Stephen W.C. Chung

Validation and use of a fast sample preparation method and liquid chromatography-tandem mass spectrometry in analysis of ultra-trace levels of 98 organophosphorus pesticide and carbamate residues in a total diet study involving diversified food types.

This paper reports a comprehensive sensitive multi-residue liquid chromatography-tandem mass spectrometry (LC-MS/MS) method for detection, identification and quantitation of 73 pesticides and their related products, a total of 98 analytes, belonging to organophosphorus pesticides (OPPs) and carbamates, in foods. The proposed method makes use of a modified QuEChERS (quick, easy, cheap, effective, rigged, and safe) procedure that combines isolation of the pesticides and sample clean-up in a single step. Analysis is performed by liquid chromatography-electrospray ionization-tandem mass spectrometry operated in the multiple reaction monitoring (MRM) mode, acquiring two specific precursor-product ion transitions per target compound. Two main fragment ions for each pesticide were obtained to achieve the identification according to the SANCO guidelines 10684/2009. The method was validated with various food samples, including edible oil, meat, egg, cheese, chocolate, coffee, rice, tree nuts, citric fruits, vegetables, etc. No significant matrix effect was observed for tested pesticides, therefore, matrix-matched calibration was not necessary. Calibration curves were linear and covered from 1 to 20 microg L(-1) for all compounds studied. The average recoveries, measured at 10 microg kg(-1), were in the range 70-120% for all of the compounds tested with relative standard deviations below 20%, while a value of 10 microg kg(-1) has been established as the method limit of quantitation (MLOQ) for all target analytes. Similar trueness and precision results were also obtained for spiking at 200 microg kg(-1). Expanded uncertainty values were in the range 21-27% while the HorRat ratios were below 1. The method has been successfully applied to the analysis of 700 food samples in the course of a baseline monitoring study of OPPs and carbamates.

Determination of organochlorine pesticide residues in fatty foods: A critical review on the analytical methods and their testing capabilities

Organochlorine pesticide (OCP) residues in foods have been of concern for several decades. However, the analysis of some of the OCPs and their metabolites or derivatives, such as endrin aldehyde, endrin ketone, nonachlor, etc. in fatty foods (including foods of animal and plant origin), was not commonly included in routine monitoring programme. Recently, the Stockholm Convention introduced nine plus one new persistent organic pollutants (POPs) that included chlordecone and some other OCPs. Is there a method available that can analyze both traditional OCPs, together with their metabolites and derivatives in fatty foods? Furthermore, is there a suitable method that can monitor OCPs and the newly added POPs including chlordecone in fatty foods together in a pot? This review aims to provide some background information to answer these questions.

Trimethylamine oxide, dimethylamine, trimethylamine and formaldehyde levels in main traded fish species in Hong Kong.

Levels of trimethylamine oxide (TMAO), dimethylamine (DMA), trimethylamine (TMA) and formaldehyde (FA) were studied in 266 different fishes, including fresh/frozen raw whole fishes of 89 different species that traded in Hong Kong, China. Determination of TMAO can confirm the source of DMA and FA if present in the sample. These samples were purchased from different commercial outlets between April and August 2007. All samples of raw whole fish were identified for their species by the Agriculture, Fisheries and Conservation Department. The content of TMAO was determined by high-performance liquid chromatography (HPLC) coupled with a chemiluminescent nitrogen detector. The possible decomposition products of TMAO, DMA and TMA were analysed by headspace solid-phase micro-extraction gas chromatography-mass spectrometry (HS-SPME-GC-MS), while FA was conducted by steam distillation then quantified by a HPLC. The range for TMAO of all samples was <5–3800 mg kg−1 with median of 970 mg kg−1, while the endogenous enzymatic cleavage products DMA, TMA and FA were in the range of <2–320, <1–190 and <1–160 mg kg−1, respectively. These cleavage products were mainly found in three fish species, Harpadon nehereus, Saurida elongata and Saurida tumbil, that belong to the family Synodontidae (Lizardfishes) and subfamily Harpadontinae. Besides, freshwater fish species, namely, Micropterus salmoides, Oreochromis niloticus niloticus and Siniperca chuatsi, were found to contain TMAO in the range of 510–760, 85–720 and 400–640 mg kg−1, respectively.

