Kandungan logam-logam berat Pb, Zn, Ni, Co dan Cd pada empat bahagian tumbuhan Nepenthes sp. (akar, batang, daun dan periuk) serta substrat tanih yang menyokong pertumbuhannya dari kawasan bekas lombong bijih timah dan besi di Lombong Pelepah Kanan, Kota Tinggi, Johor telah ditentukan. Komposisi logam-logam berat dalam sampel tanih diekstrak menggunakan campuran asid nitrik pekat dan asid perklorik. Pengekstrakan logam berat dalam tumbuhan pula dilakukan menggunakan kaedah penghadaman basah. Kandungan logam berat di dalam ekstrak larutan tanih dan tumbuhan ditentukan menggunakan Spektrofotometer Penyerapan Atom kaedah nyalaan (FAAS-model Perkin Elmer 3300). Nilai koefisien Penyerapan Biologi (BAC) yang merupakan nisbah kandungan logam berat dalam tumbuhan kepada kandungan logam berat dalam tanih ditentukan secara kiraan. Hasil kajian menunjukkan bahawa tanih di kawasan kajian adalah berasid dan didominasi oleh pasir. Kandungan bahan organik dan kepekatan garam dalam tanih pula adalah rendah, manakala nilai pH adalah berasid. Logam Zn (698.5 mg/kg) menunjukkan kepekatan yang tinggi di dalam substrat tanih diikuti oleh logam Co (182.9 mg/kg), Pb (58.2 mg/kg), Ni (12.2 mg/kg) dan Cd (2.09 mg/kg). Kepekatan logam berat di dalam tumbuhan mengikut kepekatan menurun adalah Ni>Co>Cd>Pb>Zn. Kepekatan logam di dalam bahagian-bahagian tumbuhan tidak menunjukkan perbezaan signifikan bagi semua logam. Tumbuhan Nepenthes sp. didapati menumpukkan logam Ni dalam kepekatan yang tinggi sebagaimana yang ditunjukkan nilai BACnya yang tinggi. Tumbuhan ini mungkin boleh digunakan sebagai bio-penunjuk bagi kehadiran Ni dalam kepekatan yang tinggi di dalam tanih.
This study was carried out at an ultrabasic area, Selaru and Felda Rokan Barat, Kuala Pilah, Negeri Sembilan. Eighteen samples of plant and its substrates were collected for determination of heavy metal contents such as Ni, Co, Cr, Mn and Fe in soils and plants. The plants were separated into different portion such as root, stem and leaf and extracted for their heavy metal content by wet digestion method whereas the soils heavy metal available and resistant content were extracted by sequential extraction. Heavy metals content in soil and plant extract was determined using Flame Atomic Absorption Spectrophotometer. The result showed that total content of heavy metals for Ni, Cr, Co, Mn and Fe was at 84.13 - 740.36 mg/kg, 23.51 - 135.53 mg/kg, 188.23 - 848.92 mg/kg, 245.00 - 545.33 mg/kg and 1176.77 - 1243.90 mg/kg, respectively. Bio-available heavy metals content in soil is at 0.09-6.32 mg/kg for Ni, 0-0.51 mg/kg for Co, 0 mg/kg for Cr, 7.78-21.07 mg/kg for Mn and 2.23-4.47 mg/kg for Fe. Based on BAC, Mn and Fe were detected to have a high concentration in plant parts compared to other heavy metals.
A preliminary study on the concentration and distribution of heavy metals (Cd, Co, Cr, Cu, Ni, Pb and Zn) was carried out for the whole of Ranau District. Topsoil samples (0-15 cm depth) were collected randomly in accordance with the distribution of soil associations in the area. It was found that only three of the heavy metals (Ni, Cr, and Cu) were present above the threshold of toxicity level, whilst the others were below this level. These higher levels of heavy metal concentration were most likely associated with the mining activities in the headwater of the study area and also to the occurrence of serpentinite parent material. The area affected is confined only to the northern part of the study area.
