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  1. Dioxin-like polychlorinated biphenyls, polychlorinated dibenzo-p-dioxins, and polychlorinated dibenzofurans in seafood samples from Malaysia: estimated human intake and associated risks
    Leong YH, Gan CY, Majid MI
    Arch Environ Contam Toxicol, 2014 Jul;67(1):21-8.
    PMID: 24651928 DOI: 10.1007/s00244-014-0019-5
    A total of 127 and 177 seafood samples from Malaysia were analyzed for polychlorinated dibenzo-p-dioxins/dibenzofurans (PCDD/Fs) and dioxin-like polychlorinated biphenyls (dl-PCBs), respectively. The World Health Organization-toxic-equivalency quotients (WHO-TEQ) of PCDD/Fs varied from 0.13 to 1.03 pg TEQ g(-1), whereas dl-PCBs ranged from 0.33 to 1.32 pg TEQ g(-1). Based on food-consumption data from the global environment monitoring system-food contamination monitoring and assessment programme, calculated dietary exposures to PCDD/Fs and dl-PCBs from seafood for the general population in Malaysia were 0.042 and 0.098 pg TEQ kg(-1) body weight day(-1), respectively. These estimations were quite different from the values calculated using the Malaysian food-consumption statistics (average of 0.313 and 0.676 pg TEQ kg(-1) body weight day(-1) for PCDD/Fs and PCBs, respectively). However, both of the dietary exposure estimations were lower than the tolerable daily intake recommended by WHO. Thus, it is suggested that seafood from Malaysia does not pose a notable risk to the health of the average consumer.
  2. Exposure measurement of aflatoxins and aflatoxin metabolites in human body fluids. A short review
    Leong YH, Latiff AA, Ahmad NI, Rosma A
    Mycotoxin Res, 2012 May;28(2):79-87.
    PMID: 23606045 DOI: 10.1007/s12550-012-0129-8
    Aflatoxins are highly toxic secondary fungal metabolites mainly produced by Aspergillus flavus and A. parasiticus. Human exposure to aflatoxins may result directly from ingestion of contaminated foods, or indirectly from consumption of foods from animals previously exposed to aflatoxins in feeds. This paper focuses on exposure measurement of aflatoxins and aflatoxin metabolites in various human body fluids. Research on different metabolites present in blood, urine, breast milk, and other human fluids or tissues including their detection techniques is reviewed. The association between dietary intake of aflatoxins and biomarker measurement is also highlighted. Finally, aspects related to the differences between aflatoxin determination in food versus the biomarker approach are discussed.
  3. Exposure assessment and risk characterization of aflatoxin B1 in Malaysia
    Leong YH, Rosma A, Latiff AA, Ahmad NI
    Mycotoxin Res, 2011 Aug;27(3):207-14.
    PMID: 23605801 DOI: 10.1007/s12550-011-0097-4
    Aflatoxin B1 (AFB1) was detected in 57% of the nuts and nut products marketed in Penang, Malaysia using the liquid chromatography tandem mass spectrometry. The contamination levels ranged from 0.40 to 222 μg/kg and 17 out of 128 samples (13.3%) contained AFB1 above the European Commission permitted level (2 μg/kg). Estimated dietary exposure of AFB1 in nuts and nut products were 0.36 ng per kg body weight and day and 8.89 ng per kg body weight and day, representing the low and high-level of exposure, respectively. Dose-response modelling resulted in benchmark dose lower confidence limit (BMDL10) values of 0.305 ng per kg body weight and day, with the best fitted from the log-logistic model. The derived margin of exposure (MoE) values ranged from 34 to 847 suggested that AFB1 would be of public health concern and might reasonably be considered as a high priority for risk management actions.
  4. Associations of serum aflatoxin B1-lysine adduct level with socio-demographic factors and aflatoxins intake from nuts and related nut products in Malaysia
    Leong YH, Rosma A, Latiff AA, Izzah AN
    Int J Hyg Environ Health, 2012 Apr;215(3):368-72.
    PMID: 22230243 DOI: 10.1016/j.ijheh.2011.12.005
    Aflatoxins are one of the major risk factors in the multi-factorial etiology of human hepatocellular carcinoma. Therefore, the information on aflatoxins exposure is very important in the intervention planning in order to reduce the dietary intake of aflatoxins, especially among the children. This study investigated the relationship between aflatoxin B(1) (AFB(1)) lysine adduct levers in serum and socio-demographic factors and dietary intake of aflatoxins from nuts and nut products in Penang, Malaysia. A cross-sectional field study was conducted in five districts of Penang. A survey on socio-demographic characteristics was administered to 364 healthy adults from the three main ethnic groups (Malay, Chinese and Indian). A total of 170 blood samples were successfully collected and tested for the level of AFB(1)-lysine adduct. 97% of the samples contained AFB(1)-lysine adduct above the detection limit of 0.4 pg/mg albumin and ranged from 0.20 to 23.16 pg/mg albumin (mean±standard deviation=7.67±4.54 pg/mg albumin; median=7.12 pg/mg albumin). There was no significant association between AFB(1)-lysine adduct levels with gender, district, education level, household number and occupation when these socio-demographic characteristics were examined according to high or low levels of AFB(1)-lysine. However, participants in the age group of 31-50 years were 3.08 times more likely to have high AFB(1) levels compared to those aged between 18 and 30 years (P=0.026). Significant difference (P=0.000) was found among different ethnic groups. Chinese and Indian participants were 3.05 and 2.35 times more likely to have high AFB(1) levels than Malay. The result of AFB(1)-lysine adduct suggested that Penang adult population is likely to be exposed to AFB(1) but at a level of less than that needed to cause direct acute illness or death.