A reliable method to determine methylmercury and ethylmercury simultaneously in foods by gas chromatography with inductively coupled plasma mass spectrometry after enzymatic and acid digestion

A reliable and sensitive method for determination simultaneously of monomethylmercury (MeHg) and monoethylmercury (EtHg) in various types of foods by gas chromatography inductively coupled plasma mass spectrometry (GC-ICP/MS) was developed and validated. Samples were digested with pancreatin and then hydrochloric acid. MeHg and EtHg in the extract were derivatized in an aqueous buffer with sodium tetraphenylborate. After phase separation, the extract was directly transferred to analysis. The analyses were conducted by GC-ICP/MS with monopropylmercury chloride (PrHgCl) as surrogate standard. Concentrations of 254±5.1, 13.7±0.69 and 162±6.2 μg Hg kg(-1) (one standard deviation, n=3) were obtained for MeHg in NIST SRM 1947 (Superior Lake fish), SRM 1566b (oyster tissue) and NRC Tort-2 (lobster Hepatopancreas), respectively. These are in good agreement with the certified values of 233±10, 13.2±0.7 and 152±13 μg Hg kg(-1) (as 95% confidence interval), respectively. The method detection limits (3σ) for MeHg and EtHg are 0.3 μg Hg kg(-1). The method detection limit was estimated by using a 0.5 g of subsample, sufficiently low for the risk assessment of MeHg and EtHg in foods. The spiked recoveries of MeHg and EtHg in different food matrices were between 87 and 117% and the RSDs were less than 15%. When isotopic dilution mass spectrometry (IDMS) analysis was performed with a commercial available (201)Hg-enriched monomethylmercury (Me(201)Hg) solution as internal standard, concentrations of 244±13.4, 13.9±0.25 and 161±1.3 μg Hg kg(-1) were obtained for MeHg in NIST SRM 1947, SRM 1566b and NRC Tort-2, respectively. It shown clearly that IDMS analysis got improvement in precision and accuracy, however, EtHg cannot be analyze simultaneously and the cost of analysis is higher.

Dietary exposure to aluminium of the Hong Kong population.

A total of 256 individual food samples were collected in Hong Kong for aluminium testing. Most of food samples were analysed in ready-to-eat form. High aluminium levels were found in steamed bread/bun/cake (mean: 100–320 mg kg−1), some bakery products such as muffin, pancake/waffle, coconut tart and cake (mean: 250, 160, 120 and 91 mg kg−1, respectively), and jellyfish (ready-to-eat form) (mean: 1200 mg kg−1). The results demonstrated that aluminium-containing food additives have been widely used in these food products. The average dietary exposure to aluminium for a 60 kg adult was estimated to be 0.60 mg kg−1 bw week−1, which amounted to 60% of the new PTWI established by JECFA. The main dietary source was “steamed bread/bun/cake”, which contributed to 60% of the total exposure, followed by “bakery products” and “jellyfish”, which contributed to 23 and 10% of the total exposure, respectively. However, the estimation did not include the intake of aluminium from natural food sources, food contact materials or other sources (e.g. drinking water). Although the results indicated that aluminium it is unlikely to cause adverse health effect for the general population, the risk to some populations who regularly consume foods with aluminium-containing food additives cannot be ruled out.

Dietary exposure to antimony, lead and mercury of secondary school students in Hong Kong

The aim of this first study was to determine the dietary exposure of antimony, lead, mercury in foodstuffs consumed by secondary school students in Hong Kong. Around 100 composite food items were purchased and then cooked prior to analysis. Antimony was measured by hydrogen generation (HG)/inductively coupled plasma–mass spectrometry (ICP–MS), while lead was determined by ICP–MS. Total mercury was measured by cold vapour atomic absorption spectrometry. The detection limits for antimony, lead and total mercury were 1, 0.6 and 3 µg kg−1, respectively. The dietary intake of antimony, lead and total mercury for an average secondary student were estimated to be 0.252, 1.98 and 0.92 µg (kg bw)−1 week−1, respectively. The dietary intake of antimony, lead and total mercury for high-consumer secondary student were estimated to be 0.567, 5.09 and 2.33 µg (kg bw)−1 week−1, respectively. The main contribution to antimony, lead and mercury were milk, vegetables and seafood, respectively. The Tolerable Daily Intake (TDI) of antimony, as recommended by WHO, is 6 µg (kg bw)−1 week−1, while the Provisional Tolerable Weekly Intakes (PTWI) of lead and mercury, as recommended by JECFA, are 25 and 5 µg (kg bw)−1 week−1, respectively. The estimated exposure values for secondary school students were compared to these safety reference values. For the relevant population, this study confirms the low probability of health risks from these metals via food consumption.