Kajian awal bagi menentukan taburan dan kepekatan logam-logam berat (Cd, Co, Cr, Cu, Ni, Pb dan Zn) telah dijalankan bagi seluruh daerah Ranau. Sample tanah atas (kedalaman 0-15 cm) telah dikutip secara rawak bergantung kepada taburan asosiasi tanah di kawasan tersebut. Didapati bahawa hanya tiga daripada logam berat ini (Ni, Cr dan Cu) melebihi had keracunan, sementara yang lain berada di bawah paras keracunan. Kepekatan logam berat yang tinggi di dalam sampel kajian' dapat dikaitkan dengan aktiviti pelombongan tembaga di kawasan punca air dan juga dengan batuan serpentinit yang menjadi bahan induk tanah. Kawasan yang terlibat terhad di bahagian utara kawasan kajian sahaja.
The sorption parameters of two heavy metals (i.e. Pb and Cu) in clay soils from Selangor were studied using batch equilibrium test. The test was conducted in two separate systems, i.e. single and mix solutions. The sorption isotherms data from this test were then used to calculate the sorption parameters, i.e. distribution coefficient (Kd) and maximum adsorption capacity (Am). Langmuir sorption equation was used to model the sorption data with the correlation coefficients (r2) higher than 0.6. The study has revealed that different soils have different sorption capacity for different heavy metals. The Kd values are proportional to the sorption capacity of the soils. The sorption of Pb and Cu in single solution is higher than in mix solution, due to the competition for sorption sites among heavy metals in mix solution. The Kd values for Pb in single solution ranging from 36.18-334.48 L/g and for Cu is 9.29-66.19 L/g. In mix solution, the Kd values for Pb and Cu are much smaller, ranging from 23.13-31.79 L/g and 3.95-18.53 L/g respectively. The Am values in single solution for both Pb and Cu are ranging from 0.48-1.09 mg/g dan 0.18-0.70 mg/g respectively. While in mix solution, the values of Am for Pb ranging from 0.20-1.11 mg/g and Cu within 0.18-0.60 mg/g.
Kajian kandungan logam berat Cd, Co, Cr, Ni, Pb, dan Zn telah dilakukan ke atas tumbuhan Arundina graminifolia daripada kawasan Lombong Pelepah Kanan, Kota Tinggi, Johor. Kandungan logam berat yang sama turut ditentukan ke atas substrata tanih di tempat di mana tumbuhan itu diambil. Kandungan logam berat dalam tiga bahagian tumbuhan iaitu akar, batang dan daun telah diekstrak secara penghadaman basah manakala kandungan logam berat tersedia dan resistan dalam tanih diekstrak dengan kaedah pengekstrakan berjujukan. Kandungan logam berat jumlah didapati dengan menjumlahkan logam berat tersedia dengan logam berat resistant. Kandungan logam berat di dalam larutan ekstrak tanih dan tumbuhan ditentukan menggunakan Spektrofotometer Serapan Atom Nyalaan. Kandungan logam berat Cd, Cr, Ni dan Pb adalah setara kandungannya dalam semua bahagian tumbuhan manakala kepekatan Co dan Zn adalah tiga hingga lima kali lebih tinggi berbanding tumbuhan kawalan. Bagi kandungan logam berat di dalam bahagian tumbuhan yang berbeza didapati kepekatan Cd adalah lebih tinggi dalam akar (2.03 mg/kg) diikuti oleh daun (1.67 mg/kg) dan batang (1.49 mg/kg). Kepekatan Co adalah lebih tinggi dalam daun (9.26 mg/kg) diikuti oleh akar (9.18 mg/kg) dan batang (6.94 mg/kg). Kepekatan Cr mengikut susunan menurun adalah akar (0.46 mg/kg) > daun (0.19 mg/kg) > batang (0.08 mg/kg). Kepekatan Ni adalah lebih tinggi dalam daun (2.78 mg/kg) diikuti oleh akar (2.71 mg/kg) dan batang (1.66 mg/kg). Kepekatan Pb mengikut susunan menurun adalah akar (10.34 mg/kg) > daun (4.18 mg/kg) > batang (3.75 mg/kg). Kepekatan Zn lebih tinggi dalam daun (44.03 mg/kg) diikuti oleh akar (32.30 mg/kg) dan batang (13.21 mg/kg). Kandungan logam berat jumlah dalam tanih adalah masing-masing 2.07-5.59 mg/kg, 8.72-39.93 mg/kg, 1.81-2.14 mg/kg, 2.66-6.87 mg/kg, 23.02-51.56 mg/kg and 0.64-2.61 mg/kg bagi Ni, Zn, Cd, Pb, Co dan Cr. Didapati bahawa kandungan fraksi tersedia dalam tanih adalah 21.9% bagi Ni, 15.3% bagi Zn, 49.9% bagi Cd, 19.3% bagi Pb, 45.7% bagi Co and 0% bagi Cr. Koefisien penyerapan biologi tumbuhan ke atas logam berat yang dikaji adalah rendah keculai bagi Zn yang nilainya lebih daripada 1. Tumbuhan ini tidak sesuai digunakan sebagai agen fitoremediasi untuk logam-logam di atas.
