International Journal of Environmental Research and Public Health Article Invasive Weed Asystasia gangetica as a Potential Biomonitor and a Phytoremediator of Potentially Toxic Metals: A Case Study in Peninsular Malaysia Chee Kong Yap 1,* , Weiyun Chew 1,† , Khalid Awadh Al-Mutairi 2, Salman Abdo Al-Shami 3 , Rosimah Nulit 1 , Mohd Hafiz Ibrahim 1, Koe Wei Wong 1 , Alireza Riyahi Bakhtiari 4, Moslem Sharifinia 5 , Wan Hee Cheng 6, Hideo Okamura 7, Mohamad Saupi Ismail 8 and Muhammad Saleem 9 1 Department of Biology, Faculty of Science, Universiti Putra Malaysia, UPM, Serdang 43400, Malaysia; [email protected] (W.C.); [email protected] (R.N.); mhafi[email protected] (M.H.I.); [email protected] (K.W.W.) 2 Department of Biology, Faculty of Science, University of Tabuk, Tabuk 741, Saudi Arabia; [email protected] 3 Indian River Research and Education Center, IFAS, University of Florida, Fort Pierce, FL 34945, USA; [email protected] 4 Department of Environmental Sciences, Faculty of Natural Resources and Marine Sciences, Tarbiat Modares University, Noor 46417-76489, Iran; [email protected] 5 Shrimp Research Center, Iranian Fisheries Science Research Institute, Agricultural Research, Education and Extension Organization (AREEO), Bushehr 75169-89177, Iran; moslem.sharifi[email protected] 6 Faculty of Health and Life Sciences, Inti International University, Persiaran Perdana BBN, Citation: Yap, C.K.; Chew, W.; Nilai 71800, Malaysia; [email protected] 7 Graduate School of Maritime Sciences, Faculty of Maritime Sciences, Kobe University, Kobe 658-0022, Japan; Al-Mutairi, K.A.; Al-Shami, S.A.; [email protected] Nulit, R.; Ibrahim, M.H.; Wong, K.W.; 8 Fisheries Research Institute, Pulau Pinang 11960, Malaysia; [email protected] Bakhtiari, A.R.; Sharifinia, M.; Cheng, 9 Department of Chemistry, Government Post Graduate College Mirpur, Affiliated Mirpur University of W.H.; et al. Invasive Weed Asystasia Science and Technology, Mirpur 10250, Pakistan; [email protected] gangetica as a Potential Biomonitor * Correspondence: [email protected] and a Phytoremediator of Potentially † Present address: Centre for Pre-University Study, Level, 6, Unity Building, MAHSA University, Bandar Toxic Metals: A Case Study in Saujana Putra, Jenjarom 42610, Malaysia. Peninsular Malaysia. Int. J. Environ. Res. Public Health 2021, 18, 4682. Abstract: The invasive weed Asystasia gangetica was investigated for its potential as a biomonitor https://doi.org/10.3390/ and as a phytoremediator of potentially toxic metals (PTMs) (Cd, Cu, Ni, Pb, and Zn) in Peninsular ijerph18094682 Malaysia owing to its ecological resistance towards unfavourable environments. The biomonitoring potential of PTMs was determined based on the correlation analysis of the metals in the different Academic Editor: Paul B. Tchounwou parts of the plant (leaves, stems, and roots) and its habitat topsoils. In the roots, the concentrations (mg/kg dry weight) of Cd, Cu, Ni, Pb, and Zn ranged from 0.03 to 2.18, 9.22 to 139, 0.63 to 5.47, 2.43 Received: 22 February 2021 Accepted: 26 March 2021 to 10.5, and 50.7 to 300, respectively. In the leaves, the concentrations (mg/kg dry weight) of Cd, Published: 28 April 2021 Cu, Ni, Pb, and Zn ranged from 0.03 to 1.16, 7.94 to 20.2, 0.03 to 6.13, 2.10 to 21.8, and 18.8 to 160, respectively. In the stems, the concentrations (mg/kg dry weight) of Cd, Cu, Ni, Pb, and Zn ranged Publisher’s Note: MDPI stays neutral from 0.03 to 1.25, 5.57 to 11.8, 0.23 to 3.69, 0.01 to 7.79, and 26.4 to 246, respectively. On the other with regard to jurisdictional claims in hand, the phytoremediation potential of the five metals was estimated based on the bioconcentration published maps and institutional affil- factor (BCF) and the translocation factor (TF) values. Correlation analysis revealed that the roots iations. and stems could be used as biomonitors of Cu, the stems as biomonitors of Ni, the roots and leaves as biomonitors of Pb, and all three parts of the plant as biomonitors of Zn. According to the BCF values, in the topsoil, the “easily, freely, leachable, or exchangeable” geochemical fractions of the five metals could be more easily transferred to the roots, leaves, and stems when compared with total Copyright: © 2021 by the authors. concentrations. Based on the TF values of Cd, Ni, and Pb, the metal transfer to the stems (or leaves) Licensee MDPI, Basel, Switzerland. from the roots was efficient (>1.0) at most sampling sites. The results of BCF and TF showed that This article is an open access article A. gangetica was a good phytoextractor for Cd and Ni, and a good phytostabilizer for Cu, Pb, and Zn. distributed under the terms and Therefore, A. gangetica is a good candidate as a biomonitor and a phytoremediator of Ni, Pb, and Zn