Fish consumption survey
Between February 2008 and May 2009, a household-based cross-sectional study was undertaken in Peninsular Malaysia, with data collected through face-to-face interviews using pre-designed questionnaires. Based on the National Household Sampling Frame (NHSF), Department of Statistics, Malaysia, a sampling frame made up of Enumeration Blocks (EBs) constructed for the 2000 Population and Housing Census was used to pick study subjects' household addresses (Department of Statistics Malaysia 2000). The sample size was calculated using data from a Selangor population consumption survey, which revealed that 16.2% of the adult population consumed fish (153g/person/day vs 944g/person/day total food) (Ahmad 2007). Factors from two separate places (urban and rural), three different ethnic groups (Malay, Chinese, and Indian), and two different age groups were used. A number of 2,496 subjects were required in order to obtain 95% confidence interval and 5% margin of error. Taken into account a 20% dropped-off rate, 2,996 subjects were identified from 1,500 household addresses received from the NHSF. In this study, a minimum of two adults and all adolescence ages 10 to 17 years were chosen from each family. The final count of 2,675 adult had completed the questionnaire. A number of 890 children/adolescent participated in the survey but only 484 completed the questionnaires.
The questionnaires were divided into two sections. The first portion was a self-administered questionnaire that included sections on socio-demographic information, fish consumption patterns, frequency of fish intake, and knowledge, perceptions, and practices related to fish eating. The three copies of 24-hour dietary diary forms made up the second half. In this portion, participants were instructed to keep track of what they ate and drank at each meal of the day. The interviewers were instructed how to read and understand the questionnaires and how to give instructions to the subjects. They were given a series of questionnaire tools which included pictures of serving dishes, fish commonly found in Malaysia and common household measure like standard measuring cups, bowls, ladles and spoons. The questionnaire was provided between the hours of 9:00 a.m. and 6:00 p.m., however interviewers were sometimes required to come at night if individuals were not at home during the day. Parents were asked to assist their children in filling out the 24-hour dietary diary forms and answering questions on the surveys. Interviewers were also re-checked all food recorded in dietary diary forms to verify types and amount of food consumed by subjects.
The portion weight of food was determined using the “Atlas Makanan: Saiz pertukaran dan Porsi” (Suzana et al 2002, 2009) and “Nutrient and composition of Malaysian foods” (Tee et al 1997). If the food consumed was not listed in all of these references, mean values were determined as the weight of that particular food from at least five different sources. The collections of the three days dietary diary were conducted during weekdays and weekends. Details on the calculation of sample size, questionnaires and interviews involved adults from Peninsular Malaysia for the whole study entitled “Seafood consumption survey in Peninsular Malaysia, 2008-2009” were as described elsewhere (Ahmad et al 2016), while similar information for survey that involved adolescence was reported recently (Ahmad et al 2019). Information on the demographic background of study subjects from both groups were presented in both published articles, accordingly (Ahmad et al 2016; 2019). The Medical Research and Ethics Committee (MREC) of the Ministry of Health Malaysia (MOH) approved the project, which was funded by the MOH. Informed consent and confidentiality were obtained from the subjects beforehand.
Seafood collection and preparation
Sampling was conducted from June to December 2009. Samples were obtained from six major Fisheries Development Authority of Malaysia (LKIM) fish landing complexes and five wholesale wet marketplaces across Peninsular Malaysia. During three trips to each location, a total of 394 seafood samples were gathered. Details on how to collect, prepare, process, and store fish can be found elsewhere (Ahmad et al. 2015ab).