Kajian ini dijalankan di kawasan tanih ultrabes di Felda Rokan Barat (FRB), Negeri Sembilan. Sebanyak dua puluh sampel cili, kunyit, pandan dan serai serta substratnya telah diambil secara rawak untuk penentuan kandungan logam berat Fe, Cd, Co, Cu, Mn, Ni, Pb, Cr dan Zn. Kandungan logam berat dalam tumbuhan diekstrak secara penghadaman basah, manakala kandungan logam berat resistan dan tersedia dalam tanih diekstrak dengan kaedah pengekstrakan berjujukan. Kandungan logam berat jumlah diperoleh dengan menjumlahkan kandungan logam berat rintang dan tersedia. Kandungan logam berat di dalam larutan ekstrak tanih dan tumbuhan ditentukan dengan menggunakan Spektrofotometer Penyerapan Atom Nyalaan (FAAS). Hasil kajian menunjukkan logam Fe adalah dominan di dalam tanih di kawasan kajian manakala kepekatan logam Cd paling rendah dengan nilai < 10 mg/kg. Sela kepekatan logam-logam berat dalam tanih ialah Fe (2618.4 hingga 4248 mg/kg), Mn (240.9 hingga 741.9 mg/kg), Zn (81.9 hingga 324.8 mg/kg), Cr (46.8 hingga 438.7 mg/kg), Cu (15.7 hingga 81.7 mg/kg), Pb (14.9 hingga 116.8 mg/kg), Ni (10.1 hingga 545.6 mg/kg), Cd (5.6 hingga 10.6 mg/kg) dan Co (0.8 hingga 126.1 mg/kg). Nilai kepekatan Fe tersedia mencatatkan nilai tertinggi bagi semua substrat tumbuhan, diikuti oleh Mn, Zn, Pb, Ni, Cr, Cu, Co dan Cd. Berdasarkan peratusan tersedia Mn, Pb dan Zn merupakan logam berat yang paling banyak tersedia diambil oleh tumbuhan dengan nilai 8 hingga 10%. Kepekatan Fe, Mn, Ni dan Zn menunjukkan purata kepekatan yang tinggi pada bahagian tumbuhan yang dikaji berbanding dengan logam lain. Nilai koefisien penyerapan biologi (BAC) bagi cili, kunyit, pandan dan serai masing-masing dalam julat 0.02-0.36, 0.03-0.41, 0.03-0.63 dan 0.03-1.15. Boleh disimpulkan bahawa penyerapan logam berat oleh tumbuhan adalah normal walaupun kepekatan logam berat dalam tanih ultrabes adalah tinggi.
The concentrations of the heavy metal in Pacific white shrimp (Litopenaeus vannamei) purchased from the local wet markets throughout the state of Selangor were investigated using flame atomic absorption spectrometry. The order of the heavy metal concentrations were Zn>Cu>Pb>Cd, whereby the metal concentrations in most samples exceeded the limits of the Malaysian Food Regulation, 1985 and the guidelines set by the Food and Agriculture Organisation (1983). A health risk analysis based on the mean target hazard quotient (THQ) yielded values <1 for all metals for average and maximal consumers. The total THQ (tTHQ) which measures the aggregated risk due to heavy metal uptake via the ingestion of L. vannamei was 0.124 and 0.372 for average and maximal consumers, respectively. This suggests that although the metal concentrations are exceeding the limit, there is no calculated significant risk from metal toxicity by the consumption of shrimp.
