## 1 Introduction  
Heavy metal contamination of water is a growing problem, because of the industrial and technological development and the wide use of the associated materials. Toxic heavy metals released during manufacturing processes pose a serious threat to the environment, due to their non-degradable character and high possibility of bioaccumulation, particularly in plants [1]. The intake and accumulation of heavy metals also have serious health consequences for humans, such as cancer, organ failure, nervous system disorder, growth retardation, etc. [2; 3; 4]. The toxicity of lead has been known since antiquity, and remains a problem today [5]. Lead can be found in water, soil, air, in water transport systems due to the corrosion of lead pipes, from industrial discharges, and through the use of leaded gasoline. Therefore, policymakers and researchers are looking for sustainable ways to treat wastewater containing toxic metals released from industrial sources. Established technologies for removing toxic metals from wastewater include membrane filtration [6], chemical precipitation [7], and ion exchange [8], as well as reverse osmosis and adsorption on activated carbon [9]. However, many of these methods are expensive, have unpredictable performance, and/or generate toxic byproducts that are difficult to manage. Hence, their applications are limited [9]. The adsorption technique is a relatively successful one, since it features a simple design, easy operation, and high separation efficiencies [10,11]. Activated carbon is the most common sorbent for separating heavy metal from wastewater. However, it still suffers from a high cost, problems in regeneration and disposal, and dissolution under extremely acidic conditions. Therefore, there is a growing research effort to find cheaper and greener alternative adsorbents [12, 13, 14]. Many researchers have used natural biomaterials, such as agricultural or plant wastes for immobilizing environmental pollutants, because they are inexpensive, renewable, abundant, environmentally friendly, and biodegradable [15]. Example adsorbents for removing toxic metals include vegetable peels, banana peels, coffee grounds, cactus, rice straw, wheat straw, _Diplotaxis harra_ (wall rocket), and _Glebionis coronaria_ (crown daisy) [9, 15, 16, 17, 18, 19]. The biosorption processes could occur through different mechanisms (e.g., chemisorption, complexation, adsorption-complexation on surfaces and pores, ion exchange, microprecipitation, and sorption by physical forces). They are also influenced by many parameters modulating the interaction between the adsorbate and absorbent, such as pH, initial metal ion concentration, biomass dosage, temperature, contact time, and the presence of other metal ions in solution [4,15]. _Lavandula pubescens_ (_L. pubescens_) belongs to the genus of lavender (_Lamiaceae_ family). It grows abundantly as a shrub in the wild across Saudi Arabia. _L. pubescens_ has been predominantly used in aromatherapy as a relaxant and a carminative, antimicrobial, antitumor, and sedative agent, owing to its phytochemical components, such as essential oil, flavonoids, coumarins, polyphenolics, alkaloids, and terpen [20,21]. To our best knowledge, however, only a few studies have employed this plant material for heavy metal removal [22]. Herein, the dried aerial part of _L. pubescens_ was used for the first time as adsorbent without any physical or chemical pretreatment for removing Pb(II) ions from water. This method does not require any toxic and costly material or complicated procedure. To gain better insight into the plant constituents-adsorption activity relationship, before the adsorption experiments, the plant was first characterized by gas chromatography-mass spectrometry (GC/MS), gas liquid chromatography (GLC), and Fourier transform infrared (FTIR) spectroscopy. Therefore, the following influencing parameters for adsorption were considered: the contact time, initial concentration of Pb(II) ions, adsorbent dosage, pH, and temperature.