  5. Exposure and risk assessment of polychlorinated dibenzo-p-dioxins (PCDDs), polychlorinated dibenzofurans (PCDFs) and dioxin-like polychlorinated biphenyls (dl-PCBs) for primiparous mothers and breastfed infants in Penang, Malaysia
    Leong YH, Azmi NI, Majid MIA, Wen S
    Food Addit Contam Part A Chem Anal Control Expo Risk Assess, 2021 Aug;38(8):1416-1426.
    PMID: 34014804 DOI: 10.1080/19440049.2021.1922758
    An average 50 ml breast milk samples were collected from 21 lactating primiparous mothers (range 25 to 45 years, mean 33 years), 4-8 weeks after delivery in Penang Island, Malaysia. The geometric mean concentration of the most toxic congeners, 2,3,7,8-tetrachlorodibenzo-p-dioxin (2,3,7,8-TCDD) was 0.14 pg WHO2005-TEQ g-1 zlipid. The most abundant congeners of PCDD/Fs were octachlorodibenzo-p-dioxin (OCDD) (5.9-75.4%), followed by 1,2,3,4,6,7,8-heptachlorodibenzo-p-dioxin (1,2,3,4,6,7,8-HpCDD) (1.1-30.7%). The geometric mean level of total dioxins and dl-PCBs was 2.2 pg WHO2005-TEQ g-1 lipid, significantly lower than those in developed countries or highly contaminated areas. The total dioxins and dl-PCBs in pg WHO2005-TEQ levels in breast milk were significantly correlated with years of residence at potential contaminated site. The average daily intake of 11.8 pg WHO2005-TEQ kg-1 body weight was estimated for a breastfed infant at 6 months of age. This demonstrates the exposure risk to infants, especially from Penang region, to these pollutants from human milk intake are potentially high during the lactation period.
  6. Fulltext Present status and future concerns of expanded newborn screening in malaysia: sustainability, challenges and perspectives
    Leong YH, Gan CY, Tan MA, Majid MI
    Malays J Med Sci, 2014 Mar;21(2):63-7.
    PMID: 24876809 MyJurnal
    Newborn screening (NBS) program is an important tool for the early diagnosis and preventive treatment of life-long impairments. NBS is one of the strategies recommended by the World Health Organization to promote the primary prevention of congenital anomalies and the health of children with these conditions. However, NBS initiation and implementation in developing countries, especially South-East Asian and North African regions, are slow and challenging. Expanded NBS is not mandatory and has not yet been incorporated into the public healthcare system in our country. Limited funding, manpower shortages, inadequate support services, low public awareness, and uncertain commitment from healthcare practitioners are the main challenges in establishing this program at the national level. Involvement and support from policy makers are very important to the success of the program and the benefit of the entire population.
  7. Contamination of food samples from Malaysia with polychlorinated dibenzo-p-dioxins and dibenzofurans and estimation of human intake
    Leong YH, Chiang PN, Jaafar HJ, Gan CY, Majid MI
    Food Addit Contam Part A Chem Anal Control Expo Risk Assess, 2014 Apr;31(4):711-8.
    PMID: 24392728 DOI: 10.1080/19440049.2014.880519
    A total of 126 food samples, categorised into three groups (seafood and seafood products, meat and meat products, as well as milk and dairy products) from Malaysia were analysed for polychlorinated dibenzo-p-dioxins (PCDDs) and polychlorinated dibenzofurans (PCDFs). The concentration of PCDD/Fs that ranged from 0.16 to 0.25 pg WHO05-TEQ g(-1) fw was found in these samples. According to the food consumption data from the Global Environment Monitoring System (GEMS) of the World Health Organization (WHO), the dietary exposures to PCDD/F from seafood and seafood products, meat and meat products, as well as milk and dairy products for the general population in Malaysia were 0.064, 0.183 and 0.736 pg WHO05-TEQ kg(-1) bw day(-1), respectively. However, the exposure was higher in seafood and seafood products (0.415 pg WHO05-TEQ kg(-1) bw day(-1)) and meat and meat products (0.317 pg WHO05-TEQ kg(-1) bw day(-1)) when the data were estimated using the Malaysian food consumption statistics. The lower exposure was observed in dairy products with an estimation of 0.365 pg WHO05-TEQ kg(-1) bw day(-1). Overall, these dietary exposure estimates were much lower than the tolerable daily intake (TDI) as recommended by WHO. Thus, it is suggested that the dietary exposure to PCDD/F does not represent a risk for human health in Malaysia.
  8. Paraquat poisoning calls to the Malaysia National Poison Centre following its ban and subsequent restriction of the herbicide from 2004 to 2015
    Leong YH, Ariff AM, Khan HRM, Rani NAA, Majid MIA