The prime objective of the present research work was to evaluate the efficiency of bio-machine for the removal of Cadmium (Cd) from aquatic systems. Aspergillus niger fungus was used as bio-machine to remove Cd from aquatic systems. Twenty three different strains (IIB-1 to IIB-23) were isolated from industrial effluents and the Langmuir and Freundlich models were applied to the best Cadmium removal strain IIB-23 in order to obtain the adsorption parameters. Different parameters such as pH, temperature, contact time, initial metal concentratio, and biomass dosage on the biosorption of Cd were studied. The percent removal of Cd initially increased with an increase in pH ranging from 5.5-6.5 and then decreased by increasing pH from 7.0-7.5. An optimized pH used for Cd removal from aquatic systems was found to be 6.5. Additionally, an optimum amount of biomass was 1.33 g for the maximum removal of Cd from the aqueous solutions with initial metal concentration of 75 mg/L. The results obtained thus indicated that Langmuir model is the best suited for the removal of Cd from aquatic systems.
This work reviews design aspects of liquid metal antennas and their corresponding applications. In the age of modern wireless communication technologies, adaptability and versatility have become highly attractive features of any communication device. Compared to traditional conductors like copper, the flow property and lack of elasticity limit of conductive fluids, makes them an ideal alternative for applications demanding mechanically flexible antennas. These fluidic properties also allow innovative antenna fabrication techniques like 3D printing, injecting, or spraying the conductive fluid on rigid/flexible substrates. Such fluids can also be easily manipulated to implement reconfigurability in liquid antennas using methods like micro pumping or electrochemically controlled capillary action as compared to traditional approaches like high-frequency switching. In this work, we discuss attributes of widely used conductive fluids, their novel patterning/fabrication techniques, and their corresponding state-of-the-art applications.
Recently, natural fiber-reinforced polymers (NFRPs) have become important materials in many engineering applications; thus, to employ these materials some final industrial processes are needed, such as cutting, trimming, and drilling. Because of the heterogeneous nature of NFRPs, which differs from homogeneous materials such as metals and polymers, several defects have emerged when processing the NFRPs through traditional cutting methods such as high surface roughness and material damage at cutting zone. In order to overcome these challenges, unconventional cutting methods were considered. Unconventional cutting methods did not take into account the effects of cutting forces, which are the main cause of cutting defects in traditional cutting processes. The most prominent unconventional cutting processes are abrasive waterjet (AWJM) and laser beam (LBM) cutting technologies, which are actually applied for cutting various NFRPs. In this study, previously significant studies on cutting NFRPs by AWJM and LBM are discussed. The surface roughness, kerf taper, and heat-affected zone (HAZ) represent the target output parameters that are influenced and controlled by the input parameters of each process. However, this topic requires further studies on widening the range of material thickness and input parameter values.
As one of the potential bionanomaterials, nanocellulose has appeared as a favorable candidate for photoremediation of the environment because of its abundance in nature, inexpensive, eco-friendly, decomposable, high surface area, and outstanding mechanical properties. The current review carefully summarized the diverse type of nanocellulose, their preparation approaches, and several previous works on the use of nanocellulose for photoremediation. These include the role of nanocellulose for the increased surface active site of the hybrid photocatalysts by providing a large surface area for enhanced adsorption of photons and pollutant molecules, as a dispersing agent to increase distribution of metal/non-metal dopants photocatalysts, as well as for controlled size and morphology of the dopants photocatalysts. Furthermore, the recommendations for upcoming research provided in this review are anticipated to ignite an idea for the development of other nanocellulose-based photocatalysts. Other than delivering beneficial information on the present growth of the nanocellulose biomaterials photocatalysts, this review is expected will attract more interest to the utilization of nanocellulose photocatalyst and distribute additional knowledge in this exciting area of environmental photoremediation. This could be attained by considering that a review on nanocellulose biomaterials for environmental health photoremediation has not been described elsewhere, notwithstanding intensive research works have been dedicated to this topic.
This paper presents the design and analysis of a novel split-H-shaped metamaterial unit cell structure that is applicable in a multi-band frequency range and that exhibits negative permeability and permittivity in those frequency bands. In the basic design, the separate split-square resonators are joined by a metal link to form an H-shaped unit structure. Moreover, an analysis and a comparison of the 1 × 1 array and 2 × 2 array structures and the 1 × 1 and 2 × 2 unit cell configurations were performed. All of these configurations demonstrate multi-band operating frequencies (S-band, C-band, X-band and Ku-band) with double-negative characteristics. The equivalent circuit model and measured result for each unit cell are presented to validate the resonant behavior. The commercially available finite-difference time-domain (FDTD)-based simulation software, Computer Simulation Technology (CST) Microwave Studio, was used to obtain the reflection and transmission parameters of each unit cell. This is a novel and promising design in the electromagnetic paradigm for its simplicity, scalability, double-negative characteristics and multi-band operation.
