Journal of Radioanalytical and Nuclear Chemistry, Voi. 217, No. 1 (1997) 53-56 Determination of mercury and organic mercury contents in Malaysian seafood S. A. Rahman,* A. K. Wood,* S. Sarmani,** A. A. Majid** * Malaysian Ins~tutefor Nuclear Technology Research, Bangi, 43000 Kajang, Selangor, Malaysia ** Department of Nuclear Science, National University of Malaysia, 43600 Bangi, Selangor, Malaysia (Received June 20, 1996) The contents of mercury and organic mercury in various types of seafood from various location in Malaysia were determined by neutron activation analysis. Total mercury was detemfined by instrumental neutron activation analysis (INAA) whilst organic mercury was detennined 6y INAA after chemical separation. Samples were digested in acid media and into the solution was added copper ion and KBr to release organic mercury compound from sulphur component of the tissue. The organic mercury was then extracted into toluene and then treated with cysteine paper to convert the compound into sub-organo-mercuryfoma. The paper was then transferred into polyethylene vials and irradiated in the MINT TRIGA Reactor. Analytical results of organic mercury in Indian mackerel (Rastrelliger kanagurta), Spanish mackerel (Scomberomurus commersoni), shrimp (Peneaus sp.), squid (Loligo sp.) and cockle (Anadara granosa) is in the range of 45%-94% of the total mercury. Introduction Although the environmental level of mercury is generally low, some species have high capacity to accumulate mercury, thus, the metal can be widely found in both aquatic and terrestrial animals and plants. Mercury maybe present in food in three different forms: elemental mercury, inorganic mercury and organic mercury. Generally, the concentration of mercury occurs in lrace amount in foods except in special situation as a result of extreme pollution or misuse of certain compounds. The toxicity of mercury to humans and animals have been recognised for many centuries. In most cases of mercury poisoning, alkyl mercury, especially methyl- mercury was found to be the predominant form in seafood or in the head hair population samples from the polluted area) The compound causes a more serious problem than either metallic or mercuric mercury since it may penetrate the blood-brain barrier and remains in the body for longer periods. Studies with labeled methylmercury showed that methylmercury remains in fish and is released with a biological half-life of 110 days.2 It can be accumulated even at low dose rates. Studies have also shown that prenatal exposure to methylmercury and early postnatal exposure to ingestion of methylmercury by breast-fed infants affect on early childhood development and mental ability of the children. 1, 3, 4 Fish is a main source of mercury through food consumption on account of their accumulating mercury compounds more than other aquatic organisms. Most of the mercury consumed by man is in the form of methyl- mercury and the bulk of this consumption comes from fish. Consequently, the level of fish consumption will indicate the level of organic mercury present in man. Since fishes are the major source of protein to Malaysian, it is important to determine the content of organic mercury in ftshes and other types of seafood. The uptake of mercury by Malaysian is in the range 5--40 ~tg/day based on the 0236-5731197/USD 17.00 9 1997 AkadJmiai Kiadt, Budapest All rights reserved mercury content of fishes.5 This is an extension of the previous work on the analysis of toxic trace elements in seafood samples by neutron activation.6 Experimental Sample preparation 22 samples were collected from various places in Malaysia (Fig. 1). The samples were brought to the laboratory in a container packed with ice. The samples were cleaned with distilled water and kept in a deep freezer. Only body muscles was used for analysis. The samples were dried in a freeze dryer and the dried samples were then blended into powder form and kept in a plastic bottle. The samples are ready for analysis. Determination of total mercury About 0.1 g of each sample was weighed into clean polyethylene vials. The standard was prepared by dropping 1001,tl of freshly prepared HgCI2 standard solution (10 I, tg/ml) on ashless filter paper which has been treated with 50 ~tl of 10% solution of thioacetamide to preserve mercury. Samples and standards were then irradiated in the MINT TRIGA Reactor for 6 hours at a neutron flux of 1 9 12 n 9 cm-2. s-L Extraction of organic mercury The extraction of organic mercury from fish tissue was carried out according to the method developed by HOaVAT et al. 7 2 ml of 2M I-I2SO 4 saturated with CuSO 4, 2 ml of 4M KBr solution and 3 ml of toluene were added to 2 g of samples. The mixture was shaken for 15 minutes and centrifuge for 10 minutes at 2000 rpm. The upper layer toluene was transferred quantitatively and the extraction process was then repeated with another 3 ml toluene. Elsevier Science S. A., Lausanne Akad~mlai Kiadt, Budapest