Nitrate and nitrite levels in commonly consumed vegetables in Hong Kong

Levels of nitrate and nitrite in 73 different vegetables, a total of 708 individual samples grouped into leafy, legumes, root and tuber, and fruiting vegetables, which are traded mainly in Hong Kong, were measured. Where available, five samples of each vegetable type were purchased from different commercial outlets during the winter of 2008 and summer of 2009. Levels of nitrate and nitrite were determined by ion chromatography and flow injection analysis, respectively. Nitrate and nitrite levels of all samples ranged <4–6300 and <0.8–9.0  mg kg−1, respectively. Nitrate concentrations for the different groups, in descending order, were leafy > root and tuber > fruiting and legume vegetables. More than 80% of vegetables had mean nitrate concentrations less than 2000 mg kg−1, but mean nitrate concentrations of three types of leafy vegetables, namely Chinese spinach, Shanghai cabbage and Chinese white cabbage, were >3500 mg kg−1. On the other hand, nitrite concentrations were generally low – <1 mg kg−1 on average. Nitrate in vegetables (i.e. Chinese flowering cabbage, Chinese spinach and celery) can be reduced significantly (12–31%) after blanching for 1–3 min, but not after soaking.

Mercury and methylmercury levels in the main traded fish species in Hong Kong

Levels of total mercury (tHg) and mono-methylmercury (MeHg) were measured in 280 different fish, including fresh/frozen raw whole fish of 89 different species and canned tuna fish of three different species, that are traded mainly in Hong Kong, China. These samples were purchased from different commercial outlets between April and August 2007. All samples of raw whole fish were identified at species level by the Agriculture, Fisheries and Conservation Department. The range for tHg and MeHg of all samples were 3–1370 and 3–1010 µg kg−1, respectively, with medians of 63 and 48 µg kg−1, respectively. The results show that, according to Hong Kong legislation, the products on the market are generally ‘safe’. A total of 277 samples (99?) contained tHg and MeHg below the legal limit of 500 µg kg−1. The remaining three samples of alfonsino (species: Beryx splendens) were found to contain tHg and MeHg at levels higher than 500 µg kg−1 (tHg: 609–1370 µg kg−1; MeHg: 509–1010 µg kg−1). The ratios of MeHg to tHg in the different fish species ranged from 0.46 to 0.99.

Development of a 15-class multiresidue method for analyzing 78 hydrophilic and hydrophobic veterinary drugs in milk, egg and meat by liquid chromatography-tandem mass spectrometry

The development of a multiclass, multiresidue method for analyzing veterinary drugs in food is the recent trend of research for regulatory monitoring laboratories. This work reports a multiclass method for the determination of both hydrophilic and hydrophobic veterinary drug residues, including anthelmintics, avermectins, benzimidazoles, β-agonists, β-lactams, coccidiostats, corticosteroids/steroids, lincosamides, macrolides, non-steroidal anti-inflammatory drugs, phenicols, quinolones, tranquillisers, antiviral drugs and some other veterinary drugs, in milk, egg and meat. By using liquid–liquid extraction low temperature partition with centrifugation for acetonitrile (MeCN)/aqueous phase separation, hydrophilic and hydrophobic drugs were recovered separately. The MeCN phase was cleaned up with dispersive solid phase extraction. To achieve retention and separation of veterinary drugs with a wide range of polarity, ultra-performance hydrophilic interaction liquid chromatography (HILIC) and reversed phase liquid chromatography (RPLC) coupled to a tandem mass spectrometer (MS/MS) were employed. The method was successfully validated. The recoveries of the method in general ranged from 70 to 120% with precision RSD ≤20%. The limits of quantification of the method ranged from 0.1 to 10 μg kg−1 for the targeted veterinary drugs.

Dietary exposure of Hong Kong secondary school students to total mercury and methylmercury from fish intake.

Fish is the main source of dietary exposure to methylmercury (MeHg), which is a public health concern owing to its potential neurotoxicity. To evaluate the public health risk, this study estimated the total mercury (tHg) and MeHg exposure from fish intake in Hong Kong secondary school students. Median tHg and MeHg concentrations of 280 samples purchased from different commercial outlets (covering 89 species of whole fish and three types of canned tuna), together with the local food consumption data of secondary school students obtained by semi-quantitative food frequency questionnaire in 2000, were used to estimate dietary exposure from fish intake for the average and high consumer (95th percentile exposure). For tHg, the median concentration was 63 µg kg–1 (range 3–1370 µg kg–1) and estimated exposures ranged 0.5–0.6 µg kg–1 body weight (bw) week–1 for an average consumer and 1.6–1.9 µg kg–1 bw week–1 for a high consumer. For MeHg, median concentration was 48 µg kg–1 (range 3–1010 µg kg–1) and estimated dietary exposures were 0.4–0.5 µg kg–1 bw week–1 for an average consumer and 1.2–1.4 µg kg–1 bw week–1 for a high consumer. These values are below the respective provisional tolerable weekly intake (PTWI) established by the Joint Food and Agriculture Organization/World Health Organization Expert Committee on Food Additives (JECFA). The health risk is greater for high consumers since MeHg exposures may approach or exceed the PTWI when other dietary sources are taken into account.