conditions of the Creative Commons for sustainable contaminant remediation subject to suitable field management strategies. Attribution (CC BY) license (https:// creativecommons.org/licenses/by/ 4.0/). Int. J. Environ. Res. Public Health 2021, 18, 4682. https://doi.org/10.3390/ijerph18094682 https://www.mdpi.com/journal/ijerph Int. J. Environ. Res. Public Health 2021, 18, 4682 2 of 28 Keywords: potentially toxic metals; invasive weeds; phytoremediation; biomonitoring 1. Introduction The natural ability to withstand harsh environments, such as degraded land, of the invasive weed Asystasia gangetica (L.) makes this species a potential biomonitor and phytore- mediator for potentially toxic metal (PTM) pollution [1]. Its potential in the biomonitoring and phytoremediation of PTMs is owing to its ecological characteristics, as shown below: (a) It has a wide geographical distribution. It is a herb originally from India and Sri Lanka [2], but it is now a highly invasive weed species that is widely naturalised in Southeast Asia (Malaysia and Indonesia in particular) and in the Pacific Islands [3], Taiwan [4], and Northern Australia [5,6]. (b) It has high abundance. It produces seeds in large quantities [7]. This causes the weed to be utilised as a cover crop in oil palm plantations [8,9]. It is an evergreen herb that forms mat-like structures that smother more desirable ground plants, hence affecting the biodiversity and agricultural aspects of a particular environment [6]. (c) It is easy to grow and at a fast growth rate [10]. Under experimental polybags in greenhouse conditions, Kumalasari et al. [11] reported that the dry matter yields of both the leaf and stem of A. gangetica increased (p < 0.001) progressively with age and reached 11.6 g leaf dry matter, 19.0 g stem dry matter/plant, and 30.6 g total dry matter/plant at 90 days after transplanting. Even though the biomass is not substantial when compared with other plants, the fast growth rate of the weeds can still justify A. gangetica as a phytoremediator of PTMs. (d) It is adaptable to different environmental conditions [12], being high shade toler- ant [10], it can even grow well under 90% shade [7]. It thrives best in full light and open areas [3,13]. It has high resistance towards metals stress and toxic effects, able to translocate metals from root to shoot, highly resistant towards pathogens and pests, easy adaptability to the climatic conditions of the growth area, and is not part of the food chain as it is not edible by nature [14–17]. (e) It grows well in various types of soil all year round [18] and it can tolerate high levels of pollutants [19]. Thus, the plant is widely distributed and is found in abundance in unattended open areas such as roadsides and riverbanks [2]. (f) It had been reported to enhance the contents of N, P, and K in the soil and to create a nutrient balance [20]. In addition to contributing N, P, and K to the soil [20], it is also rapidly decomposed [21], and hence can serve as a soil carbon stock [20]. (g) It was proposed as a biomonitor for PTM metal pollution such as Hg [22,23]. In Peninsular Malaysia, it is an invasive non-native weed that can be potentially used as a good biomonitor in different land uses because this weed species is widely distributed here [24]. To study the plant’s potential for phytoremediation (phytoextraction and phytosta- bilisation) quantitatively, the bioconcentration factor (BCF) and the translocation factor (TF) can be used [25–28]. For the selection of good hyperaccumulators for the phytoex- traction of metals, both BCF and TF are equally crucial to select plants that are capable of phytoextracting metals from the surrounding environment [29]. The BCF is the evaluation of the ability of a plant to accumulate metals from its surrounding environment (such as habitat soil) into its tissues (such as roots, stems, and leaves) [30]. On the other hand, TF is the evaluation of a plant’s ability to transfer the accumulated metals from its below-ground parts (such as roots) to the plant above-ground parts (shoots such as stems or leaves) via the translocation pathway [31]. Reports using plants as biomonitors of anthropogenic sources of PTM pollution are commonly found in the literature [32–36]. These showed that the metal levels in plant parts (leaves and roots) reflect the ambient air pollutant levels and the anthropogenic sources of pollutants in the habitats. In the study by Divan et al. [37], the wild plant Int. J. Environ. Res. Public Health 2021, 18, x FOR PEER REVIEW 3 of 29 parts (leaves and roots) reflect the ambient air pollutant levels and the anthropogenic Int. J. Environ. Res. Public Health 2021,sources18, 4682 of pollutants in the habitats. In the study by Divan et al.