    J Forensic Leg Med, 2018 May;56:16-20.
    PMID: 29525581 DOI: 10.1016/j.jflm.2018.03.007
    This study analyses the incidences and patterns of paraquat poisoning from calls received at the Malaysia National Poison Centre (NPC) since 2004 following the ban of the herbicide (2004-2006) and subsequent restriction up to year 2015. Related reported cases to the centre over twelve years (2004-2015) were retrieved and studied in respect to socio-demographic characteristics, mode and type of poisonings, exposure routes and location of incident. Ages of poisoned victims range from 10 months old to 98 years with males being intoxicated more frequently than females (ratio male to female = 2.7). The age group mainly involved in the poisoning was 20-39 years. The most common mode was intentional (62.8%) followed by unintentional (36.9%). Among the 1232 reported cases, suicidal poisoning was the highest (57.2%); accidental poisoning (30.8%) and occupational poisoning (3.3%). The findings showed an upward trend of suicidal poisoning over the years, clearly emphasizing the need for more stringent and effective enforcement to ensure the safe use of paraquat.
  9. Occurrence and risk assessment of 3-monochloropropanediols esters (3-MCPDE), 2-monochloropropanediol esters (2-MCPDE), and glycidyl esters (GE) in commercial infant formula samples from Malaysia
    Nik Azmi NNA, Tan TC, Ang MY, Leong YH
    Food Addit Contam Part A Chem Anal Control Expo Risk Assess, 2023 Feb;40(2):212-221.
    PMID: 36602442 DOI: 10.1080/19440049.2022.2163054
    The presence of 3-monochloropropanediol esters (3-MCPDE), 2-monochloropropanediol esters (2-MCPDE) and glycidyl esters (GE) in infant formula products has raised serious concerns. They incorporate vegetable oils, particularly palm-based oils, which are well-known to contain large amounts of these process contaminants. An analysis was conducted on infant formula samples (n = 16) obtained from the Malaysian market to determine the levels of 3-MCPDE, 2-MCPDE and GE using gas chromatography-mass spectrometry (GC-MS). The method was validated, with a limit of quantification (LOQ) on instrument of 0.10 µg/g for all analytes. The median concentrations of 3-MCPDE, 2-MCPDE and GE in infant formula in this study were 0.008 µg/g, 0.003 µg/g and 0.002 µg/g respectively. The estimated dietary intakes calculated from consumption of infant formula show higher exposures to infants within the age group of 0 to 5 months, highest for GE (1.61 µg/kg bw/day), followed by 3-MCPDE (0.68 µg/kg bw/day) and 2-MCPDE (0.41 µg/kg bw/day) compared to the age group of 6 to 12 months. Only one sample, relating to GE exposure is a potential risk for both age groups with MOE value below 25,000.
  10. Fulltext A Scoping Review on Fungus and Mycotoxin Studies in the Building's Environment: Mycotoxin Analysis by Mass Spectrometry
    Abdul Rahman S, Ahmad NI, Mohd Salim RJ, Muhamad NJ, Omar Hamdan AS, Leong YH
    Int J Anal Chem, 2024;2024:8581029.
    PMID: 38312506 DOI: 10.1155/2024/8581029
    It has been well-established that mycotoxins are poisonous chemical metabolites secreted by certain molds. Some of them significantly affect the health of humans and livestock. Increasing attention is now being paid to uncovering and identifying mycotoxins' presence in the building's environment. However, the main challenge remains in suitable and reliable analytical methods for their identification and detection in infected structures. GC-MS and LC-MS/MS techniques have been used extensively for mycotoxin analysis, and advancement in these techniques enabled a more comprehensive range of mycotoxins to be detected. As such, this study aimed to address a brief overview of various phenomena of existing sample collection, preparation, and analysis to detect mycotoxins in the building's environment. This scoping review includes articles from 2010 to 2020 available from PubMed, Scopus, Cochrane, Wiley, Google Scholar, and ScienceDirect. Duplicate articles were removed, and exclusion criteria were applied to eliminate unrelated studies, resulting in 14 eligible articles. The present study provides an overview of mycotoxin analysis by GC-MS and LC-MS/MS in buildings. Many techniques are available for analyzing and detecting multiple mycotoxins using these methods. Future efforts would focus on rapid assays and tools enabling measuring a broader range of mycotoxins in a single matrix and lower detection limits. In addition, it would assist future findings on new techniques and mycotoxins that existed in the building's environment.
  11. Fulltext Epidemiological analysis of reported acute glyphosate poisoning in Malaysia: identifying risk factors and high-risk groups (2006-2023)
    Razali MF, Amir Shah Ruddin NI, Abdul Rani NA, Mohamed F, Ahmad NI, Leong YH
    BMJ Open, 2025 Jan 28;15(1):e092681.
    PMID: 39880440 DOI: 10.1136/bmjopen-2024-092681
    OBJECTIVE: Glyphosate is widely used in Malaysian agriculture but poses a significant under-reported public health concern due to poisoning. This paper aims to study the epidemiology of glyphosate poisoning in Malaysia, assessing severity, identifying risk factors, and high-risk groups.

