| Budget Amount *help |
¥6,400,000 (Direct Cost: ¥6,400,000)
Fiscal Year 1991: ¥1,900,000 (Direct Cost: ¥1,900,000)
Fiscal Year 1990: ¥1,900,000 (Direct Cost: ¥1,900,000)
Fiscal Year 1989: ¥2,600,000 (Direct Cost: ¥2,600,000)
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| Research Abstract |
Element flow in a regional ecosystem in Papua New Guinea, which includes a human population called Gidra-Speaking people who subsist on hunting, gathering, and slash-and burn horticulture, was investigated employing multi-element analysis and carbon and nitrogen stable isotope analysis. Emphasis was placed on the analysis of element flow in man-food system because consumption of foods is the main route of element intake in non-exposed general population such as the Gidra.
Fifty-seven food items, which include 52 local plants and animals and 5 purchased items, consumed by, and 59 scalp hair samples obtained from, the Gidra were subjected to carbon and nitrogen stable isotope analysis to characterize the ecological niches of animals and humans. From this analysis information has been obtained concerning habitat and/or trophic level of animals and humans in the Gidra's territory.
To the multi-element data (Na, Mg, Al, P, Ca, K, V, Cr, Mn, Fe, Cu, Zn, Sr, Cd, Hg, Pb) of the present food and
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hair samples, which have been obtained from our previous project, we added selenium data in the present project. Selenium content was found to be highest in fish, followed by reptiles, herbivorous animals and plant foods in this order.
Based on the multi-element data and carbon and nitrogen stable isotope ratios (delta13C, delta15N) of the local animal food, correlation analysis was conducted to investigate the relationship between element concentrations and parameters of the ecological niche of the animals. Mercury and selenium significantly positively correlated with delta15N. However multiple regression analysis extracted mercury as the single significant variable to explain delta15N variation, indicating mercury-selenium inter-relationship rather than that of selenium-delta15N. From this result it was concluded that mercury was the element which accumulates in the organisms through the food chain (biomagnification). The slope of regression function between mercury (log-transformed) and delta15N indicated that concentration factor of mercury per one trophic level was calculated to be 5. Other element such as lead was found at higher concentration in some animals than in the other, but it did not have any accosiation with delta15N. This indicated that lead is the element which shows bioconcentration but not biomagnification. Correlation analysis also revealed the significant positive correlation between mercury and delta15N in human hair with similar value of the slope of the regression function to that found in animals. This indicates that biomagnification of mercury also occurred with flow of mercury from animals to humans without any modification which will occur when other mercury source other than food exists. Hair samples from one of the 4 study villages showed slightly deviated distribution from the regression curve of mercury-delta15N. The cause and implication of this deviation is not clear at present and it is a subject of further research. Less
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