6.3.2.0(2,5).0(1,8)]tridecan-9-ol	C15H24O	220	–	–	0.10
29	Tetradecanoic acid	C14H28O2	228	0.36	–	–
30	n-hexadecanoic acid	C16H32O2	256	0.52	–	–
31	6,10,14-trimethyl-2-pentadecanone	C18H36O	268	0.73	–	0.31
32	2,6,11,15-tetramethyl-hexadeca-2,6,8,10,14-pentane	C20H32	272	0.32	–	0.16
33	2,3-dimethyl-5-(2,6,10-trimethylundecyl) furan	C20H36O	292	–	–	0.10
34	9,12,15-octadecatrienoic acid,2-phenyl-1,3-dioxan-5-yl ester	C28H40O4	440	0.15	–
Total				95.32	86.66	80.18

^*WFE: variation of E. argyi from Sanmen Pb/Zn mined area

PFE1: E. argyi from Sanmen Pb/Zn mined area

PFE2: E. argyi from Jiuxi uncontaminated agricultural area

Description: Compound structures in the article, expressed as a supplementary figure

Compared to PFE1, PFE2 contained lower level of 2,6-octadienoic acid,3,7-dimethyl-methyl ester (1) (31.8%) and 7,11-dimethyl-3-methylene-1,6,10-dod ecatriene (Z)- (2) (5.9%), but exhibited greater level of dehydroelsholtzia ketone (10.3%), 3,7-dimethyl-2,6-octadienoal (Z)- (5.4%), 3,7-dimethyl-2,6-octadienoal (E)- (7.8%) and caryophyllene (3) (5.9%), indicating that the difference in geographical areas where the plants of Purple Flower Elsholzta grow resulted in distinct difference in essential oil components in the flower of the both plants.

Among the common components in the essential oils, 10 compounds out of the total oils in PFE1 and WFE, while 12 compounds of the total oils in PFE1 and PFE2, were observed. PFE1 and WFE contained many more of the components such as 3,7-dimethyl-2,6-octadienal (Z)-, caryophyllene, dehydroelsholtzia ketone, elsholtzia ketone, and caryophyllene oxide. All the three Elsholtzia plants contain Elsholtzia ketone, which is the bacterium and epiphyte resisting characteristic of Elsholtzia plants. While WFE contain much more caryophyllene than other E. argyi plants. Caryophyllene is the perfume ingredient in plants, and can be exploited for versatile uses as fragrances.

Phytoremediation has been considered as a promising approach to remove metals from contaminated soils. Disposal of remedial plant materials after harvest is an unsolved problem (Sas-Nowosielska et al., 2004). Several methods such as composting, compaction, incineration, ashing, pyrolysis, direct disposal and liquid extraction are used for the disposal of the contaminated plant materials after phytoextraction process (Kumar et al., 1995; Salt et al., 1995; 1998; Raskin et al., 1997; Blaylock et al., 1997; Garbisu and Alkorta, 2001; Mulligan et al., 2001). But these disposal treatments are based on the idea that the contaminated plant materials are dealt with as castoff rather than better utilized as resources. Thlaspi can be incinerated to obtain Zn in its ash after harvest from Zn contaminated soil, which is called plant mining. The selected Elsholtzia argyi plants exhibited difference in their volatile components, but the perfume ingredient and antibacterial and antiseptic compounds in the essential oils of the three Elsholtzia plants can be fully utilized for the manufacture of perfumery products and antimicrobial and antiseptic agents.

CONCLUSION

Mined ecotypes of Elsholtzia argyi are Pb-accumulating plant species native to China, and have been suggested to be used for phytoremediation of metal contaminated soils, due to its great biomass and wide adaptation. The disposal of remedial materials after removal of their heavy metals from contaminated soil has become a key problem. The results from this study indicate that the flowers of the selected Elsholtzia argyi plants contain many perfume components, antibacterial and antiseptic ingredients, which can be utilized for flavor and antiseptics manufacture. The full utilization of phytoremediated plant materials is particularly important for implementation of innovative environmental biotechnology.