    SETTING: All glyphosate-related data of the Malaysia National Poison Centre from 2006 to 2023.

    PARTICIPANTS: Telephone inquiries of incidents involving glyphosate made by healthcare professionals across Malaysia. Information received was recorded according to WHO guidelines.

    OUTCOMES: The outcome is to provide an overview of national glyphosate poisoning epidemiology, including identifying risk factors and high-risk groups to strategise appropriate measures.

    RESULTS: A total of 4548 glyphosate poisoning cases were reported, with males comprising 67.3% of cases. The most affected age groups were 21-30 years (25.5%) and 31-40 years (23.5%). Ingestion was the primary exposure route (93.0%). Intentional poisonings, mainly suicides, accounted for 68.4% (n=3078) of cases. Among the 1420 unintentional cases, 78.2% resulted from ingestion exposures. The incidence rate declined from 1.17 per 100 000 in 2011 to 0.61 in 2023. Significant associations were found between intentional ingestion and sociodemographic factors. From 2013 to 2023, 73.7% of cases were minor, 11.5% moderate, 0.8% severe and 0.1% fatal.

    CONCLUSIONS: In Malaysia, the reported intentional glyphosate poisoning most commonly affects young adults, resulting in generally minor to moderate symptoms. The study highlights the need for stricter regulations on glyphosate use and improved mental health support, to mitigate poisoning risks. Continued surveillance and public education are essential to address this public health issue.