An electromagnetic pulse (EMP) explodes in real-time and causes critical damage within a short period to not only electric devices, but also to national infrastructures. In terms of EMP shielding rooms, metal plate has been used due to its excellent shielding effectiveness (SE). However, it has difficulties in manufacturing, as the fabrication of welded parts of metal plates and the cost of construction are non-economical. The objective of this study is to examine the applicability of the arc thermal metal spraying (ATMS) method as a new EMP shielding method to replace metal plate. The experimental parameters, metal types (Cu, Zn-Al), and coating thickness (100-700 μm) used for the ATMS method were considered. As an experiment, a SE test against an EMP in the range of 103 to 1010 Hz was conducted. Results showed that the ATMS coating with Zn-Al had similar shielding performance in comparison with metal plate. In conclusion, the ATMS method is judged to have a high possibility of actual application as a new EMP shielding material.
The aim of this study is to compare antioxidant level and activities (i.e. primary and secondary) in pulps and peels of two species of dragon fruits, Hylocereus undatus (white dragon fruit) and Hylocereus polyrhizus (red dragon fruit). Total phenolic content (TPC) assay demonstrated that peels of both Hylocereus species contained higher phenolic content than the pulps. The phenolic content in peels of H. undatus was higher than H. polyrhizus, but the phenolic content in pulps of H. undatus was much lower than H. polyrhizus. 2, 2, diphenyl-1-picrylhydrazyl (DPPH) assay showed that radical scavenging activities of peels for both species were higher than the pulps. For ferrous ion chelating (FIC) assay, peels and pulps of both Hylocereus species showed moderate metal ion chelating effect as compared to EDTA. Overall, the results suggested that the TPC showed good relationship with the primary antioxidant activities for general comparison between the peels and the pulps.
Ferroelectric photoelectrodes, other than conventional semiconductors, are alternative photo-absorbers in the process of water splitting. However, the capture of photons and efficient transfer of photo-excited carriers remain as two critical issues in ferroelectric photoelectrodes. In this work, we overcome the aforementioned issues by decorating the ferroelectric BiFeO3 (BFO) surface with Au nanocrystals, and thus improving the photoelectrochemical (PEC) performance of BFO film. We demonstrate that the internal field induced by the spontaneous polarization of BFO can (1) tune the efficiency of the photo-excited carriers' separation and charge transfer characteristics in bare BFO photoelectrodes, and (2) modulate an extra optical absorption within the visible light region, created by the surface plasmon resonance excitation of Au nanocrystals to capture more photons in the Au/BFO heterostructure. This study provides key insights for understanding the tunable features of PEC performance, composed of the heterostructure of noble metals and ferroelectric materials.
A feasible and cost-effective process for utilization of toluene and heavy reformate is the conversion of its streams by transalkylation reaction into highly valuable xylenes. The process is usually catalysed by zeolites and the challenges to overcome in transalkylation of heavy reformate with toluene over zeolites are their selectivity, activity, long-term stability, and coke formation. Current study aimed to investigate xylenes production by transalkylation reaction on the synthesized metal-doped zeolite catalysts and to characterize prepared catalysts by FTIR, SEM, EDS and BET analysis. Toluene/heavy reformate modelled mixture was utilized as a feed. For the first time Beta and ZSM-5 catalysts with 10% (w/w) cerium and 0.1% (w/w) palladium were synthesized by calcination and wet impregnation method. Catalytic tests were performed by continuous-flow gas/solid catalytic fixed bed reactor at atmospheric pressure, 2 h-1 and 5 h-1 and 250, 300, 350 and 400 °C. Experimental results revealed that the highest heavy reformate conversion (98.94%) and toluene conversion (9.82%) were obtained over H-ZSM-5, at 400 °C and 2 h-1 WHSV. The highest xylene selectivity (11.53) was achieved over H-ZSM-5, and the highest p-xylene percentage (62.40%), using Ce-ZSM-5 catalyst. ZSM-5 catalysts showed more resistance to coke deposition than Beta zeolites. The present study delivers novel approach and catalysts, which have immense potential for developing safer and inexpensive transalkylation process in industry.
