Momoko Chiba
Juntendo University School of Medicine, Tokyo

Environment, foods, and human health are tightly correlated. Nowadays transportation system has been widely developed and the residents living in the big cities consume imported foods, however, most of people eat local products. Depending on the sorts and natures of the local products, the sorts and amounts of contaminants are different. Health status of the local residents is also correlated with their food custom. From the aspect of hydrosphere marine products are paid attention. It is known that fish concentrate some sorts of elements by food chain. Recently analytical equipments and techniques have been developed, and enable to determine very low level and species analyses.

Arsenic (As): As concentration in seawater is reported as 3.7µg/dm³. Our analytical results in marine shellfishes were 0.12 to 1.33 mg/100 g wet weigh of edible portion. According to the data book As concentrations in fish are widely scattered; 0.08-0.55 mg/100 g wet weight of edible portion. In general Japanese urine contains 21 to 585 As µg/L, and more than 50% of As is arsenobetain which is the chemical form containing in fish and non-toxic.

Tin (Sn): Organic tin compounds such as tributyltin or triphenyltin were used as antifouling paints. These compounds make female sea snails have male organs. There have been no reports suggesting correlation between human health and abnormal sea snails containing organic tin through food chain.

Mercury (Hg): Hg concentration in seawater is very low, 2 x 10^-3 µg/dm³. Hg concentrations in fish are relatively high; 0.01-0.04 mg/100 g in fresh water fish, 0.001-0.03 mg/100 g in inshore fish, and 0.03-0.2 mg/100 g in pelagic fish like tuna fish in wet weight base of edible portion. Hg concentration in shellfish is low. Hg in fish is resulted of biological concentration by food chain. Absorption rate from gastro-enteric tract of inorganic-Hg is low, less than 10%. Hg²⁺ is deposited in kidney and causes renal dysfunction. Methyl-Hg is easily absorbed more than inorganic-Hg, and passing through blood-brain barrier and placental barrier. Methyl-Hg has high affinity with nervous system and damages central nervous system. This is the reason why Minamata disease and fetal Minamata disease happened by methyl-Hg. There have been reported on health problem due to methyl-Hg not only in Japan, but also Iraq, Pakistan, and other countries. It is doubtlessness that population at risk of methyl-Hg is fetuses. There are two large scale cohort studies concerning the effects of prenatal exposure to low dose of methyl-Hg in fish; the Faroese birth cohort study (FBCS) and the Seychelles child developmental study (SCDS). Residents in Fareo Islands, where locate in the Atlantic Ocean, about 2 hours by airplane from Copenhagen, have custom consuming whales and cod fishes. Residents in Seychell Islands, where locate in the Western Indian Ocean, north of the Madagascar, have custom consuming small fishes such as jackfish, pike, and pickerel. In these two studies methyl-Hg concentrations in mothers’ hair were 4.5µg/g (mean) in Faroese, and 6.6µg/g (median) in Seychelles. The results of FBCS showed that significant dose-effect relationship between prenatal methyl-Hg exposure and both neurobehavioral and neurophysiologic end-points in the children at 1, 7, or 14 years old. The results of SCDS, on the other hands, did not show clear positive correlation between methyl-Hg exposure and tested end-points in the children at 5 to 109 weeks, 6.5, 19, 29, 66, or 108 months old.

As the conclusion, when health effects of chemicals is considered, it is important to take account of food custom, confounding factors, chemical species, and co-existing factors.