Determination of total mercury concentrations in seafood
In a microwave digestion device, a dried sample was digested (Multiwave 3000 - Anton Paar). Total mercury was measured using a Perkin Elmer Flow Injection Mercury System (FIMS) apparatus with a programmable sample dispenser and a cold vapour atomic absorption spectrometry (AAS) methodology, as described by Mohd Fairulnizal et al (1998). Analytical control was accompanied by analysis of reagent blanks and standard reference samples. Details on the analysis were described elsewhere (Ahmad et al. 2015ab). It was essential to convert mercury contents in fish samples to wet basis values, and the quantity of moisture content was determined using Tee et al. (1997) and other sources (Nurnadia et al. 2011). Results were compared to the recommended guideline levels by the joint FAO/WHO Expert Committee on Food Additives (FAO/WHO 2006) and the Malaysian Food Regulation 1985 (Food Act 1983, (Act 281), and Regulations 2006), under the Fourteenth Schedule of Regulation 38, the level at 0.5 mg/kg meHg in fish and seafood.
Health risk assessment of mercury from seafood consumption
Estimated Weekly Intake (EWI) and Maximum Safe Weekly Consumption (MSWC)
The EWI of total Hg and/or meHg from consumption of seafood can be calculated by multiplying the total Hg and/or meHg contamination levels in seafood with the consumption levels per week dividing by the average body weight of the population by age group. The equation is as shown below:
EWI = Concentration of meHg (mg/Kg WW) x weekly consumption (g)
Body weight (kg)
The typical adult body weight varies between 55 and 62 kg depending on demographic factors, while the average adolescent body weight is 45 kg (Ahmad et al 2016; 2019). The JECFA has defined a PTWI of 1.6 g/kg bodyweight/week for inorganic MeHg (WHO 2011).
MSWC to reach the PTWI for Malaysian population at different socio-demographic characteristics was also estimated. The MSWC was calculated using the PTWI (g/kg body weight/week) value of 1.6 g/kg body weight/week multiplied by body weight for each population group and divided by total Hg and/or meHg concentrations.
PTWI at 1.6 μg/kg body weight/week = Concentration of meHg (mg/Kg WW) x MSWC (g)
Body weight (kg)
Hazard Quotient (HQ)
Risk assessment is a tool to estimate the probability of health effects due to exposure to the hazard, in which this study is the exposure through consumption of fish. The oral reference dosage (RfDs) for mercury was set at 1 x 10-4 (mg/kg-day) by the USEPA (Risk Information System (IRIS) (USEPA 2000). The HQ meHg was estimated using the equation below (Wan Azmi et al 2019):
HQ = EF x ED x FIR x C x 10-3
RfD x BW x AT
where HQ is chemical-specific Hazard Quotient; EF is the exposure frequency (350 days/year); ED is the duration of human exposure for children and adults is 6 and 30 years, respectively; FIR is the seafood ingestion rate (based on total intake per day in gram by different groups of population); C is the metal concentration in the muscle of fishes (mg/kg wet weight); RfD is the oral reference dose (IRIS, USEPA); BW is the average body weight of population group (55 to 62 kg for adult, 45 kg for adolescent and 60 kg for total population) and AT is average time of human exposure to non-carcinogenic (ED x 365 days).
Target hazard is a ratio of the determined dose of a contaminant to oral reference dose considered detrimental. HQ values were more than or equal to 1, it is assumed that the intake of meHg through the consumption of fish and seafood poses a potential non-carcinogenic health risk to the exposed population.
IBM SPSS Statistics 26 was used to analyze the data. Before analyzing the THg data, it was cleaned and examined for discrepancies. The demographic features of different categories and groups were keyed in using data from a dietary survey. After completing the data entry, it was checked for any discrepancies, such as coding numbers, typo errors, and so on. At first, descriptive statistics were used to assess data normality using the one-sample Kolmogorov-Smirnov test, and/or the skewness of descriptive statistics was regulated between -1 and +1, whichever was true. Because of the outliers, the descriptive statistical analysis revealed that both groups of data were not regularly distributed. As a result, non-parametric statistics were employed. The medians and interquartile range were calculated The Mann-Whitney U and Kruskall-Wallis tests were used to analyze differences across groups. A level of significance at 0.05 is set to determine the result is statistically significant. Significance values have been adjusted by the Bonferroni correction for multiple tests. Higher consumers were chosen among participants who consumed fish and seafood at the 75th, 90th, and 95th percentiles, and their consumption was compared to the median consumption at the 50th percentile.