The use of various machines, equipment and power tools at TVET Institute causes the institute's environment to be exposed to noise hazards that are similar to the industry. However, not much data has been published regarding noise exposure at TVET institutes. This study was carried out to document the noise exposure of work activities training in public TVET institutes in Malaysia that implement skill training programs in metal fabrication, furniture manufacturing and automotive maintenance. The identification of excessive noise, task-based noise exposure monitoring and source measurement was conducted. The noise contribution from each work activity to the daily A-weighted noise exposure level and sound pressure level emitted by machines and equipment was documented. The findings of this study recorded 20 activities with task-based noise contribution to the daily A-weighted noise exposure level between 75.3 dB and 95 dB. Based on the findings, the training environment at the TVET institutes has a risk of operating with excessive noise. The documented data can be used in planning the implementation of suitable noise control measures in TVET institutes.
Natural enzymes possess several drawbacks which limits their application in industries, wastewater remediation and biomedical field. Therefore, in recent years researchers have developed enzyme mimicking nanomaterials and enzymatic hybrid nanoflower which are alternatives of enzyme. Nanozymes and organic inorganic hybrid nanoflower have been developed which mimics natural enzymes functionalities such as diverse enzyme mimicking activities, enhanced catalytic activities, low cost, ease of preparation, stability and biocompatibility. Nanozymes include metal and metal oxide nanoparticles mimicking oxidases, peroxidases, superoxide dismutase and catalases while enzymatic and non-enzymatic biomolecules were used for preparing hybrid nanoflower. In this review nanozymes and hybrid nanoflower have been compared in terms of physiochemical properties, common synthetic routes, mechanism of action, modification, green synthesis and application in the field of disease diagnosis, imaging, environmental remediation and disease treatment. We also address the current challenges facing nanozyme and hybrid nanoflower research and the possible way to fulfil their potential in future.
Ultrasound (US) demonstrates remarkable potential in synthesising nanomaterials, particularly nanobiomaterials targeted towards biomedical applications. This review briefly introduces existing top-down and bottom-up approaches for nanomaterials synthesis and their corresponding synthesis mechanisms, followed by the expounding of US-driven nanomaterials synthesis. Subsequently, the pros and cons of sono-nanotechnology and its advances in the synthesis of nanobiomaterials are drawn based on recent works. US-synthesised nanobiomaterials have improved properties and performance over conventional synthesis methods and most essentially eliminate the need for harsh and expensive chemicals. The sonoproduction of different classes and types of nanobiomaterials such as metal and superparamagnetic nanoparticles (NPs), lipid- and carbohydrate-based NPs, protein microspheres, microgels and other nanocomposites are broadly categorised based on the physical and/or chemical effects induced by US. This review ends on a good note and recognises US-driven synthesis as a pragmatic solution to satisfy the growing demand for nanobiomaterials, nonetheless some technical challenges are highlighted.
With rapid urbanization and large-scale industrial activities, modern human populations are being increasingly subjected to chronic environmental heavy metal exposures. Elemental uptake in tooth dentine is a bioindicator, the uptake occurring during the formation and mineralization processes, stored to large extent over periods of many years. The uptake includes essential elements, most typically geogenic dietary sources, as well as non-essential elements arising through environmental insults. In this study, with the help of the Dental Faculty of the University of Malaya, a total of 50 separate human teeth were collected from dental patients of various ethnicity, age, gender, occupation, dietary habit, residency, etc. Analysis was conducted using inductively coupled plasma-mass spectrometry (ICP-MS), most samples indicating the presence of the following trace elements, placed in order of concentration, from least to greatest: As, Mn, Ba, Cu, Cr, Pb, Zn, Hg, Sb, Al, Sr, Sn. The concentrations have been observed to increase with age. Among the ethnic groups, the teeth of ethnic Chinese showed marginally greater metal concentrations than those of the Indians and Malays, the teeth dentine of females generally showing greater concentrations than that of males. Greater concentrations of Hg, Cu and Sn were found in molars while Pb, Sr, Sb and Zn were present in greater concentrations in incisors. With the elevated concentration levels of heavy metals in tooth dentine reflecting pollution from industrial emissions and urbanization, it is evident that human tooth dentine can provide chronological information on exposure, representing a reliable bio-indicator of environmental pollution.