  12. Phenolic compounds determination in stingless bee by dispersive liquid-liquid microextraction coupled with capillary electrophoresis - diode array detection
    Al Wade A, Hassan NH, Saaid M, Althakafy JT, Chong NS, Leong YH, et al.
    Food Chem, 2025 Mar 05;481:143720.
    PMID: 40168866 DOI: 10.1016/j.foodchem.2025.143720
    A dispersive liquid-liquid microextraction (DLLME) coupled to capillary electrophoresis with diode array detection (CE-DAD) for determination of sixteen phenolic compounds (PCs) is described. DLLME conditions that affect extraction performance were investigated using single-factor variable experiments. The PCs were extracted using ethyl acetate as extraction solvent and acetonitrile as dispersive solvent. The separation was achieved using fused-silica capillary with buffer constituted of 40 mmol L-1 borax (pH 9.3) and 10 % (v/v) ethanol. Voltage of 20 kV, cassette temperature of 25 °C, hydrodynamic injection (30 mbar for 6 s) and variable UV detection wavelengths were applied. The PCs were separated in < 32 min. Calibration curves were linear (r2 > 0.998) within 1-20 mg L-1 for naringin and catechin hydrate, and 0.3-20 mg L-1 for other PCs. Detection limits were 0.01-0.52 mg L-1, relative standard deviations of ≤ 2.39 % (migration times) and ≤ 5.66 % (peak areas) were obtained. The method exhibited good recoveries (85.2-110.7 %), with enrichment factors of 1.79-13.94 and greenness score of 0.35 (AGREEprep) and 0.54 (AGREE). The validated method was applied for determination of PCs in Tualang and stingless bee honey. These results demonstrated the potential of DLLME-CE-DAD as a simple, and environmentally friendly method to quantify PCs in SBH.
  13. Maternal acceptance of human papillomavirus vaccine in Malaysia
    Sam IC, Wong LP, Rampal S, Leong YH, Pang CF, Tai YT, et al.
    J Adolesc Health, 2009 Jun;44(6):610-2.
    PMID: 19465327 DOI: 10.1016/j.jadohealth.2008.11.014
    Acceptability rates of human papillomavirus (HPV) vaccination by 362 Malaysian mothers were 65.7% and 55.8% for daughters and sons, respectively. Younger mothers, and those who knew someone with cancer, were more willing to vaccinate their daughters. If the vaccine was routine and cost free, acceptability rate was 97.8%.
  14. Acute and repeated dose 28-day oral toxicity of poly(3-hydroxybutyrate-co-4-hydroxybutyrate) nanoparticles in Sprague-Dawley rats
    Leong YH, Isa ASM, Mohamed Mahmood M, Moey CEJ, Utar Z, Soon YI, et al.
    Regul Toxicol Pharmacol, 2018 Jun;95:280-288.
    PMID: 29567329 DOI: 10.1016/j.yrtph.2018.03.011
    This study aimed to investigate the oral acute and subacute toxicity of Poly [3-hydroxybutyrate-co-4-hydroxybutyrate], P(3HB-co-4HB) in the form of nanoparticles in Sprague-Dawley rats. Acute oral administration of P(3HB-co-4HB) nanoparticles was performed as a single dose up to 2000 mg/kg in six female rats for 14 days. Subacute toxicity study via oral administration for 28 days at doses of 0 (control), 500, 1000 and 2000 mg/kg in rats (10 rats in each group, female:male = 1:1) was conducted. The estimated lethal dose (LD50) of P(3HB-co-4HB) nanoparticles was >2000 mg/kg. No mortality, unusual changes in behaviour, adverse clinical signs, abnormal changes in body weights or food consumption were observed on all animals treated with P(3HB-co-4HB) nanoparticles during 14 days of the acute toxicity study. In the subacute test, there was no mortality and toxicologically significant changes in clinical signs, body weights, food consumption, hematology, clinical biochemistry, urinalysis, macroscopic findings, organ weights as well as histopathological examination were observed.
  15. Fulltext Epidemiology and risk factors of pesticide poisoning in Malaysia: a retrospective analysis by the National Poison Centre (NPC) from 2006 to 2015
    Kamaruzaman NA, Leong YH, Jaafar MH, Mohamed Khan HR, Abdul Rani NA, Razali MF, et al.
    BMJ Open, 2020 06 01;10(6):e036048.
    PMID: 32487578 DOI: 10.1136/bmjopen-2019-036048
    OBJECTIVE: Pesticide poisoning is a global health problem, and its progressive deterioration is a major cause of concern. The objective of this study is to assess epidemiological characteristics and identify risk factors of pesticide poisoning in Malaysia.

    SETTING: Pesticide poisoning database of Malaysia National Poison Centre (NPC) from 2006 to 2015.

    PARTICIPANTS: Telephone enquiries regarding pesticide poisoning were made by healthcare professionals. Information received by the NPC was entered into a retrievable database of standardised Poison Case Report Form, as adapted from the World Health Organization (WHO).

    OUTCOMES: The outcome of the study is to provide an overview of national epidemiological profile of pesticide poisoning. High-risk groups of people and their circumstances were also identified to ensure that appropriate measures are strategised.

    RESULTS: Within the study period, a total of 11 087 pesticide poisoning cases were recorded. Sixty per cent of these cases were intentional in nature and most were found among male individuals (57%) of the Indian race (36.4%) aged between 20 and 29 years (25.5%), which occurred at home (90%) through the route of ingestion (94%). The highest number of poisoning was due to herbicides (44%) followed by agricultural insecticides (34%), rodenticides (9.9%), household insecticides (9.5%) and fungicides (0.5%). In addition, 93.6% of intentional pesticide poisoning cases were caused by suicide attempts. The results of this study show that there was an increasing trend in pesticide poisoning incidents over the 10-year duration. This indicates that pesticide poisoning is a prevalent public health problem in Malaysia, resulting in an average incidence rate of 3.8 per 100 000 population.

    CONCLUSIONS: Deliberate pesticide ingestion as a method of suicide has become a disturbing trend among Malaysians. Therefore, regulation of highly hazardous pesticides must be enforced to ensure controlled and limited access to these chemicals by the public.

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